OOLOGY 
5RAR1 


A   MANUAL   OF   PHYSIOLOGY. 


(oik  the.flai} 


Frog's  corputtle 
after  addition  ofifater 


Camel  Wotd  of  mammal 


&    -' 


Mammalian  Mammalian 

after  addition  of  tyrvp  after  addition  of  tail 


1.  Bed  blood-corpuscles. 


_js» 

ji^L- 

1  ^ 
f 


- 


2.  The  colourless  corpuscles  of  human  blood,  x  1000.  a,  coarsely  granular 
oxyphile  cells ;  ft,  finely  granular  oxyphile  cells ;  c,  hyaline  cells ,  d, 
lymphocyte ;  e,  finely  granular  basophile  cells  (Kanthack  and  Hardy). 
The  magnification  is  much  greater  than  in  1. 


Blood  in  capillary 


Nucleus 


MturkftbT' 


Transverse  section 

at  level  of  K«clt.u*         Mutcle  cell  more  highly  magn&e* 


Tran*ver*c  tcctitn.  ^gSr 
of  branch  of  *nv*clt  cell 


'•* 


3.  Hiemin  crystals, 


4.  Section  of  heart,  x  300.     (Stained  with  haamstoxylin.) 


MANUAL  OF  PHYSIOLOGY. 


WITH  PRACTICAL  EXERCISES. 


BY 

G.  N.  STEWART,  M.A.,  D.Sc.,  M.D.  EDIN,  D.P.H.  CAMB., 

PROFESSOR   OF   PHYSIOLOGY   IN   THE   WESTERN   RESERVE   UNIVERSITY,   CLEVELAND  ; 

FORMERLY   GEORGE    HENRY   LEWES   STUDENT  J 

EXAMINER    IN    PHYSIOLOGY    IN   THE   UNIVERSITY   OF   ABERDEEN  J 

SENIOR  DEMONSTRATOR  OF   PHYSIOLOGY   IN   THE  OWliNS  COLLEGE,    VICTORIA   UNIVERSITY, 

ETC. 


WITH   NUMEROUS   ILLUSTRATIONS,   INCLUDING 
FIVE   COLOURED   PLATES. 


THIRD    EDITION. 


PHILADELPHIA : 

W.     B.     SAUNDERS, 

925  WALNUT  STREET. 

LONDON:   BAILL1ERE,    TINDALL  &   COX. 
1899. 


S2 


BiOLOdy 
LIBRARY 

• 


FROM  THE  PREFACE  TO    THE  FIRST  EDITION. 


IN  this  book  an  attempt  has  been  made  to  interweave  formal 
exposition  with  practical  work,  in  the  way  my  experience  at 
the  Harvard  Medical  School  and  the  Western  Reserve 
University  has  shown  to  be  best  suited  to  the  needs  and  the 
opportunities  of  the  American  student.  An  arrangement  of 
the  Practical  Exercises  with  reference  to  the  systematic 
course  has  this  great  advantage — that  by  a  little  care  it  is 
possible  to  secure  that  the  student  shall  be  actually  working 
at  a  given  subject  at  the  time  it  is  being  lectured  on. 
Cross-reference  from  lecture-room  to  laboratory,  and  from 
laboratory  to  lecture-room,  from  the  detailed  discussion  of 
the  relations  of  a  phenomenon  to  the  living  fact  itself,  is 
thus  rendered  easy,  natural,  and  fruitful. 

As  some  teachers  may  wish  to  know  how  a  course  such  as 
that  described  in  the  Practical  Exercises  may  be  conducted 
for  a  fairly  large  class,  a  few  words  on  the  method  we  have 
followed  may  not  be  out  of  place.  It  is  obvious  that  many 
of  the  exercises  require  more  than  one  person  for  their  per- 
formance ;  and  it  may  be  said  that,  except  in  the  case  of 
the  simpler  experiments  and  the  chemical  work  as  a  whole, 
which  each  student  does  for  himself,  it  has  been  found 
convenient  to  divide  the  class  into  groups  of  four,  each 
group  remaining  together  throughout  the  session.  It  is 
possible  that  some  may  find  a  group  of  four  too  large  a  unit, 
and  it  is  certain  that  three,  or  perhaps  even  two,  would  be 
better ;  but  in  a  large  school  so  minute  a  subdivision  is 

RR2ROA 


6  FROM  THE  PREFACE  TO  THE  FIRST  EDITION 

hardly  possible,  without  entailing  excessive  labour  on  the 
teachers. 

The  systematic  portion  of  the  book  is  so  arranged  that  it 
can  equally  well  be  used  independently  of  the  practical 
work,  and  aims  at  being  in  itself  a  complete  exposition  of 
the  subject,  adapted  to  the  requirements  of  the  student  of 
medicine. 

As  to  the  matter  of  the  text,  it  is  hardly  necessary  to  say 
that  this  book  does  not  aspire  to  the  dubious  distinction 
of  originality ;  and  it  is  literally  impossible  to  acknowledge 
all  the  sources  from  which  information  has  been  derived. 
In  many  cases  names  have  been  quoted,  but  names  no  less 
worthy  of  mention  have  often  been  of  necessity  omitted. 

G.  N.  STEWART. 
CAMBRIDGE,  September -,  1895. 


PREFACE    TO    THE  THIRD  EDITION. 


THE  first  edition  was  quickly  exhausted,  and  the  second  was 
simply  a  reprint.  In  the  present  edition  the  book  has  been 
revised,  and  in  parts  rewritten.  A  considerable  amount  of 
new  matter  has  been  added,  especially  in  the  Practical 
Exercises.  These  additions,  however,  have  in  part  been 
balanced  by  the  omission  of  some  passages  and  the  abridg- 
ment of  others,  and  the  bulk  of  the  volume  is  only  a  little 
increased.  I  am  indebted  to  my  friend  Dr.  Arthur  Clarkson 
for  Fig.  112  and  all  the  coloured  drawings,  except  Plate  I., 
11-13,  taken  from  a  paper  by  Dr.  Kanthack  and  Mr.  Hardy, 
and  Plates  III.,  4,  and  IV.,  4,  supplied  by  my  former  pupil. 
Dr.  Kelly.  Figs.  2,  94-98,  106,  116,  119,  120,152,  174,  234, 
264,  and  277,  have  been  borrowed  from  Beaunis' '  Physiologic.' 
Messrs.  Jung  and  Zeiss  have  lent  me  several  electrotypes  of 

instruments. 

G.  N.  STEWART. 

CAMBRIDGE,  August  15,  1898, 


CONTENTS 


INTRODUCTION     -  -  17 

CHAPTER  I. 

THE  CIRCULATING  LIQUIDS  OF  THE  BODY    -  -  25 

Blood-corpuscles         -  -                -  26 

Life-history  of  the  corpuscles  •  31 

Coagulation  of  blood  -  36 

Chemical  composition  of  blood  -                -  45 

Haemoglobin  and  its  derivatives  -                -  46 

Quantity  of  blood        -  51 

Lymph  and  chyle       -  -  52 

Functions  of  blood  and  lymph  -  54 

CHAPTER  II. 

THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH  -  67 

Flow  of  a  liquid  through  tubes  -  -  71 

The  beat  of  the  heart  -  74 

The  sounds  of  the  heart  -  77 

The  cardiac  impulse  -  -  79- 

Endocardiac  pressure  -  81 

The  pulse    -  -  88 

Arterial  blood-pressure  -                -  99 

Velocity  of  the  blood  -  105 

The  volume-pulse       -  -  116 

The  circulation  in  the  capillaries  117 

The  circulation  in  the  veins  -  120 

The  circulation-time       -  122 

The  relation  of  the  nervous  system  to  the  circulation  -  127 

Intrinsic  nerves  of  the  heart      -  -  128 

Extrinsic  nerves  of  the  heart     -  -  133 

Vaso-motor  nerves     -  •                -  148 

The  lymphatic  circulation  -  166 

CHAPTER  III. 

RESPIRATION  -  194 

Mechanical  phenomena  of  respiration      -  -  197 

Types  of  respiration   -  -  202 

Frequency  of  respiration  •                 -  206 


io  CONTENTS 

PAGE 

RESPIRATION— continued 

Vital  capacity  -  208 

Intra-thoracic  pressure  -  209 

Respiratory  pressure  -  -  210 

Relation  of  respiration  to  the  nervous  system          -  211 

Chemistry  of  respiration  -  223 

Solution  and  pressure  of  gases                                    -  -  229 

The  gases  of  the  blood                                                 -  -  234 

Seats  of  oxidation       -  -  243 

Respiration  of  muscle  '  •  245 

Influence  of  respiration  on  blood  pressure                -  -  249 

Effects  of  breathing  condensed  and  rarefied  air      -  -  255 

Voice  and  speech       -                                                -  -  259 

CHAPTER  IV. 

DIGESTION                                                      .              -  -  279 

Mechanical  phenomena  of  digestion         -  •  283 

Vomiting     -                                                                     -  -  292 

Chemistry  of  the  digestive  juices              -  -  294 

Saliva  -  295 

Gastric  juice  -  300 

Pancreatic  juice                               ...  305 

Bile  -                                                                 -  -  309 

Succus  entericus  -  315 

Secretion  of  the  digestive  juices  -  317 

Changes  in  pancreas  and  parotid  during  secretion       -  319 

Changes  in  gastric  glands  during  secretion  -  -  320 

Changes  in  mucous  glands  during  secretion  -  322 

Mode  of  formation  of  the  digestive  juices      -  -  326 

Why  the  stomach  does  not  digest  itself  •  330 

Influence  of  the  nervous  system  on  the  salivary  glands  -  332 

Influence  of  the  nervous  system  on  the  gastric  glands  -  342 

Influence  of  the  nervous  system  on  the  pancreas  -  344 

Influence  of  the  nervous  system  on  the  secretion  of  bile  345 

Influence  of  the  nervous  system  on  the  secretion  of  intestinal 

juice  347 

Secretion  of  the  digestive  juices  (summary)             -  -  348 

Digestion  as  a  whole  -  348 

Bactericidal  function  of  the  gastric  juice  -  -  355 

CHAPTER  V. 

ABSORPTION  -  360 

Diffusion  and  osmosis  -  360 

Absorption  of  the  food                                                 -  -  363 

Formation  of  lymph                                                      •  •  368 

Absorption  of  fat         -  -  3 70 

Absorption  of  water,  salts,  and  sugar        -  -  371 

Absorption  of  proteids                                 -  -  372 

CHAPTER  VI. 

EXCRETION                                        .              .              -  -  384 

Excretion  by  the  kidneys                                             .  -  385 

Chemistry  of  urine      -                 .                -                .  -  385 

The  urine  in  disease  -                -                                 -  -  391 

Secretion  of  urine                        ....  395 


CONTENTS  1 1 

PAGE 

EXCRETION— continued 

Influence  of  the  circulation  on  the  secretion  of  urine  405 

Micturition  -  410 

Excretion  by  the  skin  -  412 

CHAPTER  VII. 

METABOLISM,  NUTRITION  AND  DIETETICS  -  430 

Metabolism  of  proteids  -  430 

Formation  of  urea      -  -  432 

Metabolism  of  carbo-hydrates — glycogen  -  439 

Diabetes      -  -                -  444 

Metabolism  of  fat       -  -  446 

Income  and  expenditure  of  the  body  -  450 

Nitrogenous  equilibrium  -  452 

Laws  of  nitrogenous  metabolism  -                •  457 

Carbon  equilibrium    -  -                -  461 

Dietetics  .  464 

Internal  secretion  -                >  471 

CHAPTER  VIII. 

ANIMAL  HEAT  -              -  477 

Calorimetry                  -  •                -  479 

Heat-loss     -  ...  482 

Heat- product!  on  -                -  484 

Thermotaxis  -                -  491 

Fever  -  501 

Distribution  of  heat    -  -  505 

Temperature  topography  -  507 

CHAPTER  IX. 

MUSCLE  -                             -  517 

Physical  introduction  -  517 

Physical  properties  of  muscle    -  531 

Stimulation  of  muscle  -  533 

The  muscular  contraction  -  537 

Optical  phenomena  of  (and  structure  of  muscle)  -  538 

Mechanical  phenomena  of  -  541 

Influence  of  fatigue  on    -  -  549 

Thermal  phenomena  of  -  559 

Chemical  phenomena  of  -  562 

Source  of  the  energy  of  muscular  contraction  -  5^4 

Rigor  mortis  -  565 

CHAPTER  X. 

NERVE  -  -  570 

The  nerve-impulse  ;  its  initiation  and  conduction   -  -  571 

Stimulation  of  nerve  -  -  572 

Electrotonus  -  574 

Conduction  in  the  nerve  -  579 

Velocity  of  the  nerve-impulse    -  •                                 -  5^J 

Nutrition  of  nerve       -  •  5^4 

Trophic  nerves  -                                  -  5^7 

Classification  of  nerves               -  -                                 -  5^9 


j  2  CONTENTS 

CHAPTER  XL 

PAGE 

ELECTRO-PHYSIOLOGY                      -  -              •              -    605 

Currents  of  rest  and  action  -                -     606 

Polarization  of  muscle  and  nerve  -     615 

Electrotonic  currents  -                                      6 16 

Heart-currents                             -  -     621 

Glandular  currents     -  •                                       623 

Eye-currents  -     624 

Electric  fishes             -                -  -                -                -     624 


CHAPTER  XII. 

THE  CENTRAL  NERVOUS  SYSTEM  -  -  635 

Structure  -  -  636 

Development  •  637 

Histology  -  638 
General  arrangement  of  grey  and  white  matter  in  the  central 

nervous  system  -  -  644 
Arrangement  of  grey  and  white  matter  in  the  spinal  cord  -  646 
Arrangement  of  grey  and  white  matter  in  the  upper  part  of 

the  cerebro-spinal  axis  651 

Functions  of  the  central  nervous  system  -  663 

Functions  of  the  spinal  cord  -  665 

Decussation  of  impulses  in  the  cord  -  670 

Reflex  action  -  674 

Automatism  of  the  spinal  cord  -  68 1 

The  cranial  nerves  -  -  685 

The  functions  of  the  brain  692 

Functions  of  the  cerebellum  -  -  694 

Co-ordination  of  movements  -  700 

Functions  of  the  cerebral  cortex  703 

Motor  areas  707 

Sensory  areas  -  711 


CHAPTER  XIII. 

THE  SENSES  -    732 

Vision  -     734 

Physical  introduction  -                                                       734 

Structure  of  the  eye  -     742 

Refraction  in  the  eye  -                                                        743 

Accommodation  747 

Iris   -  -     75° 

Defects  of  the  eye  -     755 

Ophthalmoscope  761 

Diplopia  765 

Rods  and  cones  in  vision  773 

Blind  spot         -  -     7?8 

Talbot's  law  780 

Colour  vision    -  781 

Hearing       -  797 

Smell  and  taste  806 

Tactile  senses  809 

Muscular  sense  -                -                                 -     812 


CONTENTS 

CHAPTER  XIV. 

REPRODUCTION    - 

Regeneration  of  tissues 

Reproduction  in  the  higher  animals 

Menstruation 

Development  of  the  ovum 

Physiology  of  the  embryo 
INDEX   -  ... 


PAGE 

-  822 

-  822 
'  823 

-  824 

-  824 

-  827 

-  835 


PRACTICAL     EXERCISES. 

INTRODUCTION. 

1.  General  reactions  of  proteids 

2.  Special  reactions  of  groups  of  proteids 

3.  Carbo-hydrates 

4.  Fats 

CHAPTER  I. 

1.  Reaction  of  blood 

2.  Specific  gravity  of  blood 

3.  Coagulation  of  blood 

4.  Preparation  of  fibrin-ferment 

5.  Serum 

6.  Enumeration  of  the  corpuscles 

7.  Opacity  of  blood 

8.  Laking  of  blood 

9.  Globulicidal  action  of  serum 
10.  Blood-pigment 

(1)  Preparation  of  haemoglobin  crystals 

(2)  Spectroscopic    examination    of   haemoglobin    and 

derivatives 

(3)  Guaiacum  test  for  blood  - 

(4)  Quantitative  estimation  of  haemoglobin 

(5)  Haemin  test  for  blood-pigment 

CHAPTER  II. 

1.  Microscopic  examination  of  the  circulating  blood 

2.  Anatomy  of  the  frog's  heart 

3.  The  beat  of  the  heart 

4.  Apex  of  the  heart 

5.  Heart-tracings 

6.  Dissection  of  vagus  and  cardiac  sympathetic  in  frog  - 

7.  Stimulation  of  the  vagus  in  the  frog 

8.  Stimulation  of  the  junction  of  the  sinus  and  auricles   - 

9.  Action  of  muscarine  and  atropia  on  the  heart 

10.  Stannius'  experiment 

11.  Stimulation  of  cardiac  sympathetic  in  frog  - 

12.  The  action  of  the  mammalian  heart 

13.  Action  of  the  valves  of  the  heart   - 

14.  Sounds  of  the  heart 

15.  Cardiogram     -  .   '    • 

16.  Sphygmographic  tracings 

17.  Plethysmographic  tracings 


its 


20 
21 

23 

24 


57 
57 
58 
60 
60 
61 
61 
61 
62 
62 
62 

62-64 
64 
65 
66 


168 
168 
168 
169 
169 
171 
173 
174 
174 

175 

I71 
176 

179 
182 
182 
182 
183 


14  CONTENTS 

PAGE 

1 8.  Pulse- rate        -                                                                                 -  184 

19.  Blood-pressure  tracing   -                                                                   -  185 

20.  Influence  of  position  of  the  body  on  blood-pressure     -                 -  187 

21.  Effects  of  haemorrhage  and  transfusion  on  blood-pressure          -  188 

22.  The  influence  of  albumoses  on  the  blood-pressure       -  188 

23.  Effect  of  suprarenal  extract  on  the  blood-pressure  -  189 

24.  Section  and  stimulation  of  cervical  sympathetic  in  rabbit           -  189 

25.  Stimulation  of  the  depressor  nerve                                                  -  190 

26.  Determination  of  the  circulation-time  •* :  192 


CHAPTER  III. 

1.  Tracing  of  the  respiratory  movements                                            -  272 

2.  Heat-dyspnoea                                                                                    -  272 

3.  Measurement  of  volume  of  air  inspired  and  expired    -                 -  274 

4.  Measurement  of  the  respiratory  pressure      -  274 

5.  Determination  of  carbon  dioxide  and  oxygen  in  inspired  and 

expired  air  -                                                                                    -  275 

6.  Estimation  of  carbon  dioxide  and  water  given  off  by  an  animal  -  276 

7.  Section  of  both  vagi                                                                           -  278 


CHAPTERS  IV.  AND  V. 

1.  Chemistry  and  digestive  action  of  saliva  -  374 

2.  Stimulation  of  the  chorda  tympani  -  375 

3.  Effect  of  drugs  on  the  secretion  of  saliva     -  -  376 

4.  Digestive  action  of  gastric  juice    -  -  376 

5.  To  obtain  chyme  and  gastric  juice  -  378 

6.  Digestive  action  of  pancreatic  juice  -  378 

7.  To  obtain  pancreatic  juice  379 

8.  Chemistry  of  bile  380 

9.  Microscopical  examination  of  fasces  381 

10.  Absorption  of  fat  381 

11.  Time  required  for  digestion  and  absorption  of  food  substances  -  381. 

12.  Quantity  of  cane-sugar  inverted  and  absorbed  in  a  given  time  -  382 

13.  Auto-digestion  of  the  stomach       -  -  383 

14.  Time  required  for  food  to  pass  through  alimentary  canal  -  383 


CHAPTER  VI. 

1.  Specific  gravity  of  urine  -  416 

2.  Reaction  of  urine  •  416 

3.  Chlorides  in  urine  -                 -  416 

4.  Phosphates  in  urine  -                                                  -                -  417 

5.  Sulphates  in  urine  -  418 

6.  Indoxyl  in  urine  -                -                -                -  418 

7.  Urea  -                                 -  4'9    . -, 

8.  Total  nitrogen  in  urine  -                                                                   -  421   /.-> 

9.  Uric  acid  -  422 
TO.  Kreatinin  -  424 

11.  Hippuric  acid  -  -  424 

12.  Proteids  in  urine  424 

13.  Sugar  in  urine  426 

14.  Catheterism     -  429 


CONTENTS  1 5 
CHAPTERS  VII.  AND  VIII. 

PAGE 

1.  Glycogen  -                -511 

2.  Experimental  glycosuria  -  512 

(1)  Injection  of  sugar  into  the  blood    -  512 

(2)  Phloridzin  diabetes  -  512 

(3)  Puncture  diabetes  -  5I3«6"~ 

(4)  Alimentary  glycosuria  -  513 

3.  Measurement  of  the  heat  given  off  in  respiration  -                •  513 

4.  Excretion  of  urea  and  proteids  in  food  -  515 

5.  Thyroidectomy  -  515 

6.  Thy roidectomy  with  thyroid  feeding  -                -  516 


CHAPTERS  IX.  AND  X. 

1.  Difference  of  make  and  break  induction  shocks  -     590 

2.  Stimulation  by  the  voltaic  current-  -     592 

3.  Mechanical  stimulation  -  -     593 

4.  Thermal  stimulation       -  -     593 

5.  Chemical  stimulation      -  -     593 

6.  Ciliary  motion  593 

7.  Direct  excitability  of  muscle— curara  -     593 

8.  Graphic  record  of  '  twitch '  -                -     594 

9.  Influence  of  temperature  on  the  muscle-curve  594 

10.  Influence  of  load  on  the  muscle-curve  -     596 

11.  Influence  of  fatigue  on  the  muscle-curve  5967^ 

12.  Seat  of  exhaustion  in  fatigue  of  the  muscle-nerve  preparation  -     596 

13.  Seat  of  exhaustion  in  fatigue  for  voluntary  contraction  597 

14.  Influence  of  veratria  on  muscular  contraction  -     598 

15.  Measurement  of  the  latent  period  598 

16.  Summation  of  stimuli     -  -     599 

17.  Superposition  of  contractions        -  599 

1 8.  Composition  of  tetanus  -  •     599 

19.  Velocity  of  the  nerve-impulse  -     600 

20.  Chemistry  of  muscle      -  -    601 

21.  Reaction  of  muscle  in  rest,  activity  and  rigor  -                -     603 

22.  Action  of  suprarenal  extract  603 


CHAPTER  XL 

1.  Galvani's  experiment      -  -  627 

2.  Contraction  without  metals                                              -  -  627 

3.  Stimulation  of  a  nerve  by  its  own  demarcation  current  -  627 

4.  Secondary  contraction    -  -  627 

5.  Demarcation  and  action  currents  with  capillary  electrometer     -  628 

6.  Action-current  of  the  heart  629 

7.  Electrotonus   -  -  629   ' 

8.  Paradoxical  contraction  -  -  630 

9.  Alterations  in  excitability  and  conductivity  produced  in  nerve  by 

a  voltaic  current  -  630 

10.  Formula  of  contraction  -  632 

11.  Ritter's  tetanus  -  633 

12.  Positive  polarization        -  -  633 

13.  Galvanotropism  634 


1  6  CONTENTS 

CHAPTER  XII. 


PAGE 


1.  Hemisection  of  the  spinal  cord     -  ...  728 

2.  Section  and  stimulation  of  nerve-roots  .  -  729 

3.  Reflex  action  -  .  .  729 

4.  Action  of  strychnia  .  -  729 

5.  Excision  of  cerebral  hemispheres  (frog)  -  -  729 

6.  Excision  of  cerebral  hemispheres  (pigeon)  -  -  730 

7.  Stimulation  of  the  motor  areas  in  the  dog  -  -  -  730 

8.  Removal  of  the  motor  areas  in  the  dog  .  -  -731 

CHAPTER  XIII. 

1.  Formation  of  inverted  image  on  retina  -  -  -  815 

2.  Phakoscope     -  -  -  815 

3.  Scheiner's  experiment    -  -  -  -  816 

4.  Ktihne's  artificial  eye     -  -  -  -  817 

5.  Mapping  the  blind  spot  -  -  -  -  819 

6.  Ophthalmoscope  -  .  -  819 

7.  Pupillo-  dilator  and  constrictor  fibres  -  -  820 

8.  Colour-mixing"                                  -  -  .  -  821 

9.  Talbot's  law     -  .  -  -  821 

10.  Purkinje's  figures  -  .  -  821 

11.  Relation  of  pitch  and  vibration  frequency  -  -  -  821 

12.  Beats                                              -  -  .  -  821 

13.  Acuity  of  touch              •               -  -  -  .821 


A   MANUAL  OF    PHYSIOLOGY. 


INTRODUCTION. 

*  Life  is  a  power  superadded  to  matter  ;  organization  arises 
from,  and  depends  on,  life,  and  is  the  condition  of  vital  action  ; 
but  life  never  can  arise  out  of,  or  depend  on,  organization.' — 
JOHN  HUNTER. 

LIVING  matter,  whether  it  is  studied  in  plants  or  in  animals, 
has  certain  peculiarities  of  chemical  composition  and  struc- 
ture, but  especially  certain  peculiarities  of  action  or  function 
which  mark  it  off  from  the  unorganized  material  of  the  dead 
world  around  it. 

Chemical  Composition  of  Living  Matter. — Although  we  cannot 
analyze  the  living  substance  as  such,  we  can  to  a  certain, 
but  limited,  extent  reconstruct  it,  so  to  speak,  from  its  ruins. 
When  subjected  to  analytical  processes,  which  necessarily 
kill  it,  living  matter  invariably  yields  bodies  of  the  class  of 
proteids,  which  have  approximately  the  following  composition : 
Carbon,  51*5  to  5-4*5  per  cent.;  oxygen,  20*9  to  23*5  per  C 
cent. ;  nitrogen,  15*2  to  17  per  cent.  ;  hydrogen,  6*9  to  7*3  ( 
per  cent.,  with  small  quantities  of  sulphur  and  generally  of 
phosphorus.  Nucleo  -  proteids,  which  are  compounds  of 
proteid  with  nucleins,  a  series  of  bodies  very  rich  in  phos- 
phorus, are  also  constantly  met  with.  Certain  carbo-hydrates, 
composed  of  carbon,  hydrogen,  and  oxygen  (the  last  two  in 
the  proportions  necessary  to  form  water),  of  which  glycogen 
(C6H10O5)  may  be  taken  as  a  type,  appear  to  be  always 
present.  Fats,  which  consist  of  carbon,  hydrogen,  and 
oxygen,  and  of  which  tristearin,  a  compound  of  stearic  acid 
with  glycerine,  of  the  formula  C3H5,  3(C18H35O2),  may  be 

2 


i8  ;;  A  A  MAMUAfr  OF  PHYSIOLOGY 


given  as9  ^  exartrple,  ate  often,  but  perhaps  not  always, 
found.  Finally,  water  and  Certain  inorganic  salts,  such  as 
the  chlorides  and  phosphates  of  sodium,  potassium,  and 
calcium,  are  constantly  present. 

Structure  of  Living  Matter  —  The  Cell.  —  The  investigations  of  the 
last  few  years  have  shown  that  protoplasm,  the  primitive  living 
substance,  when  examined  with  sufficiently  high  powers,  is  by  no 
means  the  '  homogeneous,  structureless  material  '  it  was  at  one  time 
believed  to  be.  It  is  rather  a  substance  of  porous  or  reticulated 
structure,  a  spongework  or  network,  holding  a  fluid  in  its  meshes. 
And  in  all  probability  the  network  is  the  true  living  machinery,  the 
liquid  in  its  interstices  being  perhaps  pabulum,  from  which  the 
waste  of  the  living  framework  is  made  good,  or  material  upon  which 
it  works,  and  which  it  is  its  business  to  transform.  So  that  in  build- 
ing up  our  typical  cell  we  start  with  a  piece  of  protoplasm  of  reticular 
structure,  the  network  in  which  is  called  the  intracellular  network. 
Somewhere  in  the  midst  of  this  cell-substance  we  find  a  body  which, 
if  not  absolutely  different  in  kind  from  the  protoplasm  of  the  cell,  is 
yet  marked  off  from  it  by  very  definite  morphological  and  chemical 
characters.  This  is  the  nucleus,  generally  of  round  or  oval  shape, 
and  bounded  by  an  envelope.  Within  the  envelope  lies  a  second 
network,  which,  when  the  nucleus  is  about  to  divide  in  the  manner 
known  as  indirect  division,  or  karyokinesis,  becomes  converted  into 
one  or  more  coiled  filaments  or  skeins.  Both  the  network  and  the 
filaments  are  made  up  of  rows  of  highly  refractive  particles,  embedded 
in  a  homogeneous  matrix.  These  particles  possess  the  property  of 
staining  readily  and  deeply  with  dyes,  and  have,  therefore,  been 
described  as  consisting  of  chromatin  ;  and  there  is  a  certain  amount 
of  evidence  that  this  chromatin  is  either  made  up  of  nucleins 
(substances  composed  of  a  sulphur-free  organic  acid,  nucleic  acid, 
combined  in  various  proportions  with  proteids),  or  yields  nucleins  by 
its  decomposition  (Zacharias).  In  any  case,  it  is  believed  that  it  is 
to  the  presence  of  nucleic  acid  that  the  chromatic  material  owes  its 
affinity  for  such  basic  dyes  as  methyl-green.  The  meshes  of  the 
nuclear  reticulum  contain  a  semi-fluid  material,  which  does  not 
readily  stain. 

When  we  carry  back  the  analysis  of  an  organized  body  as 
far  as  we  can,  we  find  that  every  organ  of  it  is  made  up  of 
cells,  which  upon  the  whole  conform  to  the  type  we  have 
been  describing,  although  there  are  many  differences  in 
details.  Some  organisms  there  are,  low  down  in  the  scale, 
whose  whole  activity  is  confined  within  the  narrow  limits  of 
a  single  cell.  The  Amoeba  sets  up  in  life  as  a  cell  split  off 
from  its  parent.  It  divides  in  its  turn,  and  each  half  is  a 
complete  Amoeba.  When  we  come  a  little  higher  than  the 


INTRODUCTION  19 

Amoeba,  we  find  organisms  which  consist  of  several  cells, 
and  '  specialization  of  function '  begins  to  appear.  Thus 
the  Hydra,  the  *  common  fresh-water  Polyp '  of  our  ponds 
and  marshes,  has  an  outer  set  of  cells,  the  ectoderm,  and  an 
inner  set,  the  endoderm.  Through  the  superficial  portions 
of  the  former  it  learns  what  is  going  on  in  the  world ;  by 
the  contraction  of  their  deeply-placed  processes  it  shapes  its 
life  to  its  environment.  As  we  mount  in  the  animal  scale, 
specialization  of  structure  and  of  function  are  found  con- 
tinually advancing,  and  the  various  kinds  of  cells  are  grouped 
together  into  colonies  or  organs. 

The  Functions  of  Living  Matter. — The  peculiar  functions  of 
living  matter  as  exhibited  in  the  animal  body  will  form  the 
subject  of  the  main  portion  of  this  book;  and  we  need  only  say 
here  (i)  that  in  all  living  organisms  certain  chemical  changes  go 
on,  the  sum  total  of  which  constitutes  the  metabolism  of  the 
body.  These  may  be  divided  into  (a)  integrative  or  anabolic 
changes,  by  which  complex  substances  (including  the  living 
matter  itself)  are  built  up  from  simpler  materials ;  and 
(6)  disintegrative  or  katabolic  changes,  in  which  complex  sub- 
stances (including  the  living  substance)  are  broken  down 
into  comparatively  simple  products.  In  plants,  upon  the 
whole,  it  is  integration  which  predominates ;  from  sub- 
stances so  simple  as  the  carbon  dioxide  of  the  air  and  the 
nitrates  of  the  soil  the  plant  builds  up  its  carbo-hydrates  and 
its  proteids.  In  animals  the  main  drift  of  the  metabolic 
current  is  from  the  complex  to  the  simple ;  no  animal  can 
construct  its  own  protoplasm  from  the  inorganic  materials 
that  lie  around  it ;  it  must  have  ready-made  proteid  in  its 
food.  But  in  all  plants  there  is  some  disintegration ;  in  all 
animals  there  is  some  synthesis.  (2)  The  living  substance  is 
excitable — that  is,  it  responds  to  certain  external  impressions, 
or  stimuli,  by  actions  peculiar  to  each  kind  of  cell.  (3)  The 
living  substance  reproduces  itself.  All  the  manifold  activities 
included  under  these  three  heads  have  but  one  source,  the 
transformation  of  the  energy  of  the  food.  It  is  not,  however, 
upon  the  whole,  peculiarities  in  food,  but  in  molecular 
structure,  that  underlie  the  peculiarities  of  function  of 
different  living  cells.  A  locomotive  is  fed  with  coal ;  a 

2 — 2 


20  A  MANUAL  OF  PHYSIOLOGY 

steam-pump  is  fed  with  coal.  The  one  carries  the  mail, 
and  the  other  keeps  a  mine  from  being  flooded.  Wherein 
lies  the  difference  of  action  ?  Clearly  in  the  build,  the 
structure  of  the  mechanism,  which  determines  the  manner 
in  which  energy  shall  be  transformed  within  it,  not  in  any 
difference  in  the  source  of  the  energy.  So  one  animal  cell, 
when  it  is  stimulated,  shortens  or  contracts ;  another,  fed 
perhaps  with  the  same  food,  selects  certain  constituents 
from  the  blood  or  lymph  and  passes  them  through  its  sub- 
stance, changing  them,  it  may  be,  on  the  way ;  and  a  third 
sets  up  impulses  which,  when  transmitted  to  the  other  two, 
initiate  the  contraction  or  secretion.  In  the  living  body  the 
cell  is  the  machine  ;  the  transformation  of  the  energy  of  the 
food  is  the  process  which  '  runs '  it.  The  structure  and 
arrangement  of  cells  and  the  steps  by  which  energy  is  trans- 
formed within  them  sum  up  the  whole  of  biology. 

PRACTICAL  EXERCISES. 
Reactions  of  Proteids 

i.  Genetal  Reactions  of  Proteids. — Egg-albumin  may  be  taken  as 
a  type.  Prepare  a  solution  of  it.  In  breaking  the  egg,  take  care 
that  none  of  the  yolk  gets  mixed  with  the  white.  Snip  the  white  up 
with  scissors  in  a  large  capsule,  then  add  ten  or  fifteen  times  its 
volume  of  distilled  water.  The  solution  becomes  turbid  from  the 
precipitation  of  traces  of  globulin,  since  globulins  are  insoluble  in 
distilled  water.  Stir  thoroughly,  strain  through  several  layers  of 
muslin,  and  then  filter  through  paper 

(1)  Add  to  a  little  of  the  solution  in  a  test-tube  a  few  drops  of 
strong  nitric  acid.     A  precipitate  is  thrown  down,  which   becomes 
yellow  on    boiling.      Cool,   and  add  strong  ammorua_:    the  colour 
changes  to  orange  (xantho-proteic  reaction}. 

(2)  Acidify  another  portion  strongly  with  acetic  acid,  and  add  a 
few  drops  of  a  solution  of  potassium  ferrocyanide.     A  white  pre- 
cipitate is  obtained.     Peptones  do  not  give  this  reaction. 

(3)  To  a  third  portion  add  a  drop  or  two  of  very  dilute  cupric 
sulphate  and  excess  of  sodium  or  potassium  hydrate  :  a  violet  colour 
appears.     Peptones  and  proteoses  (albumoses)  give  a  pink  (biuret 
reactioti)*     See  p.  377. 

(4)  To  another  portion  add  Millon's  reagent  :t  a  precipitate  comes 

*  The  reaction  is  also  given,  although  more  faintly,  with  the  hydrates 
of  lithium,  strontium,  and  barium. 

f  Millon's  reagent  consists  of  a  mixture  of  the  nitrates  of  mercury  with 
nitric  acid  in  excess,  and  some  nitrous  acid.  To  make  it,  dissolve  mercury 


PRACTICAL  EXERCISES  21 

down,  which  is  turned  reddish  on  boiling.     If  only  traces  of  proteid 
are  present,  no  precipitate  is  caused,  but  the  liquid  takes  on  a  red  tinge. 

(5)  Heat  a  portion  to  30°  C.  on  a  water-bath.  Saturate  with 
crystals  of  ammonium  sulphate  ;  the  albumin  is  precipitated.  Filter, 
and  test  the  filtrate  for  proteids  by  (3).  None,  or  only  slight  traces, 
will  be  found.  The  sodium  hydrate  must  be  added  in  more  than 
sufficient  quantity  to  decompose  all  the  ammonium  sulphate.  It 
will  be  best  to  add  a  piece  of  the  solid  hydrate.  Peptones  are  not 
precipitated  by  ammonium  sulphate,  but  all  other  proteids  are. 

2.  Special  Reactions  of  Groups  of  Proteids— (i)  Coagulable  Pro- 
teids :  (a)  Native  Albumins. — (a)  Heat  a  little  of  the  solution  of 
egg-albumin  in  a  test-tube ;  it  coagulates.  With  another  sample 
determine  the  temperature  of  coagulation,  first  slightly  acidulating 
with  dilute  acetic  acid — a  drop  or  two  of  a  2  per  cent,  solution. 

To  determine  the  Temperature  of  Coagulation, — Support  a  beaker 
by  a  ring  which  just  grips  it  at  the  rim.  Nearly  fill  the  beaker  with 
water,  and  slide  the  ring  on  the  stand  till  the  lower  part  of  the  beaker  J"  - 
is  immersed  in  a  small  water-bath  (a  tin  can  will  do  quite  well).  In 
this  beaker  place  a  test-tube,  and  in  the  test-tube  a  thermometer, 
both  supported  by  rings  or  clamps  attached  to  the  same  stand.  Put 
into  the  test-tube  at  least  enough  of  the  albumin  solution  to  com- 
pletely cover  the  bulb  of  the  thermometer,  and  heat  the  bath,  stirring 
the  water  in  the  beaker  occasionally  with  a  feather,  or  a  splinter  of 
wood,  or  a  glass  rod,  the  end  of  which  is  guarded  with  a  piece  of 
indiarubber  tubing,  n  Note  the  temperature  at  which  the  solution 
becomes  turbid,  and  then  the  temperature  at  which  a  distinct  coagu- 
lum  or  precipitate  is  formed. 


A  similar  experiment  may  be  performed  with  serum- albumin. 


obtained  as  on  p.  60. 

(<£)  Globulins. — Use  serum-globulin  (p.  60),  or  myosin  (p.  602), 
Fibrinogen  is  also  a  globulin,  but  cannot  easily  be  obtained  in 
quantity.  Verify  the  following  properties  of  globulins  : 

(a)   They  coagulate  on  heating. 

(/3)  They  are  insoluble  in  distilled  water  (p.  60). 

(y)  They  are  precipitated  by  saturation  with  magnesium  sulphate 
or  sodium  chloride  (p.  60). 

They  give  the  general  proteid  tests  (i)  to  (5). 

(2)  Derived  Albumins  or  Albuminates — (a)  Acid-albumin. — To 
a  solution  of  egg-albumin  add  a  little  '2  per  cent,  hydrochloric  acid, 
and  heat  to  about  body  temperature — say  40°  C. — for  a  few  minutes. 
Acid-albumin  is  formed.  It  can  be  produced  from  all  albumins  and 
globulins  by  the  action  of  dilute  acid.  Make  the  following  tests  : 

(a)  Add  to  a  portion  of  the  solution  in  a  test-tube  a  few  drops  of 
a_splution  of  litmus  :  the  colour  becomes  red.  Now  add  drop  by 
drop  j>odium  carbonate  or  dilute  sodium  hydrate  solution  till  the 
tint  just  begins  to  change  to  blue.  A  precipitate  of  acid-albumin  is 

in  its  own  weight  of  strong  nitric  acid,  and  add  to  the  solution  thus 
obtained  twice  its  volume  of  water.  Let  it  stand  for  a  short  time,  and 
then  decant  the  clear  liquid,  which  is  the  reagent. 


22  A  MANUAL  OF  PHYSIOLOGY 

thrown  down.  Add  a  little  more  of  the  alkali,  and  the  precipitate  is 
redissolved.  It  can  be  again  brought  down  by  neutralizing  with  acid. 

(/3)  Heat  a  portion  of  the  solution  to  boiling  ;  no  precipitate  is 
formed. 

(y)  Add  strong  nitric  acid  :  a  precipitate  appears,  which  dissolves 
on  heating,  and  the  liquid  becomes  yellow. 

(b)  Alkali-albumin.  —  To  a  solution  of  egg-albumin  add  a  little 
,  and  heat  gently  for  a  few  minutes.  Alkali-  albumin 


,/ 


is  produced.     It  can  also  be  derived  by  similar  treatment  from  any 
albumin  or  globulin. 

^  (a)  Neutralize,  after  colouring  with  litmus  solution,  by  the  addition 
of  dilute  hydrochloric  or  acetic  acid.  Alkali-albumin  is  precipitated 
when  neutralization  has  been  reached.  It  is  redissolved  in  excess  of 
the  acid. 

(J3)  To  another  portion  of  the  solution  of  alkali-albumin  add  a  few 
drops  of  sodium  phosphate  solution,  then  litmus,  and  then  dilute  acid 
till  the  alkali-albumin  is  precipitated.  More  of  the  dilute  acid  should 
now  be  required  to  precipitate  the  alkali-albumin,  since  the  sodium 
phosphate  must  first  be  changed  into  acid  sodium  phosphate. 
x/rv^  (y)  On  heating  the  solution  of  alkali-albumin  there  is  no  coagu- 
lation. 

(3)  Proteoses  (Albumoses).  —  For  preparation  and  reactions,  see 
p.  377.     They  differ  from  group  (i)  in  not  being  coagulated  by  heat, 
and   from  group   (2)    in   not    being   precipitated  by  neutralization. 
They  are  soluble  (with  the  exception  of  hetero-  and  dys-albumose), 
in  distilled  water,   and  are  not  precipitated  by  saturation  of  their 
solutions  with  magnesium  sulphate  or  sodium  chloride.     Saturation 
with  ammonium    sulphate   precipitates    them.     With  a  solution    of 
commercial   '  peptone,'   which    consists   chiefly   of  albumoses,   and 
contains  only  a  little  true  peptone,  perform  the  following  tests  : 

(a)    Boil  the  solution  ;  there  is  no  coagulation. 

(/?)  Biuret  reaction,  (3)  p.  20. 

(y)  Add  to  a  little  of  the  solution  a  drop  of  strong  nitric  acid  by 
means  of  a  glass  rod  or  small  pipette  ;  a  precipitate  is  formed,  which 
dissolves  on  heating,  and  reappears  on  cooling. 

(4)  Peptones.  —  For  preparation  and  tests,  see  p.  377.     They  differ 
from  groups  (i)   and  (2)  in  the  same  way  as  albumoses,  and  they 
differ   from   albumoses   in    not   being   precipitated   by   ammonium 
sulphate.     Saturate  the    solution    of   commercial    '  peptone  '   with 
ammonium  sulphate  ;  the  albumoses  are  precipitated.     Filter  ;  the 
peptones  are  contained  in  the  filtrate.     On  it  perform  the  biuret 
test,  as  described  in  (5),  p.  21  ;  and  note  that  the  pink  colour  is  the 
same  as  that  given  by  albumoses. 

(5)  Coagulated  Proteids.  —  These  are  divided  into  two  classes  : 

(a)  Proteids  coagulated  by  heat,  such  as  boiled  white  of  egg. 

(b)  Proteids  whose  coagulation  is   determined  by  the  action   of 
ferments.     Of  these,  fibrin  is  a  type.     Both  classes  give  such  of  the 
general  proteid  tests,  (i),  (3),  (4),  p.  20,  as  with  suitable  modifica- 
tions can  be  instituted  on  solid  substances.     Thus,  in  performing 
(3),  a  flake  of  fibrin  or  a  small  piece  of  the  boiled  egg-white  should 


PRACTICAL  EXERCISES  23 

be  soaked  for  a  few  minutes  in  a  dilute  solution  of  cupric  sulphate. 
Then  the  excess  of  the  cupric  sulphate  should  be  poured  off,  and 
sodium  hydrate  added,  when  the  coagulated  proteid  will  become 
violet.  Heat-coagulated  proteids  are  insoluble  in  water,  weak  acids 
and  alkalies,  and  saline  solutions,  but  fibrin  is  slightly  soluble  in  the 
latter. 

Carbo-hydrates. 

^  i.  Glucose  or  Dextrose. — Make  a  solution  of  dextrose,  in  water, 
and  apply  to  it  Trommer's  test  for  reducing  sugar.  Put  some  of 
the-dextrose  sc-lutrorr  in  ar  test-tube,  <Jtheff-a  few  drops  of  cupric 
sulphate,  and  then  excess  of  sodium  or  potassium  hydrate.  The 
blue  precipitate  of  cupric  hydrate  which  is  first  thrown  down  is 
immediately  dissolved  in  the  presence  of  dextrose  and  many  other 
organic  substances.  Now  boil  the  blue  liquid,  and  a  yellow  or  red 
precipitate  (cuprous  hydrate  or  oxide)  is  formed. 

2.  Cane-sugar. — Perform  Trommer's  test  with  a  sample  of  a  solu- 
tion.    A  blue  liquid  is  obtained,  which  is  not  changed  on  boiling. 
Now  put  the  rest  of  the  solution  in  a  flask.     Add  ^th  of  its  bulk  of 
strong  hydrochloric  acid,  and  boil  for  a  quarter  of  an  hour.     Again 
perform  Trommer's  test.     It  shows  that  much  reducing  sugar  is  now 
present.     The  cane-sugar  has  been  '  inverted,'  i.e.,  changed  into  a 
mixture  of  dextrose  and  levulose. 

3.  Starch. — (i)  Cut  a  slice  from  a  well-washed  potato;  take  a 
scraping  from  it  with   a  knife,  and  examine  with  the  microscope. 
Note  the  starch  granules  with   their  concentric  markings,  using  a 
small  diaphragm.     Run  a  drop  of  dilute  iodine  solution  under  the 
cover-slip,  and  observe  that  the  granules  become  bluish.    ""Examine 

.also  with  a  polarization  microscope.  (2)  Rub  up  a  little  starch  in  a 
mortar  with  cold  water,  then  add  boiling  water  and  stir  thoroughly. 
Decant  into  a  capsule  or  beaker,  and  boil  for  a  few  minutes.  After 
the  liquid  has  cooled,  perform  the  following  experiments  : 

(a)  Adda  few  drops  of  iodine  solution  to  a  little  of  the  thin  starch 
mucilage  in  a  test-tube.     A  blue  colour  is  produced,  which  disappears 
on  heating,  returns  on  cooling,  is  bleached  by  the  addition  of  a  little 
sodium  hydrate,  and  restored  by  dilute  acid. 

(b)  Test  the  starch   solution   for  reducing  sugar  by  Trommer's 
test.      If  none  is   found,  boil  some  of  the  mucilage  with  a  little 
dilute    sulphuric   acid   in    a   flask   for   twenty  minutes,    and   again 
perform  Trommer's  test.     Abundance  of  reducing  sugar  will  now  be 
present. 

4.  Dextrin. — Dissolve  some  dextrin  in  boiling  water.    Cool.    Add 
iodine  solution  to  a  portion  ;  a  reddish-brown  (port-wine)  colour 
results,  which  disappears  on  heating  and  returns  on  cooling.     The 
colour  is  also  bleached  by  alkali,   restored  by  acid.     If  too  little 
iodine  has  been  added  there  may  be  no  restoration  of  the  colour  by 
the  acid.     The  addition  of  a  little  more  iodine  to  the  acid  solution 
will  then  cause  the  port-wine  colour  to  return,  arid  this  may  be  again 
bleached  by  alkali,  and  will  now  be  restored  by  acid. 

5.  Glycogen. — Seep.  511. 


24  A  MANUAL  OF  PHYSIOLOGY 

Fats. 

ix^a)  Take  a  little  lard  or  olive-oil,  and  observe  that  fat  is  soluble  in 
ether  or  warm  alcohol,  but  not  in  water.  Put  a  drop  of  the  ethereal 
solution  of  fat  on  a  piece  of  paper,  and  note  that  it  leaves  a  greasy 
stain. 

(fi)  Boil  a  little  lard  with  potassium  hydrate  in  a  capsule.  The 
fat  is  broken  up  into  glycerine  and  fatty  acid,  and  the  latter  unites 
with  the  alkali  to  form  a  soap.  Add  a  small  quantity  of  a  20  per 
cent,  solution  of  sulphuric  acid,  and  heat.  The  fatty  acids  are  set 
free  and  collect  on  the  surface. 

(7)  Emuhification. — Put  in  one  watch-glass  a  few  drops  of  neutral 
(fresh)  olive-oil,  and  in  another  a  few  drops  of  a  rancid  oil  containing 
fatty  acids.  Add  a  dilute  solution  (0-25  per  cent.)  of  sodium 
carbonate  to  each.  An  emulsion  will  be  formed  in  the  second 
\\atch-glass,  but  not  in  the  first.  Examine  it  under  the  microscope, 
and  note  the  globules  of  oil  of  various  sizes. 

Or  the  watch-glasses  may  first  be  filled  with  the  sodium  carbonate 
solution,  and  a  drop  of  fresh  oil  then  placed  on  the  surface  of  the 
solution  in  one  and  of  rancid  oil  in  the  other,  by  means  of  a  small 
pipette.  A  creamy  white  ring  will  soon  spread  out  from  the  rancid 
oil,  and  cover  the  sodium  carbonate  solution. 

5"  7- 


CHAPTER  I. 
THE  CIRCULATING  LIQUIDS  OF  THE  BODY. 

IN  the  living  cells  of  the  animal  body  chemical  changes  are 
constantly  going  on ;  energy,  on  the  whole,  is  running 
down;  complex  substances  are  being  broken  up  into  simpler 
combinations.  So  long  as  life  lasts,  food  must  be  brought 
to  the  tissues,  and  waste  products  carried  away  from  them. 
In  lowly  forms  like  the  amoeba,  these  functions  are  per- 
formed by  interchange  at  the  surface  of  the  animal  without 
any  special  mechanism  ;  but  in  all  complex  organisms  they 
are  the  business  of  special  liquids,  which  circulate  in  finely 
branching  channels,  and  are  brought  into  close  relation  at 
various  parts  of  their  course  with  absorbing  organs,  with 
eliminating  organs,  and  with  the  tissue  elements  in  general. 
In  the  higher  animals  three  circulating  liquids  have  been 
distinguished :  blood,  lymph,  and  chyle.  But  it  is  to  be 
remarked  that  chyle  is  only  lymph  derived  from  the  walls 
of  the  alimentary  canal,  and  therefore,  during  digestion, 
containing  certain  freshly  -  absorbed  constituents  of  the 
food ;  while  both  ordinary  lymph  and  chyle  ultimately  find 
their  way  into  the  blood,  and  are  in  their  turn  recruited 
from  it.  The  blood  contains  at  one  time  or  another  every- 
thing which  is  about  to  become  part  of  the  tissues,  and 
everything  which  has  ceased  to  belong  to  them.  It  is  at 
once  the  scavenger  and  the  food-provider  of  the  cell.  But 
no  bloodvessel  enters  any  cell ;  and  if  we  could  unravel  the 
complex  mass  of  tissue  elements  which  essentially  constitute 
what  we  call  an  organ,  we  should  see  a  sheet  of  cells,  with 
capillaries  in  very  close  relation  to  them,  but  everywhere 


26  A  MANUAL  OF  PHYSIOLOGY 

separated  from  them  by  a  thin  layer  of  lymph.  And  to 
describe  in  a  word  the  circulation  of  the  food  substances,  we 
may  say  that  the  blood  feeds  the  lymph,  and  the  lymph  feeds  the  cell. 

Morphology  of  the  Blood. 

The  blood  consists  essentially  of  a  liquid  part,  the  plasma, 
in  which  are  suspended  cellular  elements,  the  corpuscles. 
When  the  circulation  in  a  frog's  web  or  lung  or  in  the  tail 
of  a  tadpole  is  examined  under  the  microscope,  the  blood- 
vessels are  seen  to  be  crowded  with  oval  bodies — of  a 
yellowish  tinge  in  a  thin  layer,  but  in  thick  layers  crimson — 
which  move  with  varying  velocity,  now  in  single  file,  now 
jostling  each  other  two  or  three  abreast,  as  they  are  borne 
along  in  the  axis  of  an  apparently  scanty  stream  of  trans- 
parent liquid.  Nearer  the  walls  of  the  vessels,  sometimes 
clinging  to  them  for  a  little  and  then  being  washed  away 
again,  may  be  seen,  especially  as  the  blood-flow  slackens,  a 
few  comparatively  small,  round,  colourless  cells.  The  oval 
bodies  are  the  red  or  coloured  corpuscles ;  the  colourless 
elements  are  the  white  blood-corpuscles  or  leucocytes  ;  the 
liquid  in  which  they  float  is  the  plasma  ('  Practical  Exercises,' 
p.  168). 

The  Bed  Blood-corpuscles  differ  in  shape  and  size  and  in 
other  respects  in  different  animal  groups.  In  amphibians, 
such  as  the  frog  and  the  newt,  they  are  flattened  ellipsoids 
containing  a  nucleus,  and  the  same  is  true  of  nearly  all  the 
other  vertebrates,  except  mammals.  In  mammals  they  are 
discs,  hollowed  out  on  both  the  flat  surfaces,  or  biconcave, 
and  possess  no  nucleus.  But  the  red  corpuscles  of  the 
llama  and  the  camel,  although  non-nucleated,  are  ellipsoidal 
in  shape  like  those  of  the  lower  vertebrates.  As  to  size,  the 
average  diameter  in  man  is  between  7  and  8  p.*  In  the 
frog  the  long  diameter  is  about  22  //,,  while  in  Proteus  it  is  as 
much  as  60  /u-,  and  in  Amphiuma,  the  corpuscles  of  which 
can  be  seen  with  the  naked  eye,  nearly  80  ^  (Plate  I.,  i). 

As  regards  the  structure  of  the  red  corpuscles  two  views 
are  held :  (i)  That  they  are  hollow  vesicles  or  globules, 
bounded  by  a  delicate  but  resistant  envelope,  perhaps  of 

*  A  micro-millimetre,  represented  by  symbol  //,  is  ^Q<5  millimetre. 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  27 

fatty  nature  (Schafer) ;  (2)  that  they  are  solid  bodies,  with 
a  spongy  and  elastic  framework,  denser  at  the  surface  of  the 
corpuscle  than  in  its  centre,  but  continuous  throughout  its 
whole  mass  (Rollett). 

Envelope  and  spongework  are  sometimes  spoken  of  as  the 
stroma  of  the  corpuscle,  in  contradistinction  to  its  most 
important  constituent,  a  highly  complex  pigment,  the 
haemoglobin,  which,  either  in  solution  as  such,  or  in 
solution  as  a  compound  with  some  other  unknown  sub- 
stance, or  bound  in  some  solid  or  semi-solid  combination 
to  the  stroma,  fills  up  the  whole  space  within  the  envelope, 
or  all  the  interstices  of  the  spongework.  To  the  physical 
properties  of  the  stroma  it  is  usual  to  attribute  the  great 
elasticity  of  the  corpuscles — that  is,  the  power  of  recovering 


FIG.  i. — DIAGRAM  SHOWING  RELATIVE  SIZE  OF  RED  CORPUSCLES  OF  VARIOUS 

ANIMALS. 

their  original  shape  after  distortion — for  their  elasticity  is  no 
wise  impaired  by  the  removal  of  the  haemoglobin. 

When  blood  with  disc-shaped  corpuscles  is  shed,  there  is 
a  great  tendency  for  the  corpuscles  to  run  together  into 
groups  resembling  rouleaux,  or  piles  of  coin.  No  satisfactory 
explanation  of  this  curious  fact  has  yet  been  given. 

Crenation  of  the  corpuscles,  a  condition  in  which  they  t 
become  studded  with  fine  projections,  is  caused  by  the 
addition  of  moderately  strong  salt  solution,  by  the  passage 
of  shocks  of  electricity  at  high  potential,  as  from  a  Leyden 
jar,  by  simple  exposure  to  the  air,  and  in  poisoning  with 
Calabar  bean.  Concentrated  saline  solutions,  which  abstract 
water  from  the  corpuscles  and  cause  them  to  shrink,  make 
the  colour  of  blood  a  brighter  red,  because  more  light  is 
now  reflected  from  the  crumpled  surfaces.  On  the  other 


28  A  MANUAL  OF  PHYSIOLOGY 

hand,  the  addition  of  water  renders  the  corpuscles  spheri- 
cal ;  more  of  the  light  passes  through  them,  less  is  reflected, 
and  the  colour  becomes  dark  crimson  (Plate  I.). 

The  White  Blood-corpuscles,  or  Leucocytes. — The  red  cor- 
puscles are  peculiar  to  blood.  The  white  corpuscles  may 
be  looked  upon  as  peripatetic  portions  of  the  mesoblast  (see 
Chap.  XIV.),  and  some  of  them  ought  not  in  strictness  to  be 
called  blood-corpuscles.  They  are  more  truly  body  cor- 
puscles. Similar  cells  are  found  in  many  situations,  and 
wander  everywhere  in  the  spaces  of  the  connective  tissue. 
They  pass  into  the  bloodvessels  with  the  lymph,  and  may 
pass  out  of  them  again  in  virtue  of  their  amoeboid  power. 
They  consist  of  undifferentiated  living  substance  or  '  proto- 


FIG.  2.— AMCEBOID  MOVEMENT. 
A,  B,  C,  D,  successive  changes  in  the  form  of  an  amoeba. 

plasm,'  and  under  the  microscope  appear  as  granular, 
colourless,  transparent  bodies,  spherical  in  form  when  at 
rest,  and  containing  a  nucleus,  often  tri-  or  multi-lobed. 
Many  of  the  leucocytes  of  frog's  blood  at  the  ordinary 
temperature,  and  of  mammalian  blood  when  artificially 
heated  on  the  warm  stage,  may  be  seen  to  undergo  slow 
changes  of  form.  Processes  called  pseudopodia  are  pushed 
out  at  one  portion  of  the  surface,  retracted  at  another,  and 
thus  the  corpuscle  gradually  moves  or  *  flows  '  from  place  to 
place,  and  envelops  or  eats  up  substances,  such  as  grains  of 
carmine,  which  come  in  its  way.  This  kind  of  motion  was 
first  observed  in  the  amoeba,  and  is  therefore  called  amoeboid. 
t*  The  leucocytes  of  human  blood  are  not  all  of  the  same  size, 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  29 

and  differ  also  in  other  respects.     They  may  be  classified 

(1)  according  to  the  presence  or  absence  of  granules  in  their 
protoplasm,  and  the  fineness  or  coarseness  of  the  granules ; 

(2)  according   to   the   chemical    nature   of   the   dyes   with 
which    the    granules    stain.      The    most    important   recent 
work  on  this  subject  is  that  of  Kanthack  and  Hardy.     They 
find  that  Ehrlich's  '  neutrophile  '  cells  are  in  reality  oxyphile 
— that  is,  their  granules  do  not  stain  with   neutral  dyes, 
such   as  fuchsin  or  methyl  green,   but  do  stain  with  acid 
dyes  like  eosin  (Plate  I.,  2).     They  classify  the  wandering 
cells  of  the  blood  into  five  varieties,  as  follows  : 

i 

'(i)  Coarsely  granular  (eosino- 

phile  cell  of  Ehrlich)          -  10-11  \i  in  diam. 

(2)  Finely  granular  (  neutro- 
phile and  amphophile  cells 

of  Ehrlich)  -  8-9  n  „ 

(3)  Finely  granular  (tri-lobed 

nucleus)    -  -  7  \i  „ 

(4)  Hyaline  cells,  free  from 
granules      (one      nucleus, 
generally  spherical)  -        -  S'5-io  /*       „ 

(5)  Lymphocytes,  possessing 
a  single  large  nucleus  with 


Oxyphile  (granules  stain- 
ing with,eosin). 
vM^^K  v>*>  fk  fr-o 

Basophile  (granules  stain- 
ing with  methylene  blue). 


comparatively  little  proto- 
plasm around  it 


In  human  blood  the  finely  granular  oxyphile  cells  make 
up  60  to  80  per  cent,  of  the  whole  number  of  leucocytes,  the 
lymphocytes  (and  hyaline  cells)  20  to  30  per  cent.,  and  the 
coarsely  granular  oxyphile  cells  less  than  5  per  cent. ;  but 
these  proportions  are  far  from  being  constant. 

Blood-plates. — When  blood  is  examined  immediately  after 
being  shed,  small  colourless  bodies  (0-5  to  5  /a  in  diameter) 
of  various  shapes — sometimes  fiat  and  of  nearly  circular 
outline,  sometimes  irregular — may  be  seen.  These  are  the 
blood-plates  or  platelets.  They  can  be  best  studied  when 
the  blood  is  run  directly  into  some  fixing  solution.*  Their 
significance  is  unknown  ;  but  they  are  not  produced  by  the 
breaking  up  of  other  elements  of  the  shed  blood,  for  they 
have  been  observed  within  the  freshly  excised  and  therefore 
still  living  capillaries — in  the  mesentery  of  the  guinea-pig 
and  rat  (Osier). 

*  Such  as  Hayem's  solution  (sodium  chloride,  i  grm. ;  sodium  sulphate, 
5  grm. ;  mercuric  chloride,  o'5  grm.  ;  water,  200  grm.). 


30  A  MANUAL  OF  PHYSIOLOGY 

Enumeration  of  the  Blood-corpuscles. — This  is  done  by 
taking  a  measured  quantity  of  blood,  diluting  it  to  a  known 
extent  with  a  liquid  which  does  not  destroy  the  corpuscles, 
and  counting  the  number  in  a  given  volume  of  the  diluted 
blood  (p.  61). 

The  average  number  of  red  corpuscles  in  a  cubic  milli- 
metre of  blood  is  about  5,000,000  in  a  healthy  man,  and 
about  4,500,000  in  a  healthy  woman,  but  a  variation  of 
1,000,000  up  or  down  can  hardly  be  considered  abnormal. 
In  persons  suffering  from  profound  anaemia  the  number 
may  sink  to  1.000,000  per  cubic  millimetre,  or  even  less, 
while  in  new-born  children  and  in  the  inhabitants  of  high 
plateaus  or  mountains  it  may  rise  to  8,000,000,  or  even 
more.  In  the  latter  instance  a  residence  of  a  fortnight  in 

FIG.  3.— CURVE  SHOWING  THE 
NUMBER  OF  RED  CORPUSCLES 
AT  DIFFERENT  AGES  (AFTER 
SORENSEN'S  ESTIMATIONS). 

The  figures  along  the  horizontal  axis 
are  years  of  age,  those  along  the 
vertical  axis  millions  of  corpuscles 
per  cub.  mm.  of  blood. 

the  rarefied  air  is  sufficient  to  bring  about  the  increase,  and 
a  subsequent  residence  of  a  fortnight  in  the  lowlands  to 
annul  it.* 

The  number  of  white  blood-corpuscles  is  on  the  average 
about  10,000  per  cubic  millimetre  of  blood,  or  one  leucocyte 
/  f°r  every  5°°  red  blood -corpuscles.  In  leukaemia  the 
number  of  white  corpuscles  is  enormously  increased — it  may 
be  in  extreme  cases  to  500,000  per  cubic  millimetre — while 
at  the  same  time  the  number  of  the  red  corpuscles  is 
diminished  ;  and  the  ratio  of  white  to  red  may  approach 
i  :  4.  An  increase  has  also  been  observed  in  certain  infec- 
tive diseases  as  part  of  the  inflammatory  reaction.  There 
are  also  physiological  variations,  even  within  short  periods 
of  time  ;  for  example,  the  number  of  lymphocytes  is  in- 

*  In  86  apparently  healthy  students  (male)  the  average  number  of  red 
corpuscles  was  5,145,000  per  cubic  millimetre.  In  79  of  these,  the  number 
ranged  from  4,000,000  to  6,400,000  ;  in  49  (or  57  per  cent,  of  the  whole), 
from  4,500,000  to  5,400,000;  in  3,  from  3,500,000  to  3,900,000  ;  in  3,  from 
6, 500,000  to  6,900,000.  In  one  observation  the  number  reached  7,300,000. 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  31 

creased  when  digestion  is  going  on.     The  number  of  blood- 
plates  is  about  300,000  to  the  cubic  millimetre  of  blood. 

Life-history  of  the  Corpuscles. — The  corpuscles  of  the  blood, 
like  the  body  itself,  fulfil  the  allotted  round  of  life,  and  then  » 
die.  They  arise,  perform  their  functions  for  a  time,  and 
disappear.  But  although  the  place  and  mode  of  their  origin, 
the  seat  of  their  destruction  or  decay,  and  the  average 
length  of  their  life,  have  been  the  subject  of  active  research 
and  still  more  active  discussion  for  many  years,  much  yet 
remains  unsettled. 

In  the  embryo  the  red  corpuscles,  even  of  those  forms 
(mammals)  which  have  non-nucleated  corpuscles  in  adult 
life,  are  at  first  possessed  of  nuclei.  In  the  human  foetus, 
at  the  fourth  week  all  the  red  corpuscles  are  nucleated. 


FIG.  4.— CURVE  SHOWING  PROPORTION  OF  WHITE  CORPUSCLES  TO  RED  AT 
DIFFERENT  TIMES  OF  THE  DAY  (AFTER  THE  RESULTS  OF  HIRT). 

At  I  the  morning  meal  was  taken;  at  II  the  mid-day  meal;  at  III  the  evening 
meal.  During  active  digestion  the  number  of  lymphocytes  in  the  blood  is  greatly 
increased,  both  absolutely  and  relatively  to  the  number  of  the  other  leucocytes. 

Later  on  the  nucleated  corpuscles  gradually  diminish  in 
number,  and  at  birth  they  have  almost  or  altogether  dis- 
appeared, some  of  them,  at  least,  having  been  converted  by 
a  shrivelling  of  the  nucleus  into  the  ordinary  non-nucleated 
form.  In  the  newly-born  rat,  which  comes  into  the  world 
in  a  comparatively  immature  state,  many  of  the  red 
corpuscles  may  be  seen  to  be  still  nucleated.  The  first 
corpuscles  formed  in  embryonic  life  are  developed  outside  of 
the  embryo  altogether  (in  the  guinea-pig).  Even  before  the 
heart  has  as  yet  begun  to  beat,  certain  cells  of  the  mesoblast 
(see  Chap.  XIV.)  in  a  zone  ('  vascular  area ')  around  the 
growing  embryo  begin  to  sprout  into  long,  anastomosing 
processes,  which  afterwards  become  hollowed  out  to  form 


32  A  MANUAL  OF  PHYSIOLOGY 

capillary  bloodvessels.  At  the  same  time  clumps  of  nuclei, 
formed  by  division  of  the  original  nuclei  of  the  cells,  gather 
at  the  nodes  of  the  network.  Around  each  nucleus  clings  a 
little  lump  of  protoplasm,  which  soon  develops  haemoglobin 
in  its  substance ;  and  the  new-made  corpuscles  float  away 
witbin  the  new-made  vessels.  In  later  embryonic  life  the 
nucleated  corpuscles  seem  in  part  to  be  developed  in  the 
liver,  spleen,  red  bone-marrow,  and  the  blood  itself  by 
division  of  previously  existing  nucleated  corpuscles,  in  part 
to  be  formed  endogenously  within  special  cells  in  the  liver, 
spleen,  and  perhaps  the  lymphatic  glands. 

In  the  mammal  in  extra-uterine  life  the  chief  seat  of 
formation  of  the  red  blood-corpuscles  seems  to  be  the  red 
marrow  of  the  bones  of  the  skull  and  trunk,  and  of  the  ends 
of  the  long  bones  of  the  limbs.  For  a  short  time,  however, 
after  birth  the  formation  of  non-nucleated  corpuscles  may 
still  go  on  in  other  situations,  as  in  certain  cells  in  the 
omentum  of  the  rabbit  (Ranvier),  and  in  the  subcutaneous 
connective-tissue  corpuscles  (Schafer) ;  while  at  any  time  the 
spleen  (Bizzozero  and  Salvioli)  in  dogs  and  guinea-pigs,  and 
probably  other  organs,  may  in  emergency — for  instance, 
when  the  number  of  blood-corpuscles  has  been  seriously 
diminished  by  haemorrhage — take  on  a  blood-forming  func- 
tion. In  the  red  marrow  special  nucleated,  feebly  amoeboid 
cells,  originally  colourless  or  nearly  so,  multiply  by  karyo- 
kinesis  or  indirect  division,  and  are  transformed  by  various 
stages  into  the  ordinary  non-nucleated  red  corpuscles,  which 
are  washed  away  in  the  blood-stream.  These  blood-forming 
cells  have  received  the  name  of  erythroblasts  or  haemato- 
blasts. 

A  constant  destruction  of  red  blood-corpuscles  must  go 
on,  for  the  bile-pigment  and  the  pigments  of  the  urine  are 
derived  from  blood-pigment.  The  bile-pigment  is  formed  in 
the  liver.  It  contains  no  iron  ;  but  the  liver-cells  are  rich 
in  iron,  and  on  treatment  with  hydrochloric  acid  and 
potassium  ferrocyanide,  a  section  of  liver  is  coloured  by 
Prussian  blue.  Iron  must,  therefore,  be  removed  by  the 
liver  from  the  blood-pigment  or  from  one  of  its  derivatives  ; 
and  there  is  other  evidence  that  the  liver  is  one  of  the  places 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  33 

in  which  red  corpuscles  are  actually  destroyed.  Destruction 
of  the  corpuscles  also  seems  to  take  place  in  the  spleen  and 
bone-marrow.  Although  the  statement  that  free  blood- 
pigment  exists  in  the  plasma  of  the  splenic  vein  is  incorrect, 
red  corpuscles  have  been  seen  in  various  stages  of  decom- 
position within  large  amoeboid  cells  in  the  splenic  pulp  ;  and 
deposits  containing  iron  have  been  found  there  and  in  the 
red  bone-marrow  in  certain  pathological  conditions.  It  is 
not  unlikely  that  the  coloured  corpuscles  may  break  up  also 
in  other  localities,  and  even  to  some  extent  in  the  blood  itself. 

The  lymphocytes  are  undoubtedly,  the  coarsely  granular 
oxyphile  cells  probably,  and  the  hyaline  cells  possibly,  derived 
from  the  lymph.  The  lymphocytes  are  probably  identical 
with  the  small  lymph-corpuscles,  and  have  little,  if  any,  power 
of  amoeboid  movement.  They  are  formed  largely  in  the 
lymphatic  glands,  for  the  lymph  coming  to  the  glands  is 
much  poorer  in  corpuscles  than  that  which  leaves  them. 
The  lymphatic  glands,  however,  are  not  the  only  seat  of 
formation  of  leucocytes,  for  lymph  contains  some  corpuscles 
before  it  has  passecl  through  any  gland ;  and  although  a  certain 
number  of  these  may  have  found  their  way  by  diapedesis5& 
from  the  blood,  others  are  formed  in  the  diffuse  adenoid 
tissue,  or  in  special  collections  of  it,  such  as  the  tonsils,  the 
Peyer's  patches  and  solitary  follicles  of  the  intestine,  and 
the  jsplenic  corpuscles.  To  a  very  small  extent  white  blood- 
corpuscles  may  multiply  by  karyokinesis  in  the  blood. 

The  fate  of  the  leucocytes  is  even  less  known  than  that 
of  the  red  corpuscles,  for  they  contain  no  characteristic 
substance,  like  the  blood-pigment,  by  which  their  destruction 
may  be  traced.  That  they  are  constantly  breaking  down  is 
certain,  for  they  are  constantly  being  produced.  But  we  do 
not  know  whether,  under  normal  conditions,  this  process 
takes  place  exclusively  in  the  blood-plasma  or  in  particular 
organs  or  tissues. 

Physical  and  Chemical  Properties  of  the  Blood. 

Fresh  blood  varies  in  colour,  from  scarlet  in  the  arteries 
to  purple-red  in  the  veins.  It  is  a  somewhat  viscid  liquid, 
with  a  saline  taste  and  a  peculiar  odour.  Its  reaction  is 

3 


34  A  MANUAL  OF  PHYSIOLOGY 

alkaline  to  litmus-paper,  chiefly  owing  to  the  presence  of 
di-sodium  phosphate  (Na2HPO4)  and  sodium  carbonate. 
The  alkalinity  is  not  constant  ;  it  is  increased  during 
digestion,  when  the  acid  of  the  gastric  juice  is  being 
formed  ;  it  is  lowest  in  the  morning,  and  highest  in  the 
afternoon.  It  is  diminished  by  muscular  exertion,  owing 
to  the  formation  of  lactic  acid ;  and  since  acid  substances 
seem  to  be  produced  in  all  active  tissues,  the  alkalinity  of 
venous  is  less  than  that  of  arterial  blood.  In  herbivorous 
animals  the  alkalinity  of  the  blood  is  easily  lessened  by  the 
administration  of  acids,  but  in  carnivora  and  in  man  it  is 
much  more  difficult  to  bring  about  such  a  change,  the  acid 
being  neutralized  by  ammonia,  which  is  split  off  from  the 
proteids.  In  many  diseases,  however,  and  particularly  in 
those  accompanied  by  fever,  this  protective  mechanism 
breaks  down,  the  alkalinity  of  the  blood  becomes  seriously 
reduced,  or  even,  as  has  sometimes  been  observed  in 
diabetic  coma,  gives  place  to  an  acid  reaction.  The 
average  alkalinity  of  human  blood,  as  estimated  by  titra- 
tion  with  a  standard  acid  after  the  corpuscles  have  been 
broken  up,  is  that  of  a  "4  per  cent,  solution  of  sodium 
hydrate  (Loewy). 

The  average  specific  gravity  of  blood  is  about  1066  at 
birth.  It  falls  during  infancy  to  about  1050  in  the  third 
year,  then  rises  till  puberty  is  reached  to  about  1058  in 
males  (at  the  seventeenth  year),  and  1055  in  females  (at  the 
fourteenth  year).  It  remains  at  this  level  during  middle  life 
in  males,  but  falls  somewhat  in  females.  In  chlorotic 
anaemia  of  young  women  it  may  be  as  low  as  1030  or  1035. 
It  rises  in  starvation.  Sleep  and  regular  exercise  increase 
it  (Lloyd  Jones).* 

The  Electrical  Conductivity  of  Blood. — The  liquid  portion  of  the 
olood  conducts  the  current  entirely  by  means  of  the  electrolytes  dis- 
solved in  it,  the  most  important  of  these  being  the  inorganic  salts ; 

*  In  136  students  (male)  the  average  specific  gravity  of  the  blood,  as 
determined  by  Hammerschlag's  method  (p.  57)  was  1053-8.  In  121  of 
these  the  variation  was  from  1050  to  1065  ;  in  70  (or  51-4  per  cent,  of  the 
whole),  from  1054  to  1060  ;  in  4,  from  1046  to  1049  '•>  in  9>  from  1066  to 
1070.  In  2  the  specific  gravity  was  only  1040. 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  35 

and  the  conductivity  of  the  serum  varies,  in  different  specimens  of 
blood,  within  a  comparatively  narrow  range.  The  conductivity  of  entire 
(defibrinated)  blood,  on  the  contrary,  varies  within  wide  limits;  and  the 
most  influential  factor  which  governs  this  variation  is  the  number  of 
the  corpuscles  suspended  in  it.  When  the  blood  is  relatively  rich  in 
corpuscles  and  poor  in  serum,  its  conductivity  is  low ;  when  it  is 
poor  in  corpuscles  and  rich  in  serum,  its  conductivity  is^high.  The 
explanation  is  that  the  intact  red  corpuscles  have  an  electrical  con- 
ductivity so  many  times  less  than  that  of  serum,  that  they  may,  in 
comparison,  be  looked  upon  as  non-conductors.  This  must  be  either 
because  the  envelope  of  the  corpuscle  refuses  passage  to  the  dis- 
sociated molecules  (the  ions),  which,  in  virtue  of  their  electrical 
charges,  render  a  liquid  like  blood  a  conductor,  or  permits  them 
only  to  pass  very  slowly,  or  because  substances  (salts,  e.g.)  which  would 
otherwise  act  as  electrolytes  within  the  corpuscles  are  united  to  non- 
conducting substances  (proteids  or  haemoglobin)  in  such  a  way  that 
they  are  never  dissociated  into  their  ions,  and  therefore  do  not 
conduct  (p.  362). 

The  Relative  Volume  of  Corpuscles  and  Plasma  in  Unclotted 
Blood,  or,  what  can  be  converted  into  this  by  a  small  correction, 
the  relative  volume  of  corpuscles  and  serum  in  defibrinated 
blood,  can  be  easily  determined,  with  approximate  accuracy,  by 
comparing  the  electrical  conductivity  of  entire  blood  with  that  of  its 
serum.  Another  simple  method  is  to  centrifugalize  a  small  quantity 
of  blood,  after  mixing  it  with  a  known  amount  of  a  2\  per  cent, 
solution  of  potassium  bichromate,  in  a  glass  tube  of  narrow  bore 
(hsematocrite)  until  the  corpuscles  have  been  collected  into  a  solid 
*  thread '  at  the  outer  extremity  of  the  tube.  Their  volume  and  that 
of  the  clear  liquid  which  has  been  separated  from  them  are  then  read 
off  on  an  adjacent  scale.  By  these  and  other  methods  too  elaborate 
for  description  here,  it  has  been  shown  that  the  plasma  or  serum 
makes  up  about  two-thirds,  and  the  corpuscles  about  one-third,  of  the 
blood.  But  this  proportion  is,  of  course,  liable  to  the  same  variations 
as  the  number  of  corpuscles  in  a  cubic  millimetre  of  blood.  It 
depends,  further,  the  number  of  corpuscles  being  given,  on  the 
average  volume  of  each  corpuscle.  For  instance,  when  the  molecular 
concentration,  and  therefore  the  osmotic  pressure  (p.  360),  of  the 
plasma  is  reduced,  as  by  the  addition  of  water  or  the  abstraction  of 
salts,  water  passes  into  the  corpuscles  and  they  swell;  when  the 
molecular  concentration  of  the  plasma  is  increased,  by  the  abstraction 
of  water  or  the  addition  of  salts,  water  passes  out  of  the  corpuscles, 
and  they  shrink. 

Laking  of  Blood. — Even  in  thin  layers  blood  is  opaque,  owing  to 
reflection  of  the  light  by  the  red  corpuscles.  It  becomes  trans- 
parent or  '  laky  '  when  by  any  means  the  pigment  is  brought  out  of 
the  corpuscles  and  goes  into  true  solution.  Repeated  freezing  and 
thawing  of  the  blood,  the  addition  of  water,  the  passage  of  electrical 
currents,  constant  and  induced,  putrefaction,  heating  the  blood  to 
60°  C.,  and  many  chemical  agents  (as  bile-salts,  ether,  saponin),  cause 
this  change.  The  blood-serum  of  certain  animals  breaks  up  the 

3—2 


36  A  MANUAL  OF  PHYSIOLOGY 

coloured   corpuscles   of  others,   and   sets   free   their   pigment — for 
example,  the  serum  of  the  dog  destroys  the  corpuscles  of  the  rabbit. 

It  has  been  customary  to  speak  of  '  laking '  as  if  in  every  case  the 
process  was  essentially  the  same.  But  this  is  far  from  being  the 
fact.  For  instance,  when  defibrinated  blood  is  laked  by  freezing  and 
thawing,  its  electrical  conductivity  and  its  molecular  concentration 
(as  shown  by  a  determination  of  its  freezing-point,  p.  361)  are  practic- 
ally unaltered;  the  haemoglobin  has  made  its  way  into  the  serum,  but 
the  electrolytes  of  the  corpuscles  remain  in  their  original  seat  or  in 
their  original  combinations.  The  same  is  true  at  first,  when  the  laking 
is  accomplished  by  the  action  of  putrefactive  bacteria,  although 
later  on  both  the  conductivity  and  the  molecular  concentration  are 
markedly  increased.  On  the  other  hand,  when  the  laking  is 
brought  about  by  the  addition  of  water,  such  alterations  take  place 
in  the  conductivity  and  freezing-point  as  indicate  that  the  electro- 
lytes of  the  corpuscles  have  been  liberated  and  have  passed  into 
solution  in  the  serum  along  with  the  haemoglobin. 

Since  changes  begin  in  the  blood  as  soon  as  it  is  shed, 
having  for  their  outcome  clotting  or  coagulation,  we  have  to 
gather  from  the  composition  of  the  stable  factors  of  clotted 
blood,  or  of  blood  which  has  been  artificially  prevented 
from  clotting,  some  notion  of  the  composition  of  the  un- 
altered fluid  as  it  circulates  within  the  vessels.  The  first 
step,  therefore,  in  the  study  of  the  chemistry  of  blood  is  the 
study  of  coagulation. 

Coagulation  of  the  Blood. — When  blood  is  shed,  its  viscidity 
soon  begins  to  increase,  and  after  an  interval,  varying  with 
the  kind  of  blood,  the  temperature  of  the  air,  and  other 
conditions,  but  in  man  seldom  exceeding  ten,  or  falling 
below  three,  minutes,  it  sets  into  a  firm  jelly.  This  jelly 
gradually  shrinks  and  squeezes  out  a  straw-coloured  liquid, 
the  serum.  Under  the  microscope  the  serum  is  seen  to 
contain  few  or  no  red  corpuscles ;  these  are  nearly  all  in  the 
clot,  entangled  in  the  meshes  of  a  kind  of  network  of  fine 
fibrils  composed  of  fibrin.  In  uncoagulated  blood  no  such 
fibrils  are  present ;  they  have  accordingly  been  formed  by  a 
change  in  some  constituent  or  constituents  of  the  normal 
blood.  Now,  it  has  been  shown  that  there  exists  in  the 
plasma — the  liquid  portion  of  unclotted  blood — a  substance 
from  which  fibrin  can  be  derived,  while  no  such  substance 
is  present  in  the  corpuscles.  In  various  ways  coagulation 
can  be  prevented  or  delayed,  and  the  plasma  separated  from 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  37 

the  corpuscles.  For  example,  the  blood  of  the  horse  clots 
very  slowly,  and  a  low  temperature  lessens  the  rapidity  of 
coagulation  of  every  kind  of  blood.  If  horse's  blood  is  run 
into  a  vessel  surrounded  by  ice  and  allowed  to  stand,  the 
corpuscles,  being  of  greater  specific  gravity  than  the  plasma, 
gradually  sink  to  the  bottom,  and  the  clear  straw-yellow 
plasma  can  be  pipetted  off.  Or,  again,  the  addition  of 
neutral  salts  to  blood  may  be  used  to  delay  coagulation, 
the  blood  being  run  direct  from  the  animal  into,  say,  a 
third  of  its  volume  of  saturated  magnesium  sulphate 
solution.  The  plasma  may  then  be  conveniently  separated 
from  the  corpuscles  by  means  of  a  centrifugal  machine. 
Again,  two  ligatures  may  be  placed  on  a  large  bloodvessel, 
so  that  a  portion  of  it  can  be  excised  full  of  blood  and 
suspended  vertically ;  coagulation  is  long  delayed,  and  the 
corpuscles  sink  to  the  lower  end.  In  these  and  many  other 
ways  plasma  free  from  corpuscles  can  be  got ;  and  it  is  found 
that  when  the  conditions  which  restrain  coagulation  are 
removed — when,  for  instance,  the  temperature  of  the  horse's 
plasma  is  allowed  to  rise,  or  the  magnesium  sulphate  plasma 
is  diluted  with  several  times  its  bulk  of  water — clotting  takes 
place,  with  formation  of  fibrin  in  all  respects  similar  to  that 
of  ordinary  blood-clot.  The  corpuscles  themselves  cannot 
form  a  clot.  From  this  we  conclude  that  the  essential 
process  in  coagulation  of  the  blood  is  the  formation  of 
fibrin  from  some  constituent  of  the  plasma,  and  that  the 
presence  of  corpuscles  in  ordinary  blood-clot  is  accidental. 
In  accordance  with  this  conclusion,  we  find  that  lymph 
entirely  free  from  red  corpuscles  clots  spontaneously,  with 
formation  of  fibrin ;  and  when  fibrin  is  removed  from  newly- 
shed  blood  by  whipping  it  with  a  bundle  of  twigs  or  a  piece 
of  wood,  it  will  no  longer  coagulate,  although  all  the  cor- 
puscles are  still  there. 

What,  now,  is  the  substance  in  the  plasma  which  is 
changed  into  fibrin  when  blood  coagulates  ?  If  plasma, 
obtained  in  any  of  the  ways  described  above,  be  saturated 
with  sodium  chloride,  a  precipitate  is  thrown  down.  The 
filtrate  separated  from  this  precipitate  does  not  coagulate 
on  dilution  with  water  ;  but  the  precipitate  itself — the  so- 


38  A  MANUAL  OF  PHYSIOLOGY 

called  plasmine  of  Denis — on  being  dissolved  in  a  little  water, 
does  form  a  clot.  Fibrin  is  therefore  derived  from  some- 
thing in  this  precipitate.  Now,  '  plasmine '  contains  two 
proteid  bodies — fibrinogen,  which  coagulates  by  heat  at 
about  56°  C.,  and  serum- globulin,  which  coagulates  at  about 
75°  C.,  and  it  was  at  one  time  believed  that  both  of  these 
entered  into  the  formation  of  fibrin  (Schmidt).  Hammer- 
sten,  however,  has  shown  that  fibrinogen  alone  is  a  precursor 
of  fibrin ;  pure  serum-globulin  neither  helps  nor  hinders 
its  formation.  This  observer  isolated  fibrinogen  from  blood- 
plasma  by  adding  sodium  chloride  till  about  13  per  cent. 
was  present.  With  this  amount  the  fibrinogen  is  precipi- 
tated, while  serum-globulin  is  not  precipitated  till  20  per 
cent,  of  salt  is  reached.  After  precipitation  of  the  fibrinogen 
the  plasma  no  longer  coagulates  ;  and  a  solution  of  pure 
fibrinogen  can  be  made  to  clot  and  to  form  fibrin,  while  a 
solution  of  serum-globulin  cannot.  Blood-serum,  too,  which 
contains  abundance  of  serum-globulin,  but  no  fibrinogen, 
will  not  coagulate. 

So  far,  then,  we  have  reached  the  conclusion  that  fibrin  is 
formed  by  a  change  in  a  substance,  fibrinogen,  which  can  be 
obtained  by  certain    methods  from  blood-plasma.     It  may 
be   added  that  there  is  evidence  that  fibrinogen  exists  as 
such    in  the  circulating  blood  ;    for  if  unclotted    blood    be 
suddenly    heated   to    about   56°,  the   temperature    of  heat- 
coagulation   of  fibrinogen,    the   blood   loses    its    power   of 
clotting.     Since  fibrinogen  is  readily  soluble  in  dilute  saline 
solutions  and  fibrin  only  soluble  with  great  difficulty,  we 
ma)7  say  that  in  coagulation  of  the  blood  a  substance  soluble 
*M     !in  the  plasma  passes  into  an  insoluble  form.     But  this  is 
|not  a  mere  physical  change,  for  it  seems  to  be  initiated  by  a 
splitting  up   of  the   fibrinogen  into   two    proteid   bodies — 
'thrombosin  and  fibrinoglobulin — only  the  former  of  which 
I  is  transformed  into  fibrin,  while  the  latter  remains  in  solution . 
How  is  this  change  determined  when  blood  is  shed  ?    We 
have  said  that  a  solution  of  pure  fibrinogen  can  be  made  to 
coagulate,  but  it  does  not  coagulate  of  itself.     The  addition 
of  another  substance  in  extremely  minute  quantity  is  neces- 
sary.    This  other  substance  is  fibrin  ferment,  which  can  be 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  39 

obtained  by  precipitating  blood-serum,  or  defibrinated  blood, 
with  fifteen  to  twenty  times  its  bulk  of  alcohol,  letting  the 
whole  stand  for  a  month  or  more,  and  then  extracting  the 
precipitate  with  water  (Schmidt).  All  the  ordinary  proteids 
of  the  blood  having  been  rendered  insoluble  by  the  alcohol, 
the  fibrin-ferment  passes  into  solution  in  the  water,  and  the 
addition  of  a  trace  of  the  extract  to  a  solution  of  fibrinogen 
causes  coagulation.  The  active  substance  itself  does  not 
seem  to  be  used  up  in  the  process,  nor  to  enter  bodily  into 
the  fibrin  formed ;  a  small  quantity  of  it  can  cause  an 
indefinitely  large  amount  of  fibrinogen  to  clot ;  its  power  is 
abolished  by  boiling.  For  these  reasons  it  is  considered  to 
be  a  ferment. 

This  action  of  the  fibrin-ferment  on  fibrinogen  helps  to 


FIG.  5.— DIAGRAM  OF  CLOT  WITH  BUFFY  COAT. 

v,  Lower  portion  of  clot  with  red  corpuscles  ;  w,  white  corpuscles  in  upper  layer 
of  clot  ;  c,  cupped  upper  surface  of  clot  ;  s,  serum. 

explain  many  experiments  in  coagulation.  Thus,  transuda- 
tions  like  hydrocele  fluid  do  not  clot  spontaneously,  although 
they  contain  fibrinogen,  which  can  be  precipitated  from 
them  by  a  stream  of  carbon  dioxide  or  by  sodium  chloride. 
But  the  addition  of  a  little  fibrin-ferment  causes  hydrocele 
fluid  to  coagulate.  So  does  the  addition  of  serum,  not 
because  of  the  serum-globulin  which  it  contains,  as  was 
once  believed,  but  because  of  the  fibrin-ferment  in  it.  The 
addition  of  blood-clot,  either  before  or  after  the  corpuscles 
have  been  washed  away,  or  of  serum -globulin  obtained 
from  serum,  also  causes  coagulation  of  hydrocele  fluid,  and 
for  a  similar  reason,  the  fibrin-ferment  having  a  tendency  to 
cling  to  everything  derived  from  a  liquid  containing  it.  On 
the  other  hand,  serum,  which  does  not  of  itself  clot,  although 


A  MANUAL  OF  PHYSIOLOGY 


fibrin-ferment  is  present  in  it,  because  the  fibrinogen  has  all 
beer,  changed  into  fibrin  during  coagulation  of  the  blood, 
can  be  made  to  coagulate  by  the  addition  of  hydrocele  fluid, 
which  contains  fibrinogen.  We  have  thus  arrived  a  step 
farther  in  our  attempt  to  explain  the  coagulation  of  the 
blood :  it  is  essentially  due  to  the  formation  of  fibrin  from  the 
fibrinogen  of  the  plasma  under  the  influence  of  fibrin-ferment. 

What  is  the  nature  of  the  fibrin-ferment,  and  what  is  its 
source  ?  There  seems  good  reason  for  believing  that  it 
has  very  close  relations  with  a  substance  or  substances 
belonging  to  the  group  of  nucleo-proteids,  for  nucleo-proteid 
can  be  obtained  from  solutions  of  fibrin-ferment,  and,  by 
appropriate  treatment  and  in  the  presence  of  proper  con- 
ditions, solutions  of  nucleo-proteid  can  either  be  made  to 
yield  fibrin-ferment  or  to  develop  that  influence  on  coagula- 
tion which  is  the  characteristic  test  by  which  we  recognise 
it.  Nucleo-proteids  are  contained  in  the  nuclei  and  proto- 
plasm of  cells,  and  have  been  prepared  from  the  thymus, 
testis,  kidney,  lymphatic  glands,  and  other  organs,  by  pre- 
cipitating their  watery  extracts  with  dilute  acetic  acid 
(Wooldridge),  or  by  extracting  with  sodium  chloride  and 
then  precipitating  with  excess  of  water  (Halliburton).  The 
precipitated  nucleo  -  proteid  can  be  dissolved  in  dilute 
sodium  carbonate  solution.  When  it  is  injected  slowly  or 
in  small  amount  into  the  veins  of  an  animal,  it  abolishes  for 
a  time  the  power  of  coagulation  of  the  blood  ;  and  when  this 
'  negative  phase/  as  it  is  called,  has  been  once  established, 
even  a  very  large  and  rapid  injection  produces  no  further 
effect.  If,  however,  a  considerable  quantity  of  the  solution  has 
been  injected  at  the  first,  the  result  is  very  different :  exten- 
sive intravascular  clotting  instantly  ensues ;  the  animal  dies 
in  a  few  minutes ;  and  the  right  side  of  the  heart,  the  venae 
cavse,  the  portal  vein,  and  perhaps  the  pulmonary  arteries, 
may  be  found  choked  with  thrombi.  Curiously  enough,  no 
such  effects  are  produced  in  albino  rabbits  or  in  Norway  hares 
in  their  albino  condition  (Pickering).  A  solution  of  fibrin- 
ferment  prepared  by  Schmidt's  method  behaves,  when  in- 
jected into  the  blood-stream,  like  a  weak  solution  of  nucleo- 
proteid,  readily  producing  the  negative  phase,  but  causing 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  41 

with  difficulty  intravascular  coagulation.  On  the  other 
hand,  while  fibrin-ferment  favours,  in  a  high  degree,  the 
clotting  of  blood-plasma  after  it  has  been  shed,  nucleo- 
proteid  is  a  much  less  efficient  coagulant  outside  than 
inside  the  vessels.  There  are  other  facts,  to  which  we 
shall  immediately  refer,  which  show  that  fibrin-ferment  is 
not  precisely  identical  with  nucleo-proteid,  although  it  is 
derived  from  it. 

Our  discussion  of  the  nature  and  relationships  of  the 
fibrin-ferment  throws  light  upon  its  source.  It  exists 
only  in  small  amount  in  the  circulating  blood ;  for  when 
blood  is  received  into  alcohol  direct  from  an  artery,  but 
little  ferment  is  found  in  it.  In  shed  and  clotting  blood 
the  only  possible  sources  of  nucleo-proteid,  so  far  as  we 
know,  are  the  corpuscles  and  the  blood-plates.  The  red 
corpuscles  we  may  at  once  dismiss,  for  although  they  con- 
tain a  small  amount  of  nucleo-proteid,  not  only  do  they 
remain  intact  under  ordinary  circumstances  during  coagula- 
tion, but  there  is  the  strongest  evidence,  as  has  already 
been  pointed  out,  that  they  do  not  make  any  essential 
contribution  to  the  process.  We  have  left  over  the  leuco- 
cytes and  the  platelets.  The  latter  are  said,  and  the  former 
are  known,  to  yield  nucleo-proteids  when  they  are  broken 
up  in  the  laboratory ;  and  it  is  highly  probable  that  from 
both,  but  especially  from  the  white  corpuscles,  nucleo- 
proteid  is  liberated  in  the  first  moments  after  blood  is  shed, 
and  that  this  nucleo-proteid  is  then  changed  into  actual 
fibrin-ferment.  This  surmise  is  strengthened  by  the  fact 
that  in  freshly-shed  blood  destruction  of  leucocytes  and 
blood-plates  takes  place  ;  and  Hardy  has  shown  that  the 
blood  of  the  crayfish,  which  coagulates  with  extreme  rapidity, 
contains  certain  colourless  corpuscles  which,  immediately 
it  is  shed,  break  up  with  explosive  suddenness,  and  that 
substances  which  hinder  the  breaking  up  of  these  corpuscles 
restrain  coagulation.  Further,  the  white  layer  or  'buffy 
coat '  which  tops  the  tardily-formed  clot  of  horse's  blood 
(Fig.  5),  and  consists  of  the  lighter,  and  therefore  more 
slowly  sinking,  white  corpuscles,  causes  clotting  in  other- 
wise incoagulable  liquids  like  hydrocele  fluid,  much  more 


42  A  MANUAL  OF  PHYSIOLOGY 

readily  than  the  red  portion  of  the  clot,  and  yields  far  more 
fibrin-ferment  on  treatment  with  alcohol. 

But  when  we  have  traced  the  fibrin-ferment  to  tfie  nucleo- 
proteid  of  the  leucocytes,  and  the  fibrinogen  to  the  plasma, 
and  have  seen  that  the  interaction  of  the  two  causes,  first  a 
splitting  up  of  the  fibrinogen,  and  then   the  formation  of 
fibrin  from  its  thrombosin  constituent,  we  have  not  yet  got 
to  the  bottom  of  coagulation.     We  have  still  to  ask  what  it 
is   that    happens    to    the    inert  nucleo-proteid    in   the   first 
moments  after  the  blood  has  been  shed  and  converts  it  into 
active  fibrin-ferment.      The   researches  of  late  years  have 
shown  that  a  third  factor  is  involved  :  calcium  is  present  in 
some  form  or  other  wherever  coagulation  occurs.     The  following 
facts    illustrate   the   role    of    the   calcium :    A    solution    of 
fibrinogen    free    from    calcium   will    not    coagulate    on    the 
addition  of  calcium-free  nucleo-proteid,  but  will  coagulate 
if  a  soluble  calcium  salt   be  also  added.     The  addition  of 
a  soluble  oxalate  to   blood    ('2  or    '3    per   cent,  potassium 
oxalate)  prevents  coagulation  by  precipitating  the  calcium 
as  insoluble  calcium  oxalate.    From  plasma  prepared  in  this 
way  a  nucleo-proteid  may  be  separated  which  contains  little 
or  no  calcium  and  does  not  cause  coagulation,  but  which  on 
treatment  with    a   calcium   salt   acquires  the  properties  of 
fibrin-ferment.     The   same  is   true   of  the   nucleo-proteid 
which  can  be  extracted  from   so   many  organs  by  Wool- 
dridge's  method.    And  the  most  probable  explanation  of  the 
intravascular  coagulation  caused  by  the  injection  of  nucleo- 
proteid  is  that  in  the  presence  of  the  calcium  salts  of  the 
plasma  it  produces  fibrin-ferment,  although  it  has  not  as  yet 
been  conclusively  shown  that  the  amount  of  fibrin-ferment 
obtainable  from  the   blood  is  increased   after  injection   of 
nucleo-proteid.     In  the  curious  hereditary  disease  known  as 
haemophilia,  a  deficiency  of  calcium  seems  occasionally  to 
be  responsible  for  the  diminished  coagulability  of  the  blood  ; 
and    the    internal   administration   of  a  solution  of  calcium 
chloride  has  sometimes  been  thought  to  lessen  the  tendency 
to    haemorrhage,   or    its   local  application    to  cut    short  an 
actual  attack.      Injection  of  commercial  peptone  into  tjie- 
veins  of  a  dog,  though  not  of  a  rabbit,  deprives  the  blood 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  43 

for  a  time  of  its  power  of  coagulation,  apparently  in  part  by 
reason  of  the  affinity  of  peptone  for  calcium  salts,  for  its 
action  can  be  prevented  by  injection  of  calcium  chloride 
(Pekelharing),  and  imitated  by  injection  of  potassium  oxalate, 
while  the  peptone  plasma  outside  of  the  body  can  sometimes, 
though  not  invariably,  be  caused  to  clot  by  the  addition  of 
a  soluble  salt  of  calcium.  (But  see  p.  45.)  Soaps  hinder 
coagulation  in  the  same  way.  The  precise  action  of  the 
calcium  has  not  yet  been  made  clear.  Pekelharing  supposes 
that  active  fibrin-ferment  is  a  compound  of  calcium  with 
nucleo-proteid,  and  that  in  coagulation  calcium  is  handed 
over  to  the  fibrinogen  by  the  fibrin-ferment.  Lilienfeld 
imagines  that  the  nucleo-proteid  first  acts  on  the  fibrinogen, 
causing  it  to  split  up  into  thrombosin  and  fibrinoglobulin, 
and  that  the  thrombosin  then  unites  with  calcium  to  form 
fibrin.  To  sum  up,  we  may  say  that  there  is  a  general  agreement 
that  the  presence  of  calcium  is  essential  to  the  formation  of  fibrin, 
and  a  preponderance  of  opinion  that  the  fibrin  is  formed  by  the 
union  of  calcium  with  fibrinogen  (or  thrombosin}  under  the 
influence  of  fibrin-ferment  (or  nucleo-proteid}. 

To  a  certain  extent  the  action  of  nucleo-proteid  in  coagulation  can 
be  imitated  by  other  substances  of  animal  origin,  such  as  the 
albumoses  of  snake  venom  (Martin),  and  even  by  certain  artificial 
products  of  the  laboratory,  the  synthesized  colloids  of  Grimaux, 
which,  when  injected  into  the  blood,  produce  the  same  phenomena 
of  intravascular  coagulation  down  to  the  finest  detail,  and  including 
the  negative  phase.  It  is  not  known  whether  these  substances  act 
on  the  leucocytes  or  other  cells,  and  thus  cause  an  increased  pro- 
duction or  an  increased  liberation  of  nucleo-proteid,  or  whether  they 
actually  take  its  place. 

So  far  we  have  been  considering  the  problem  of  coagulation  as  if 
all  the  data  for  its  solution  could  be  obtained  by  a  study  of  the  blood 
itself.  In  other  words,  our  main  business  up  to  this  point  has  been 
the  explanation  of  coagulation  in  the  shed  blood ;  it  has  been  only 
incidentally,  and  with  the  object  of  casting  light  on  the  question  of 
extravascular  clotting,  that  we  have  touched  on  the  coagulation  of 
the  blood  within  the  living  vessels.  It  is  not  possible  here  to 
adequately  discuss,  nor  even  to  define,  the  differences  between  the 
two  problems.  All  we  can  do  is  to  warn  the  student,  and  to 
emphasize  our  warning  by  one  or  two  illustrations,  that  valuable  as  is 
the  knowledge  derived  from  experiments  on  extravascular  coagula- 
tion, it  would  be  totally  misleading  if  applied  without  modification 
to  the  circulating  blood.  For  instance,  we  have  recognised  in  the 
leucocytes  an  important  source  of  the  nucleo-proteid  which  plays  so 


44  A  MANUAL  OF  PHYSIOLOGY 

great  a  part  in    the   clotting   of  shed   blood  ;  but   we   know   that 
leucocytes  are   constantly  breaking  down    in    the  lymph   and   the 
blood,  and  we  have  to  inquire  how  it  is  that  coagulation  does  not 
occur,  except  in  disease,  within  the  vessels.     Calcium  is  not  wanting 
to  the  circulating  plasma,  fibrinogen  is  not  wanting,  and  it  has  already 
been  mentioned  (p.  41)  that  a  small  amount  of  fibrin-ferment  can 
be  obtained  from  the  perfectly  fresh  and,  as  we  might  almost  say, 
still  living  blood.     Why,  then,  does  it  not  coagulate  ?     Some  have 
said  that  the  quantity  of  fibrin-ferment  is  too  small ;  but  if  any  is 
present,  some  coagulation  ought  to  occur  if  the  conditions  were 
exactly  the  same  as  in  a  test-tube.     Others  have  said  that  coagulation 
is  '  restrained  '  by  the  contact  of  the  living  walls  of  the  bloodvessels  ; 
but  although  it  is  certain  that  the  contact  of  foreign  matter,  and  all 
dead  matter  is  foreign  to  living  cells,  does  hasten  the  destruction  of 
leucocytes,   and    therefore   the   liberation   of    fibrin-ferment,    it    is 
evident   that   it   is  just  this   'restraining'  influence  of  the  vessels 
which  has  to   be  explained.     Schmidt  has   attempted   a   chemical 
explanation.     He  starts  with  the  assumption  that  some  ready-made 
fibrin-ferment,  or  its  precursor,  exists   not  only  in  the  circulating 
blood,  but  in  the  circulating  plasma,  for  he  finds  that  the  blood- 
plasma   of    the    horse,    entirely   freed    from    formed    elements   by 
filtration    through   several   folds   of    filter-paper    at   a   temperature 
of  o°  to  0*5°  C.,  remains  fluid  at  the  ordinary  temperature  of  the 
air  for  hours,  but  eventually  coagulates.     On  this  and  other  evidence 
he  bases  the  view  that  substances  formed  by  the  breaking  down 
of  white  blood-corpuscles  in  shed   blood  are   not   the   only  cause 
of  coagulation,   although    they   undoubtedly   greatly   accelerate    it. 
According  to  Schmidt,  a  precursor,  or  mother-substance  of  fibrin- 
ferment,    is    produced    in    the    body    from    all,    or    most,    proto- 
plasmic cells,  from  white  blood-corpuscles  among  the  rest,  but  not 
exclusively,   nor  even  pre-eminently,  from  them.     This  substance 
passes  continually  into  the  blood,  and  fibrin-ferment  is  continually 
formed  from  it,  but  is  always  being  neutralized  by  other  chemical 
processes.     So  that  living  blood  within  the  living  vessels  may  be  said 
to  be  acted  upon  by  two  sets  of  influences,  one  tending  to  coagula- 
tion, the  other  opposing  it.     Under  normal  conditions,  the  processes 
that  make  for  coagulation  never  obtain  the  upper  hand ;  but  any- 
thing which  interrupts  the  circulation,  and  consequently  the  free 
interchange  between  blood  and  tissues,  interferes  with  the  entrance 
of  the  substances  that  render  the  fibrin-ferment  inactive.     In  the 
clotting  of  extravascular  plasma,  free  from  corpuscles,  Schmidt  sees 
the  continuation,  under  modified  conditions,  of  a  normal  process 
always  going  on  within  the  bloodvessels.     In  the  lungs  it  would 
seem  that  the  forces  which  favour  coagulation  are  feeble,  or  the 
forces   that   resist   it   strong,  for   blood,  after  passing  many  times 
through  the  pulmonary  circulation  without  being  allowed  to  enter 
the  systemic  vessels,  loses  its  power  of  clotting  (Ludwig  and  Pawlow). 
The  liver  is  another  organ  whose  relations  to  the  coagulation  of 
the  blood  are  peculiar.     We  have  already  mentioned  that  the  injection 
of  proteoses  ('  peptone ')  into  the  blood  of  dogs  causes  it  to  lose  its 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  45 

coagulability.  The  effect  gradually  passes  away,  till  after  some  hours 
the  original  power  of  coagulation  is  restored  (p.  1.89).  The  liver  is 
known  to  be  intimately  concerned  in  the  production  of  this  remarkable 
result,  for  if  the  circulation  through  it  be  interrupted,  the  injection  of 
proteose  is  ineffective.  Further,  if  a  solution  of  proteose  is  artificially 
circulated  through  an  excised  liver,  a  substance  is  formed  which  is 
capable  of  suspending  the  coagulation  of  blood  outside  of  the  body,  a 
property  which  proteoses  themselves  do  not  possess.  It  is  not  believed 
that  the  proteose  is  actually  changed  into  this  anticoagulant  substance, 
but  rather  that  the  liver  cells  produce  it  as  a  '  reaction  '  to  the 
presence  of  the  foreign  substance,  being  perhaps  stimulated  in  some 
way  by  the  circulating  proteose.  Under  certain  conditions,  some  of 
which  are  known  and  others  not,  the  injection  of  proteose  causes  not 
retardation,  but  hastening,  of  coagulation  ;  and  if  this  has  been  the 
result  of  a  first  injection,  a  second  is  equally  unsuccessful.  It  is 
possible  that  by  an  effort  of  the  organism  to  restore  the  normal 
coagulability  of  the  blood,  on  which  its  very  existence  depends,  a 
second  substance  with  fibrinoplastic  powers  is  produced,  and  that 
the  result  of  an  injection  of  proteose  is  determined  by  the  relative 
amount  of  coagulant  and  anticoagulant  secreted  in  a  given  time. 


FIG.  6. — DIAGRAM  SHOWING  RELATIVE  QUANTITY  OF  SOLIDS  AND  WATER 
IN  RED  CORPUSCLES  AND  PLASMA. 

The  Chemical  Composition  of  Blood. 

The  serum  of  coagulated  blood  represents  the  plasma 
minus  fibrinogen  (or  its  thrombosin  element) ;  the  clot  repre- 
sents the  corpuscles  plus  fibrin.  Thus  : 

Plasma  —  Fibrin(ogen) =Serum. 
Corpuscles + Fibrin = Clot. 
Plasma+Corpuscles= Serum + Clot  =  Blood. 

Bulky  as  the  clot  is,  the  quantity  of  fibrin  is  trifling  ('2  to 
•4  per  cent,  in  human  blood).  The  plasma  contains  about 
10  per  cent,  of  solids,  the  red  corpuscles  about  40  per  cent., 
the  entire  blood  about  20  per  cent. 

Serum  contains  8  to  9  per  cent,  of  proteids,  about  '8  per 
cent,  of  inorganic  salts,  and  small  quantities  of  neutral  fats, 
urea,  kreatin,  grape-sugar,  lactic  acid,  and  other  substances. 
The  proteids  are  serum-albumin  and  serum- globulin.  In  the 
rabbit  the  former,  in  the  horse  the  latter,  is  the  more 
abundant ;  in  man  they  exist  in  not  far  from  equal  amount. 


46  A  MANUAL  OF  PHYSIOLOGY 

In  cold-blooded  animals  the  serum-albumin  is  scantier  than  in 
mammals,  the  globulin  relatively  more  plentiful. 

Serum-albumin  belongs  to  the  class  of  native  albumins.  It  has 
been  obtained  in  a  crystalline  form  from  the  serum  of  horse's  blood. 
It  is  soluble  in  distilled  water,  and  is  not  precipitated  by  saturating 
its  solutions  with  certain  neutral  salts.  Heated  in  neutral  or  slightly 
acid  solution,  it  coagulates  first  at  73°,  then  at  77°,  then  at  84°  C. 
But  this  is  not  sufficient  proof  that  it  consists  of  a  mixture  of  three 
proteids,  as  has  been  held. 

Serum-globulin  belongs  to  the  globulin  group  of  proteids.  It  is 
insoluble  in  distilled  water,  and  is  precipitated  in  saturated  solutions 
of  neutral  salts.  When  heated,  it  coagulates  at  75°  C.  (p.  60). 

Of  the  inorganic  salts  of  serum,  the  most  important  are 
sodium  chloride  and  sodium  carbonate.  Small  amounts  of 


FIG.  7.— DIAGRAM  OF  SPECTROSCOPE. 

A,  source  of  light ;  B,  layer  of  blood  ;  C,  collimator  for  rendering  rays  parallel ; 
D,  prism  ;  E,  telescope. 

potassium,  calcium,  and  magnesium,  united  with  phosphoric 
acid  or  chlorine,  and  a  trace  of  a  fluoride,  are  also  present. 

The  Red  Corpuscles  consist  of  rather  less  than  60  per  cent, 
of  water  and  rather  more  than  40  per  cent,  of  solids.  Of 
the  solids  the  pigment  hsemoglobin  makes  up  about  go  per 
cent. ;  the  proteids  and  nucleo-proteid  of  the  stroma  about 
8  per  cent.  ;  lecithin  and  cholesterin  less  than  i  per  cent.  ; 
inorganic  salts  (which  vary  greatly  in  their  relative  propor- 
tions in  different  animals,  but  in  man  consist  chiefly  of  phos- 
phates and  chloride  of  potassium,  with  a  much  smaller 
amount  of  sodium  chloride)  1*5  per  cent. 

Hemoglobin. — Of  all  the  solid  constituents  of  the  blood  haemo- 
globin is  present  in  greatest  amount,  constituting,  as  it  does,  no  less 
than  13  per  cent.,  by  weight,  of  that  liquid.  It  is  an  exceedingly 
complex  body,  containing  carbon,  hydrogen,  nitrogen,  and  oxygen  in 
much  the  same  proportions  in  which  they  exist  in  proteids  (p.  17). 
Iron  is  also  present  to  the  extent  of  almost  exactly  one-third 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  47 

of  T  per  cent.,  and  there  is  also  a  little  sulphur,  the  amount  of 
which  stands  in  a  very  simple  relation  to  the  quantity  of  iron  (i  atom 
of  iron  to  3  of  sulphur  in  dog's  haemoglobin,  and  i  atom  of  iron  to 
2  of  sulphur  in  the  haemoglobin  of  the  horse,  ox,  and  pig).  Haemo- 
globin appears  to  be  made  up  of  a.  proteid  element  which  contains 
all  the  sulphur,  and  a  pigment  which  contains  all  the  iron,  the  proteid 
constituting  by  far  the  larger  portion  of  the  gigantic  molecule,  whose 
weight  has  been  estimated  at  more  than  16,000  times  that  of  a 
molecule  of  hydrogen.  Since  its  percentage  composition  is  still 
undetermined  with  absolute  precision,  it  is  impossible  to  give  an 
empirical  formula  that  is  more  than  approximately  correct.  For 
dog's  haemoglobin  Jaquet  gives  C758H1203N195S3FeO21s,  which  would 
make  the  molecular  weight  16,669. 

The  most  remarkable  property  of  haemoglobin  is  its  power 
of  combining  loosely  with  oxygen  when  exposed  to  an  j 
atmosphere  containing  it,  and  of  again  giving  it  up  in  the 
presence  of  oxidizable  substances  or  in  an  atmosphere  in 
which  the  partial  pressure  of  oxygen  (pp.  231,  236),  has  been 
reduced  below  a  certain  limit.  It  is  this  property  that 
enables  haemoglobin  to  perform  the  part  of  an  oxygen- 
carrier  to  the  tissues,  a  function  of  the  first  importance, 
which  will  be  more  minutely  considered  when  we  come  to 
deal  with  respiration. 

The  bright-red  colour  of  blood  drawn  from  an  artery  or 
of  venous  blood  after  free  exposure  to  air  is  due  to  the  fact 
that  the  haemoglobin  is  in  the  oxidized  state — in  the  state  of 
oxyhaemoglobin,  as  it  is  called.  If  the  oxygen  is  removed 
by  means  of  reducing  agents,  such  as  ammonium  sulphide, 
or  by  exposure  to  the  vacuum  of  an  air-pump,  the  colour 
darkens,  the  blood-pigment  being  now  in  the  form  of  reduced 
haemoglobin.  In  ordinary  venous  blood  a  large  proportion 
of  the  pigment  is  in  this  condition,  but  there  is  always 
oxyhaemoglobin  present  as  well.  In  asphyxia  (p.  217),  how- 
ever, the  whole  of  the  oxyhaemoglobin  may  disappear. 

Crystallization  of  Hemoglobin. — In  the  circulating  blood  the 
haemoglobin  is  related  in  such  a  way  to  the  strorna  of  the  corpuscles 
that  although  the  latter  are  suspended  in  a  liquid  readily  capable  of 
dissolving  the  pigment,  it  yet  remains  under  ordinary  circumstances 
strictly  within  them.  In  a  few  invertebrates,  however,  it  is  normally 
in  solution  in  the  circulating  liquid.  As  a  rare  occurrence  haemo- 
globin may  form  crystals  inside  the  corpuscles.  When  it  is  in  any 
way  brought  into  solution  outside  the  body,  it  shows  in  many  animals, 


48 


A  MANUAL  OF  PHYSIOLOGY 


but  not  in  the  same  degree  in  all,  a  tendency  to  crystallization ;  and 
the  ease  with  which  crystallization  can  be  induced  is  in  inverse  pro- 
portion to  the  solubility  of  the  haemoglobin.  Thus,  it  is  far  more 
difficult  to  obtain  crystals  of  oxyhaemoglobin  from  human  blood  than 
from  the  blood  of  the  rat,  guinea-pig,  or  dog,  whose  blood-pigment 
is  less  soluble  than  that  of  man,  and  for  a  like  reason  the  oxyhaemo- 
globin  of  the  bird,  the  rabbit,  or  the  frog  crystallizes  still  less  readily 
than  that  of  human  blood. 

As  to  the  form  of  the  crystals,  in  the  vast  majority  of  animals  they 


B    C 


E   5  F 


Oxyhaemoglobin 


Reduced  haemoglobin 


Carbonic  oxide 
haemoglobin 


Methsemoglobin  (in 
acid  solution) 


Acid-haematin  (in 
ethereal  solution). 


Alkaline-haematin 


Haemochromogen 


Haematpporphyrin 
(in  acid  solution) 


Haematoporphyrin 
(in  alkaline  solu- 
tion) 

a   c  D  E."1 

FIG.  8. — TABLE  OF  SPECTRA  OF  HAEMOGLOBIN  AND  ITS  DERIVATIVES. 
B,  oxygen  line;  D,  sodium  line;  C  and  F,  hydrogen  lines;  b,  magnesium  line. 


are  rhombic  prisms  or  needles,  but  in  the  guinea-pig  they  are  tetra- 
hedra  belonging  to  the  rhombic  system,  and  in  the  squirrel  six-sided 
plates  of  the  hexagonal  system. 

Reduced  haemoglobin  can  also  be  caused  to  crystallize,  though 
with  more  difficulty  than  oxyhaemoglobin,  since  it  is  more  soluble. 
Crystals  of  reduced  haemoglobin  were  first  prepared  from  human 
blood  by  Hiifner,  who  allowed  it  to  putrefy  in  sealed  tubes  for 
several  weeks. 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  49 

When  a  solution  of  oxyhaemoglobin  of  moderate  strength 
is  examined  with  the  spectroscope,  two  well-marked  absorp- 
tion bands  are  seen,  one  a  little  to  the  right  of  Fraunhofer's 
line  D,  and  the  other  a  little  to  the  left  of  E.  A  third  band 
exists  in  the  extreme  violet  between  G  and  H.  It  cannot 
be  detected  with  an  ordinary  spectroscope,  but  has  been 
studied  by  the  aid  of  a  fluorescent  eye-piece  (Soret),  by 
projecting  the  spectrum  on  a  fluorescent  screen,  and  by 
photographing  the  spectrum  (Gamgee).  The  addition  of  a 
reducing  agent,  such  as  ammonium  sul- 
phide, causes  the  bands  in  the  visible 
spectrum  to  disappear,  and  they  are 
replaced  by  a  less  sharply-defined  band, 
of  which  the  centre  is  about  equidistant 
from  D  and  E.  This  is  the  charac- 
teristic band  of  reduced  haemoglobin. 
The  spectrum  of  ordinary  venous  blood 
shows  the  bands  of  oxyhaemoglobin. 

Carbonic  oxide  hemoglobin  is  a  representa- 
tive of  a  class  of  haemoglobin   compounds     FlG   9. —CRYSTALS  OF 
analogous  to  oxyhaemoglobin,  in   which  the        OXY-H/EMOGLOBIN. 
loosely-combined  oxygen  has  been  replaced      a,  human  ;  b,  squirrel ; 
by   other    gases    (carbon    monoxide,    nitric  c>  guinea-pig, 

oxide)  in  firmer  union.     Its  spectrum  shows 

two  bands  very  like  those  of  oxyhaemoglobin,  but  a  little  nearer  the 
violet  end.  Carbonic  oxide  haemoglobin  is  formed  in  poisoning 
with  coal  gas.  Owing  to  the  great  stability  of  the  compound,  the 
haemoglobin  can  no  longer  be  oxidized  in  the  lungs,  and  death  may 
take  place  from  asphyxia.  It  is,  however,  gradually  broken  up,  and 
this  is  an  indication  that  artificial  respiration  may  sometimes  be  of 
use  in  such  cases. 

Methaemoglobin  is  a  derivative  of  oxyhaemoglobin  which  can  be 
formed  from  it  in  various  ways,  e.g.,  by  the  addition  of  ferricyanide 
of  potassium  or  nitrite  of  amyl  (Gamgee),  or  by  electrolysis  (in  the 
neighbourhood  of  the  anode).  It  very  often  appears  in  an  oxyhaemo- 
globin solution  which  is  exposed  to  the  air.  It  has  been  found  in 
the  urine  in  cases  of  haemoglobinuria,  in  the  fluid  of  ovarian  cysts, 
and  in  haematoceles.  The  strongest  band  in  its  spectrum  is  in  the 
red,  between  C  and  D,  but  nearer  C,  nearly  in  the  same  position  as 
the  band  of  acid-haematin.  Reducing  agents,  such  as  ammonium 
sulphide,  change  methaemoglobin  first  into  oxyhaemoglobin  and  then 
into  reduced  haemoglobin.  It  has  by  some  been  regarded  as  a  more 
highly  oxidized  haemoglobin  than  oxyhaemoglobin.  Rebutting 
evidence  has,  however,  been  offered  to  the  effect  that  the  same 

4 


50  A  MANUAL  OF  PHYSIOLOGY 

quantity  of  oxygen  is  required  to  saturate  both  pigments,  and  this 
evidence  appears  to  be  sound.  The  difference  seems  to  lie  rather  in 
the  manner  in  which  the  oxygen  is  united  to  the  haemoglobin 
in  the  methaemoglobin  molecule  than  in  the  quantity  of  oxygen 
which  it  contains.  For  methaemoglobin,  unlike  oxyhsemoglobin.  parts 
with  no  oxygen  to  the  vacuum,  while,  on  the  other  hand,  in  the 
presence  of  reducing  agents  it  yields  up  its  oxygen  even  more  readily 
than  oxyhsemoglobin  does  (Haldane). 

By  the  action  of  acids  or  alkalies  oxyhaemoglobin  is  split  into 
haematin  and  proteid  bodies,  of  which  the  exact  nature  is  little  known. 
When  the  haemoglobin  is  acted  on  by  acids  in  the  absence  of  oxygen, 
haemochromogen  is  first  formed,  which  then  gradually  loses  its  iron 
and  is  changed  into  haematoporphyrin.  If  oxygen  be  present, 
haematin  is  the  final  product  By  the  action  of  alkalies  reduced 


FIG.  10. — DIAGRAM  TO  SHOW  THE  CHIEF  CHARACTERISTICS  T?Y  WHICH 
HEMOGLOBIN  AND  SOME  OF  ITS  DERIVATIVES  MAY  BE  RECOGNISED 
SPECTROSCOPICALLY.  THE  POSITION  OF  THE  MIDDLE  OF  EACH  BAND 
IS  INDICATED  ROUGHLY  BY  A  VERTICAL  LlNE. 

haemoglobin  yields  hcemochromogen,  which  is  stable  in  alkaline  solu- 
tion, and  gives  a  beautiful  spectrum  with  two  bands,  bearing  some 
resemblance  to  those  of  oxyhsemoglobin,  but  placed  nearer  the  violet 
end.  The  band  next  the  red  end  of  the  spectrum  is  much  sharper 
than  the  other. 

Hamatin,  the  most  frequent  result  of  the  splitting  up  of  haemo- 
globin, is  generally  obtained  as  an  amorphous  substance  with  a  bluish- 
black  colour  and  a  metallic  lustre,  insoluble  in  water,  but  soluble  in 
dilute  alkalies  and  acids,  or  in  alcohol  containing  them.  In  addition 
to  the  iron  of  the  haemoglobin,  haematin  contains  the  four  chief 
elements  of  proteid  bodies,  carbon,  hydrogen,  nitrogen  and  oxygen. 

Hamatoporphyrin,  or  iron-free  haematin,  may  be  obtained  from 
blood  or  haemoglobin  by  the  action  of  strong  sulphuric  acid.  Its 
spectrum  in  acid  solution  shows  two  bands,  one  just  to  the  left  of  D, 
the  other  about  midway  between  D  and  E.  Like  oxyhaemoglobin,  re- 
duced haemoglobin,  carbonic  oxide  haemoglobin,  methaemoglobin  and 
other  derivatives  of  haemoglobin,  it  also  has  a  band  in  the  ultra-violet. 

Hamin  is  a  compound  of  haematin  and  hydrochloric  acid,  which 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  51 

crystallizes  in  the  form  of  small  rhombic  plates,  of  a  brownish  or 
brownish- black  colour.  They  are  insoluble  in  water,  but  readily 
soluble  in  dilute  alkalies  (see  Practical  Exercises,  p.  66). 

Chemistry  of  the  White  Blood  Corpuscles. — The  composition  of 
pus-cells  and  the  leucocytes  of  lymphatic  glands  has  alone  been 
investigated.  The  chief  constituents  of  the  latter  are  a  globulin 
coagulating  by  heat  at  48°  to  50°  C.  ;  a  nucleo-proteid  coagulating  in 
5  per  cent,  magnesium  sulphate  solution  at  75°  C.,  and  causing 
coagulation  of  the  blood  on  injection  into  the  veins  of  rabbits  ;  an 
albumin  coagulating  at  73°  C. ;  and  a  ferment  with  powers  like  the 
pepsin  of  the  gastric  juice.  In  pus-cells  glycogen  has  been  found. 

The  Quantity  of  Blood. — The  quantity  of  blood  in  an  animal 
is  best  determined  by  the  method  of  Welcker.  The  animal 
is  bled  from  the  carotid  into  a  weighed  flask.  When  blood 


FIG.  IT. — DIAGRAM  TO  ILLUSTRATE  THE  DISTRIBUTION  OF  THE  BLOOD  IN 

THE  VARIOUS  ORGANS  OF  A  RABBIT  (AFTER  RANKE'S  MEASUREMENTS). 

The  numbers  are  percentages  of  the  total  blood. 

has  ceased  to  flow,  the  vessels  are  washed  out  with  water 
•or  normal  saline  solution,  and  the  last  traces  of  blood  are 
removed  by  chopping  up  the  body,  after  the  intestinal 
contents  have  been  cleared  away,  and  extracting  it  with 
water.  The  extract  and  washings  are  mixed  and  weighed ; 
a  given  quantity  of  the  mixture  is  placed  in  a  haematino- 
meter  (a  glass  trough  with  parallel  sides,  e.g.),  and  a  weighed 
quantity  of  the  unmixed  blood  diluted  in  a  similar  vessel 
till  the  tint  is  the  same  in  both.  From  the  amount  of 
dilution  required,  the  quantity  of  blood  in  the  watery  solu- 
tion can  be  calculated.  This  is  added  to  the  amount  of 
unmixed  blood  directly  determined. 

Many  other  methods  have  been  devised  on  the  principle    n^- 
of  injecting  a  known  quantity  of  some  substance  into  the 
circulating   blood,    and    then,    after    an    interval    has    been 
allowed  for  mixture,  determining  the  change  produced  in  a 

4—2 


52  A  MANUAL  OF  PHYSIOLOGY 

sample.  Thus,  the  specific  gravity  of  a  drop  of  blood  having 
been  measured,  a  certain  quantity  of  normal  saline  (a  '5  to 
7  per  cent,  solution  of  sodium  chloride)  may  be  injected 
into  a  vein,  and  the  specific  gravity  again  determined.  Or 
the  electrical  resistance  of  a  small  sample  of  blood  may 
be  measured  before  and  after  injection  of  a  given  quantity 
of  a  substance,  such  as  sodium  chloride,  which  reduces  it. 
Or  the  total  solids  may  be  determined  in  a  specimen  before 
and  after  injection  of  a  known  weight  of  distilled  water. 
Or  an  animal  may  be  caused  to  inspire  carbonic  oxide 
for  a  given  time ;  from  the  quantity  taken  in,  and  the 
quantity  fixed  by  a  known  weight  of  blood  withdrawn  from 
the  animal,  the  weight  of  the  whole  blood  maybe  calculated. 
The  quantity  of  blood  in  the  body  was  greatly  over- 
estimated by  the  ancient  physicians.  Avicenna  put  it  at 
25  lb.,  and  many  loose  statements  are  on  record  of  as 
much  as  20  lb.  being  lost  by  a  patient  without  causing 
death.  The  proportion  of  blood  to  body-weight  has  been 
found  by  accurate  experiments  to  be  in  man  and  the  dog 
i  :  13,  new-born  child  I  :  19,  cat  I  :  14,  horse  I  :  15,  frog 
i  :  17,  rabbit  i  :  19.  Fig.  n  illustrates  the  distribution  of 
the  blood  in  the  various  organs  of  a  rabbit.  The  liver  and 
skeletal  muscles  each  contain  rather  more  than  one-fourth ; 
the  heart,  lungs,  and  great  vessels  rather  less  than  one- 
fourth  ;  and  the  rest  of  the  body  about  one-fifth,  of  the  total 
blood.  The  kidney  and  spleen  of  the  rabbit  each  contain 
one-eighth  of  their  own  weight  of  blood,  the  liver  between 
one-third  and  one-fourth  of  its  weight,  the  muscles  only 
one-twentieth  of  their  weight. 

Lymph  and  Chyle. 

Lymph  has  been  defined  as  blood  without  its  red  cor- 
puscles (Johannes  Miiller)  ;  it  is,  in  fact,  a  dilute  blood- 
plasma,  containing  leucocytes,  some  of  which  (lymphocytes) 
are  common  to  lymph  and  blood,  others  (coarsely  granular 
basophile  cells)  are  absent  from  the  blood.  The  reason  of 
this  similarity  appears  when  it  is  recognised  that  the  plasma 
of  lymph  is  derived  from  the  plasma  of  blood  by  a  process 
of  physiological  filtration  (or  secretion)  through  the  walls  of 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY 


53 


the  capillaries  into  the  lymph-spaces  that  everywhere  occupy 
the  interstices  of  areolar  tissue.  Lymph,  as  obtained  from 
one  of  the  large  lymphatic  vessels  of  the  limbs,  or  from  the 
thoracic  duct  of  a  fasting  animal,  is  a  colourless  or  some- 
times slightly  yellowish  liquid  of  alkaline  reaction.  Its 
specific  gravity  is  much  less  than  that  of  the  blood  (1015  to 
1030).  It  coagulates  spontaneously,  but  the  clot  is  always 
less  firm  and  less  bulky  than  that  of  blood.  The  plasma 
contains  fibrinogen,  from  which  the  fibrin  of  the  clot  is 
derived.  Serum-albumin  and  serum-globulin  are  present  in 
much  the  same  relative  proportion  as  in  blood,  although  in 
smaller  absolute  amount.  Neutral  fats,  urea,  and  sugar  are 
also  found  in  small  quantities.  The  inorganic  salts  are  the 
same  as  those  of  the  blood-serum,  and  exist  in  about  the 
same  amount,  sodium  preponderating  among  the  bases,  as 
it  does  in  serum.  The  following  table  shows  the  results  of 
analyses  of  lymph  from  man  and  the  horse  (Munk) : 


Man. 

Horse. 

Water 

95-0  p.c. 

95'8  p.c. 

/Fibrin 

O'l        \ 

O'l       ^ 

Other  proteids 

4-. 

2-9 

Solids  \  Fat 

trace  K'O 

trace  \A'2 

Extractives*  - 

o-3 

o-i      1 

VSalts 

o-5    J 

n     J 

Chyle  is  merely  the  name  given  to  the  lymph  coming  from 
the  alimentary  canal.  The  fat  of  the  food  is  absorbed  by 
the  lymphatics,  and  during  digestion  the  chyle  is  crowded 
with  fine  fatty  globules,  which  give  it  a  milky  appearance. 
There  may  also  be  in  chyle  a  few  red  blood-corpuscles, 
carried  into  the  thoracic  duct  by  a  back-flow  from  the 
veins  into  which  it  opens.  Chyle  clots  like  ordinary  lymph. 
The  following  is  the  composition  of  a  sample  analyzed  by 
Paton,  and  obtained  from  a  fistula  of  the  thoracic  duct  in 
a  man : 

*  The  term  '  extractives  '  is  somewhat  loosely  applied  to  organic 
substances  which  exist  in  so  small  an  amount,  or  have  such  indefinite 
chemical  characters  that  they  cannot  be  separately  estimated. 


54  A  MANUAL  OF  PHYSIOLOGY 


Water 
Solids 

Inorganic 
Organic  - 
Proteids 
Fats      - 
Cholesterin 
Lecithin 


953'4 
46-6 


40-1 

137 

24*06 
0-6 
0-36 


The  quantity  of  chyle  flowing  from  the  fistula  was  esti- 
mated at  as  much  as  3  to  4  kilos  per  twenty-four  hours,  or 
nearly  as  much  as  the  whole  of  the  blood.  The  flow  has 
been  calculated  in  various  animals  at  one-eighteenth  to  one- 
seventh  of  the  body-weight  in  the  twenty-four  hours.  The 
quantity  of  lymph  in  the  body  is  unknown,  but  it  must  be 
very  great — perhaps  two  or  three  times  that  of  the  blood. 

The  gases  of  the  blood  and  lymph  will  be  treated  of  in 
Chapter  III. 

The  Functions  of  Blood  and  Lymph. 

We  have  already  said  that  these  liquids  provide  the 
tissues  with  the  materials  they  require,  and  carry  away  from 
them  materials  which  have  served  their  turn  and  are  done 
with.  These  materials  are  gaseous,  liquid,  and  solid.  Oxygen 
is  brought  to  the  tissues  in  the  red  corpuscles;  carbon  dioxide 
is  carried  away  from  them  chiefly  in  the  plasma  of  the  blood 
and  lymph.  The  water  and  solids  which  the  cells  of  the 
body  take  in  and  give  out  are  also,  at  one  time  or  another, 
constituents  of  the  plasma.  The  heat  produced  in  the 
tissues,  too,  is,  to  a  large  extent,  conducted  into  the  blood 
and  distributed  by  it  throughout  the  body.  It  is  not  known 
whether  the  leucocytes  play  any  part  in  the  normal  nutrition 
of  other  cells,  although  it  is  probable  that  they  exercise  an 
influence  on  the  plasma  in  which  they  live ;  but  they  have 
important  functions  of  another  kind,  to  which  it  is  necessary 
to  refer  briefly  here. 

Phagocytosis. — Certain  of  the  amoeboid  cells  of  blood  and 
lymph,  and  the  cells  of  the  splenic  pulp,  are  able  to  include 
or  'eat  up '  foreign  bodies  with  which  they  come  in  contact,  in 
the  same  way  as  the  amoeba  takes  in  its  food.  Such  cells  are 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  55 

called  phagocytes ;  and  it  is  to  be  remarked  that  this  term 
neither  comprises  all  leucocytes  nor  excludes  all  other  cells, 
for  some  fixed  cells,  such  as  those  of  the  endothelial  lining 
of  bloodvessels,  are  phagocytes  in  virtue  of  their  power  of 
sending  out  protoplasmic  processes,  while  the  small,  im- 
mobile, uninuclear  leucocyte,  or  lymphocyte,  is  not  a  phago- 
cyte. 

Although  it  is  not  at  present  possible  to  assign  a  physio- 
logical value  to  all  the  phenomena  of  phagocytosis,  either  as 
regards  the  phagocytes  themselves  or  as  regards  the 
organism  of  which  they  form  a  part,  there  seems  little  doubt 
that  under  certain  circumstances  the  process  is  connected 
with  the  removal  of  structures  which  in  the  course  of 
development  have  become  obsolete,  or  with  the  neutraliza- 
tion or  elimination  of  harmful  substances  introduced  from 
without,  or  formed  by  the  activity  of  bacteria  within  the 
tissues.  During  the  metamorphosis  of  some  larvae,  groups  of 
cilia  and  muscle-fibres  may  be  absorbed  and  eaten  up  by  the 
leucocytes.  In  the  metamorphosis  of  maggots,  for  example, 
the  muscular  fibres  of  the  abdominal  wall,  which  are  absent 
from  the  adult  form,  are  removed  in  this  way.  At  the  time 
when  the  tail  of  the  tadpole  disappears,  multitudes  of  leuco- 
cytes swarm  into  it,  and  some  of  them  may  be  seen  with 
fragments  of  muscle  or  nerve  inside  them. 

But  the  behaviour  of  phagocytes  towards  pathogenic 
micro-organisms  is  of  even  greater  interest  and  importance, 
Metschnikoff  laid  the  foundation  of  our  knowledge  of  this 
subject  by  his  researches  on  Daphnia,  a  small  crustacean 
with  transparent  tissues,  which  can  be  observed  under  the 
microscope.  When  this  creature  is  fed  with  a  fungus, 
Monospora,  the  spores  of  the  latter  find  their  way  into  the 
body-cavity.  Here  they  are  at  once  attacked  by  the  leuco- 
cytes, ingested,  and  destroyed.  But  after  a  time  so  many 
spores  get  through  that  the  leucocytes  are  unable  to  deal 
with  them  all ;  some  of  them  develop  into  the  first  or 
•  conidium  '  stage  of  the  fungus ;  the  conidia  poison  the 
leucocytes,  instead  of  being  destroyed  by  them,  and  the 
animal  generally  dies.  Occasionally,  however,  the  leuco- 
cytes are  able  to  destroy  all  the  spores,  and  the  life  of  the 


56  A  MANUAL  OF  PHYSIOLOGY 

Daphnia  is  preserved.  This  battle,  ending  sometimes  in 
victory,  sometimes  in  defeat,  is  believed  by  Metschnikoff  to 
be  typical  of  the  struggle  which  the  phagocytes  of  higher 
animals  and  of  man  seem  to  engage  in  when  the  germs  of 
disease  are  introduced  into  the  organism.  He  supposes 
that  the  immunity  to  certain  diseases  possessed  naturally 
by  some  animals,  and  which  may  be  conferred  on  others  by 
vaccination  with  various  protective  substances,*  is,  to  a 
large  extent,  due  to  the  early  and  complete  success  of  the 
phagocytes  in  the  fight  with  the  bacteria ;  and  that  in 
rapidly-fatal  diseases — such  as  chicken-cholera  in  birds  and 
rabbits,  and  anthrax  in  mice — the  absence  of  any  effective 
phagocytosis  is  the  factor  which  determines  the  result. 
Others  have  laid  stress  on  the  action  of  protective  sub- 
stances supposed  to  exist  in  the  living  plasma  itself,  although 
only  as  yet  demonstrated  in  the  serum.  It  is  possible  that 
such  substances  are  manufactured  by  the  leucocytes,  and 
either  given  off  by  them  to  the  plasma  by  a  process  of 
*  excretion,'  or  liberated  by  their  complete  solution.  And  it 
may  be  that  it  is  only  when  the  bacteria  have  been  crippled 
by  contact  with  these  defensive  '  alexins  '  that  the  leucocytes 
are  able  to  ingest  them  and  complete  their  destruction. 

Diapedesis. — The  fact  that  leucocytes  can  pass  out  of  the 
bloodvessels  into  the  tissues  (Waller,  Cohnheim)  has  a  very 
important  bearing  on  the  subject  of  phagocytosis.  The 
phenomenon  is  called  diapedesis,  and  is  best  seen  when  a 
transparent  part,  such  as  the  mesentery  of  the  frog,  is 

*  The  most  recent  investigations  go  to  show  that  Metschnikoff's 
phagocytic  theory  of  immunity  requires  modification  in  the  case  of  the 
higher  animals  and  man,  although  the  brilliant  biological  observations  on 
which  it  was  originally  built  retain  all  their  value.  He  supposed  that 
in  the  immunizing  process  the  leucocytes  underwent  certain  changes, 
acquired,  so  to  speak,  a  sort  of  'education'  that  enabled  them  to  cope 
with  bacteria  against  which  they  were  previously  powerless.  It  seems 
more  probable  that  in  the  presence  of  the  substances  that  confer  immunity, 
not  only  the  leucocytes,  but  other  cells,  are  stimulated  to  produce  bodies 
which  cut  short  the  life,  or  at  least  inhibit  the  growth,  of  the  bacteria.  It 
may  be,  however,  that  the  leucocytes  take  the  lead  in  this  reaction.  And 
the  voracious  and  almost  undiscriminating  appetite  displayed  by  cells 
which  englobe  with  equal  avidity  a  granule  of  carmine  or  a  particle  of 
proteid,  a  globule  of  fat  or  a  fragment  of  carbon,  renders  it  difficult  to 
believe  that  they  do  not  also  act,  to  some  extent,  directly  as  phagocytes 
in  the  presence  of  pathogenic  organisms. 


THE  CIRCULATING  LIQUIDS  OF  THE  BODY  57 

irritated.  The  first  effect  of  irritation  is  an  increase  in  the 
flow  of  blood  through  the  affected  region.  If  the  irritation 
continues,  or  if  it  was  originally  severe,  the  current  soon 
begins  to  slacken,  the  corpuscles  stagnate  in  the  vessels,  and 
inflammatory  stasis  is  produced.  The  leucocytes  adhere  in 
large  numbers  to  the  walls  of  the  capillaries,  and  particularly 
of  the  small  veins,  and  then  begin  to  pass  slowly  through 
them  by  amoeboid  movements,  the  passage  taking  place  at 
the  junctions  between,  or  it  may  be  through  the  substance 
of,  the  endothelial  cells.  Plasma  is  also  poured  out  into  the 
tissues,  the  whole  forming  an  inflammatory  exudation. 
Even  red  blood-corpuscles  may  pass  out  of  the  vessels  in 
small  numbers.  The  exudation  maybe  gradually  reabsorbed, 
or  destruction  of  tissue  may  ensue,  and  a  collection  of  pus 
be  formed.  The  cells  of  pus  are  largely,  if  not  entirely,  emi- 
grated leucocytes. 


PRACTICAL  EXERCISES  ON  CHAPTER  I. 

N.B. — In  the  following  exercises  all  experiments  on  animals  which 
would  cause  pain  are  to  be  done  under  complete  anesthesia. 

1.  Reaction  of  Blood. — With  a  clean  suture-needle  prick  one  of  the 
fingers  behind  the  nail.     Bandaging  the  finger  with  a  handkerchief 
from  above  downwards,  so  as  to  render  its  tip  congested,  will  often 
facilitate  the  getting  of  a  good-sized  drop.     Put  a  drop  of  blood  on 
a  piece  of  glazed  neutral  litmus  paper;  wash  off  in  10  to  30  seconds 
with  distilled  water.     A  blue  stain  will  be  left,  showing  that  fresh 
blood  is  alkaline. 

2.  Specific  Gravity  of  Blood — (i)  Hammerschlag s  Method. — Put  a 
mixture  of  chloroform  and  benzol  of  specific  gravity  ro6o  into  a  small 
glass  cylinder.     Obtain  a  drop  of  blood  as  in  i.     Put  it  in  the  mixture 
by  means  of  a  small  pipette.     If  it  sinks,  add  chloroform,  if  it  rises,  add 
benzol,  till  it  just  remains  suspended  when  the  liquid  has  been  well 
stirred.     Then  with  a  small  hydrometer  measure  the  specific  gravity 
of  the  mixture,  which  is  now  equal  to  that  of  the  blood.     Filter  the 
liquid  to  free  it  from  blood,  and  put  it  back  into  the  stock-bottle. 
This  is  a  convenient  method,  but  some  prefer — 

(2)  Roy's  Method. — Take  25  small  bottles  containing  mixtures  of 
glycerine  and  water  of  specific  gravity  1*027,  1*029  .  .  .  [-070. 
Begin  with  bottle  I'OSQ.  Pour  a  little  of  the  liquid  into  a  small 
vessel.  Then  prick  the  finger  with  a  sharp,  clean  suture-needle,  and 
suck  up  a  small  drop  of  blood  into  the  horizontal  limb  of  a  capillary 
tube  with  a  rectangular  elbow.  Immerse  the  horizontal  part  of  the 
tube  in  the  glycerine  mixture,  and  gently  blow  the  drop  of  blood  into 


58  A  MANUAL  OF  PHYSIOLOGY 

it.  If  it  neither  rises  nor  sinks,  the  specific  gravity  of  the  blood 
is  1*059.  If  it  sinks,  the  experiment  must  be  repeated  with  a 
mixture  of  higher  specific  gravity,  say  i'o6i  ;  if  it  rises,  with  a 
mixture  of  lower  specific  gravity,  say  i  '057,  and  so  on.  If  the  drop  of 
blood  rises  in  mixture  1*061  and  sinks  in  mixture  1*059,  the  specific 
gravity  is  between  those  two  figures,  and  may  be  taken  as  i  '060. 
/  3.  Coagulation  of  Blood. — (i)  Take  two  tumblers  or  beakers, 
label  them  a  and  ft,  and  measure  into  each  100  c.c.  of  water. 
Mark  the  level  of  the  water  by  strips  of  gummed  paper,  and  pour  it 
out.  (If  a  sufficient  number  of  graduated  cylinders  is  available,  they 
may  of  course  be  used,  and  this  measurement  avoided.)  Into  a  put 
25  c.c.  of  a  saturated  solution  of  magnesium  sulphate,  and  into 
ft  25  c.c.  of  a  i  per  cent,  solution  of  potassium  oxalate  in  normal 
saline  solution  (*6  per  cent,  solution  of  sodium  chloride).  If  the 
dog  provided  is  a  large  one,  these  quantities  may  be  all  doubled. 

(2)  Insert  a  cannula  into  the  central  end  of  the  carotid  artery  of  a 
dog  anaesthetized  with  morphia*  and  ether. 

To  put  a  Cannula  into  an  Artery. — Select  a  glass  cannula  of 
suitable  size,  feel  for  the  artery,  make  an  incision  in  its  course 
through  the  skin,  then  isolate  about  an  inch  of  it  with  forceps  or  a 
blunt  needle,  carefully  clearing  away  the  fascia,  or  connective  tissue. 
Next  pass  a  small  pair  of  forceps  under  the  artery,  and  draw  two 
ligatures  through  below  it.  If  the  cannula  is  to  be  inserted  into  the 
central  end  of  the  artery,  tie  the  ligature  which  is  farthest  from  the 
heart,  and  cut  one  end  short.  Then  between  the  heart  and  the  other 
ligature  compress  the  artery  with  a  small  clamp  (often  spoken  of  as 
•  bulldog  '  forceps).  Now  lift  the  artery  by  the  distal  ligature,  make  a 
transverse  slit  in  it  with  a  pair  of  fine  scissors,  insert  the  cannula,  and 
tie  the  ligature  over  its  neck.  Cut  the  ends  of  the  ligatures  short. 
If  the  cannula  is  to  be  put  into  the  distal  end  of  the  artery,  both 
ligatures  must  be  between  the  clamp  and  the  heart,  and  the  bulldog 
must  be  put  on  before  the  first  ligature  (the  one  nearest  the  heart) 
is  tied,  so  that  the  piece  of  bloodvessel  between  it  and  the  ligature 
may  be  full  of  blood,  as  this  facilitates  the  opening  of  the  artery. 

(3)  Run  into  a  and  ft  enough  blood  to  fill  them  to  the  mark. 

(4)  Take  a  small  thin  copper  or  brass  vessel,  and  place  it  in  a 
freezing  mixture  of  ice  and  salt.     Run  into  it  some  of  the  blood  from 
the  artery.     It  soon  freezes  to  a  hard  mass.     Now  take  the  vessel 
out  of  the  freezing  mixture  and  allow  the  blood  to  thaw.     It  will  be 
seen  that  it  remains  liquid  for  a  short  time  and  then  clots. 

"  (5)  Run  some  of  the  blood  into  a  porcelain  capsule,  stirring  it 
vigorously  with  a  glass  rod.  The  fibrin  collects  on  the  rod  ;  the 
blood  is  defibrinated  and  will  no  longer  clot. 

(6)  Now  let  the  dog  bleed  to  death,  and  collect  the  whole  of  the 
blood  in  a  jar.  Observe  that  the  flow  of  blood  is  temporarily 

*  One  to  two  centigrammes  of  morphia  hydrochlorate  per  kilogramme 
of  body-weight  should  be  injected  subcutaneously  about  half  an  hour 
before  the  operation.  It  is  convenient  to  use  a  2  per  cent,  solution,  and 
10  c.c.  of  this  is  sufficient  for  a  dog  of  good  size.  Note  that  diarrhoea  and 
salivation  are  caused  by  such  a  dose. 


PRACTICAL  EXERCISES 


59 


increased  by  pressure  on  the  abdominal  walls,  which  squeezes  it 
towards  the  heart,  by  passive  pumping  movements  of  the  hind-legs, 
and  also  during  the  convulsions '  of  asphyxia,  which  soon  appear. 
Notice  that  the  blood  begins  to  clot  in  a  few  minutes,  and  that 
very  soon  the  vessel  can  be  tilted  without  spilling  the  blood.  Set  it 
aside  in  a  cool  place,  and  observe  next  day  that  some  clear  yellow 
serum  has  separated  from  the  clot. 

(7)  Observe  that  the  blood  in  a  and  /?  has  not  coagulated.     Label 
four   test-tubes  A,   B,   C,  D, 

and  put  into  each  about  5  c.c. 
of  the  oxalated  blood.  Add 
to  A  and  B  5  or  6  drops  of  a 
2  per  cent,  solution  of  calcium 
chloride,  to  C  12  drops,  and 
to  D  as  much  as  there  is  of 
the  blood.  Leave  A  at  the 
ordinary  temperature,  put  the 
other  test-tubes  in  a  water- 
bath  at  40°  C.,  and  note  when 
clotting  occurs. 

(8)  By  means  of  a  centri- 
fuge  (Fig.    12)    separate   the 
plasma  from  the  corpuscles  in 
a  and  P.     (With  Jung's  hand 
centrifuge  fairly  clear  oxalated 
plasma  may  generally  be  ob- 
tained    in    about    twenty 
minutes.  Magnesium  sulphate 
['  salted ']  plasma  usually  takes 
a  little  longer  to  separate.) 

With  the  decalcified  plasma 
from  /3  repeat  the  observations 
in  (7). 

With  the  plasma  from  a 
perform  the  following  experi- 
ments :  (a)  Put  a  small  quan- 
tity of  the  plasma  into  eight 
test-tubes,  labelling  them  E, 
F,  G,  H,  I,  K,  L,  and  M. 
Dilute  E  and  F  with  ten  times, 
and  G  and  H  with  five  times, 


FIG.  12. — CENTRIFUGE  (JUNG). 
The  four   cylinders   shown  at  the  top  of 
the  figure  are  so  swung  that  they  become 
horizontal  as  soon  as  speed  is  got  up. 


as  much  distilled  water  as  was  taken  of  plasma ;  dilute  the  plasma 
in  I  and  K  with  ten  times,  and  in  L  and  M  with  five  times,  its 
volume  of  a  solution  of  fibrin-ferment  containing  some  calcium 
chloride.  Put  E,  G,  I,  and  L  in  the  bath  at  40°  C.,  and  leave  the 
rest  of  the  test-tubes  at  room  temperature.  Observe  m  which  of  t 
test-tubes,  if  any,  coagulation  occurs,  and  the  time  of  its  occurrence, 
and  report  the  result. 

If  no  centrifuge  is  available,  the  decalcified  and  salted  blood  mus 
be  left  standing  in  a  cool  place  for  twenty-four  hours  or  more  till  the 


6o 


A  MANUAL  OF  PHYSIOLOGY 


corpuscles  settle.  The  plasma  can  then  be  siphoned  or  pipetted  off. 
Instead  of  dog's  blood,  the  blood  of  an  ox  or  pig  may  be  obtained  at 
the  slaughter-house. 

4.  Preparation  of  Fibrin- Ferment. — Precipitate  blood-serum  with 
ten  times  its  volume  of  alcohol.     Let  it  stand  for  several  weeks,  then 
extract  the   precipitate  with   water.     The  water  dissolves   out   the 
fibrin-ferment,  but  not  the  other  coagulated  proteids. 

5.  Serum. — Test  the  reaction,  and  determine,  both  by  the  hydro- 
meter and  the  pycnometer,  or  specific  gravity  bottle,  the  specific  gravity 
of  the  serum  provided,  or  of  the  serum  obtained  in  experiment  3. 

Serum  Proteids. — (i)  Saturate    serum   with    magnesium    sulphate 
crystals  at  30°  C.     The  serum-globulin  is  precipitated.     Filter  off. 


FIG.  13. — THOMA-ZEISS  H^MOCYTOMETER. 

M,  mouth-piece  of  tube  G,  by  which  blood  is  sucked  into  5  ;  E,  bead  for  mixing  ; 
a,  view  of  slide  from  above ;  b,  in  section  ;  c,  squares  in  middle  of  B,  as  seen  under 
microscope. 

Wash  the  precipitate  on  the  filter  with  a  saturated  solution  of  mag- 
nesium sulphate.  Dissolve  the  precipitate  by  the  addition  of  a 
little  distilled  water,  and  perform  the  following  tests  for  globulins  : 

(a]  Saturate  with  magnesium  sulphate.     A  precipitate  is  obtained. 

(b)  Drop  into  a  large  quantity  of  water,  and  a  flocculent  precipitate 
falls  down,     (c)  Heat.    Coagulation  occurs.     Determine  the  tempera- 
ture of  coagulation  (p.  21). 

(2)  To  a  portion  of  the  filtrate  from  (i)  add  sodium  sulphate  to 
saturation.    The  serum-albumin  is  precipitated.    (Neither  magnesium 
sulphate  nor  sodium  sulphate  precipitates  serum-albumin  alone,  but 
the  double  salt  sodio-magnesium  sulphate  precipitates  it,  and  this  is 
formed  when  sodium  sulphate  is  added  to  magnesium  sulphate.) 

(3)  Dilute  another  portion  of  the  filtrate  from  (i)  with  its   own 
bulk  of  water.    Slightly  acidulate  with  dilute  acetic  acid,  and  determine 
the  temperature  of  heat  coagulation. 

(4)  Precipitate  the  serum-globulin  from  another  portion  of  serum 
by  adding  to  it  an  equal  volume  of  saturated  solution  of  ammonium 


PRACTICAL  EXERCISES  61 

sulphate.     Filter.    Precipitate  the  serum-albumin  from  the  filtrate  by 
saturating  with  ammonium  sulphate  crystals. 

(5)  Dilute  serum  with  ten  to  twenty  times  its  volume  of  distilled 
water,  and  pass  through  it  a  stream  of  carbon  dioxide.     The  serum- 
globulin    is   partially  precipitated.     This    is  the  starting-point  of  a 
method  said  to  be  the  best  for  obtaining  pure  serum-globulin. 

(6)  Acidulate  some  serum  with  dilute  acetic  acid  and  boil.     Filter 
off  the  coagulum,  and  to  the  filtrate  add  silver  nitrate.     A  non- 
proteid  precipitate  insoluble  in  nitric  acid  but  soluble  in  ammonia 
indicates  the  presence  of  chlorides. 

6.  Enumeration  of  the  Blood-corpuscles. — Use  the  Thoma-Zeiss 
apparatus  (Fig.  13).     Prick  the  finger  to  obtain  a  drop  of  blood. 
Suck  the  blood  up  into  the  capillary  tube  S  to  the  mark  i.*     Wipe 
off  any  blood  which  may  adhere  to  the  end  of  the  tube.     Then  fill 
it  with  Hayem's  solution  (p.  29)  or  3  per  cent,  sodium  chloride  to 
the  mark  101.     This  represents  a  dilution  of  100  times.     Mix  the 
blood  and  solution  thoroughly,  then  blow  out  a  drop  or  two  of  the 
liquid  to  remove  all  the  solution  which  remains  in  the  capillary  tube. 
Now  fill  the  shallow  cell  B  with  the  blood  mixture.     Slide  the  cover- 
glass  on,  taking  care  that  it  does  not  float  on  the  liquid,  but  that  the 
cell  is  exactly  filled.     Put  the  slide  under  the  microscope  (say  Leitz's 
oc.  III.,  obj.  5),  and  count  the  number  of  red  corpuscles  in  not  less 
than  ten  to  twenty  squares.     The   greater  the  number  of  squares 
counted,  the  nearer  will  be  the  approximation  to  the  truth.     Now 
take  the  average  number  in  a  square.     The  depth  of  the  cell  is 
YO  mm.,  the  area  of  each  square  400  scl-  mm-     The  volume  of  the 
column  of  liquid  standing  upon  a  square  is  ^oW  cub.  mm.      One 
cub.  mm.  of  the  diluted  blood  would  therefore  contain  4,000  times 
as  many  corpuscles  as  one  square.     But  the  blood  has  been  diluted 
100  times,  therefore  i  cub.  mm.  of  the  undiluted  blood  would  con- 
tain 400,000  times  the  number  of  corpuscles  in  one  square.     Suppose 
the  average  for  a  square  is  found  to  be  13.     This  would  correspond 
to  5,200,000  corpuscles  in  i  cub.  mm.  of  blood. 

7.  Opacity  of  Blood. — Smear  a  little  fresh  blood  on  a  glass  slide, 
and  lay  the  slide  on  some  printed  matter.     It  will  not  be  possible  to 
read  it,  because  the  light  is   reflected   from   the  corpuscles  in  all 
directions,  and  little  of  it  passes  through. 

8.  Laking  of  Blood.— (i)  Put  a  little  fresh  blood  in  three  test- 
tubes,  A  B  and  C.     Dilute  A  with  an  equal  volume,  B  with  two 
volumes,  and  C  with  three  volumes,  of  distilled  water,  and  repeat 
experiment   7.      The  print  can  now  be  read   probably  through  a 
layer  of  A,  but  certainly  through  B  and  C,  since  the  haemoglobin  is 
dissolved  out  of  the  corpuscles  by  the  water  and  goes  into  solution, 
the  blood  becoming  transparent  or  laked.     That  the  difference  is 
not  due  merely  to  dilution  can  be  shown  by  putting  an  equal  quantity 
of  blood  in  two  test-tubes,  and  gradually  diluting  one  with  distilled 
water  and  the  other  with  a  0*9  per  cent,  solution  of  sodium  chloride, 
which  does  not  dissolve  out  the  haemoglobin.      Print  can  be  read 

*  If  the  tube  has  not  been  properly  filled,  blow  the  blood  out  immediately. 
On  no  account  permit  it  to  clot  in  the  capillary  tube. 


62  A  MANUAL  OF  PHYSIOLOGY 

through  the  first  with  a  smaller  degree  of  dilution  than  through  the 
second.  Examine  the  laked  blood  with  the  microscope  for  the 
*  ghosts,'  or  shadows  of  the  red  corpuscles.  The  addition  of  a  drop 
or  two  of  methylene  blue  will  render  them  somewhat  more  distinct. 

(2)  Put  some  blood  in  a  test-tube,  or  flask;  cork  up,  and  let  stand 
till  it  begins  to  putrefy.  It  becomes  laked. 

9.  Globulicidal  Action  of  Serum. —  (i)  To  a  small  quantity  of 
rabbit's  blood  add  an  equal  volume  of  dog's  serum.     Mix  and  let 
stand  for  fifteen  or  twenty  minutes.     The  colour  of  the  blood  is  now 
darker   than   before,  and  it  can  be  seen   to    be   laked.     Examine 
microscopically. 

(2)  Place  a  small  drop  of  rabbit's  blood  and  a  somewhat  larger 
drop  of  the  dog's  serum  on  a  slide,  near,  but  not  quite  in  contact 
with,  each  other.     Now  put  on  a  cover-slip,  so  that  the  drops  just 
come  together,  and  examine  at  once  with  the  microscope  with  a 
moderately  high  power.     Where   the   two   drops   mingle,    the   red 
corpuscles  will  be  seen  to  fade  out,  leaving  only  their  *  ghosts.'     A 
few  of  the  corpuscles  which  come  into  contact  with  the,  as  yet, 
undiluted  serum  may  be  entirely  dissolved. 

(3)  Heat  some  of  the  dog's  serum  to  60°  C.  for  ten  minutes,  and 
repeat  (i)  and  (2).     No  effect  will  now  be  produced  on  the  rabbit's 
corpuscles. 

(4)  Repeat  (i)  and  (2)  with  dog's  blood  and  rabbit's  serum      The 
blood  will  not  be  laked. 

10.  Blood-pigment — (i)  Preparation  of  Haemoglobin  Crystals.— 
(a)  Heat  some  dog's  blood  to  60°  or  65°  C.  in  a  water-bath  for  about 
ten  minutes,  taking  care  that  the  latter  temperature  is  not  exceeded. 
Cool,  and  examine  the  oxyhaemoglobin  crystals  with  the  microscope. 
They  form  long  rhombic  prisms  and  needles. 

(b)  Add  a  little  crude  saponin  to  dog's  blood  in  a  test-tube.     Shake 
up  well,  and  allow  it  to  stand  till  the  colour  becomes  dark.     Then 
shake  vigorously,  and  a  mass  of  haemoglobin  crystals  will  be  formed. 

(c]  Put  a  small  drop  of  guinea-pig's  blood  on  a  slide.     Mix  with  a 
drop  of  Canada   balsam  and  cover.     Tetrahedral  crystals  of  oxy- 
hsemoglobin  will  soon  form.     The  slide  may  be  kept. 

( 2 )  Spectroscopic  Examination  of  Haemoglobin  and  its  Derivatives. 
— (a)  With  a  small,  direct-vision  spectroscope  look  first  at  a  bright 
part  of  the  sky.  Focus  by  pulling  out  or  pushing  in  the  eyepiece 
until  the  numerous  fine  dark  lines  (Fraunhofer's  lines),  running 
vertically  across  the  spectrum,  are  seen.  Narrow  the  slit  by  moving 
the  milled  edge  till  the  lines  are  as  sharp  as  they  can  be  made.  Note 
especially  the  line  D  in  the  orange,  the  lines  E  and  b  in  the  green 
and  F  in  the  blue.  Always  hold  the  spectroscope  so  that  the  red  is 
at  the  left  of  the  field.  Now  dip  an  iron  or  platinum  wire  with  a  loop 
on  the  end  of  it  into  water,  and  then  into  some  common  salt  or  sodium 
carbonate,  and  fasten  or  hold  it  in  the  flame  of  a  fishtail  burner.  On 
examining  the  flame  with  the  spectroscope,  a  bright  yellow  line  will  be 
seen  occupying  the  position  of  the  dark  line  D  in  the  solar  spectrum. 
This  is  a  convenient  line  of  reference  in  the  spectrum,  and  in 
studying  the  spectra  of  haemoglobin  and  its  derivatives,  the  position 


PRACTICAL  EXERCISES  63 

of  the  absorption  bands  with  regard  to  the  D  line  should  always  be 
noted.  The  dark  lines  in  the  solar  spectrum  are  due  to  the  absorp- 
tion of  light  of  a  definite  range  of  wave-lengths  by  metals  in  a  state 
of  vapour  in  the  sun's  atmosphere,  and  of  course  no  dark  lines  are 
seen  in  the  spectrum  of  a  gas-flame.  Now  arrange  the  spectroscope, 
test-tube  and  gas-flame  on  a  stand  as  in  Fig.  14.  Half  fill  the  test- 
tube  with  defibrinated  blood.  Nothing  can  be  seen  with  the  spectro- 
scope till  the  blood  is  diluted.  Pour  a  little  of  the  blood  into 
another  test-tube,  and  go  on  diluting  till,  on  focussing,  two  bands  of 
oxyhcemoglobin  are  seen  in  the  position  indicated  in  Fig.  8.  Draw 
the  spectrum  ;  then  dilute  still  more,  and  observe  which  of  the  bands 


FIG.  14.— SPECTROSCOPIC  EXAMINATION  OF  BLOOD-PIGMENT. 

first  disappears.  Now  put  5  c.c.  of  the  blood  into  another  test-tube, 
and  dilute  it  with  four  times  its  volume  of  water.  Take  5  c.c.  of  this 
dilution,  and  again  add  four  times  as  much  water,  and  so  on  till  the 
solution  is  only  faintly  coloured.  Note  with  what  degree  of  dilution 
the  bands  disappear.  Then  examine  each  of  the  solutions  with  the 
spectroscope  and  draw  its  spectrum. 

(b)  Make  a  solution    of  blood  which  shows  the  oxyhaemoglobin 
bands  sharply.     Add  a  drop  or  two  of  ammonium  sulphide  solution 
to  reduce  the  oxyhaemoglobin.     Heat  gently  to  about  body-tempera- 
ture.    A  single,  ill-defined  band  now  appears,  occupying  a  position 
midway  between  the  oxyhaemoglobin  bands,  and  the  latter  disappear. 
This  is  the  band  of  reduced  hemoglobin  (Fig.  8). 

(c)  Carbonic  Oxide  Hcemoglobin. — Pass  coal-gas  through  blood  for 


64  A  MANUAL  OF  PHYSIOLOGY 

a  considerable  time.  Examine  some  of  the  blood  (after  dilution) 
with  the  spectroscope.  Two  bands,  almost  in  the  position  of  the 
oxyhaemoglobin  bands,  are  seen  ;  but  no  change  is  caused  by  the 
addition  of  ammonium  sulphide,  since  carbonic  oxide  haemoglobin 
is  a  more  stable  compound  than  oxyhaemoglobin. 

(d)  Methamoglobin. — Put  some  blood  into  a  test-tube,  add  a  few 
drops  of  a  solution  of  ferricyanide  of  potassium,  and  heat  gently.    On 
diluting,  a  well-marked  band  will  be  seen  in  the  red.     On  addition 
of  ammonium  sulphide  this  band  disappears ;   the  oxyhaemoglobin 
bands  are  seen  for  a  moment,  and  then  give  place  to  the  band  of 
reduced  haemoglobin  (Fig.  8). 

(e)  Acid  Hcematin. — To  a  little  diluted  blood  add  strong  acetic 
acid  and  heat  gently.    The  colour  becomes  brownish.    The  spectrum 
shows  a  band  in  the  red  between  C  and  D,  not  far  from  the  position 
of  the  band  of  methaemoglobin.     The  addition  of  a  drop  or  two  of 
ammonium  sulphide  causes  no  change  in  the  spectrum,  and  this  is  a 
means   of  distinguishing   acid-haematin  from   methaemoglobin.      If 
more  ammonium  sulphide  be  added,  haematin  will  be  precipitated 
when  the  acid  solution  has  been  rendered  neutral,  and  a  further 
addition  of  ammonium  sulphide  or  sodium  hydrate  will  cause  the 
haematin  to  be  again  dissolved,  a  solution  of  alkaline  haematin  being 
formed.     This  in  its  turn  may  be  reduced  by  an  excess  of  ammonium 
sulphide,  and  the  spectrum  of  haemochromogen   may  be  obtained 
(Fig.  8). 

(/)  Alkaline  Hcematin. — To  diluted  blood  add  strong  acetic  acid 
and  warm  gently  for  a  few  minutes.  Then,  when  the  spectroscopic 
examination  of  a  sample  shows  that  acid-hsematin  has  been  formed, 
neutralize  with  sodium  hydrate.  A  brownish  precipitate  of  hsematin 
is  thrown  down,  which  dissolves  in  an  excess  of  sodium  hydrate, 
giving  a  solution  of  alkaline  haematin. 

Or  add  sodium  hydrate  to  blood  directly,  and  warm  for  a  couple 
of  minutes  after  the  colour  has  changed  decidedly  to  brownish- 
black.  The  spectrum  of  alkaline  haematin  is  a  broad  but  ill-defined 
band  just  overlapping  the  D  line,  and  situated  chiefly  to  the  red  side 
of  it  (Fig.  8). 

(g)  Hczmochromogen. — To  a  solution  of  alkaline  haematin  add  a 
drop  or  two  of  ammonium  sulphide.  The  band  near  D  disappears, 
and  two  bands  make  their  appearance  in  the  green  (Fig.  8). 

(h)  Hamatoporphyrin. — Put  some  strong  sulphuric  acid  in  a  test- 
tube.  Add  a  few  drops  of  blood,  agitate  the  test-tube  till  the  blood 
dissolves,  and  examine  the  purple  liquid,  diluting  it,  if  necessary,  with 
sulphuric  acid.  Its  spectrum  shows  two  well-marked  bands,  one  just 
to  the  left  of  D,  and  the  other  midway  between  D  arid  E  (Fig.  8). 

(3)  Guaiacum  Test  for  Blood.— A  test  for  blood — much  used  in 
hospitals,  and,  indeed,  a  delicate  one,  but  not  always  trustworthy 
unless  certain  precautions  be  taken—is  the  guaiacum  test.  A  drop 
of  freshly-prepared  tincture  of  guaiacum  is  added  to  the  liquid  to  be 
tested,  and  then  ozonic  ether  (peroxide  of  hydrogen).  If  blood  be 
present,  the  guaiacum  strikes  a  blue  colour.  The  decomposition  of 
the  peroxide  by  the  blood  seems  to  be  due  to  the  stroma  of  the  cor- 


PRACTICAL  EXERCISES  65 

puscles  rather  than  to  the  pigment,  and  other  '  oxygen  carriers ' — 
e.g.,  fresh  vegetable  protoplasm — will  cause  the  same  colour. 

(4)  Quantitative  Estimation  of  Haemoglobin — (a)  By  FleischVs 
Hamometer  (Fig.  15). — Fill  with  distilled  water  that  compartment  a' 
of  the  small  cylinder  (above  the  stage)  which  is  over  the  tinted  wedge. 
Put  a  little  distilled  water  into  the  other  compartment  a.  Now  prick 
the  finger  and  fill  one  of  the  small  capillary  tubes  with  blood.  See 
that  none  of  the  blood  is  smeared  on  the  outside  of  the  tube.  Then 
wash  all  the  blood  into  the  water  in  compartment  a,  and  fill  it  to  the 
brim  with  distilled  water.  By  means  of  the  milled  head  T  move  the 


FIG.  15. — FLEISCHL'S  H/EMOMETER. 

tinted  wedge  K  till  the  depth  of  colour  is  the  same  in  the  two  com- 
partments. The  percentage  of  the  normal  quantity  of  haemoglobin 
is  given  by  the  graduated  scale  P.  For  example,  if  the  reading  is 
90,  the  blood  contains  90  per  cent,  of  the  normal  amount ;  if  100,  it 
contains  the  normal  quantity.  The  observations  should  be  made  in 
a  dark  room,  the  white  surface  S,  arranged  below  the  compartments 
a  and  a,  being  illuminated  by  a  lamp.  Or  the  instrument  may  be 
placed  in  a  small  box,  lighted  by  a  candle.  It  is  best  that  each  result 
should  be  the  mean  of  two  readings,  one  just  too  large  and  the 
other  just  too  small. 

(b)  Hoppe-Seykr' s  Method.—  Two  parallel-sided  glass  troughs  are 
used.  In  one  is  put  a  standard  solution  of  oxy-haemoglobin  of  known 
strength,  in  the  other  a  measured  quantity  of  the  blood  to  be  tested. 
The  latter  is  diluted  with  water  until  its  tint  appears  the  same  as  that 
of  the  standard  solution,  when  the  troughs  are  placed  side  by  side 
on  white  paper.  From  the  quantity  of  water  added  it  is  easy  to 
calculate  the  proportion  of  haemoglobin  in  the  undiluted  blood, 

5 


66  A  MANUAL  OF  PHYSIOLOGY 

Greater  accuracy  is  said  to  be  obtained  if  the  haemoglobin  in  the 
standard  solution  and  that  of  the  blood  are  converted  into  carbonic 
oxide  haemoglobin  by  passing  a  stream  of  coal-gas  through  them. 

(5)  Microscopic  Test  for  Blood-pigment. — Put  a  drop  of  blood  on 
a  slide.  Allow  the  blood  to  dry  or  heat  it  gently  over  a  flame,  so  as 
to  evaporate  the  water.  Add  a  drop  of  glacial  acetic  acid  ;  put  on  a 
cover-glass,  and  again  heat  slowly  till  the  liquid  just  begins  to  boil. 
Take  the  slide  away  from  the  flame  for  a  few  seconds,  then  heat  it 
again  for  a  moment;  and  repeat  this  process  two  or  three  times. 
Now  let  the  slide  cool,  and  examine  with  the  microscope  (high  power). 
The  small  black,  or  brownish-black,  crystals  of  haemin  will  be  seen 
(Plate  I.,  3).  This  is  an  important  test  where  only  a  minute  trace  of 
blood  is  to  be  examined,  as  in  some  medico-legal  cases.  If  a  blood- 
stain is  old,  a  minute  crystal  of  sodium  chloride  should  be  added 
along  with  the  glacial  acetic  acid.  Fresh  blood  contains  enough 
sodium  chloride. 

A  blood-stain  on  a  piece  of  cloth  may  first  of  all  be  soaked  in  a 
small  quantity  of  distilled  water,  and  the  liquid  examined  with  the 
spectroscope  or  the  micro-spectroscope  (a  microscope  in  which  a 
small  spectroscope  is  substituted  for  the  eye-piece).  Then  evapo- 
rate the  liquid  to  dryness  on  a  water-bath,  and  apply  the  haemin 
test.  Or  perform  the  haemin  test  directly  on  the  piece  of  cloth.  In 
a  fresh  stain  the  blood-corpuscles  might  be  recognised  under  the 
microscope,  after  the  cloth  had  been  soaked  and  kneaded  in  a  little 
glycerine. 


CHAPTER  II. 
THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH. 

THE  blood  can  only  fulfil  its  functions  by  continual  move- 
ment. This  movement  implies  a  constant  transformation 
of  energy ;  and  in  the  animal  body  the  transformation  of 
energy  into  mechanical  work  is  almost  entirely  allotted  to 
a  special  form  of  tissue,  muscle.  In  most  animals  there 
exist  one  or  more  rhythmically  contractile  muscular  organs, 
or  hearts,  upon  which  the  chief  share  of  the  work  of  keeping 
up  the  circulation  falls. 

Comparative. — In  Echinus  a  contractile  tube  connects  the  two 
vascular  rings  that  surround  the  beginning  and  end  of  the  alimentary 
canal,  and  plays  the  part  of  a  heart.  In  the  lower  Crustacea  and 
in  insects  the  heart  is  simply  the  contractile  and  generally  sacculated 
dorsal  bloodvessel ;  in  the  higher  Crustacea,  such  as  the  lobster,  it  is 
a  weli-defined  muscular  sac  situated  dorsally.  A  closed  vascular 
system  is  the  exception  among  invertebrates.  In  most  of  them  the 
blood  passes  from  the  arteries  into  irregular  spaces  or  lacunae  in  the 
tissues,  and  thence  finds  its  way  back  to  the  heart.  Amphioxus, 
the  lowest  vertebrate,  has  a  primitive  lacunar  vascular  system ;  a 
contractile  dorsal  bloodvessel  serves  as  arterial  or  systemic  heart,  a 
contractile  ventral  vessel  as  venous  or  respiratory  heart.  From  the 
latter,  vessels  go  to  the  gills.  Fishes  possess  only  a  respiratory  heart, 
consisting  of  a  venous  sinus,  auricle,  and  ventricle.  This  drives  the 
blood  to  the  gills,  from  which  it  is  gathered  into  the  aorta ;  it  has 
thence  to  find  its  way  without  further  propulsion  through  the  systemic 
vessels.  Amphibians  have  two  auricles  and  a  single  ventricle; 
reptiles,  two  auricles  and  two  incompletely-separated  ventricles.  In 
birds  and  mammals  the  respiratory  and  systemic  hearts  are  com- 
pletely separated.  The  former,  consisting  of  the  right  auricle  and 
ventricle,  propels  the  blood  through  the  lungs ;  the  latter,  consisting 
of  the  left  auricle  and  ventricle,  receives  it  from  the  pulmonary  veins, 
and  sends  it  through  the  systemic  vessels. 

General  View  of  the  Circulation  in  Man. — The  whole  circuit 

5—2 


68  A  MANUAL  OF  PHYSIOLOGY 

of  the  blood  is  divided  into  two  portions,  very  distinct 
from  each  other,  both  anatomically  and  functionally — the 
respiratory  or  lesser  circulation,  and  the  systemic  or  greater 
circulation.  Starting  from  the  left  ventricle,  the  blood  passes 
along  the  systemic  vessels — arteries,  capillaries,  veins — and, 
on  returning  to  the  heart,  is  poured  into  the  right  auricle, 
and  thence  into  the  right  ventricle.  From  the  latter  it  is 
driven  through  the  pulmonary  artery  to  the  lungs,  passes 


FIG.  16.— DIAGRAM  OF  THE  GENERAL  COURSE  OF  THE  CIRCULATION. 
RA,  LA,  right  and  left  auricles  ;  RV,  LV,  right  and  left  ventricles. 

through  the  capillaries  of  these  organs,  and  returns  through 
the  pulmonary  veins  to  the  left  auricle  and  ventricle.  The 
portal  system,  which  gathers  up  the  blood  from  the  in- 
testines, forms  a  kind  of  loop  on  the  systemic  circulation. 
The  lymph-current  is  also  in  a  sense  a  slow  and  stagnant 
side-stream  of  the  blood  circulation  ;  for  substances  are  con- 
stantly passing  from  the  bloodvessels  into  the  lymph-spaces, 
and  returning,  although  after  a  comparatively  long  interval, 
into  the  blood  by  the  great  lymphatic  trunks. 

Physiological  Anatomy  of  the  Vascular  System.-^The  heart  is 
to  be  looked  upon  as  a  portion  of  a  bloodvessel  which  has 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      69 

been  modified  to  act  as  a  pump  for  driving  the  blood  in  a 
definite  direction.  Morphologically  it  is  a  bloodvessel ;  and 
the  physiological  property  of  rhythmical  contraction  which 
belongs  to  the  muscle  of  the  heart  in  so  eminent  a  degree 
is,  as  has  been  mentioned  (p.  67),  an  endowment  of  blood- 
vessels in  many  animals  that  possess  no  localized  heart. 
Even  in  some  mammals  contractile  bloodvessels  occur ;  the 
veins  of  the  bat's  wing,  for  example,  beat  with  a  regular 
rhythm,  and  perform  the  function  of  accessory  hearts. 

The  whole  vascular  system  is  lined  with  a  single  layer 
of  endothelial  cells.  In  the  capillaries  nothing  else  is 
present ;  the  endothelial  layer  forms  the  whole  thickness  of 
the  wall.  In  young  animals,  at  any  rate,  the  endothelial 
cells  of  the  capillaries  are  capable  of  contracting  when 
stimulated ;  and  changes  in  the  calibre  of  these  vessels  can 
be  brought  about  in  this  way.  The  walls  of  the  arteries  and 
veins  are  chiefly  made  up  of  two  kinds  of  tissue,  which 
render  them  distensible  and  elastic :  non-striped  muscular 
fibres  and  yellow  elastic  fibres.  The  muscular  fibres  are 
mainly  arranged  as  a  circular  middle  coat,  which,  especially 
in  the  smaller  arteries,  is  relatively  thick.  One  conspicuous 
layer  of  elastic  fibres  marks  the  boundary  between  the  middle 
and  inner  coats.  In  the  larger  arteries  elastic  laminae  are 
also  scattered  freely  among  the  muscular  fibres  of  the  middle 
coat.  The  outer  coat  is  composed  chiefly  of  ordinary  con- 
nective tissue.  The  veins  differ  from  the  arteries  in  having 
thinner  walls,  with  the  layers  less  distinctly  marked,  and 
containing  a  smaller  proportion  of  non-striped  muscle  and 
elastic  tissue ;  although  in  some  veins,  those  of  the  pregnant 
uterus,  for  instance,  and  the  cardiac  ends  of  the  large 
thoracic  veins,  there  is  a  great  development  of  muscular 
tissue.  Further,  and  this  is  of  prime  physiological  import- 
ance, valves  are  present  in  many  veins.  These  are  semilunar 
folds  of  the  internal  coat  projecting  into  the  lumen  in  such  a 
direction  as  to  favour  the  flow  of  blood  towards  the  heart, 
but  to  check  its  return.  In  some  veins,  as  the  venae  cavae, 
the  pulmonary  veins,  the  veins  of  most  internal  organs,  and 
of  bone,  there  are  no  valves ;  in  the  portal  system  they  are 
rudimentary  in  man  and  the  great  majority  of  mammals. 


70  A  MANUAL  OF  PHYSIOLOGY 

The  valves  are  especially  well  marked  in  the  lower  limbs, 
where  the  venous  circulation  is  uphill.  When  a  valve 
ceases  to  perform  its  function  of  supporting  the  column  of 
blood  between  it  and  the  valve  next  above,  the  foundation 
of  varicose  veins  is  laid ;  the  valve  immediately  below  the 
incompetent  one,  having  to  bear  up  too  great  a  weight  of 
blood,  tends  to  yield  in  its  turn,  and  so  the  condition  spreads. 
The  smallest  veins,  or  venules,  are  very  like  the  smallest 
arteries,  or  arterioles,  but  somewhat  wider  and  less  muscular. 
The  transition  from  the  capillaries  to  the  arterioles  and 
venules  is  not  abrupt,  but  may  be  considered  as  marked  by 
the  appearance  of  the  non-striped  muscular  fibres,  at  first 
scattered  singly,  but  gradually  becoming  closer  and  more 
numerous  as  we  pass  away  from  the  capillaries,  until  at 
length  they  form  a  complete  layer. 

In  the  heart  the  muscular  element  is  greatly  developed 
and  differentiated.  Both  histologically  and  physiologically 
the  fibres  seem  to  stand  between  the  striated  skeletal  muscle 
and  the  smooth  muscle.  In  the  mammal  the  cardiac 
muscular  fibres  are  made  up  of  short  oblong  cells,  devoid  of 
a  sarcolemma,  often  branched,  and  arranged  in  anastomosing 
rows.  Each  cell  has  a  single  nucleus  in  the  middle  of  it. 
The  fibres  are  transversely  striated,  but  the  striae  are  not  so 
distinct  as  in  skeletal  muscle.  Many  fibres  pass  from  one 
auricle  to  the  other,  and  from  one  ventricle  to  the  other. 
The  auricles  and  ventricles  are  also,  in  some  mammals  at 
least,  connected  in  early  life  by  muscular  tissue;  and  even  in 
the  adult  traces  of  this  connection  may  persist  (Plate  I.,  4). 

In  the  frog's  heart  the  muscular  fibres  are  spindle-shaped, 
like  those  of  smooth  muscle,  but  transversely  striated,  like 
those  of  skeletal  muscle.  From  the  sinus  to  the  apex  of  the 
ventricle  there  is  a  continuous  sheet  of  muscular  tissue. 

The  problems  of  the  circulation  are  partly  physical,  partly 
vital.  Some  of  the  phenomena  observed  in  the  blood-stream 
of  a  living  animal  can  be  reproduced  on  an  artificial  model ; 
and  they  may  justly  be  called  the  physical  phenomena  of  the 
circulation.  Others  are  essentially  bound  up  with  the  pro- 
perties of  living  tissues ;  and  these  may  be  classified  as  the 
vital  or  physiological  phenomena  of  the  circulation.  The 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      71 

distinction,  although  by  no  means  sharp  and  absolute,  is  a 
convenient  one — at  least,  for  purposes  of  description;  and  as 
such  we  shall  use  it.  But  it  must  not  be  forgotten  that  the 
physiological  factors  play  into  the  sphere  of  the  physical, 
and  the  physical  factors  modify  the  physiological.  Con- 
sidered in  its  physical  relations,  the  circulation  of  the  blood 
is  the  flow  of  a  liquid  along  a  system  of  elastic  tubes,  the 
bloodvessels,  under  the  influence  of  an  intermittent  pressure 
produced  by  the  action  of  a  central  pump,  the  heart.  But 
the  branch  of  dynamics  which  treats  of  the  movement  of 
liquids,  or  hydrodynamics,  is  one  of  the  most  difficult  parts 
of  physics,  and,  in  spite  of  the  labours  of  many  eminent 
men,  is  as  yet  so  little  advanced  that  even  in  the  physical 
portion  of  our  subject  we  are  forced  to  rely  chiefly  on 
empirical  methods.  It  would,  therefore,  not  be  profitable  to 
enter  here  into  mathematical  theory,  but  it  may  be  well  to 
recall  to  the  mind  of  the  reader  one  or  two  of  the  simplest 
data  connected  with  the  flow  of  liquids  through  tubes : 

Torricelli's  Theorem. — Suppose  a  vessel  filled  with  water,  the  level 
of  which  is  kept  constant ;  the  velocity  with  which  the  water  will 
escape  from  a  hole  in  the  side  of  the  vessel  at  a  vertical  depth  h 
below  the  surface  will  be  v  =  \/2gh,  where  g  is  the  acceleration  pro- 
duced by  gravity.*  In  other  words,  the  velocity  is  that  which  the 
water  would  have  acquired  in  falling  in  vacuo  through  the  distance  h. 
This  formula  was  deduced  experimentally  by  Torricelli,  and  holds 
only  when  the  resistance  to  the  outflow  is  so  small  as  to  be  negligable. 
The  reason  of  this  restriction  will  be  easily  seen,  if  we  consider  that 
when  a  mass  m  of  water  has  flowed  out  of  the  opening,  and  an  equal 
mass  m  has  flowed  in  at  the  top  to  maintain  the  old  level,  everything 
is  the  same  as  before,  except  that  energy  of  position  equal  to  that 
possessed  by  a  mass  m  at  a  height  h  has  disappeared.  If  this  has 
all  been  changed  into  kinetic  energy  E,  in  the  form  of  visible  motion 
of  the  escaping  water,  then  E  =  \iiiv1  =  mgh,  i.e.,  v=*  */2gh.  If, 
however,  there  has  been  any  sensible  resistance  to  the  outflow,  any 
sensible  friction,  some  of  the  potential  energy  (energy  of  position), 
will  have  been  spent  in  overcoming  this,  and  will  have  ultimately 
been  transformed  into  the  kinetic  energy  of  molecular  motion,  or  heat. 

Flow  of  a  Liquid  through  Tubes. — Next  let  a  horizontal  tube  of 
uniform  cross-section  be  fitted  on  to  the  orifice.  The  velocity  of 
outflow  will  be  diminished,  for  resistances  now  come  into  play.  When 
the  liquid  flowing  through  a  tube  wets  it,  the  layer  next  the  wall  of  the 
tube  is  prevented  by  adhesion  from  moving  on.  The  particles  next 

*  I.e.,  the  amount  added  per  second  to  the  velocity  of  a  falling  body 
Cr=32  feet). 


72  A  MANUAL  OF  PHYSIOLOGY 

this  stationary  layer  rub  on  it,  so  to  speak,  and  are  retarded,  although 
not  stopped  altogether.  The  next  layer  rubs  on  the  comparatively 
slowly  moving  particles  outside  it,  and  is  also  delayed,  although  not 
so  much  as  that  in  contact  with  the  immovable  layer  on  the  walls  of 
the  tube.  In  this  way  it  comes  about  that  every  particle  of  the  liquid 
is  hindered  by  its  friction  against  others — those  in  the  axis  of  the  tube 
least,  those  near  the  periphery  most — and  part  of  the  energy  of  position 
of  the  water  in  the  reservoir  is  used  up  in  overcoming  this  resistance, 
only  the  remainder  being  transformed  into  the  visible  kinetic  energy 
of  the  liquid  escaping  from  the  open  end  of  the  tube. 

If  vertical  tubes  be  inserted  at  different  points  of  the  horizontal 
tube,  it  will  be  found  that  the  water  stands  at  continually  decreasing 
heights  as  we  pass  away  from  the  reservoir  towards  the  open  end  of  the 
tube.  The  height  of  the  liquid  in  any  of  the  vertical  tubes  indicates 
the  lateral  pressure  at  the  point  at  which  it  is  inserted;  in  other 
words,  the  excess  of  potential  energy,  or  energy  of  position,  which  at 
that  point  the  liquid  possesses  as  compared  with  the  water  at  the  free 
end,  where  the  pressure  is  zero.  If  the  centre  of  the  cross-section  of 


FIG.  17. — DIAGRAM  TO  ILLUSTRATE  FLOW  OF  WATER  ALONG  A  HORIZONTAL 
TUBE  CONNECTED  WITH  A  RESERVOIR. 

the  free  end  of  the  tube  be  joined  to  the  centres  of  all  the  menisci,  it 
will  be  found  that  the  line  is  a  straight  line.  The  lateral  pressure  at 
any  point  of  the  tube  is  therefore  proportional  to  its  distance  from  the 
free  end.  Since  the  same  quantity  of  water  must  pass  through  each 
cross-section  of  the  horizontal  tube  in  a  given  time  as  flows  out  at  the 
open  end,  the  kinetic  energy  of  the  liquid  at  every  cross-section  must 
be  constant  and  equal  to  fynv'2,  where  v  is  the  mean  velocity  (the 
quantity  which  escapes  in  unit  of  time  divided  by  the  cross-section) 
of  the  water  at  the  free  end. 

Just  inside  the  orifice  the  total  energy  of  a  mass  m  of  water  is  mgh'; 
just  beyond  it  at  the  first  vertical  tube,  mgh'  +  fynv2,  where  K  is  the 
lateral  pressure.  On  the  assumption  that  between  the  inside  of  the 
orifice  and  the  first  tube,  no  energy  has  been  transformed  into  heat  (an 
assumption  the  more  nearly  correct  the  smaller  the  distance  between 
it  and  the  inside  of  the  orifice  is  made),  we  have  mgh  =  mgh'  +  fynv2, 
i.e.,  %mvz  =  mg(h  -  h').  In  other  words,  the  portion  of  the  energy  of 
position  of  the  water  in  the  reservoir  which  is  transformed  into  the 
kinetic  energy  of  the  water  flowing  along  the  horizontal  tube  is 
measured  by  the  difference  between  the  height  of  the  level  of  the 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      73 

reservoir  and  the  lateral  pressure  at  the  beginning  of  the  horizontal 
tube — that  is,  the  height  at  which  the  straight  line  joining  the 
menisci  of  the  vertical  tubes  intersects  the  column  of  water  in  the 
reservoir.  Let  H  represent  the  height  corresponding  to  that  part  of 
the  energy  of  position  which  is  transformed  into  the  kinetic  energy 
of  the  flowing  water.  H  is  easily  calculated  when  the  mean  velocity 
of  efflux  is  known.  For  v=  v/s^H  by  Torricelli's  theorem  (since 
none  of  the  energy  corresponding  to  H  is  supposed  to  be  used  up  in 

v* 
overcoming  friction),  or  H  =  —      At  the  second  tube  the   lateral 

2£ 

pressure  is  only  h".  The  sum  of  the  visible  kinetic  and  potential 
energy  here  is  therefore  fynv2  +  mgh".  A  quantity  of  energy  mg  (h1  -  h" ) 
must  have  been  transformed  into  heat  owing  to  the  resistance  caused 
by  fluid  friction  in  the  portion  of  the  horizontal  tube  between  the 
first  two  vertical  tubes.  In  general  the  energy  of  position  repre- 
sented by  the  lateral  pressure  at  any  point  is  equal  to  the  energy 
used  up  in  overcoming  the  resistance  of  the  portion  of  the  path 
beyond  this  point. 

Velocity  of  Outflow. — It  has  been  found  by  experiment  that  v,  the 
mean  velocity  of  outflow,  when  the  tube  is  not  of  very  small  calibre, 
varies  directly  as  the  diameter,  and  therefore  the  volume  of  outflow 
as  the  cube  of  the  diameter.  In  fine  capillary  tubes  the  mean  velocity 
is  proportional  to  the  square,  and  the  volume  of  outflow  to  the  fourth 
power  of  the  diameter  (Poiseuille).  If,  for  example,  the  linear  velocity 
of  the  blood  in  a  capillary  of  10  //.  in  diameter  is  -J  mm.  per  sec.,  it  will 
be  four  times  as  great  (or  2  mm.  per  sec.)  in  a  capillary  of  20  /* 
diameter,  and  one-fourth  as  great  (or  $  mm.  per  sec.)  in  a  capillary 
of  5  ^  diameter,  the  pressure  being  supposed  equal  in  all.  The 
volume  of  outflow  per  second  is  obtained  by  multiplying  the  cross- 
section  by  the  linear  velocity.  The  cross-section  of  a  circular  capillary, 
10  p  in  diameter,  is  v  (5  x  TTiW)2  =  >  sav>  TSTTTIF  scl-  mm-  The  outflow 
will  be  j-^i ¥Tr  x  \  =  oTTRTff  cu^-  mm>  Per  sec-  The  outflow  from  the 
capillary  of  20  &  diameter  would  be  sixteen  times  as  much,  from 
the  5  fjt,  capillary  only  one-sixteenth  as  much.  Some  idea  of  the 
extremely  minute  scale  on  which  the  blood-flow  through  a  single 
capillary  takes  place,  may  be  obtained  if  we  consider  that  for  the 
capillary  of  10  //,  diameter  a  flow  of  YSVUTF  cub-  mm-  Per  sec-  wou^ 
scarcely  amount  to  i  cub.  mm.  in  six  hours,  or  to  i  cc.  in  250  days. 

When  the  initial  energy  is  obtained  in  any  other  way  than  by 
means  of  a  '  head  '  of  water  in  a  reservoir — say,  by  the  descent  of  a 
piston  which  keeps  up  a  constant  pressure  in  a  cylinder  filled  with 
liquid— the  results  are  exactly  the  same.  Even  when  the  horizontal 
tube  is  distensible  and  elastic,  there  is  no  difference  when  once  the 
tube  has  taken  up  its  position  of  equilibrium  for  any  given  pressure, 
and  that  pressure  does  not  vary. 

Flow  with  Intermittent  Pressure. — When  this  acts  on  a  rigid 
tube,  everything  is  the  same  as  before.  When  the  pressure 
alters,  the  flow  at  once  comes  to  correspond  with  the  new  pressure. 
Water  thrown  by  a  force-pump  into  a  system  of  rigid  tubes  escapes 


74  ^  MANUAL  OF  PHYSIOLOGY 

at  every  stroke  of  the  pump  in  exactly  the  quantity  in  which  it  enters, 
for  water  is  practically  incompressible,  and  the  total  quantity  present 
at  one  time  in  the  system  cannot  be  sensibly  altered.  In  the 
intervals  between  the  strokes  the  flow  ceases  ;  in  other  words,  it  is 
intermittent.  It  is  very  different  with  a  system  of  distensible  and 
elastic  tubes.  During  each  stroke  the  tubes  expand,  and  make 
room  for  a  portion  of  the  extra  liquid  thrown  into  them,  so  that  a 
smaller  quantity  flows  out  than  passes  in.  In  the  intervals  between 
the  strokes  the  distended  tubes,  in  virtue  of  their  elasticity,  tend  to 
regain  their  original  calibre.  Pressure  is  thus  exerted  upon  the 
liquid,  and  it  continues  to  be  forced  out,  so  that  when  the  strokes  of 
the  pump  succeed  each  other  with  sufficient  rapidity,  the  outflow 
becomes  continuous.  This  is  the  state  of  affairs  in  the  vascular 
system.  The  intermittent  action  of  the  heart  is  toned  down  in  the 
elastic  vessels  to  a  continuous  steady  flow. 

The  Beat  of  the  Heart. — In  the  frog's  heart  the  contraction 
can  be  seen  to  begin  about  the  mouths  of  the  great  veins 
which  open  into  the  sinus  venosus.  Thence  it  spreads  in 
succession  over  the  sinus  and  auricles,  hesitates  for  a 
moment  at  the  auriculo-ventricular  junction,  and  then  with 
a  certain  suddenness  invades  the  ventricle.  In  all  prob- 
ability the  contraction  wave  is  propagated  without  the 
intervention  of  nerves,  from  fibre  to  fibre  of  the  muscular 
tissue,  which,  although  presenting  certain  variations  in  its 
character  in  the  different  divisions  of  the  heart  and  at  their 
junctions,  forms  a  more  or  less  continuous  sheet  over  the 
whole  of  the  organ.  This  conclusion  rests  in  part  upon  the 
observation  that  the  delay  of  the  wave  at  the  auriculo- 
ventricular  groove  is  much  greater  than  it  ought  to  be  if  the 
excitation  were  transmitted  by  nerves,  since  the  velocity  of  the 
nerve-impulse  is  exceedingly  great  (p.  582) ;  and  the  further 
observation  that,  when  the  ventricle  is  caused  to  contract 
by  artificial  stimulation  of  the  auricle,  this  delay  is  appre- 
ciably greater  when  the  stimulus  is  applied  as  far  from  the 
ventricle  as  possible  than  when  it  is  applied  as  near  to  it  as 
possible.  In  the  mammalian  heart  the  starting-point  of  the 
contraction  is  likewise  the  mouths  of  the  veins  opening  into 
the  auricles,  which  are  richly  provided  with  muscular  fibres 
akin  to  those  of  the  heart.  But  the  wave  advances  so 
rapidly  that  it  is  difficult,  if  not  impossible,  to  trace  in  its 
course  a  regular  progress  from  base  to  apex,  although  the 
ventricular  beat  undoubtedly  follows  that  of  the  auricle,  and 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      75 

the  capillary  electrometer  indicates  that,  in  a  heart  beating 
normally,  the  negative  change  associated  with  contraction 
begins  at  the  base  and  then  reaches  the  apex  (p.  622).  It  is 
not  definitely  known  how  in  the  mammal  the  beat  of  the 
ventricle  is  co-ordinated  with  that  of  the  auricle.  The 
alleged  absence  of  muscular  connection  has  led  to  a  very 
general  belief  that  the  link  is  of  a  nervous  nature  ;  and 
certainly  there  is  no  dearth  of  nerves  running  between  the 
auricles  and  the  ventricles  that  might  serve  as  such  a  bridge. 
But  recent  work  makes  it  possible  that,  at  least  in  some 
animals,  the  contraction  wave  may  spread,  as  in  the  frog's 
heart,  along  fibres,  apparently  muscular,  which,  in  the  form 
of  slender  strands,  interpenetrate  the  ring  of  fibrous  tissue 
between  the  auricles  and  ventricles  (Kent). 

The  most  conspicuous  events  in  the  beat  of  the  heart,  in 
their  normal  sequence,  are  :  (i)  the  auricular  contraction  or 
systole  ;  (2)  the  ventricular  contraction  or  systole  ;  (3)  the 
pause  or  diastole.  The  auricles,  into  which,  and  beyond 
which  into  the  ventricles,  blood  has  been  flowing  during  the 
pause  from  the  great  thoracic  veins,  contract  sharply.  The 
contraction  begins  in  the  muscular  rings  that  surround  the 
orifices  of  the  veins,  so  that  these,  destitute  of  valves  as  they 
are,  are  sealed  up  for  an  instant,  and  regurgitation  of  blood 
into  them  is  prevented.  The  filling  of  the  ventricles  is 
thus  completed;  their  contraction  begins  either  simul- 
taneously with  the  relaxation  of  the  auricles  or  a  little 
before  it.  The  mitral  and  tricuspid  valves,  whose  strong  but 
delicate  curtains  have  during  the  diastole  been  hanging 
down  into  the  ventricles  and  swinging  freely  in  the  entering 
current  of  blood,  are  floated  up  as  the  intraventricular 
pressure  begins  to  rise,  so  that,  in  the  first  moment  of  the 
sudden  and  powerful  ventricular  systole,  the  free  edges  of 
their  segments  come  together,  and  the  auriculo-ventricular 
orifices  are  completely  closed  (Fig.  68,  p.  181).  In  the 
measure  in  which  the  pressure  in  the  contracting  ventricle 
increases,  the  contact  of  the  valvular  segments  becomes 
closer  and  more  extensive  ;  and  their  tendency  to  belly  into 
the  auricle  is  opposed  by  the  pull  of  the  chordae  tendineae. 
whose  slender  cords,  inserted  into  the  valves  from  border  to 


76  A  MANUAL  OF  PHYSIOLOGY 

base,  are  kept  taut,  in  spite  of  the  shortening  of  the  ventricle 
by  the  contraction  of  the  papillary  muscles.  During  the 
systole,  the  ventricles  change  their  shape  in  such  a  way  that 
their  combined  cross-section — which  in  the  relaxed  state  is  a 
rough  ellipse  with  the  major  axis  from  right  to  left— becomes 
approximately  circular,  and  they  then  form  a  right  circular 
cone.  As  soon  as  the  pressure  of  the  blood  within  the  con- 
tracting ventricles  exceeds  that  in  the  aorta  and  pulmonary 
artery  respectively,  the  semilunar  valves,  which  at  the  begin- 
ning of  the  ventricular  systole  are  closed,  yield  to  the  pressure, 
and  blood  is  driven  from  the  ventricles  into  these  arteries. 

The  ventricles  are  more  or  less  completely  emptied  during 
the  contraction,  which  seems  still  to  be  maintained  for  a 
short  time  after  the  blood  has  ceased  to  pass  out.  The 
contraction  is  followed  by  sudden  relaxation.  The  intra- 
ventricular  pressure  falls.  The  lunules  of  the  semilunar 
valves  slap  together  under  the  weight  of  the  blood  as  it 
attempts  to  regurgitate,  the  corpora  Arantii  seal  up  the 
central  chink,  and  the  aorta  and  pulmonary  artery  are  thus 
cut  off  from  the  heart.  Then  follows  an  interval  during 
which  the  whole  heart  is  at  rest,  namely,  the  interval 
between  the  end  of  the  relaxation  of  the  ventricles  and  the 
beginning  of  the  systole  of  the  auricles.  This  constitutes  the 
pause.  The  whole  series  of  events  is  called  a  cardiac  cycle 
or  revolution  (see  Practical  Exercises,  p.  176). 

It  will  be  easily  understood  that  the  time  occupied  by  any 
one  of  the  events  of  the  cardiac  cycle  is  not  constant,  for 
the  rate  of  the  heart  is  variable.  If  we  take  about  70  beats 
a  minute  as  the  average  normal  rate  in  a  man,  the  ventricular 
systole  will  occupy  about  '3  second ;  the  ventricular  diastole, 
including  the  relaxation,  about  '5  second.  The  systole  of 
the  auricle  is  one-third  as  long  as  that  of  the  ventricle. 

This  rhythmical  beat  of  the  heart  is  the  ground  phe- 
nomenon of  the  circulation.  It  reveals  itself  by  certain 
tokens — sounds,  surface-movements  or  pulsations,  alterations 
of  the  pressure  and  velocity  of  the  blood,  changes  of  volume 
in  parts  —  all  periodic  phenomena,  continually  recurring 
with  the  same  period  as  the  heart-beat,  and  all  funda- 
mentally connected  together.  And  if  we  hold  fast  the  idea 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      77 

that  when  we  take  a  pulse-tracing,  or  a  blood-pressure  curve, 
or  a  plethysmographic  record,  we  are  really  investigating  the 
same  fact  from  different  sides,  we  shall  be  able,  by  following 
the  cardiac  rhythm  and  its  consequences  as  far  as  we  can 
trace  them,  to  hang  upon  a  single  thread  many  of  the  most 
important  of  the  physical  phenomena  of  the  circulation. 

The  Sounds  of  the  Heart, — When  the  ear  is  applied  to  the  (r~> 
chest,  or  to  a  stethoscope  placed  over  the  cardiac  region, 
two  sounds  are  heard  with  every  beat  of  the  heart ;  they 
follow  each  other  closely,  and  are  succeeded  by  a  period  of 
silence.  The  dull  booming  'first  sound'  is  heard  loudest  in 
a  region  which  we  shall  afterwards  have  to  speak  of  as  that 
of  the  'cardiac  impulse'  (p.  79);  the  short,  sharp,  'second 
sound'  over  the  junction  of  the  second  right  costal  cartilage 
with  the  sternum. 

There  has  been  much  discussion  as  to  the  cause  of  the 
first  sound.  That  a  sound  corresponding  with  it  in  time 
is  heard  in  an  excised  bloodless  heart  when  it  contracts,  is 
certain ;  and  therefore  the  first  sound  cannot  be  exclusively 
due,  as  some  have  asserted,  to  vibrations  of  the  auriculo- 
ventricular  valves  when  they  are  suddenly  rendered  tense 
by  the  contraction  of  the  ventricles,  for,  of  course,  in  a 
bloodless  heart  the  valves  are  not  stretched.  Part  of  the 
sound  must  accordingly  be  associated  with  the  muscular 
contraction,  as  such.  As  we  shall  see  (p.  557),  the  sound 
caused  by  a  contracting  muscle  is  probably,  in  part  at 
least,  a  resonance  tone  of  the  ear.  This  lessens  the 
difficulty  of  understanding  how  a  simple  non-tetanic  con- 
traction like  that  of  the  heart  should  give  rise  to  a 
'  muscular '  sound  of  definite  pitch.  Further,  the  fact 
that  the  first  sound  is  heard  during  the  whole,  or  nearly  the 
whole,  of  the  ventricular  systole  is  against  the  idea  that  it  is 
exclusively  due  to  the  vibrations  of  membranes  like  the 
valves,  which  would  speedily  be  damped  by  the  blood  and 
rendered  inaudible.  But  there  is  undoubtedly  a  valvular 
as  well  as  a  muscular  factor  involved ;  and,  indeed,  there  is 
reason  to  believe  that  the  valvular  note  is  the  essential 
part  of  the  sound,  which  perhaps  acquires  its  peculiar 
booming  character  from  the  resonance  tones  of  the  ear,  and 


78  A  MANUAL  OF  PHYSIOLOGY 

possibly  of  the  chest-wall,  set  up  by  the  muscular  contrac- 
tion. Some  observers  have  been  able  to  distinguish  in 
the  first  sound  the  valvular  and  the  muscular  elements, 
the  former  being  higher  in  pitch  than  the  latter,  but  a 
minor  third  below  the  second  sound.  Further,  when  the 
mitral  valve  is  prevented  from  closing  by  experimental 
division  of  the  chordae  tendineae,  or  by  pathological  lesions, 
the  first  sound  of  the  heart  is  altered  or  replaced  by  a 
'  murmur.'  This  evidence  is  not  only  important  as  regards 
the  physiological  question,  but  of  great  practical  interest 
from  its  bearing  on  the  diagnosis  of  cardiac  disease.  It 
may  be  added  that  the  point  of  the  chest-wall  at  which  the 
first  sound  is  most  easily  recognised  is  also  the  point  at 
which  a  changed  sound  or  murmur  connected  with  disease 
of  the  mitral  valve  is  most  distinctly  heard,  The  sound  is, 
therefore,  best  conducted  from  the  mitral  valve  along  the 
heart  to  the  point  at  which  it  comes  in  contact  with  the  wall 
of  the  chest.  Changes  in  the  first  sound  connected  with 
disease  of  the  tricuspid  valve  are  heard  best,  in  the  com- 
paratively rare  cases  where  they  can  be  distinctly  recognised, 
in  the  third  to  the  fifth  interspace,  a  little  to  the  right  of 
the  sternum. 

Sir  Richard  Quain  has  recently  revived  the  theory  that  the  first 
sound  is  due,  not  to  the  vibrations  of  the  auriculo-ventricular  valves, 
nor  to  the  muscle-sound  of  the  contracting  ventricles,  but  to  the  impact 
of  the  ventricular  blood  on  the  semilunar  valves  at  the  moment  of 
systole,  and  the  resistance  which  it  encounters  as  it  passes  through 
the  orifices  of  the  aorta  and  pulmonary  artery.  But  although  some 
of  the  facts  which  he  cites  seem  to  favour  such  a  view,  there  are  many 
difficulties  in  the  way  of  its  acceptance. 

The  second  sound  is  caused  by  the  vibrations  of  the  semi- 
lunar  valves  when  suddenly  closed,  'the  recoiling  blood" 
forcing  them  back,  as  one  unfurls  an  umbrella,  and  with  an 
audible  check  as  they  tighten '  (Watson).  The  sharpness 
of  its  note  is  lost,  and  nothing  but  a  rushing  noise  or  bruit 
can  be  heard,  when  the  valves  are  hooked  back  and  pre- 
vented from  closing.  It  is  altered,  or  replaced  by  a  murmur 
when  the  valves  are  diseased.  As  there  is  a  mitral  and  a 
tricuspid  factor  in  the  first  sound,  so  there  is  an  aortic  and 
a  pulmonary  factor  in  the  second.  The  place  where  the 
second  sound  is  best  heard  (over  the  junction  of  the  second 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      79 

right  costal  cartilage  and   sternum)  is  that   at  which  any 

change  produced   by  disease  of  the   aortic  valves  is  most 

easily  recognised.     The  sound  is  conducted  up   from  the 

valves  along  the  aorta,  which  comes  nearest  to  the  surface 

at  this  point.   Changes  connected 

with  disease   of   the   pulmonary 

valves  are  most  readily  detected 

over   the  second   left  intercostal 

space     near    the    edge     of    the 

sternum,  for  here  the  pulmonary  FIG.  18.—  DIAGRAM  OF  MAREY'S 

artery    most     nearly   approaches  CARDIOGRAPH. 

v         i  11  A,  knob  attached  to  flexible  mem- 

the  Chest-Wall.  brane  tied  over  end  of  metal  box— 


'  _   the  knob  is  Placed  over  the 

beat  ;   C  is  the  folded  edge  of  the 

that    is,  it   OCCUrS  during   the  ven-    membrane  ;  B  is  the  tube  communi- 

cating with  a  recording  tambour. 

tncular   systole  ;    the    second    is 

'diastolic,'  beginning  at  the  commencement  of  the  diastole. 

The  Cardiac  Impulse.  —  A  surface-movement  is  seen,  or  an 
impulse  felt,  at  every  cardiac  contraction  in  various  situa- 
tions where  the  heart  or  arteries  approach  the  surface.  The 
pulsation,  or  impulse,  of  the  heart,  often  styled  the  apex- 
beat,  is  usually  most  distinct  to  sight  and  touch  in  a  small 
area  lying  in  the  fifth  left  intercostal  space,  between  the 
mammary  and  the  parasternal  line,*  and  generally,  in  an 
adult,  about  an  inch  and  a  half  to  the  sternal  side  of  the 
former.  It  is  due  to  the  systolic  hardening  of  the  ventricles, 
which  are  here  in  contact  with  the  chest-wall,  the  contact 
being  at  the  same  time  rendered  closer  by  their  change  of 
shape,  and  by  a  slight  movement  of  rotation  of  the  heart 
from  left  to  right  during  the  contraction  (Practical  Exer- 
cises, p.  182).  Even  in  health  the  position  of  the  impulse 
varies  somewhat  with  the  position  of  the  body  and  the  res- 
piratory movements.  In  children  it  is  usually  situated  in  the 
fourth  intercostal  space.  In  disease  its  displacement  is  an 
important  diagnostic  sign,  and  may  be  very  marked,  especi- 
ally in  cases  of  effusion  of  fluid  into  the  pleural  cavity. 

Various  instruments,  called  cardiographs,  have  been  devised 

*  The  mammary  line  is  an  imaginary  vertical  line  supposed  to  be 
drawn  on  the  chest  through  the  middle  point  of  the  clavicle.  It  usually, 
but  not  necessarily,  passes  through  the  nipple.  The  parasternal  line  is  the 
vertical  line  lying  midway  between  the  mammary  line  and  the  corre- 
sponding border  of  the  sternum. 


8o  A  MANUAL  OF  PHYSIOLOGY 

for  magnifying  and  recording  the  movements  produced  by 
the  cardiac  impulse.  Marey's  cardiograph  consists  essenti- 
ally of  a  small  chamber,  or  tambour,  filled  with  air,  and 
closed  at  one  end  by  a  flexible  membrane  carrying  a  button, 
which  can  be  adjusted  to 
the  wall  of  the  chest. 
This  receiving  tambour  is 
connected  by  a  tube  with 
a  recording  tambour,  the 
flexible  plate  of  which  acts 
upon  a  lever  writing  on  a 
travelling  surface — a  uni- 
formly-rotating drum,  for 

^VPmnlp  rnvprprl       with  FlG'    '9-— CARDIOGRAM  TAKEN  WITH 

example      -  coverec      with  MAREY'S  CARDIOGRAPH. 

Smoked  paper.    Any  move-  A,  auricular  systole  ;  V,  ventricular  systole  ; 

mpnr      rnmrrmnirafprl       tn  D,  diastole.     The  arrow  shows  the  direction  in 

t0  which  the  tracing  is  to  be  read. 

the  button  forces   in  the 

end  of  the  tambour  to  which  it  is  attached,  and  thus  raises 
the  pressure  of  the  air  in  it  and  in  the  recording  tambour ; 
the  flexible  plate  of  the  latter  moves  in  response,  and  the 
lever  transfers  the  movement  to  the  paper.  The  tracing, 
or  cardiogram,  obtained  in  this  way  shows  a  small  elevation 
corresponding  to  the  auricular  systole,  succeeded  by  a  large 
abrupt  rise  corresponding  to  the  beginning  of  the  first 
sound,  and  caused  by  the  ventricular  systole.  The  rise  is 
maintained,  with  small  secondary  oscillations,  for  about 
•3  of  a  second  in  a  tracing  from  a  normal  man,  then  gives 
way  to  a  sudden  descent,  that  marks  the  relaxation  of  the 
ventricles,  the  beginning  of  the  second  sound,  and  the  closure 
of  the  semilunar  valves.  An  interval  of  about  -5  second 
elapses  before  the  curve  begins  again  to  rise  at  the  next 
auricular  contraction. 

Such  was  the  interpretation  which  Marey  put  upon  his  tracings,  and 
although  neither  his  results  nor  his  deductions  from  them  have 
escaped  the  criticism  of  succeeding  investigators,  it  is  doubtful 
whether  any  adequate  reason  has  been  brought  forward  for  dis- 
carding them.  The  difficulties  that  beset  the  subject  are  great,  for 
the  cardiogram  is  a  record  of  a  complex  series  of  events.  The  very 
rapid  variation  of  pressure  within  the  ventricles,  the  change  of  shape 
of  the  heart,  the  slight  change  of  position  of  its  apex,  if  such  occurs, 
must  all  leave  their  mark  upon  the  curve,  which  is  besides  distorted 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      81 

by  the  resistance  of  the  elastic  chest-wall,  the  inertia  of  the  recording 
lever,  and  the  compression  of  the  air  in  the  connecting  tubes.  It  is 
only  by  comparing  in  animals  the  cardiographic  record  with  the 
changes  of  blood- pressure  in  the  heart  and  arteries  that  even  our 
present  degree  of  knowledge  of  the  human  cardiogram  has  been 
attained. 

Endocardiac  Pressure. — The  function  of  the  heart  is  to 
maintain  an  excess  of  pressure  in  the  aorta  and  pulmonary 
artery  sufficient  to  overcome  the  friction  of  the  whole 
vascular  channel,  and  to  keep  up  the  flow  of  blood.  So 
long^as  the  semilunar  valves  are  closed,  most  of  the  work 


FIG.  20.— CURVES  OF  ENDOCARDIAC  PRESSURE  TAKEIN  WITH  CARDIAC  SOUNDS. 

Aur. ,  auricular  curve  ;   Vent.,  ventricular  curve  ;   AS,  period  of  auricular  systole  ; 
VS,  of  ventricular  systole;  D,  diastole. 

of  the  contracting  ventricles  is  expended  in  raising  the 
pressure  of  the  blood  within  them.  At  the  moment  when 
blood  begins  to  pass  into  the  arteries,  nearly  all  the  energy 
of  this  blood  is  potential ;  it  is  the  energy  of  a  liquid  under 
pressure.  During  a  cardiac  cycle  the  pressure  in  the  cavities 
of  the  heart,  or  the  endocardiac  pressure,  varies  from 
moment  to  moment,  and  its  variations  afford  important  data 
for  the  study  of  the  mechanics  of  the  circulation. 

For  the  study  of  the  endocardiac  pressure,  the  ordinary  mercurial     rv^,^ 
manometer  (p.  99)  is  unsuitable,  since,  owing  to  the  relatively  great 
amount  of  work  required  to  produce  a  given  displacement  of  the 

6 


82  A  MANUAL  OF  PHYSIOLOGY 

mercury,  it  does  not  readily  follow  rapid  changes  of  pressure,  and 
the  mercurial  column,  once  displaced,  continues  for  a  time  to 
execute  vibrations  of  its  own,  which  are  compounded  with  the  true 
oscillations  of  blood-pressure.  But  by  introducing  in  the  connection 
between  the  manometer  and  the  heart  a  valve  so  arranged  as  to 
oppose  the  passage  of  blood  towards  the  heart,  while  it  favours  its 
passage  towards  the  manometer,  the  maximum  pressure  attained  in 
the  cardiac  cavities  during  the  cycle  may  be  measured  with  con- 
siderable accuracy.  When  the  valve  is  reversed  the  apparatus 
becomes  a  minimum  manometer.  In  this  way  it  has  been  found 
that  in  large  dogs  the  pressure  in  the  left  ventricle  may  rise  as  high 
as  230  to  240  mm.  of  mercury,  and  sink  as  low  as  —  30  to  —40  mm.  ; 
while  in  the  right  ventricle  it  may  be  as  much  as  70  mm.,  and 


FIG.  21. — DIAGRAM  OF  PICK'S  C-SPRING  MANOMETER. 

A,  hollow  spring  filled  with  alcohol.  Its  open  end  B  is  covered  with  a  membrane  and 
is  fixed  to  ihe  upright  F  ;  the  other  end  C  is  free  to  move,  and  is  connected  with  a 
system  of  levers,  which  move  the  writing  point  D  ;  E  is  the  cannula,  which  is  connected 
with  the  bloodvessel.  When  the  pressure  in  the  spring  is  increased  it  tends  to  straighten 
itself. 

as  little  as  -  25  mm.     In  the  right  auricle  a  maximum  pressure  of 
20  mm.  of  mercury  has  been  recorded. 

Our  knowledge  of  the  maximum  and  minimum  pressure  attained 
in  the  cavities  of  the  heart,  even  if  it  were  far  more  precise  than  it 
actually  is,  would  only  carry  us  a  little  way  in  the  study  of  the  endo- 
cardiac  pressure-curve,  for  it  would  merely  tell  us  how  far  above  the 
base-line  of  atmospheric  pressure  the  curve  ascends,  and  how  far 
below  the  base-line  it  sinks.  To  exhaust  the  problem,  we  require  to 
have  tracings  of  the  exact  form  of  the  curve  for  each  of  the  cavities 
of  the  heart,  and  to  know  the  time-relations  of  the  curves  so  as  to 
be  able  to  compare  them  with  each  other,  and  with  the  pressure- 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      83 

curves  of  the  great  arteries  and  great  veins.  To  obtain  satisfactory 
tracings  of  the  swiftly-changing  endocardiac  pressure  is  a  task  of  the 
highest  technical  difficulty,  and  it  is  only  in  very  recent  years  that 
it  has  been  accomplished  with  any  approach  to  accuracy  by  the 
use  of  elastic  manometers,  in  which  the  blood-pressure  is  counter- 
balanced, not  by  the  weight  of  a  column  of  liquid,  as  in  the  mercurial 
manometer,  but  by  the  tension  of  an  elastic  disc  or  of  a  spring. 
One  of  the  earliest  of  these  was  the  now  perhaps  somewhat  obsolete 
C-spring  manometer  of  Fick  (an  adaptation  of  Bourdon's  pressure- 
gauge),  of  which  a  diagram  is  given  in  Fig.  21.  Probably  the  most 
perfect  elastic  manometers  of  the  modern  type  are  the  improved 
instrument  of  Fick  (Fig.  22),  with  the  various  modifications  it  has 
undergone  in  the  hands  of  v,  Frey  and  others,  and  especially  the 
manometers  of  Hiirthle. 

Hiirthle's  spring  manometer  consists  of  a  small  drum  covered 
with  an  indiarubber  membrane,  loosely  arranged  so  as  not  to  vibrate 
with  a  period  of  its  own.  The  drum  is  connected  with  the  heart  or 
with  a  vessel,  and  the  blood-pressure  is  transmitted  to  a  steel  spring 


FIG.  22.— FICK'S  ELASTIC  MANOMETER. 

a  a  is  a  metal  piece  tunnelled  by  a  narrow  canal  of  about  i  mm.  in  diameter,  which 
enlarges  below  to  a  shallow  saucer-shaped  space  b.  The  wide  opening  of  b  is  covered 
by  a  thin  piece  of  indiarubber  c,  to  the  centre  of  which  an  ivory  button  d  is  attached. 
The  button  presses  on  a  strong  steel  spring/  which  is  attached  at  one  end  to  the  brass 
frame  ee,  and  at  the  other,  by  means  of  an  intermediate  piece  g,  to  the  lever  h  ;  b  is 
filled  with  a  few  drops  of  water,  but  the  canal  a  contains  only  air.  When  a  is  con- 
nected with  the  interior  of  the  heart  or  of  an  artery,  the  changes  of  pressure  are  trans- 
mitted to  the  spring,  and  recorded  by  the  writing-point  of  the  lever. 

by  means  of  a  light  metal  disc  fastened  on  the  membrane.  The  spring 
acts  on  a  writing  lever.  The  instrument  is  so  constructed  that  for  a 
given  change  of  pressure  the  quantity  of  liquid  displaced  is  as  small 
as  possible,  and  it  is  on  this  that  its  capacity  to  follow  sudden 
variations  of  pressure  chiefly  depends.  The  manometer  is  connected 
with  the  cavity  of  the  heart  by  an  appropriately-curved  cannula  of 
metal  or  glass,  which,  after  being  rilled  with  some  liquid  that 
prevents  coagulation  (Practical  Exercises,  p.  185),  is  pushed  through 
the  jugular  vein  into  the  right  auricle  or  ventricle,  or  through  the . 
carotid  artery  and  aorta  into  the  left  ventricle.  Some  observers  fill 
only  the  cannula  with  liquid,  and  leave  the  capsule  of  the  elastic 
manometer  and  as  much  of  the  connections  as  possible  full  of  air. 
Others  fill  the  whole  system  with  liquid.  And  around  the  question 
of  the  relative  merits  of  '  transmission  '  by  liquid  and  by  air  has  raged 

6—* 


84  A  MANUAL  OF  PHYSIOLOGY 

a  controversy  which  does  not  even  yet  show  signs  of  coming  to  an 
end,  for  there  is  reason  to  suppose  that  the  character  of  the  curves 
obtained  is  to  some  extent  modified  by  the  manner  in  which  the 
pressure  is  transmitted. 

Thus,  the  pressure-curve  of  the  ventricle,  according  to 
Hiirthle  and  those  who,  like  him,  have  employed  manometers 
with  liquid  transmission  (Fig.  23),  remains  after  the  first 
abrupt  rise,  which  undoubtedly  corresponds  to  the  ventricular 
systole,  almost  parallel  to  the  abscissa  line  for  a  consider- 
able time,  and  then  descends  somewhat  less  suddenly  than 
it  rose.  This  systolic  '  plateau,'  although  usually  broken  by 
minor  heights  and  hollows,  perhaps  due  to  inertia  oscilla- 
tions of  the  liquid  or  the  recording  apparatus,  would  indicate 
that  the  ventricular  pressure,  after  reaching  its  maximum, 


FIG.  23. — SIMULTANEOUS  RECORD  OF  PRESSURE  IN  LEFT  VENTRICLE  (v)  AND 
AORTA  (A).    (HURTHLE.) 

The  tracings  were  taken  with  elastic  manometers  :  o  indicates  a  point  just  before  the 
closure  of  the  mitral  valve  ;  i,  the  opening  of  the  semilunar  valve  ;  3,  the  closure  of 
the  semilunar  valve  ;  4,  the  opening  of  the  mitral  valve.  The  ventricular  curve  shows 
a  '  plateau.' 

maintained  itself  there  throughout  the  greater  part  of  the 
systole.  The  tracings  yielded  by  the  best  manometers  with 
air  transmission  (Fig.  24)  show  the  same  suddenness  in  the 
first  part  of  the  upstroke  and  the  last  part  of  the  descent — 
that  is,  the  same  abruptness  in  the  beginning  of  the  con- 
traction and  the  end  of  the  relaxation.  But  they  differ 
totally  in  the  intermediate  portion  of  the  curve,  which, 
climbing  ever  more  gradually  as  it  nears  its  apex,  remains 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      85 

but  a  moment  at  the  maximum,  then  immediately  descending 
forms  a  '  peak,'  and  not  a  plateau. 

While  perhaps  it  is  hardly  possible  at  present  to  decide 
finally  between  the  plateau  and  the  peak,  yet  the  bulk  of  the 
evidence  goes  to  show  that  the  former  is  not,  as  the  advocates 
of  the  peak  have  claimed,  an  artificial  phenomenon,  but 
does  in  reality  correspond  to  that  continuation  of  the  systole 
of  the  ventricle,  that  dogged  grip,  if  we  may  so  phrase  it, 
which  it  seems  to  maintain  upon  the  blood  after  the  greater 


FIG.  24.— COMPARISON  OF  PRESSURE-CURVES  OF  LEFT  AURICLE,  LEFT  VEN- 
TRICLE, AND  AORTA,    (v.  FREY.) 

Recorded  by  elastic  manometers  with  air  transmission.    The  ventricular  curve  shows 
a  '  peak.' 

portion  of  it  has  been  expelled.  This  conclusion  is  essentially 
in  accordance  with  the  results  of  Chauveau  and  Marey, 
obtained  long  ago  by  means  of  their  '  cardiac  sound,'  which 
was  in  principle  an  elastic  manometer,  though  of  somewhat 
faulty  pattern  (Fig.  25). 

It  consisted  of  an  ampulla  of  indiarubber,  supported  on  a  frame- 
work, and  communicating  with  a  long  tube,  which  was  connected 
with  a  recording  tambour.  The  ampulla  was  introduced  into  the 
heart  through  the  jugular  vein  or  carotid  artery  in  the  way  already 


86  A  MANUAL  OF  PHYSIOLOGY 

described.  Sometimes  a  double  sound  was  employed,  armed  with 
two  ampullae,  placed  at  such  a  distance  from  each  other  that  when 
one  was  in  the  right  ventricle  the  other  was  in  the  auricle  of  the  same 
side.  Each  ampulla  communicated  by  a  separate  tube  in  the 
common  stem  of  the  instrument  with  a  recording  tambour,  and  the 
writing  points  of  the  two  tambours  were  arranged  in  the  same  vertical 
line.  When  any  change  in  the  blood-pressure  takes  place,  the 
degree  of  compression  of  the  ampullae  is  altered,  and  the  change  is 
transmitted  along  the  air-tight  connections  to  the  recording  tambours. 
Simultaneous  records  of  the  changes  in  the  blood-pressure  in  the 
right  auricle  and  ventricle  obtained  in  this  way  indicate  a  sudden 
rise  of  the  auricular  pressure  corresponding  with  the  auricular  systole, 
followed  by  a  sudden  fall  (Fig.  20).  This  is  represented  on  the  ventri- 
cular curve  by  a  smaller  elevation,  which  shows  that  the  pressure  in  the 
ventricle  has  been  raised  somewhat  by  the  blood  driven  into  it  from 
the  auricle.  Then  follows  immediately  a  great  and  abrupt  increase 
of  ventricular  pressure,  the  result  of  the  systole  of  the  ventricle. 


FIG.  25. — DIAGRAM  OF  CARDIAC  SOUND  FOR  SIMULTANEOUS  REGISTRATION 
OF  ENDOCARDIAC  PRESSURE  IN  AURICLE  AND  VENTRICLE. 

A,  elastic  ampulla  for  auricle  ;  V  for  ventricle ;  T,  tubes  connected  with  recording 
tambours. 

This  elevation  remains  for  some  time  at  the  maximum,  and  then  the 
curve  suddenly  sinks  as  the  ventricle  relaxes.  Near  the  bottom  of 
the  descent  there  is  a  slight  elevation,  due,  as  Marey  supposed,  to 
the  closure  of  the  semilunar  valves,  which  causes  a  better-marked 
and  simultaneous  elevation  in  the  curve  of  aortic  pressure  when  this 
is  registered  by  means  of  a  sound  passed  into  the  aorta  through  the 
carotid  artery.  Both  the  auricular  and  ventricular  curves  now  begin 
again  to  rise  slowly,  showing  a  gradual  increase  of  pressure  as  the 
blood  flows  from  the  great  veins  into  the  auricle,  and  through  the 
tricuspid  orifice  into  the  ventricle.  This  slow  rise  continues  till  the 
next  auricular  systole. 

It  is  probable,  however,  that  some  of  the  smaller  elevations 
on  the  curves  of  Chauveau  and  Marey,  and  particularly  that 
which  they  associated  with  the  closure  of  the  semilunar 
valves,  were  due  to  the  oscillations  of  their  apparatus.  For 
it  is  a  remarkable  fact  that  on  most  of  the  endocardiac 
pressure  tracings  of  the  best  modern  manometers,  whether 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      87 

the  curves  belong  to  the  type  of  the  peak  or  of  the  plateau, 
no  sudden  change  of  curvature,  no  nick,  or  crease,  or  undu- 
lation reveals  the  moment  of  opening  or  closure  of  any 
valve.  But  by  experimentally  graduating  a  pair  of  elastic 
manometers,  and  obtaining  with  them  simultaneous  records 
of  the  pressure  in  auricle  and  ventricle,  we  can  calculate  at 
what  points  of  the  ventricular  curve  the  pressure  is  just 
greater  than  and  just  less  than  the  pressure  in  the  auricle. 
The  first  point,  it  is  evident,  will  correspond  to  the  instant  at 
vvhich  the  mitral  or  tricuspid  valve,  as  the  case  may  be,  is 
closed,  and  the  second  to  the  instant  at  which  it  is  opened. 
And  in  like  manner,  by  comparing  the  pressure-curve  of  the 
aorta  with  that  of  the  left  ventricle,  the  moment  of  opening 
and  closure  of  the  semilunar  valves  may  be  determined 
(Figs.  23  and  24).  According  to  the  test  observations,  the 
closure  of  the  semilunar  valves  takes  place  at  a  time  corre- 
sponding to  a  point  on  the  upper  portion  of  the  descending 
limb  of  the  intraventricular  curve. 

The  study  of  the  curves  of  endocardiac  pressure  enables 
us  to  add  precision  in  certain  points  to  the  description  of 
the  events  of  the  cardiac  cycle  which  we  have  already  given, 
and,  as  regards  the  ventricles,  to  divide  the  cycle  into  four 
periods : 

(1)  A  period  during  which  the  pressure  is  lower  in  the  ventricles 
than  either   in   the  auricles   or   the   arteries,  and  the  auriculo- 
ventricular  valves  are  consequently  open,  and  the  semilunar  valves 
closed.     This  is  the  period  of '  filling  '  of  the  heart. 

(2)  A  period,  beginning  with  the  ventricular  systole,   during 
which  the  pressure  is  rising  abruptly  in  the  ventricles,  while  they 
are  as  yet  completely  cut  off  from  the  auricles  on  the  one  hand 
and  the  arteries  on  the  other  by  the  closure  of  both  sets  of  valves. 
This  is  the  period  during  which  the  ventricles  are,  to  use  a  homely 
but  expressive  phrase,  '  getting  up  steam.' 

(3)  A  period  during  which  the  pressure  in  the  ventricles  overtops 
that  in  the  arteries,  and  the  semilunar  valves  are  open,  while  the 
auriculo -ventricular  valves  remain  shut.     This  is  the  period  of 
'  discharge.' 

(4)  A  period  during  which  the  pressure  in  the  ventricles  is  again 
less  than  the  arterial,  while  it  still  exceeds  the  auricular  pressure, 


88  A  MANUAL  OF  PHYSIOLOGY 

and  both  sets  of  valves  are  closed.     This  is  the  period  of  rapid 
relaxation. 

Of  the  four  periods,  the  second  and  fourth  are  exceedingly 
brief.  The  third  is  relatively  long  and  constant,  being  but 
slightly  dependent  on  either  the  pulse-rate  or  the  pressure 
in  the  arteries.  The  duration  of  the  first  period  varies  in- 
versely as  the  frequency  of  the  heart ;  with  the  ordinary 
pulse-rate  it  is  the  longest  of  all. 

We  have  already  said  that  a  negative  pressure  may  be  detected  in 
the  cardiac  cavities  by  means  of  a  special  form  of  mercurial  mano- 
meter. This  is  confirmed  by  an  examination  of  the  tracings  written 
by  good  elastic  manometers,  for  the  curves  of  both  ventricles  may 
often  descend  below  the  line  of  atmospheric  pressure.  The  cause  of 
this  negative  pressure  has  been  much  discussed.  In  part  it  may  be 
ascribed  to  the  aspiration  of  the  thoracic  cage  when  it  expands 
during  inspiration  (p.  209).  But  since  the  pressure  in  a  vigorously- 
beating  heart  may  still  become  negative,  though  not  to  the  same 
extent  as  before,  when  the  thorax  has  been  opened,  and  the  influence 
of  the  respiratory  movements  eliminated,  we  must  conclude  that  the 
recoil  of  the  somewhat  narrowed,  or  at  least  distorted,  auriculo- 
ventricular  rings,  and  of  elastic  structures  in  the  walls  of  the  ventricles, 
exerts  of  itself  a  certain  feeble  suction  upon  the  blood. 

The  Pulse. — At  each  contraction  of  the  heart  a  quantity  of 
blood,  probably  varying  within  rather  wide  limits  (p.  127), 
is  forced  into  the  already-full  aorta.  If  the  walls  of  the 
bloodvessels  were  rigid,  it  is  evident  (p.  74)  that  exactly 
the  same  quantity  would  pass  at  once  from  the  veins  into 
the  right  auricle.  The  work  of  the  ventricle  would  all  be 
spent  within  the  time  of  the  systole,  and  only  while  blood 
was  being  pumped  out  of  the  heart  would  any  enter  it. 
Since,  however,  the  vessels  are  extensible,  some  of  the  blood 
forced  into  the  aorta  during  the  systole  is  heaped  up  in  the 
arteries,  beyond  which,  in  the  capillary  tract,  with  its  rela- 
tively great  surface,  the  chief  resistance  to  the  blood-flow 
lies.  The  arteries  are  accordingly  distended  to  a  greater 
extent  than  before  the  systole,  and,  being  elastic,  they 
keep  contracting  upon  their  contents  until  the  next  systole 
over-distends  them  again.  In  this  way,  during  the  pause 
the  walls  of  the  arteries  are  executing  a  kind  of  elastic 
systole,  and  driving  the  blood  on  into  the  capillaries.  The 
work  done  by  the  ventricle  is,  in  fact,  partly  stored  up  as 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH       89 

potential  energy  in  the  tense  arterial  wall,  and  this  energy 
is  being  continually  transformed  into  work  upon  the  blood 
during  the  pause,  the  heart  continuing,  as  it  were,  to  con- 
tract by  proxy  during  its  diastole.  Thus,  the  blood  pro- 
gresses along  the  arteries  in  a  series  of  waves,  to  which  the 
name  of  '  blood-waves  '  or  '  pulse-waves  '  may  be  given. 
Wherever  the  pulse-wave  spreads  it  manifests  itself  in 
various  ways — by  an  increase  of  blood-pressure,  an  increase 
in  the  mean  velocity  of  the  blood-flow,  an  increase  in  the 
volume  of  organs,  and  by  the  visible  and  palpable  signs  to 
which  the  name  of  pulse  is  commonly  given  in  a  restricted 
sense.  The  intermittence  in  the  flow  with  which  the  pulse- 
wave  is  necessarily  associated  is  at  its  height  at  the  begin- 
ning of  the  aorta.  In  middle-sized  arteries,  such  as  the 
radial,  it  is  still  well  marked,  but  it  dies  away  as  the  capil- 
laries are  reached,  and  only  under  special  conditions  passes 
on  into  the  veins. 

The  pulse  was  well  known  to  the  Greek  physicians,  and 
used  by  them  to  a  certain  extent  as  an  indication  in  practical 
medicine.  Harvey  demonstrated  with  some  clearness  the 
relation  of  the  pulse  to  the  contraction  of  the  heart,  but 
Thomas  Young  was  the  first  to  form  a  proper  conception  of 
it  as  the  outward  token  of  a  wave  propagated  from  heart  to 
periphery. 

When  the  finger  is  placed  over  a  superficial  artery  like  the 
carotid,  the  radial  or  the  temporal,  a  throb  or  beat  is  felt, 
which,  without  measurement,  seems  to  be  exactly  coinci- 
dent with  the  cardiac  impulse.  In  certain  situations  the 
pulse  can  be  seen  as  a  distinct  rhythmical  rise  and  fall  of 
the  skin  over  the  vessel.  The  throbbing  of  the  carotid, 
especially  after  exertion,  is  familiar  to  everyone,  and  the 
beat  of  the  ulnar  artery  can  be  easily  rendered  visible  by 
extending  the  hand  sharply  on  the  wrist.  When  the  pulse 
is  felt  by  the  finger,  it  is  not  the  expansion,  but  the 
hardening  of  the  wall  of  the  vessel,  due  to  the  increase  of 
arterial  pressure,  that  is  perceived ;  and  even  a  superficial 
artery  when  embedded  in  soft  tissues  so  that  it  cannot  be 
compressed,  gives  no  token  of  its  presence  to  the  sense  of 
touch.  Sometimes  an  artery  is  longitudinally  extended  by 


90  A  MANUAL  OF  PHYSIOLOGY 

the  pulse-wave,  and  this  extension  may  be  far  more  con- 
spicuous than  the  lateral  dilatation.  This  is  particularly 
seen  when  one  point  of  the  vessel  is  fixed  and  a  more  distal 
point  offers  some  obstruction  to  the  blood-flow,  as  at  a 
bifurcation,  or  in  an  artery  which  has  been  ligatured  and 
divided. 

By  means  of  the  sphygmograph,  the  lateral  movements  of 
the  arterial  wall,  or,  rather,  in  man,  the  movements  of  the 
skin  and  other  tissues  lying  over  the  bloodvessel,  can  be 
magnified  and  recorded.  It  would  be  very  unprofitable  to 
enumerate  all  the  sphygmographs  which  ingenuity  has  in- 
vented and  found  names  for.  The  first  rude  attempt  to 
magnifv  the  movements  of  the  pulse  was  made  by  loosely 


FIG.  26. — SCHEME  OF  MAREY'S  SHIYGMOGRAPII. 

A,  Toothed  wheel  connected  with  axle  H,  and  gearing  into  toothed  upright  B  ; 
C,  ivory  pad  which  rests  over  bloodvessel  and  is  pressed  on  it  by  moving  G,  a  screw 
passing  through  the  spring  J  ;  E,  writing-lever  attached  to  axle  H,  and  moved  by  its 
rotation  ;  E  writes  on  D,  a  travelling  surface  moved  by  clockwork  F. 

attaching  a  thin  fibre  of  glass  or  wax  to  the  skin  with  a 
little  lard,  in  order  to  demonstrate  the  venous  pulse  which 
appears  under  certain  conditions.  Vierordt  improved  on 
this  by  using  a  counterpoised  lever  writing  on  a  blackened 
surface.  But  the  inertia  of  the  lever  was  so  great  that  the 
finer  features  of  the  pulse  were  obscured.  In  all  modern 
sphygmographs  there  is  a  part,  usually  button-shaped,  which 
is  pressed  over  the  artery  by  means  of  a  spring,  as  in  Marey's 
and  Dudgeon's  sphygmographs,  or  by  a  weight,  or  by  a 
column  of  liquid.  In  Marey's  instrument,  the  button  acts 
upon  a  toothed  rod  gearing  into  a  toothed  wheel,  to  which 
a  lever,  or  a  system  of  levers,  is  attached.  The  lever  has 
a  writing-point  which  records  the  movement  on  a  smoked 
plate,  or  a  plate  covered  with  smoked  paper,  drawn  uni- 
formly along  by  clockwork.  Brondgeest's  pansphygmograph 
is  a  particular  application  of  Marey's  tambours,  for  receiving 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      91 

and  registering  the  movement  of  the  pulse,  as  is  Marey's 
own  '  sphygmograph  of  transmission.'  (Practical  Exer- 
cises, p.  182.) 

In  a  normal  pulse-tracing  (Fig.  27)  the  ascent  is  abrupt 
and  unbroken  ;  the  descent  is  more  gradual,  and  is  inter- 
rupted by  one,  two,  or  even  three  or  more,  secondary 
wavelets.  The  most  important  and  constant  of  these  is  the 
one  marked  3,  which  has  received  the  name  of  the  dicrotic 
wave.  Usually  less  marked,  and  sometimes  absent,  is  the 
wavelet  2  between  the  dicrotic  elevation  and  the  apex  of 


FIG.  27.— PULSE  TRACINGS. 

I,  Primary  elevation  ;  2,  predicrotic  or  first  tidal  wave ;  3,  dicrotic  wave.  The 
depression  between  2  and  3  is  the  dicrotic  or  aortic  notch  ;  3  is  better  marked  in  B 
than  in  A.  C,  dicrotic  pulse  with  low  arterial  pressure  ;  D,  pulse  with  high  arterial 
pressure — summit  of  primary  elevation  in  the  form  of  an  ascending  plateau.  E,  systolic 
anacrotic  pulse  ;  the  secondary  wavelet  a  occurs  during  the  upstroke  corresponding  to 
the  ventricular  systole.  F,  presystolic  anacrotic  pulse  ;  a  occurs  just  before  the  systole 
of  the  ventricle.  In  this  rarer  form  of  anacrotism,  a  may  sometimes  be  due  to  the 
auricular  systole  when  the  aortic  valves  are  incompetent. 

the  curve.  It  is  generally  termed  the  predicrotic  wave. 
Following  the  dicrotic  wave  are  sometimes  seen  one  or  more 
ripples,  which  have  been  called  by  some  elastic  elevations. 

In  the  explanation  of  the  pulse-tracing,  a  fundamental  fact  to  be 
borne  in  mind  is  the  elasticity  of  the  vessels.  When  a  wave  of 
increased  pressure  passes  along  a  rigid  tube  with  open  ends,  it  dies 
away  at  the  ends,  and  is  followed  by  no  secondary  waves.  But  when 
the  tube  is  elastic,  the  primary  wave  is  necessarily  followed  by 
secondary  waves,  the  whole  system  passing  through  a  series  of 
vibrations  to  regain  its  original  position.  When  an  incompressible 
fluid  like  water  is  injected  by  an  intermittent  pump  into  one  eno  of 
an  elastic  tube  a  wave  is  set  up,  which  is  transmitted  to  the  other 
end  of  the  tube.  It  is  a  positive  wave — that  is,  it  causes  an  increase 


92  A  MANUAL  OF  PHYSIOLOGY 

of  pressure  and  an  expansion  of  the  tube  wherever  it  arrives ;  and  if 
a  series  of  levers  be  placed  in  contact  with  the  tube,  they  will  rise 
and  sink  in  succession  as  the  wave  passes  them.  If  the  tube  is  a 
very  long  one,  the  wave,  by  the  time  it  has  reached  the  further  end, 
may  have  become  extinguished  by  the  friction ;  but  if  the  tube  is 
not  long  enough  for  this  to  happen,  it  will  be  there  reflected,  and 
run  towards  the  central  end  as  a  centripetal  wave.  Here  it  may 
again  undergo  reflexion,  and  pass  out  once  more  as  a  centrifugal, 
twice-reflected  wave. 

When  the  liquid  ceases  to  enter  the  tube  at  the  end  of  the 
stroke,  a  wave  of  diminished  pressure — a  negative  wave— is  generated 
at  the  central  end,  and  is  propagated  to  the  distal  end,  where  it  may 
be  reflected  just  like  the  positive  wave. 

Although  under  certain  conditions  the  dicrotic  wave  is  so 
marked  that  the  double  beat  of  the  pulse  was  discovered 
and  named  by  physicians  long  before  the  invention  of  any 
sphygmograph,  perhaps  no  physiological  question  has  been 
more  discussed  or  is  less  understood  than  the  mechanism  of 
its  production.  Two  points,  however,  seem  to  be  clear : 
(i)  That  it  is  a  centrifugal,  and  not  a  centripetal,  wave — 
that  is  to  say,  it  travels  away  from,  and  not  towards,  the 
heart ;  (2)  that  the  aortic  semilunar  valves  have  something 
to  do  with  its  origin. 

It  is  not  a  centripetal  wave,  for  when  tracings  are  taken 
simultaneously  from  arteries  at  different  distances  from  the 
heart  (say,  from  the  carotid  and  the  radial),  the  dicrotic 
wave  is  always  separated  by  the  same  interval  of  time  from 
the  primary  elevation.  This  can  only  be  explained  by 
supposing  that  it  has  the  same  point  of  origin,  and  travels 
with  the  same  velocity  and  in  the  same  direction  as  the 
primary  wave.  It  is  not,  then,  a  wave  reflected  directly 
from  the  peripheral  distribution  of  the  artery  from  which  the 
pulse-tracing  is  taken.  Nor  does  the  contention  of  v.  Frey 
and  v.  Kries,  that  it  is  a  twice-reflected  wave,  seem  more 
likely,  although  they  have  indeed  by  experiments  on  n-ewly- 
killed  animals  been  able  to  detect  the  traces  of  such  waves, 
which,  reflected  first,  as  they  suppose,  from  the  small  arteries 
in  general,  run  towards  the  heart,  and  are  then  again  re- 
flected outwards  from  the  semilunar  valves. 

Perhaps  the  explanation  that  best  takes  account  of  the 
facts  and  renders  most  clear  the  role  of  the  semilunar  valves 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      93 

is  somewhat  as  follows :  When  the  systole  abruptly  comes 
to  an  end  and  the  outflow  from  the  ventricle  ceases,  the 
column  of  blood  in  the  aorta  tends  still  to  move  on  in  virtue 
of  its  inertia,  and  a  diminution  of  pressure,  accompanied  by 
a  corresponding  contraction  of  the  aorta,  takes  place  behind 
it,  just  as  a  negative  wave  is  set  up  in  the  central  end  of  the 
elastic  tube  when  the  stroke  of  the  pump  is  over.  At  the 
same  moment,  and  while  the  semilunar  valves  are  still  for 
an  instant  incompletely  closed,  the  diminution  of  pressure 
in  the  beginning  of  the  aorta  is  intensified  by  the  aspiration 
of  the  relaxing  ventricle,  which  sucks  the  blood  back  against 
the  valves,  and  draws  them  a  little  way  into  its  cavity. 
A  negative  wave,  therefore — a  wave  of  diminished  pressure, 
represented  in  the  pulse-curve  by  the  '  aortic  notch  ' — travels 
out  towards  the  periphery.  The  diminution  of  pressure  is 
quickly  followed  by  a  rebound,  as  always  happens  in  an 
elastic  system,  the  recoiling  blood  meets  the  closed  semi- 
lunar  valves,  the  aorta  expands  again,  and  the  expansion  is 
propagated  once  more  along  the  arteries  as  the  dicrotic 
elevation. 

Of  the  origin  and  significance  of  the  predicrotic  wave  we 
know  so  little  that  it  would  not  be  profitable  to  discuss  it. 
It  seems,  however,  to  be  a  secondary  wave  of  oscillation.  The 
so-called  elastic  oscillations  (Landois)  are  probably  due,  in 
large  part  at  least,  to  vibrations  of  the  recording  apparatus. 

When  the  semilunar  valve  becomes  incompetent  in  disease,  or  is 
rendered  insufficient  in  animals  by  the  artificial  rupture  of  one  or 
more  of  its  segments,  the  dicrotic  wave,  as  will  be  readily  understood 
from  the  manner  in  which  it  is  produced,  either  disappears 
altogether  or  is  markedly  enfeebled.  But  apart  from  any  anatomical 
lesion  or  functional  defect  in  the  aortic  valves,  the  prominence 
of  the  wave  varies  with  a  great  number  of  circumstances,  some  of 
which  are  in  a  measure  understood,  while  others  remain  obscure. 
It  varies  in  particular  with  the  abruptness  of  discharge  of  the 
ventricle  and  the  extensibility  of  the  arteries.  The  conditions  are 
usually  favourable  when  the  arterial  pressure  is  low,  for  the  blood  then 
passes  quickly  from  the  ventricle  into  the  arteries,  which,  already 
only  moderately  tense,  are  easily  dilated  by  the  primary  wave,  then 
sharply  collapse,  and  are  again  abruptly  distended  when  the  dicrotic 
wave  arrives.  And,  in  fact,  an  exaggeration  of  the  dicrotic  wavelet 
may  be  artificially  produced  by  nitrite  of  amyl  (Fig.  70,  p.  183), 
a  drug  which  lessens  the  blood-pressure  by  dilating  the  small 


94  A  MANUAL  OF  PHYSIOLOGY 

arteries,  or  by  muscular  exercise  (Fig.  69,  p.  183),  running,  for 
instance,  which  is  supposed  to  lower  the  arterial  pressure,  partly  by 
dilatation  of  the  muscular  and  cutaneous  arterioles,  and  partly  by 
accelerating  the  venous  flow  (p.  121).  The  increase  in  the  pulse- 
rate  may  also  have  something  to  do  in  this  case  with  the  exaggeration 
of  the  dicrotism,  which  is  very  frequently,  although  by  no  means 
invariably,  associated  with  a  rapidly-beating  heart,  and  therefore  is 
often  seen  in  fever.  On  the  other  hand,  in  certain  diseases  asso- 
ciated with  a  high  arterial  pressure  the  dicrotic  elevation  almost 
disappears.  Atheromattms  arteries,  being  very  inextensible,  do  not 
allow  a  dicrotic  pulse. 

Since  the  pulse  represents  a  periodical  increase  and  diminution  in 
the  amount  of  distension  of  an  artery  at  any  point,  the  line  joining 
all  the  minima  of  the  pulse-curve  will  vary  in  its  height  above  the 
base-line,  or  line  of  no  pressure,  according  to  the  amount  of  per- 
manent distension,  i.e.,  permanent  blood-pressure,  which  the  heart  in 
any  given  circumstances  is  able  to  maintain.  Any  circumstance 
that  tends  to  lessen  the  permanent  distension  will  cause  a  fall  of  the 
line  of  minima,  and  any  circumstance  tending  to  increase  the 
distension  will  cause  that  line  to  rise.  If,  for  example,  the  arm  be 
raised  while  a  pulse-tracing  is  being  taken  from  the  wrist,  the  line  of 
minima  falls  because  the  permanent  pressure  in  the  radial  artery  is 
diminished. 

The  form  of  the  pulse-curve  varies  in  the  different  arteries, 
and  therefore  in  making  comparisons  the  same  artery  should 
be  used.  When  the  wave  of  blood  only  enters  an  artery 
slowly,  the  ascending  part  of  the  curve  will  be  oblique. 
This  is  normally  the  case  in  a  pulse-curve  of  a  distant  artery, 
such  as  the  posterior  tibial.  The  height  of  the  wave  is  also 
less  than  in  an  artery  nearer  the  heart,  such  as  the  carotid, 
or  even  the  axillary,  where  the  primary  elevation  is  rela- 
tively abrupt  (Fig.  71,  p.  183). 

Anacrotic  Pulse. — As  a  rule,  the  ascent  of  the  tracing  is 
unbroken  by  secondary  waves,  but  in  certain  circumstances 
these  may  appear  on  it.  This  condition,  which,  when  well 
marked  at  any  rate,  may  be  considered  pathological,  is 
called  anacrotism  (Fig.  27).  It  is  seen  when  the  discharge 
of  the  left  ventricle  into  the  aorta  is  slow  and  difficult — e.g., 
in  old  people  whose  arteries  have  been  rendered  less 
extensible  by  the  deposit  of  lime-salts  in  their  walls 
(atheroma),  and  in  cases  where  the  orifice  of  the  aorta  has 
been  narrowed  from  disease  of  the  semilunar  valves  (aortic 
stenosis).  Since  these  conditions  are  in  general  associated 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      95 

with  hypertrophy  and  dilatation  of  the  left  ventricle,  the 
slow  emptying  of  the  ventricle  is,  perhaps,  partly  due  to  the 
greater  quantity  of  blood  which  it  contains. 

In  whatever  way  the  delay  in  the  emptying  of  the  ventricle 
is  brought  about,  the  most  probable  explanation  of  the 
anacrotic  pulse  is  that  the  delay  affords  time  for  one  or 
more  secondary  waves  to  be  developed  in  the  arterial  system 
before  the  summit  of  the  curve  has  been  reached,  and  that 
these  are  superposed  upon  the  long-drawn  primary  elevation. 
In  aortic  insufficiency,  where  the  left  side  of  the  heart  is 
never  cut  off  entirely  from  the  aorta,  the  auricular  impulse 
is  sometimes  marked  on  the  pulse-curve  as  a  distinct 
elevation ;  and  this  gives  rise  to  a  peculiar  kind  of  anacrotic 
pulse,  especially  in  the  arteries  nearest  the  heart  (Fig.  27,  F). 
Frequency  of  the  Pulse.— In  health,  the  working  of  the 
cardiac  pump  is  so  smooth  and  apparently  so  self-directed, 
that  it  needs  a  certain  degree  of  attention  to  perceive  that 
the  rate  of  the  stroke  is  not  absolutely  constant,  It  is,  in 
reality,  affected  by  many  internal  conditions  and  external 
influences. 

At  the  end  of  foetal  life  the  rate  is  given  as  144-133  ;  from 
birth  till  the  end  of  the  first  year,  140-123 ;  from  10  to  15 
years,  91-76  ;  from  20  to  25  years,  73-69.  It  remains  at  this 
till  60  years,  and  increases  again  somewhat  in  old  age.*  At 
all  ages  the  pulse  is  somewhat  quicker  in  the  female  than  in 
the  male,  the  excess  amounting  to  about  8  beats  a  minute. 
So  that  if  we  take  the  average  rate  for  a  man  (in  the  sitting 
position)  as  72,  the  average  for  a  woman  will  be  80.  The 
difference  is  partly  due  to  the  fact  that  the  average  man 
is  taller  than  the  average  woman  ;  and  it  is  known  that  in 
persons  of  the  same  sex  and  age  the  pulse-rate  has  an 
inverse  relation  to  the  stature.  But  there  may  be,  in 

*  It  must  be  remembered  that  these  numbers  are  merely  averages. 
Some  healthy  individuals  have  a  much  slower  pulse-rate  than  72  per 
minute,  and  some  a  rate  considerably  greater.  Thus,  while  the  average 
pulse-rate  (taken  in  the  sitting  position)  of  74  healthy  (male)  students, 
whose  ages  ranged  from  1 8  to  36  years,  was  73,  the  extreme  variation  was 
from  54  to  98.  In  the  standing  position  the  average  was  80,  and  the  varia- 
tions 64  to  105.  In  the  supine  position,  average  69,  and  variations  48  to 
98.  After  a  short  spell  of  muscular  exercise  (generally  running  up  and 
down  some  flights  of  stairs)  the  average  in  the  standing  position  was  119, 
the  variations  75  to  164,  and  the  average  increase  32. 


96  A  MANUAL  OF  PHYSIOLOGY 

addition,  a  real  sexual  difference.  The  position  of  the  body 
(exercises  a  small,  but  relatively  constant,  influence  on  the 
«~»e  fr. '  *L  {rate,  which  is  greater  in  the  standing  than  in  the  sitting 
'posture,  and  greater  in  the  latter  than  in  the  recumbent 
position.  And  this  is  true  even  when  muscular  action  is  as 
far  as  possible  eliminated  by  fastening  the  person  to  a  board. 
The  pulse  is  further  affected  by  the  respiratory  movements, 
especially  when  they  are  exaggerated  in  forced  breathing, 
being  accelerated  during  each  inspiration  (p.  249).  It  is 
also  increased  by  the  taking  of  food,  and  especially  of 
alcoholic  stimulants,  by  muscular  exercise,  in  fever  and 
many  other  pathological  conditions,  and  by  a  high  external 
temperature.  A  warm  bath,  for  example,  causes  a  very 
distinct  acceleration  of  the  heart ;  and  Delaroche  found  that 
in  air  at  the  temperature  of  65°  C.  his  pulse  went  up  to  160. 
A  cold  bath  may  depress  the  pulse-rate  to  60,  or  even  less. 
During  sleep  it  may  fall  to  50.  It  is  greatly  influenced  by 
psychical  events,  and  that  in  the  direction  either  of  an 
increase  or  a  decrease.  Finally,  it  ought  to  be  remembered 
as  of  some  practical  importance  that  the  pulse-rate  in  women 
and  children,  but  particularly  in  the  latter,  is  less  steady 
than  in  men,  and  more  apt  to  be  affected  by  trivial  causes. 
And  it  is  a  good  general  rule  to  let  a  short  interval  elapse 
after  the  finger  is  laid  on  the  artery  before  beginning  to 
count  the  pulse,  so  that  the  acceleration  due  to  the  agitation 
of  the  patient  may  have  time  to  subside. 

Various  Characters  of  the  Pulse. — Certain  terms  which  have 
come  down  from  the  older  medicine,  and  are  still  used  clinically  to 
describe  various  conditions  of  the  circulation  as  investigated  by 
feeling  the  pulse,  must  here  be  briefly  touched  on  : 

1  Hard '  pulse  (pulsus  durus\  Here  the  mean  blood-pressure  is 
high,  the  vessels  are  considerably  distended,  and  the  pulse  therefore 
feels  hard.  With  a  'soft'  pulse  (pulsus  mollis]  the  mean  blood- 
pressure  is  low. 

With  a  '  quick  '  pulse  (pulsus  celer]  the  artery  is  rapidly  distended 
by  the  pulse-wave.  With  a  *  slow '  pulse  (pulsus  tardus)  the  disten- 
sion is  slow. 

The  terms  '  strong  '  pulse  (pulsus  fortis)  and  '  weak '  pulse  (pulsus 
debilis)  refer  to  the  amount  by  which  the  pulse- wave  increases  the 
blood-pressure  at  the  point. 

'  Large '  pulse  (pulsus  magnus)  and  '  small '  or  '  thready '  pulse 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     97 

(pulsus  parvus)  refer  to  the  increase  in  the  quantity  of  blood  which 
every  pulse-wave  causes  in  the  vessel. 

The  '  force  of  the  pulse '  is  a  phrase  which  is  often  ambiguously 
used,  sometimes  apparently  as  synonymous  with  'strength/  and 
sometimes  with  '  size,'  as  above  defined.  In  fact,  the  quantitative 
information  obtained  by  feeling  the  pulse  with  the  finger,  although 
more  valuable  for  clinical  purposes  than  anything  that  can  be 
deduced  from  an  ordinary  sphygmographic  record,  is  far  inferior  in 
precision  to  the  qualitative  notion  which  that  time-honoured  pro- 
ceeding affords.  The  *  force  of  the  pulse '  does  not  necessarily 
correspond  with  the  force  of  the  heart.  It  depends  partly  on  the 
suddenness  with  which  the  pulse-wave  distends  the  artery,  partly  on 
the  amount  of  this  distension  in  relation  to  the  previous  permanent 
distension,  and  to  some  extent  on  the  calibre  of  the  vessel.  Other 
things  being  equal,  the  pulse  in  a  large  vessel  will  feel  stronger  than 
that  in  a  smaller  vessel.  This  last  factor  accounts  for  the  inequality 
in  the  force  of  the  pulse  which  is  not  infrequently  found  between  the 
two  radials  even  of  a  healthy  person. 

Rate  of  Propagation  of  the  Pulse-wave. — When  pulse -tracings 
are  taken  simultaneously  at  two  points  of  the  arterial  system 
unequally  distant  from  the  heart,  by  two  sphygmographs 
whose  writing-points  move  in  the  same  vertical  straight  line, 
it  is  found  that  the  ascent  of  the  curve  begins  later  at  the 
more  distant,  than  at  the  nearer  point.  Since  waves  like 
the  pulse-wave  travel  with  approximately  the  same  velocity 
in  different  parts  of  an  elastic  system  like  the  arterial '  tree,' 
this  '  delay  '  must  be  due  to  the  difference  in  the  length  of 
the  two  paths.  The  difference  in  length  can  be  measured ; 
the  time-value  of  the  '  delay  '  can  be  deduced  from  the  rate 
of  movement  of  the  recording  surface ;  dividing  the  length 
by  the  time,  we  arrive  at  the  rate  of  propagation  of  the 
pulse-wave.  This  rate  has  been  found  to  be  about  8*5  metres 
per  second  in  man  in  the  arteries  of  the  upper  limb,  and 
9*5  metres  in  those  of  the  lower  limb,  the  difference  being 
due  to  the  smaller  distensibility  of  the  latter.  The  mean 
velocity  of  the  puise-wave  would  correspond  to  not  much 
less  than  500  miles  in  twenty-four  hours,  or  about  the  same  pLVla_Tt^ 
as  the  speed  of  a  fast  Atlantic  liner  or  of  a  wave  of  the  sea 
in  a  strong  gale.  The  velocity  of  the  pulse-wave  must  fl£ 
not  be  confounded  with  that  of  the  blood-stream  itself, 
which  is  not  one-thirtieth  as  great.  A  ripple  passes  over 
the  surface  of  a  river  at  its  own  rate — a  rate  that  is 

7 


98  A  MANUAL  OF  PHYSIOLOGY 

independent  of  the  velocity  of  the  current.  The  passage 
ot  the  ripple  is  not  a  bodily  transference  of  the  particles 
of  water  of  which  at  any  given  moment  the  wave  is  com- 
posed, but  the  propagation  of  a  change  of  relative  position 
of  the  particles.  The  mere  fact  that  the  ripple  can  pass  up 
stream  as  well  as  down  is  sufficient  to  illustrate  this.  The 
pulse-wave  does  not,  however,  correspond  in  every  respect 
to  a  ripple  on  a  stream,  for  the  bodily  transfer  of  the  blood 
depends  upon  the  series  of  blood-waves  which  the  heart 
sets  travelling  along  the  arteries.  Every  particle  of  blood 
is  advanced,  on  the  whole,  by  a  certain  distance  with  every 
pulse-wave  in  which  for  the  time  it  takes  its  place.  But 
no  particle  continues  in  the  front  of  the  pulse-wave  from 
beginning  to  end  of  the  arterial  system.  The  *  delay '  or 
'  retardation '  of  the  pulse  (the  interval,  say,  between  the 
beginning  of  the  ascent  of  the  carotid  and  radial  curves)  is 
practically  constant  in  the  same  individual,  not  only  in 
health,  but  also  in  most  diseases.  But  the  retardation  is 
markedly  increased  when  the  pulse-wave  has  to  pass 
through  a  portion  of  an  artery  whose  lumen  is  either  greatly 
widened  (aneurism),  or  greatly  constricted  (endarteritis 
obliterans). 

The  velocity  of  the  pulse-wave  has  sometimes  been  de- 
duced by  comparing  a  tracing  of  the  cardiac  impulse  with 
a  pulse-tracing  taken  at  the  same  time  from  a  distant  artery. 
But,  as  we  have  seen  in  dealing  with  the  action  of  the  heart, 
the  ventricle  does  not  at  the  very  beginning  of  its  contraction 
acquire  sufficient  force  to  cause  the  opening  of  the  semi- 
lunar  valves.  The  pulse,  therefore,  even  in  the  aorta,  must 
lag  behind  the  ventricular  pulse ;  and  the  amount  of  this 
4  lag '  must  be  subtracted  from  the  total  retardation.  But 
since  the  aortic  '  lag,'  unlike  the  retardation  between  two 
arteries,  varies  greatly  even  in  health,  depending  as  it  does 
on  the  arterial  blood-pressure,  this  method  of  determining 
the  velocity  of  the  pulse-wave  is  not  satisfactory. 

The  Blood-pressure  Pulse. — In  man  it  is  only  possible  to 
trace  the  pulse-wave  along  the  arteries  by  movements  of 
the  walls  of  the  vessels  transmitted  through  the  overlying 
tissues.  In  animals  the  changes  of  pressure  that  occur  in 


1HE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH      99 

the  blood  itself  can  be  directly  registered,  and  these  changes 
may  be  spoken  of  as  the  blood-pressure  pulse.  At  bottom, 
as  already  pointed  out,  the  phenomenon  is  exactly  the  same 
as  that  we  have  been  dealing  with  in  our  study  of  the 
external  pulse.  We  are  only  now  to  follow,  by  a  more 
direct,  and  in  some  respects  a  more  perfect  method,  the 
same  wave  of  blood  along  the  same  channel. 

Measurement  of  the  Blood-pressure. — Hales  was  the  first  to 
measure  the  blood-pressure.     This  he  did  by  connecting  a 


FIG.  28. — DIAGRAM  OF  MERCURIAL  KYMOGRAPH. 

The  record  is  taken  on  the  endless  strip  of  paper  E,  which  is  made  to  revolve  at  a 
uniform  rate,  or  on  an  ordinary  drum  ;  D  is  a  float  carrying  a  writing  point ;  C  is  the 
manometer,  the  difference  of  level  of  the  mercury  (Hg]  in  the  two  limbs  of  which 
measures  the  blood-pressure  ;  A  is  a  pressure  bottle  filled  with  sodium  carbonate  or 
magnesium  sulphate  solution  and  connected  by  the  flexible  tube  B  with  the  manometer ; 
F  is  the  bloodvessel ;  G,  the  connecting  cannula. 

tall  glass  tube  with  the  crural  artery  of  a  horse.  The  height 
to  which  the  blood  rose  in  the  tube  indicated  the  pressure 
in  the  vessel.  Poiseuille,  nearly  half  a  century  later,  applied 
the  mercury  manometer,  which  had  already  been  used  in 
physics,  to  the  measurement  of  blood-pressure.  Ludwig 
and  others  improved  this  method  by  making  the  manometer 
self-registering  by  means  of  a  float  in  the  open  limb,  sup- 
porting a  style  which  writes  on  a  revolving  drum,  the  whole 
arrangement  being  called  a  kymograph.  (For  the  method 
of  taking  a  blood-pressure  tracing,  see  p.  185.) 

7—2 


ioo  A  MANUAL  OF  PHYSIOLOGY 

For  reasons  already  mentioned  the  mercurial  manometer 
is  better  suited  for  measuring  the  mean  blood-pressure,  or 
for  recording  changes  in  the  pressure  which  last  for  some 
time,  than  for  following  the  rapid  variations  of  the  pulse- 
wave.  For  the  latter  purpose,  one  of  the  class  of  elastic 
manometers  is  required  (p.  82). 

A  blood-pressure  tracing  taken  from  an  artery  with  a 
manometer  of  this  sort  yields  the  truest  picture  of  the 
pulse-wave  which  it  is  possible  to  obtain,  because  the  re- 
production of  it  is  the  most  direct.  The  fact  that  such  a 
tracing  shows  a  close  agreement  with  the  trace  of  a  good 


FIG.  29.— CURVES  OF  BLOOD-PRESSURE  TAKEN  WITH  A  SPRING  MANOMETER 
FROM  THE  CAROTID  ARTERY  OF  A  DOG  (HURTHLE). 

When  i  was  taken  the  blood -pressure  was  high  ;  2  corresponds  to  a  medium,  3  to  a 
low,  and  4  to  a  very  low  blood-prrssure  ;  p  is  the  primary  elevation— this  and  the 
succeeding  elevations  between  p  and  a  are  called  systolic  waves  ;  the  systolic  waves  are 
followed  by  a  marked  elevation  d,  which  corresponds  to  the  dicrotic  pulse-wave. 

sphygmograph  applied  to  the  corresponding  artery  on  the 
other  side,  is  a  striking  proof  of  the  general  accuracy  of  the 
sphygmographic  method  for  physiological  purposes,  and 
enables  us  to  guide  ourselves  in  transferring  to  man,  in 
whom,  of  course,  the  sphygmograph  can  alone  be  used,  the 
information  derived  from  direct  manometric  observations  in 
animals. 

For  the  same  reason  it  is  unnecessary  to  discuss  tne 
manometric  tracings,  as  regards  the  pulsatory  phenomena, 
in  all  their  details.  It  will  be  sufficient  to  say  that  while 
the  form  of  the  blood-pressure  pulse-curve  varies  with  the 


THE  CIRCULATION  OF  TJIE ^RLOOD  AND  LYMPH    101 

mean  blood-pressure,  the  di  or  otic,  .wave  »is  always-  marked  on 
it,  preceded  by  one  or  more  oscillations  falling  within  the 
period  of  the  systole,  and  followed  by  one  or  more  within  the 
period  of  the  diastole.  When  the  blood-pressure  is  low,  the 
first  or  primary  elevation  is  the  highest  of  the  whole  curve 
(Fig.  29).  When  the  blood-pressure  is  high,  the  maximum 
falls  later,  coinciding  with  one  of  the  secondary  systolic 
waves,  but  always  preceding  the  dicrotic  wave ;  and  the 
curve  assumes  an  anacrotic  character. 

That  all  the  secondary  oscillations,  including  the  dicrotic 
wavelet,  are  of  central,  and  not  of  peripheral  origin,  may 
be  shown,  just  as  in  the  sphygmographic  method,  by  re-  ^ 
cording  the  blood-pressure  simultaneously  at  two  points  of 
the  arterial  system  at  different  distances  from  the  heart — 
e.g.,  in  the  crural  and  carotid  arteries.  The  secondary 
waves  are  found,  by  measuring  the  tracings,  to  reach  the 
more  distal  point  later  than  the  more  central. 

The  increase  of  pressure  during  the  systole,  as  indicated  by  the 
height  of  the  primary  elevation,  is  always  very  large,  much  larger 
than  it  appears  in  a  tracing  taken  with  a  mercury  manometer.  In 
the  rabbit  this  pulsatory  variation  is  one-third  to  one-fourth  of  the 
minimum  pressure.  In  the  dog  it  is  still  greater,  owing  to  the  slower 
rate  of  the  heart,  and  oftens  amounts  to  50  mm.  of  mercury,  while 
under  favourable  conditions  (low  minimum  pressure  and  slowly  beat- 
ing heart)  the  systolic  increase  of  pressure  may  be  actually  more  than 
double  the  minimum  (Hiirthle).  Fick  found  also,  by  means  of  his 
spring  manometer,  that  the  pulsatory  variations  of  blood-pressure 
were  greater  than  the  respiratory  variations  (p.  249),  although  in  the 
records  of  the  mercury  manometer  the  reverse  appears  often  to  be 
the  case.  Landois,  too,  in  the  course  of  experiments  in  which  a 
divided  artery  was  allowed  to  spout  against  a  moving  surface,  and 
to  trace  on  it  a  sort  of  pulse-curve  painted  in  blood  (a  haemautogram 
as  it  is  called),  observed  that  the  rate  of  escape  of  the  blood  was 
nearly  50  per  cent,  greater  during  the  systole,  than  during  the  diastole, 
of  the  heart.  The  existence  of  the  dicrotic  wave  on  this  tracing 
was  long  looked  on  as  the  best  proof  that  it  was  not  an  artificial 
phenomenon. 

The  wave  of  increased    pressure,   as  it    runs    along  the    <  ^ 
arterial   system,   carries    with    it    wherever   it   arrives    an 
increase  of  potential  energy.     But  this  excess  of  potential 
energy  is  continually  being  worn  down,  owing  to  the  friction 
of  the  vascular  bed  ;    and  although  in  the  comparatively 


IO2 


MA WVA£ : Off  PHYSIOL OGY 


large  artenes 'the  Llossc  ^ of:  energy  is  not  great,  it  rapidly 
increases  as  the  arteries  approach  their  termination,  and 
begin  to  branch.  For  not  only  is  the  total  surface,  and 
therefore  the  friction,  increased  with  every  bifurcation,  but 
the  mere  change  of  direction  and  division  of  the  wave  cannot 
take  place  without  loss  of  energy.  For  this  reason  the 
fluctuations  of  blood-pressure  are  greater  in  the  large 
arteries  near  the  heart  than  in  arteries  smaller  and  more 
remote.  In  the  wide  and  much-branched  capillary  bed  the 
pulse-wave  disappears  altogether,  and  the  blood-pressure 
becomes  relatively  constant  or  permanent.  And  it  is  for 
some  purposes  convenient  to  look  upon  the  blood-pressure 
in  the  arteries  as  made  up  of  a  permanent  element,  with 
pulsatory  oscillations  superposed  on  it.  Since  no  portion  of 
the  arterial  system  is  more  than  partially  emptied  in  the 


FIG.  30. — BLOOD-PRESSURE  TRACING. 
The  horizontal  straight  line  intersecting  the  curves  is  the  line  of  mean  pressure. 

interval  between  two  blood-waves,  the  minimum  or  perma- 
nent pressure  is  always  positive — i.e.,  always  above  that  of 
the  atmosphere.  The  only  reason  for  this  is  that  the  beats 
of  the  heart  succeed  each  other  so  rapidly  that  the  succes- 
sive waves  overlap  or  '  interfere,'  and  are  only  separated  at 
their  crests. 

If  the  heart  is  stopped  while  a  blood-pressure  tracing  is 
being  taken — and  we  shall  see  later  on  how  this  can  be  done 
(p.  134) — the  minimum  line  of  the  tracing  goes  on  falling 
towards  the  zero-line.  When  the  heart  begins  beating  again, 
the  pressure-curve  rises,  not  by  a  continuous  ascent,  but  by 
successive  leaps,  each  corresponding  to  a  beat  of  the  heart, 
and  each  overtopping  its  predecessor,  till  the  old  line  of 
minimum  or  of  mean  pressure  is  again  reached. 

The  mean  arterial  blood-pressure  is  the  permanent  pressure 
plus  one-half  of  the  average  pulsatory  oscillation.  In  a 
blood-pressure  tracing  the  line  of  permanent  pressure  joins 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    103 

all  the  minima  ;  the  line  of  maximum  pressure  joins  all  the 
maxima ;  the  line  of  mean  pressure  is  drawn  between  them 
in  such  a  way  that  of  the  area  included  between  it  and  the 
blood-pressure  curve  as  much  lies  above  as  below  it  (Fig.  30). 
As  has  been  said,  a  tracing  taken  with  a  mercury  manometer 
gives  approximately  the  mean  blood-pressure.     Each  beat 
of  the  heart  is  represented  on  it  by  a  single  elevation  of  no 
great  size,  sometimes  not  amounting  to    more   than  one- 
twentieth  of  the  height  of  the  curve  above  the  line  of  zero 
or  atmospheric  pressure.     The  small  oscillations  due  to  the,'  /:,. 
heart-beat  are  superposed  upon  much  longer,  and  often,  as  J1^ 
registered  in  this  way,  larger  waves,  caused  by  the  move-)  T" 
ments  of  respiration.     The  line  of  mean  pressure  intersects^ 
the  respiratory  waves  midway  between  crest   and  trough 
(Fig.  30). 

So  much  having  been  said  by  way  of  definition,  we  have 
now  to  consider  the  amount  of  the  mean  arterial  pressure, 
the  variations  which  it  undergoes,  and  the  factors  on  which 
its  maintenance  depends. 

As  to  its  amount,  it  will  be  sufficiently  accurate  to  say 
that  in  the  systemic  arteries  of  warm-blooded  animals  in 
general    (including   birds),  and   of  man   in   particular,  the    fV^-JCf 
mean  pressure  does  not,  under  ordinary  conditions,  descend 
much  below  100  mm.  of  mercury,  nor  rise  much  above  200  $i\n\* 
mm. ;  while  in  cold-blooded  animals  it  seldom  exceeds  50 
mm.,  and  may  fall  as  low  as  20  mm. 

It  does  not  seem  possible,  at  least  with  our  present  data,  to  further  \_  gj^ 
subdivide  these  two  great  groups ;  nor  do  we  know  precisely  whether 
the  distinction  depends  mainly  on  morphological  or  mainly  on 
physiological  differences,  whether,  that  is  to  say,  the  warm-blooded 
animal  has  a  higher  blood-pressure  than  the  cold-blooded  chiefly 
because  its  vascular  system  (and  especially  its  heart)  is  anatomically 
more  perfect,  or  because  its  heart  beats  faster  and  works  harder.  It 
may  be  that  it  is  for  both  of  these  reasons  that  the  birds,  which  in 
certain  other  respects  are  more  nearly  related  to  the  reptiles  than 
to  the  mammals,  mount,  as  regards  the  pressure  of  the  blood,  into 
the  mammalian  class,  and  that  a  manometer  in  the  carotid  of  a  goose 
will  rise  as  high,  or  almost  as  high,  as  in  the  carotid  of  a  horse,  a 
sheep,  or  a  dog,  while  the  pressure  in  the  aorta  of  a  tortoise  is  no 
higher  than  in  the  aorta  of  a  frog.  But  we  know  that  the  mere 
average  rate  of  the  heart  has  of  itself  comparatively  little  influence 
on  the  blood-pressure  within  either  group,  for  the  heart  of  a  rabbit 

&  0 


104  A  MANUAL  OF  PHYSIOLOGY 

beats,  oo  the  average,  very  much  faster  than  the  heart  of  a  dog,  and 
yet  the  aiterial  pressure  in  the  dog  is  certainly  at  least  as  great  as 
in  the  rabbit.  Nor  does  the  size  of  the  body  seem  to  have  any 
definite  relation  to  the  mean  pressure,  even  in  animals  of  the  same 
species ;  and  there  is  no  reason  to  suppose  that  the  pressure  is  less 
in  the  radial  artery  of  a  dwarf  than  in  the  radial  artery  of  a  giant. 

In  man  the  blood-pressure  has  been  estimated  by  adjust- 
ing over  an  artery  an  instrument  known  as  a  sphygmo- 
manometer,  which,  in  its  most  modern  form,  consists 
essentially  of  a  hollow  rubber  pad  containing  liquid  or 
air,  and  connected  with  a  metallic  (spring)  manometer, 
graduated  beforehand  by  comparison  with  a  mercurial 
manometer.  The  pad  is  pressed  down  over  the  artery  till 
the  pulse  beyond  it  is  just  felt  to  disappear  under  the  finger. 
The  reading  of  the  manometer  is  then  taken  as  approxi- 
mately equal  to  the  maximum  blood-pressure.  A  slight 
deduction  must,  however,  be  made  on  account  of  the 
resistance  to  compression  of  the  artery  itself  and  the  tissues 
over  it.  In  the  radial  artery  of  a  healthy  man  the  blood- 
pressure  may,  perhaps,  average  150  mm.  of  mercury.  In 
the  anterior  tibial  artery  of  a  boy  whose  leg  was  to  be 
amputated  the  blood-pressure,  measured  by  means  of  a 
manometer  connected  directly  with  the  artery,  was  found 
to  vary  from  100  to  160  mm.,  according  to  the  position  of 
the  body  and  other  circumstances. 

In  a  woman  sixty  years  old,  in  good  health,  the  following 
readings  were  obtained  with  the  sphygmomanometer  : 


June  28 
»  29 

Aug.  3 
»  7 

12 


126 — 130  mm.  of  mercury. 
126—136 
132—144        „ 
134—140 


-      136—144          „  (ZADEK.) 

Such  measurements  on  man,  so  far  as  they  can  be  trusted, 
show  that  the  mean  blood-pressure  in  one  and  the  same 
artery  may  vary  for  a  considerable  time  only  within  com- 
paratively narrow  limits. 

This  relative  constancy  of  the  general  arterial  pressure  is  the  result 
of  a  delicate  adjustment  between  the  work  of  the  heart,  the  resistance 
of  the  vessels,  and  the  volume  of  the  circulating  liquid.  The 
quantity  of  the  blood  is  tolerably  steady  in  health,  and  considerable 
changes  may  be  artificially  produced  in  it  (p.  165)  without  affecting 
the  pressure  in  any  great  degree.  On  the  other  hand,  the  work  of 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    105 

the  heart  and  the  peripheral  resistance  are  highly  variable  and  vastly 
influential.  A  narrowing  of  the  arterioles  throughout  the  body  or  in 
some  extensive  vascular  tract  increases  the  peripheral  resistance ; 
and  if  the  heart  continues  to  beat  as  before,  the  pressure  must  rise. 
If  the  arterioles  are  widened,  while  the  heart's  action  remains  un- 
changed, the  pressure  must  fall.  In  like  manner  an  increase  or  a 
decrease  in  the  activity  of  the  heart,, in  the  absence  of  any  change  in 
the  peripheral  resistance,  will  cause  a  rise  or  a  fall  in  the  blood- 
pressure.  But  if  a  slowing  of  the  heart  is  accompanied  by  an  increase 
in  the  peripheral  resistance,  or  a  dilatation  of  the  arterioles  by  an 
increase  in  the  activity  of  the  heart,  the  one  change  may  be  partially 
or  completely  balanced  by  the  other,  and  the  pressure  may  vary 
within  narrow  limits  or  not  at  all. 

Not  only  is  the  mean  pressure,  as  measured  in  a  large  artery, 
tolerably  constant,  but  if  recorded  simultaneously  in  two  arteries  at 
different  distances  from  the  heart,  it  is  seen  to  decrease  very 
gradually  so  long  as  the  arteries  remain  large  enough  to  hold  a 
cannula.  It  is  nearly  as  high,  for  instance,  in  the  crural  artery  of  a 
dog  as  in  the  carotid.  It  is  easy  to  see  that  this  must  be  so,  for 
the  resistance  of  the  arteries  between  the  point  where  the  arterioles 
are  given  off  and  the  heart  is  only  a  small  fraction  of  the  total 
resistance  of  the  vascular  path;  and  we  have  said  (p.  73)  that  the 
lateral  pressure  at  any  cross  section  of  a  system  of  tubes  through 
which  liquid  is  flowing  is  proportional  to  the  resistance  still  to  be 
overcome.  This  is  also  the  reason  why  the  pressure  is  always  much 
lower  in  the  pulmonary  artery  and  right  ventricle  than  in  the  aorta 
and  left  ventricle  (only  one-third  to  one-sixth  as  great),  for  the  total 
resistance  of  the  vascular  path  through  the  lungs  is  much  less  than 
that  of  the  systemic  circuit. 

The  Velocity-pulse. — We  have  seen  that  the  blood  is  pro- 
pelled through  the  arteries  in  a  series  of  waves  that  travel 
from  the  heart  towards  the  periphery.  The  particles  in  the 
front  of  the  pulse-wave  are  constantly  changing,  but  since 
every  section  of  the  arterial  tree  is  successively  distended, 
every  section  contains  more  blood  while  the  pulse-wave  is 
passing  over  it  than  it  contained  immediately  before.  And 
since  there  is  always  a  fairly  free  passage  for  this  blood 
towards  the  periphery,  there  is  a  bodily  transfer  on  the 
whole  of  a  certain  quantity  with  every  wave. 

The  translation  of  the  blood,  instead  of  being  entirely  inter- 
mittent, as  it  would  be  in  a  rigid  tube  or  in  an  elastic  system 
with  a  slow  action  of  the  central  pump,  is  to  some  extent 
constantly  going  on ;  for  a  portion  of  a  blood-wave  is  always 
passing  through  every  section  of  the  arterial  channel.  Thus, 
we  arrive  at  the  same  distinction  as  to  the  onward  move- 


io6  A  MANUAL  OF  PHYSIOLOGY 

ment  of  the  blood  itself  as  we  previously  reached  in  regard 
to  the  blood-pressure,  the  distinction  between  the  constant 
or  permanent  factor  of  the  velocity  and  the  periodical  factor, 
which  we  may  call  the  velocity-pulse. 

The  Velocity  of  the  Blood.— By  the  velocity  or  rate  of  flow 
of  a  river  we  should  mean,  if  the  flow  were  uniform  through- 
out the  whole  cross-section,  the  rate  of  movement  of  any 
given  portion  or  particle  of  the  water.  If  we  could  identify 
a  portion  of  the  water,  we  could  determine  the  velocity  by 
measuring  the  distance  travelled  over  by  that  portion  in  a 
given  time.  If  the  velocity  was  uniform  over  the  channel, 
we  could  predict  the  actual  time  which  would  be  re- 
quired to  traverse  any  fractional  part  of  the  measured 
distance.  If,  however,  the  velocity  of  the  current  changed 
from  point  to  point,  then  we  could  only  deduce  from  our 
observation  the  mean  rate  of  the  river  for  the  measured 
distance.  To  determine  the  actual  rate  for  any  given 
portion  of  this  distance  over  which  the  rate  was  uniform, 
we  should  have  to  make  a  separate  observation  for  this 
portion  alone. 

But  as  soon  as  we  pass  from  an  ideal  frictionless  river  to 
an  actual  stream,  in  which  the  water  at  the  bottom  and  near 
the  banks  flows  more  slowly  than  that  in  the  middle  and  on 
the  surface,  we  are  in  every  case  restricted  to  the  notion  of 
mean  velocity.  We  may  distinguish  between  the  velocity  of 
different  parts  of  the  current,  between  that  of  the  mid-stream 
and  the  side  current,  the  bottom  and  the  surface  layers ;  but 
when  we  consider  the  river  as  a  whole,  we  take  cognizance 
only  of  the  mean  or  average  velocity.  And  at  any  cross- 
section  this  may  be  defined  as  the  volume  of  water  passing 
per  hour,  or  whatever  the  unit  of  time  may  be,  divided  by 
the  cross-section  of  the  current.  It  is  evident  that  this 
does  not  enable  us  to  determine  the  actual  velocity  of  any 
given  particle  of  the  water  at  any  given  moment  within  a 
measured  interval ;  nor  does  it  tell  us  whether  or  not  the 
average  velocity  of  the  current  has  itself  undergone  varia- 
tions within  the  period  of  observation. 

We  have  dwelt  upon  this  point  because  the  measurement 
of  the  velocity  of  the  blood,  to  which  we  must  now  turn, 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     107 

involves  the  same  considerations.  Within  the  smaller 
arteries,  as  the  microscope  shows  us,  and  as  we  should  in  any 
case  expect  from  what  we  know  of  fluid  motion,  the  blood- 
current,  apart  from  the  periodical  variations  in  its  velocity, 
due  to  the  action  of  the  heart,  varies  in  speed  from  point 
to  point  of  the  same  cross-section.  The  layer  next  the 
periphery  of  the  vessel,  the  so-called  peripheral  plasma- 
layer  or  Poiseuille's  space,  moves  more  slowly  than  the 
central  portion,  the  axial  stream.  In  fact,  we  must  suppose 
that  in  the  large  as  well  as  in  the  small  vessels  the  layer  just 
in  contact  with  the  vessel-wall  is  at  rest,  while  the  stratum 
internal  to  this  slides  on  it  and  has  its  velocity  diminished 
by  the  friction.  The  next  layer  again  slides  on  the  last,  but 
since  this  is  already  in  motion,  its  velocity  is  not  so  much 
diminished,  and  so  on.  The  velocity  must  therefore  in- 
crease as  we  pass  towards  the  axis  of  the  bloodvessel,  and 
reach  its  maximum  there  (p.  168). 

Again,  the  velocity  must  be  altered  wherever  an  alteration 
occurs  in  the  width  of  the  bed,  that  is,  in  the  total  cross- 
section  of  the  vascular  system  ;  for  since  as  much  blood 
comes  back  in  a  given  time  to  the  right  side  of  the  heart 
as  leaves  the  left  side,  the  same  quantity  must  pass  in  a 
given  time  through  every  cross-section  of  the  circulation. 
Wherever  the  total  section  of  the  vascular  tree  increases, 
the  blood-current  must  slacken  ;  wherever  it  diminishes,  the 
current  must  become  more  rapid.  Now  the  total  section 
increases  as  we  pass  from  the  heart  along  the  branching 
arteries,  and  reaches  its  maximum  in  the  capillary  region.  It 
gradually  diminishes  again  along  the  veins,  but  never  becomes 
so  small  as  in  the  arterial  tract.  We  must,  therefore,  expect 
the  mean  velocity  to  be  greatest  in  the  large  arteries,  less 
in  the  veins,  and  least  in  the  arterioles,  capillaries  and 
venules.  Although  in  strictness  we  are  only  at  present  con- 
cerned with  the  arteries,  it  will  be  well  to  consider  here  what 
a  change  of  velocity  at  any  part  of  the  vascular  channel  really 
implies.  To  say  that  wrhen  the  channel  widens  the  velocity 
diminishes,  is  not  to  explain  the  meaning  of  this  diminution. 
A  diminution  of  velocity  implies  a  diminution  of  kinetic 
energy,  and  it  is  necessary  to  know  what  becomes  of  the 


io8  A  MANUAL  OF  PHYSIOLOGY 

energy  that  disappears.  The  stock  of  energy  imparted  by 
the  contraction  of  the  heart  to  a  given  mass  of  blood  con- 
stantly diminishes  as  it  passes  round  from  the  aorta  to  the 
right  side  of  the  heart,  for  friction  is  constantly  being  over- 
come and  heat  generated.  This  energy,  as  we  have  seen, 
exists  in  a  moving  liquid  in  two  forms,  potential  and  kinetic, 
the  former  being  measured  by  the  lateral  pressure,  the  latter 
varying  directly  as  the  square  of  the  velocity.  Whenever 
the  velocity,  and  therefore  the  kinetic  energy,  of  a  given  mass 
of  the  blood  is  diminished  without  a  corresponding  increase 
in  the  potential  energy,  some  of  the  total  stock  of  energy 
must  have  been  used  up  to  overcome  resistance  (p.  73). 

In  a  uniform,  rigid,  horizontal  tube,  as  has  been  already  remarked, 
the  velocity  (and  consequently  the  kinetic  energy)  is  the  same  at 
every  cross-section  of  the  tube,  while  the  potential  energy,  represented 
by  the  lateral  pressure,  diminishes  regularly  along  the  tube.  When 
the  calibre  of  the  tube  varies,  it  is  different.  Suppose,  for  instance, 
that  the  liquid  passes  from  a  narrower  to  a  wider  part,  the  velocity 
must  diminish  in  the  latter.  The  kinetic  energy  of  visible  motion 
which  has  disappeared  must  have  left  something  in  its  room.  Here 
there  are  three  possibilities:  (i)  The  kinetic  energy  that  has  dis- 
appeared may  be  just  enough  to  overcome  the  extra  friction  in  the 
wider  part  of  the  tube  due  to  eddies  and  consequent  change  of 
direction  of  the  lines  of  flow ;  in  this  case  the  potential  energy  of  a 
given  mass  of  the  liquid  will  be  the  same  at  the  beginning  of  the 
wider  part  as  in  the  narrower  part.  The  lost  kinetic  energy  will 
have  been  transformed  into  heat.  (2)  The  kinetic  energy  which  has 
disappeared  may  be  greater  than  is  enough  to  overcome  the  extra 
resistance ;  a  portion  of  it  must,  therefore,  have  gone  to  increase  the 
potential  energy,  and  the  lateral  pressure  will  be  greater  in  the  wide 
than  in  the  narrow  part.  (3)  The  lost  kinetic  energy  may  be  less 
than  enough  to  overcome  the  extra  resistance ;  in  this  case  both  the 
lateral  pressure  and  the  velocity  will  be  less  in  the  wide  than  in  the 
narrow  part.  It  has  been  experimentally  shown  that  when  a  narrow 
portion  of  a  tube  is  succeeded  by  a  considerably  wider  portion, 
and  this  again  by  a  narrow  part,  case  (2)  holds  •  and  the  liquid  may, 
under  these  conditions,  actually  flow  from  a  place  of  lower  to  a  place 
of  higher  lateral  pressure. 

In  the  vascular  system  the  conditions  are  not  the  same. 
The  widening  of  the  bed  which  takes  place  as  we  proceed  in 
the  direction  of  the  arterial  current  is  not  due  to  the  widen- 
ing of  a  single  trunk,  but  to  the  branching  of  the  channel 
into  smaller  and  smaller  tubes.  In  the  larger  arteries  the 
increase  of  resistance  is  so  gradual  that  both  the  potential 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     109 

and  the  kinetic  energy  diminish  only  slowly,  and  the  lateral 
pressure  and  velocity  are  not  much  less  in  the  femoral  artery 
than  in  the  aorta  or  carotid.  But  in  the  capillary  region 
the  friction  increases  so  much  that  although  the  velocity, 
and  therefore  the  kinetic  energy,  is  greatly  less  than  in  the 
arteries,  the  amount  of  kinetic  energy  lost  is  not  upon  the 
whole  equivalent  to  the  energy  consumed  in  overcoming  the 
extra  resistance ;  the  potential  energy  of  the  blood  is  also 
drawn  upon,  and  the  lateral  pressure  falls  sharply  in  the  capil- 
lary region,  as  well  as  the  velocity.  Where  the  capillaries 
open  into  the  veins,  the  lateral  pressure  again  sinks  abruptly, 
while  the  velocity  begins  to  increase,  till  in  the  largest  veins 
it  is  probably  about  half  as  great  as  in  the  aorta. 

Where  does  the  extra  kinetic  energy  of  the  blood  in  the 
veins  come  from  ?  To  say  that  the  vascular  channel  again 
contracts  as  the  blood  passes  from  the  capillaries  into  the 
veins,  and  that,  since  the  same  quantity  must  flow  through 
every  cross-section  of  the  channel,  the  velocity  must  neces- 
sarily be  greater  in  the  narrower  than  in  the  wider  part,  does 
not  answer  the  question.  The  greater  portion  of  the  kinetic 
energy  of  the  arterial  blood  is,  as  we  have  seen,  destroyed, 
or,  rather,  changed  into  an  unavailable  form,  into  heat,  in 
the  capillary  region.  The  mean  velocity  of  the  blood  in  the 
capillaries  is  not  more  than  -^  to  o-^  of  the  velocity  in  the 
aorta ;  the  kinetic  energy  of  a  given  mass  of  blood  in  the 
capillaries  cannot  therefore  be  more  than  (ufo)2,  or  -^^-^  of 
its  kinetic  energy  in  the  aorta.  In  the  veins,  taking  the 
velocity  at  half  the  arterial  velocity,  the  kinetic  energy  of  the 
mass  would  be  one-fourth  of  that  in  the  aorta,  or  at  least 
10,000  times  as  great  as  in  the  capillary  region.  This  extra 
kinetic  energy  comes  partly  from  the  transformation  of  some 
of  the  potential  energy  of  the  blood.  The  resistance  in  the 
veins  is  very  small  compared  with  that  in  the  capillaries  ;  less 
of  the  potential  energy  represented  by  the  lateral  pressure 
at  the  end  of  the  capillary  tract  is  required  to  overcome  this 
resistance,  and  some  of  it  is  converted  into  the  kinetic 
energy  of  visible  motion,  the  lateral  pressure  at  the  same 
time  falling  somewhat  abruptly.  Contributory  sources  of 
kinetic  energy  in  the  veins  are  the  aspiration  caused  by  the 


10 


A  MANUAL  OF  PHYSIOLOGY 


respiratory  movements  and  the  pressure  caused  by  muscular 
contraction  in  general,  which,  thanks  to  the  valves,  always 
aids  the  flow  towards  the  heart.  From  these  two  sources 

new  energy  is  supplied,  to  rein- 
force the  remnant  due  to  the 
cardiac  systole  (p.  121). 

Measurement    of   the    Velocity   of 
the  Blood.  —  i.   Direct  Observation. — 

(a)  This  method  can   be   applied   to 
transparent  parts  by  observing  the  rate 
of   flow  of  the  corpuscles   under  the 
microscope.     But  it  is  only  where  the 
blood  moves  slowly,  as  in  the  capil- 
laries,   that    the   method    is    of    use. 

(b)  Part   of    the   path   of    the   blood 
through    a   large  vessel    may  be   arti- 
ficially  rendered    transparent   by   the 
introduction  of  a   glass    tube,   of  ap- 
proximately the  same  bore  as  the  vessel 
(Volkmann).     The  tube  is  filled  with 
salt  solution,  and  the  blood  admitted 
by  means  of  a  stop-cock  at  the  moment 

FIG.  31.— STROMUHR  OF  LUD-  of  observation.     The  time  which  the 

WIG  AND  DOGIEL.  blood  takes  to  pass  from  one  end  of 

A,  B,  glass  bulbs ;  a,  a  metal  disc,  the  tube  to  the  other  is  noted,  and  the 

'SJ^S^ffS&ffi  len§th  divided  by  th<=  time  g^es  the 

E,   F,  cannulse  attached  to  b,  and    velocity  of  the  blood   in   the  tube.       If 

connected  with  the  peripheral  and  the  calibre  of  the  tube  is  the  same  as 

central  ends  of  a  divided  bloodvessel.    ,,  ,      .  ,  .       .         .  , 

At  the  beginning  of  the  experiment,  that  of  the  artery,  this  is  also  the 
A  and  the  junction  between  A  and  B  velocity  in  the  vessel ;  but  if  the  calibre 
are  filled  with  oil  ;B  is  filled  with  -  different,  a  correction  would  have 

normal  saline  or  dehbnnated  blood  :  J  . 

a    being   turned    into  the  position    to    DC    made.       1  ne   method    IS    not    a 

shown  in  the  figure,  the  blood  passes  good  one,  for  the  reason,  among  others, 
?S£fS?l*£'£?S'&  that  the  long  tube  introduces  an  extra 

blood  has  reached  the  mark  m,  the  resistance. 

disc  a,  with  the  bulbs,  is  rapidly        2>  Ludwigs  Stromuhr.—TKis  instru- 

S'^eWcod'now^resTn^a  ™ent  measures  the  quantity  of  blood 

and  the  oil  is  again  driven  into  A.  which  passes  in  a  given  time  through 

When  the  oil  has-reachedD,  reversal  the  vessd  at  the  cross-section  where  it 
i.  agam  made,  and  so  on.  .g  .^^  ^  ^.^  Qf  ^  ^^ 

tube,  with    the    limbs   widened    into 

bulbs,  but  narrow  at  the  free  ends,  which  are  connected  with  a 
metal  disc.  By  rotating  the  instrument,  these  ends  can  be  placed 
alternately  in  communication  with  a  cannula  in  the  central,  and 
another  in  the  peripheral  portion  of  a  divided  artery ;  or  they  can 
be  placed  so  that  none  of  the  blood  passes  through  the  bulbs, 
but  all  goes  by  a  short-cut.  One  limb  of  the  instrument  is 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    in 

filled  with  oil,  and  the  other  with  defibrinated  blood.  The  limb  con- 
taining the  oil  is  first  put  into  communication  with  the  central  end, 
and  that  containing  the  blood  with  the  peripheral  end  of  the  artery. 
The  blood  from  the  artery  rushes  in  and  displaces  the  oil  into  the 
other  limb,  the  defibrinated  blood  passing  on  into  the  circulation.  As 
soon  as  the  blood  has  reached  a  certain  height,  indicated  by  a  mark, 
the  instrument  is  reversed,  and  the  oil  is  again  displaced  into  the 
limb  it  originally  occupied.  This  process  is  repeated  again  and  again, 
the  time  from  beginning  to  end  of  an  experiment  being  carefully 
noted.  The  number  of  times  the  blood  has  filled  a  bulb  in  that 
period,  the  capacity  of  the  bulb  and  the  cross-section  of  the  vessel 
being  known,  all  the  data  required  for  calculating  the  velocity  of  the 
blood  in  the  vessel  have  been  obtained. 

Suppose,  for  example,  that  the  capacity  of  the  bulb  up  to  the  mark 
is  5  c.c.,  and  that  it  is  filled  twelve  times  in  a  minute,  the  quantity 
flowing  through  the  cross-section  of  the  artery  is  i  c.c.,  or  1,000  cub. 
mm.  per  second.  Let  the  diameter  of  the  vessel  be  3  mm.,  then  its 

sectional  area  is  ?r  x  (-)  =  J_        _?  =  7-05  ^  mm      The  velocity  is 

IOOO  i 

—  =  141  mm.  per  second 
7'oo 

Various  improvements  in  this  method  have  been  made,  such  as 
graphic  registration  of  the  reversals  of  the  stromuhr. 

3.  A  tube  or  box,  in  which  swings  a  small  pendulum,  is  inserted 
in  the  course  of  the  vessel.     The  pendulum  is  deflected  by  the  blood, 
and  the  amount  of  the  deflection  bears  a  relation  to  the  velocity 
of  the  stream  (Vierordt's  hcematachometer ;  Chauveau  and  Lortet's 
much  more  perfect  dronwgrapli)  (Fig.  33). 

4.  Pitofs  Tubes. — If  two  vertical   tubes,  a  and  b,  of  the  form 
shown  in  Fig.  32,  be  inserted  into  a  horizontal  tube  in  which  liquid 
is  flowing  in  the  direction  of  the  arrow,  the  level  will  be  higher  in  a 
than  would  be  the  case  in  an  ordinary  side-tube  without  an  elbow ; 
in  b  it  will  be  lower.     For  the  moving  liquid  will  exert  a  push  on  the 
column  in  a,  and  a  pull  on  that  in  b.     The  amount  of  this  push  and 
pull  will  vary  with  the  velocity,  so  that  a  change  in  the  latter  will 
correspond  to  an  alteration  in  the  difference  of  level  in  the  two  tubes. 
Instruments  on  this  principle  have  been  constructed  by  Marey  and 
Cybulski,  the  former  registering  the  movements  of  the  two  columns 
of  blood  by  connecting  the  tubes  to  tambours  provided  with  writing 
levers,  the  latter  by  photography  (Fig.  36). 

5.  The  electrical  method,  described  on  p.  123,  for  the  measurement 
of  the  circulation  time,  can  also  be  applied  to  the  estimation  of  the 
mean  velocity  of  the  blood  between  two  cross-sections  of  the  arterial 
path  which  are  separated  by  a  sufficient  distance.     For  example,  salt 
solution  can  be  injected  into  the  left  ventricle  or  the  beginning  of 
the  aorta,  and  the  interval  which  it  takes  to  reach  a  pair  of  electrodes 
in  contact  with,  say,  the  femoral  artery,  determined.     Knowing  the 
distance  between  the  point  of  injection  and  the  electrodes,  we  can 
then  calculate  the  mean  velocity. 


112 


A  MANUAL  OF  PHYSIOLOGY 


FIG.  32.— riTOT's  TUBES. 


Of  these  methods,  3  and  4  are  alone  suited  for  the  study 
of  thevelocity  -pulse,  that  is,  the  change  of  velocity  occurring 

with  every  beat  of  the  heart. 
The  curves  obtained  by 
Chauveau'sdromograph  show 
a  general  agreement  with 
blood-pressure  tracings  taken 
by  a  spring  manometer,  and 
with  records  of  the  external 
pulse  obtained  by  a  sphygmo- 
graph.  There  is  a  primary  in- 
crease of  velocity  correspond- 
ing with  the  ventricular  systole,  and  a  secondary  increase 
corresponding  with  the  dicrotic  wave  (Fig.  37).  Like  all 

the  other  pulsatory  phenomena, 
the  velocity-pulse  disappears  in 
the  capillaries,  and  is  only 
present  under  exceptional  cir- 
cumstances in  the  veins. 

Fick,  from  a  comparison  of 
sphygmographic  and  plethys- 
mographic  tracings  (p.  116), 
taken  simultaneously  from  the 
radial  artery  and  the  hand,  has 
demonstrated  that  in  man  the 
velocity-pulse  exhibits  the  same 
general  characters  as  in  animals 
(Figs.  34  and  35).  And  v.  Kries 
has  confirmed  Fick's  conclu- 
sions by  actual  records  of  the 
velocity-pulse  obtained  by  means 
of  an  arrangement  called  a  gas 

hole  in  the  centre, 'which  is  covered  by  tachograph   (Fig".  ^8) 

a  membrane,  m,  through  which  a  lever,  L            .                \     *o"  J   /• 

C,  passes  ;  C  has  a  small  disc  p,  at  its  ThlS  Consists  of  a  plethysmo- 

end,  which  projects  into  the  lumen  of  .                            j        •   i_       i 

A,  and  is  deflected  in  the  direction  of  graph  Connected  With    the   tube 

of  a  gas-burner.  When  the 
part  enclosed  in  the  plethys- 
mograph  expands,  air  issues 
from  the  connecting  tube,  and 


FIG. 


DROMO- 


33.  — CHAUVEAU'S 

GRAPH. 
A,  tube  connected  with  bloodvessel 


the  blood-stream  through  A.  The  de- 
flection is  registered  by  a  recording 
tambour  in  communication  by  the  tube 
E  with  a  tambour  D.  the  flexible 
membrane  of  which  is  connected  with 
the  lever  or  pendulum  C. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    113 

causes  an  increase  in  the  height  of  the  flame.  When  the 
part  shrinks  during  diastole,  air  is  drawn  in  from  the  flame, 
which  is  depressed.  Since  the  speed  of  the  blood  in  the 


FIG.  34.  FIG.  35. 

FIG.  34.— The  highest  of  the  three  curves  is  a  plethysmographic  record  taken  from 
the  hand  ;  the  second  curve  is  a  sphygmogram  taken  simultaneously  from  the  corre- 
sponding radial  artery  ;  the  lowest  (interrupted)  curve  is  the  curve  of  velocity  deduced 
from  a  comparison  of  the  first  two.  (Pick. 

FIG.  35.— Simultaneous  plethysmographic  and  sphygmographic  tracings. 


FIG.  36.— CYBULSKI'S  ARRANGEMENT  FOR  RECORDING  VARIATIONS  IN  THE 

VELOCITY  OF  THE  BLOOD. 

A,  tube  connected  with  central,  B  with  peripheral  end  of  divided  bloodvessel.  The 
blood  stands  higher  in  the  tube  C  than  in  D.  A  beam  of  light  passing  through  the 
meniscus  in  both  tubes  is  focussed  by  the  lens  L  on  the  travelling  photographic 
plate  E.  The  velocity  at  any  moment  is  deduced  from  the  height  of  the  meniscus  in 
the  two  tubes  C  and  D. 

veins  may  be  considered  constant  during  the  time  of  an 
experiment,  the  rate  at  which  the  volume  of  the  part  alters 

8 


ii4  A  MANUAL  OF  PHYSIOLOGY 

at  any  moment  is  a  measure  of  the  pulsatory  change  of 
velocity  in  the  arteries  of  the  part.  And  by  photographing 
the  movements  of  the  flame  on  a  travelling  sensitive  surface, 
the  velocity-pulse  is  directly  recorded. 


FIG.  37.— SIMULTANEOUS  TRACINGS  OF  THE  VELOCITY  (UPPER  CURVE)  AND 
PRESSURE  (LOWER  CURVE).     (LORTET.) 

The  tracings  were  taken  from  the  carotid  artery  of  a  horse.  The  curve  of  velocity 
was  obtained  by  the  dromograph.  The  dicrotic  wave  is  marked  on  it.  The  slightly 
curved  ordinates  drawn  through  the  curves  indicate  corresponding  points. 

The  mean  velocity,  like  the  mean  blood-pressure,  is  more 
variable  in  the  large  arteries  near  the  heart  than  in  the 
smaller  and  more  distant  arteries.  Dogiel  found  in  measure- 
ments taken  with  the  stromuhr  (a  good  instrument  for  the 


FIG.  38. — PHOTOGRAPHIC  RECORD  OF  THE  VELOCITY-PULSE  OBTAINED  BY  THE 
GAS  TACHOGRAPH  (v.  KRIES). 

The  upper  curve  is  the  photographic  representation  of  the  movements  of  the  flame, 
and  corresponds  to  the  curve  of  velocity. 

estimation  of  mean  speed),  within  a  period  of  two  minutes, 
velocities  ranging  from  over  200  mm.  to  under  100  mm.  per 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH 


second  in  the  carotid  of  the  rabbit,  and  from  over  500  mm. 
to  less  than  250  mm.  in  the  carotid  of  the  dog.  Chauveau, 
with  the  dromograph,  found  the  velocity  in  the  carotid  of  a 
horse  to  be  520  mm.  per  second  during  systole,  150  mm. 
during  diastole,  220  mm.  during  the  period  of  the  dicrotic 
wave. 

It  is  probable,  however,  that  if  these  numbers  are  at  all 
accurate  for  bloodvessels  in  the  immediate  neighbourhood 
of  the  heart,  there  must  be  a  rapid  diminution  in  the 
velocity  even  while  the  arteries  are  still  of  considerable 
calibre.  For  it  has  been  found  by  the  electrical  method 
that,  in  anaesthetized  dogs  at  any  rate,  as  is  shown  in  the 
following  table,  the  mean  velocity  between  the  origin  of  the 
aorta  and  the  crural  artery  in  the  middle  of  the  thigh  is 
usually  less  than  100  mm.  per  second. 


No.  of 
experi- 
ment- 

Body- 
weight 
in  kilos. 

Distance  between 
point  of  injection 
and  electrodes, 
in  millimetres. 

Average  time  be- 
tween injection 
and  arrival  of  the 
salt  solution, 
in  seconds. 

Average 
pulse-rate 
per  minute. 

Average 
velocity 
per  second, 
in  milli- 
metres. 

Average 
distance 
traversed  per 
heart-beat, 
in  mm. 

I. 

34-55 

420 

4*62 

105 

90-9 

5I-9 

II. 

I7-5 

495 

57 

69 

86-8 

75'4 

III. 

14-99 

400 

5-0 

102 

80 

47     i 

IV. 

10-32 

470 

7-12 

74'5 

72-9 

58-7 

V. 

7-165 

330 

7*83 

46-3 

42T 

54'5 

(weak  beat) 

In  I.  the  injecting  cannula  was  in  the  descending  part  of  the 
thoracic  aorta,  in  V.  at  the  very  origin  of  the  aorta,  and  in  II.,  III. 
.and  IV.  in  the  left  ventricle. 


As  to  the  speed  of  the  blood  in  the  arteries  of  man, 
data  are  insufficient  for  more  than  a  loose  estimate.     But  it 
does  not  seem  likely  that  the  mean  velocity  of  a  particle  of  ,-  A/J 
blood  in  moving  from  the  heart  to  the  femoral  artery  can  ! 
exceed  150  mm.  per  second  for  the  whole  of  its  path.     This  G5^tVt4A-u 
would  correspond  to  rather  more  than  a  third  of  a  mile  per 
hour.     In  the  arch  of  the  aorta  the  average  speed  may  be 
twice  as  great.     *  The  rivers  of  the  blood  '  are,  even  at  their 
fastest,  no   more   rapid   than   a   sluggish    stream.      A   red 
corpuscle,  even  if  it  continued  to  move  with  the  velocity 
Avith  which  it  set  out  through  the  aorta,  would  only  cover 

8—2 


Ii6  A  MANUAL  OF  PHYSIOLOGY 

about  15  miles  in  twenty-four  hours,  and  would  require  five 
years  to  go  round  the  world. 

The  Volume-pulse. — When  the  pulse-wave  reaches  a  part  it 
distends  its  arteries,  increases  its  volume,  and  gives  rise 
to  what  may  be  called  the  volume-pulse.  This  may  be 
readily  recorded  by  means  of  a  plethysmograph,  an  instru- 
ment consisting  essentially  of  a  chamber  with  rigid  walls 
which  enclose  the  organ,  the  intervening  space  being  filled 
up  with  liquid  (Fig.  39).  The  movements  of  the  liquid  are 
transmitted  either  through  a  tube  filled  with  air  to  a  record- 
ing tambour,  or  directly  to  a  piston  or  float  acting  upon  a 
writing  lever.  Special  names  have  been  given  to  plethys- 


FIG.  39. — PLETHYSMOGRAPH  FOR  ARM. 

F,  float  attached  by  A  to  a  lever  which  records  variations  of  level  of  the  water  in  B, 
and  therefore  variations  in  the  volume  of  the  arm  in  the  glass  vessel  C.  Or  the 
plethysmograph  may  be  connected  to  a  recording  tambour.  The  tubulure  at  the 
upper  part  of  C  is  closed  when  the  tracing  is  being  taken. 

mographs  adapted  to  particular  organs  ;  for  example,  Roy's 
oncometer  for  the  kidney.  The  method  has  been  successfully 
applied  to  the  investigation  of  circulatory  changes  in  man, 
a  finger,  a  hand  or  an  entire  limb  being  enclosed  in  the 
plethysmograph.  With  a  fairly  sensitive  arrangement,  every 
beat  of  the  heart  is  represented  on  the  tracing  by  a  primary 
elevation  and  a  dicrotic  wave.  The  general  appearance  of 
the  curve  is  very  similar  to  that  of  an  ordinary  pulse-tracing, 
though  there  are  some  differences  of  detail,  especially  in 
the  time  relations.  A  volume-pulse  has  been  actually  ob- 
served not  only  in  limbs  and  portions  of  limbs,  but  also  (in 
animals)  in  the  spleen,  kidney  and  brain,  and  other  organs,' 
and  in  the  orbit.  In  the  soft  tissues  of  the  mouth  and 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    117 

pharynx,  too,  a  volume-pulse  (the  so-called  cardio-pneumatic 
movement)  can  be  detected  by  changes  in  the  pressure  of 
the  air  in  the  respiratory  passages,  which  may  even  reveal 
themselves  by  a  variation  with  each  beat  of  the  heart  in  the 
intensity  of  a  note  prolonged  in  singing,  especially  after 
fatigue  has  set  in  (Practical  Exercises,  p.  183). 

Doubtless  the  weight  of  an  organ  would  also  show  a  pulse  cor- 
responding  to  the  beat  of  the  heart,  if  it  could  be  isolated  from  the 
surrounding  tissues  (except  for  its  vascular  connections),  and  attached 
to  a  recording  balance,  as  could  probably  be  done  with  a  kidney. 

Further,  it  is  possible  that  the  temperature,  at  least  of  the  super- 
ficial parts,  is  altered  with  every  beat  of  the  heart.  For  the  amount 
of  heat  given  off  by  the  blood  to  the  skin  increases  with  its  mean 
velocity,  and,  therefore,  although  the  difference  may  not  in  general 
be  measureable,  more  heat  is  presumably  given  off  during  the 


FIG.  40. — PLETHYSMOGRAPH  TRACING  FROM  ARM. 

The  tracing  was  taken  by  means  of  a  tambour  connected  with  the  plethysmograph. 
The  dicrotic  wave  is  distinctly  marked. 

systolic  increase  of  velocity  than  during  the  diastolic  slackening. 
In  fact,  with  a  very  sensitive  instrument  (bolometer,  or  resistance 
thermometer,  p.  479)  applied  directly  to  an  exposed  artery,  indi- 
cations of  a  change  of  temperature  of  the  vessel-wall  with  each 
beat  of  the  heart  have  been  observed.  And  this,  along  with  other 
considerations,  suggests  that,  at  any  rate  in  certain  situations  and 
under  certain  conditions,  there  may  even  be  a  pulse  of  chemical 
change  ;  that  is,  a  slight  and  as  yet  doubtless  inappreciable  ebb  and 
flow  of  metabolism  corresponding  to  the  rhythm  of  the  heart. 

The  Circulation  in  the  Capillaries. — From  the  arteries  the 
blood  passes  into  a  network  of  narrow  and  thin-walled 
vessels,  the  capillaries,  which  in  their  turn  are  connected 
with  the  finest  rootlets  of  the  veins.  Physiologically,  the 
arterioles  and  venules  must  for  many  purposes  be  included 
in  the  capillary  tract,  but  the  great  anatomical  difference — 


Ii8  A  MANUAL  OF  PHYSIOLOGY 

the  presence  of  circularly-arranged  muscular  fibres  in  the 
arterioles,  their  absence  in  the  capillaries — has  its  physio- 
logical correlative.  The  calibre  of  the  arterioles  can  be 
altered  by  contraction  of  these  fibres  under  nervous  in- 
fluences ;  the  calibre  of  the  capillaries,  although  it  varies 
passively  with  the  blood-pressure,  and  is  possibly  to  some 
extent  affected  by  active  contraction  of  the  endothelial  cells, 
cannot  be  under  the  control  of  vaso-motor  nerves  acting  on 
muscular  fibres. 

Harvey  had  deduced  from  his  observations  the  existence 
of  channels  between  the  arteries  and  the  veins.  Malpighi 
was  the  first  to  observe  the  capillary  blood-stream  with  the 


FIG.  41. — DIAGRAM  TO  ILLUSTRATE  THE  SLOPE  OF  PRESSURE  ALONG 
THE  VASCULAR  SYSTEM. 

A,  arterial ;  C,  capillary  ;  V,  venous  tract.  The  interrupted  line  represents  the  line 
of  mean  pressure  in  the  arteries,  the  wavy  line  indicating  that  the  pressure  varies  with 
each  heart-beat.  The  line  passes  below  the  abscissa  axis  (line  of  zero  or  atmospheric 
pressure)  in  the  veins,  indicating  that  at  the  end  of  the  venous  system  the  pressure 
becomes  negative. 

microscope,  and  thus  to  give  ocular  demonstration  of  the 
truth  of  Harvey's  brilliant  reasoning.  He  used  the  lungs, 
mesentery  and  bladder  of  the  frog.  The  web  of  the  frog, 
the  tail  of  the  tadpole,  the  wing  of  the  bat,  the  mesentery  of 
the  rabbit  and  rat,  and  other  transparent  parts,  have  also 
been  frequently  employed  for  such  investigations.  From 
the  apparent  velocity  of  the  corpuscles  and  the  degree  of 
magnification,  it  is  easy  to  calculate  the  velocity  of  the 
capillary  blood-stream.  It  has  been  estimated  at  from 
•2  to  '8  mm.  per  second  in  different  parts  and  different 
animals. 

The   comparative  slowness  of  the  current  and   the   dis 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    119 

appearance  of  the  pulse  are  the  chief  characteristics  of 
the  capillary  circulation.  The  explanation  we  have  already 
found  in  the  great  resistance  of  the  narrow  and  much- 
branched  vessels.  Although  the  average  diameter  of  a 
capillary  is  only  about  10  /-i  (5  to  20  //,  in  different  parts  of 
the  body),  the  number  of  branches  is  so  prodigious  that  the 
total  cross-section  of  the  systemic  capillary  tract  has  been 
estimated  at  500  to  700  times  that  of  the  aorta. 

The  total  cross-section  of  the  vascular  channel  gradually 
widens  as  it  passes  away  from  the  left  ventricle.  In  the 
capillary  region  it  undergoes  a  great  and  sudden  increase. 
At  the  venous  end  of  this  region  the  cross-section  is  again 
somewhat  abruptly  contracted,  and  then  gradually  lessens  as 
the  right  side  of  the  heart  is  approached ;  but  the  united 
sectional  area  of  the  large  thoracic  veins  is  greater  than  that 
of  the  aorta. 

The  blood-pressure  in  the  capillaries  has  been  measured  by 
weighting  a  small  plate  of  glass  laid  on  the  back  of  one  of  the 
fingers  behind  the  nail,  until  the  capillaries  are  just  emptied,  as 
shown  by  the  paling  of  the  skin  (v.  Kries),  or  by  observing  the 
height  of  a  column  of  liquid  that  just  stops  the  circulation  in  a 
transparent  part  (Roy  and  Graham  Brown).  The  last-named 
observers  found  that  a  pressure  of  100  to  150  mm.  of  water  (about 
7  to  1 1  mm.  of  Hg)  was  needed  to  bring  the  blood  to  a  standstill  in 
the  capillaries  and  veins  of  the  frog's  web  ;  that  is,  about  a  third  of 
the  blood-pressure  in  the  frog's  aorta.  The  pressure  in  the  capil- 
laries at  the  root  of  the  nail  in  man  varies  from  30  to  50  mm.  of 
mercury. 

Under  certain  conditions  the  pulse-wave  may  pass  into 
the  capillaries  and  appear  beyond  them  as  a  venous  pulse. 
Thus,  we  shall  see  that  when  the  small  arteries  of  the 
submaxillary  gland  are  widened,  and  the  vascular  resistance 
lessened,  by  the  stimulation  of  the  chorda  tympani  nerve, 
the  pulse  passes  through  to  the  veins.  And,  normally,  a 
pulse  may  be  seen  in  the  wide  capillaries  of  the  nail-bed 
— especially  when  they  are  partially  emptied  by  pressure- 
as  a  flicker  of  pink  that  comes  and  goes  with  every  beat  of 
the  heart. 

We  have  seen  that  the  lateral  pressure  at  any  point  of  a      <t/£C_ 
uniform  rigid  tube  through  which  water  is  flowing  is  propor- 
tional to  the  amount  of  resistance  in  the  portion  of  the  tube 


120  A  MANUAL  OF  PHYSIOLOGY 

between  this  point  and  the  outlet.  In  any  system  of  tubes 
the  sum  of  the  potential  and  kinetic  energy  must  diminish 
in  the  direction  of  the  flow ;  and  although  the  problem  is 
complicated  in  the  vascular  system  by  the  branching  of  the 
channel  and  the  variation  in  the  total  cross-section,  yet 
theory  and  experiment  agree  that  in  the  larger  arteries  the 
lateral  pressure  diminishes  but  slowly  from  the  heart  to 
the  periphery,  the  resistance  being  small  compared  with  the 
resistance  of  the  whole  circuit  In  the  capillary  region  the 
vascular  resistance  abruptly  increases ;  the  velocity  (and 
therefore  the  kinetic  energy)  abruptly  diminishes,  and  the 


FIG.   42. — RELATION  OF  BLOOD-PRESSURE,  VELOCITY,  AND  CROSS-SECTION. 

The  curves  P,  V  and  S  represent  the  blood-pressure,  velocity  of  blood,  and  total 
cross-section  respectively  in  the  arteries  A,  capillaries  C,  and  veins  V. 

lateral  pressure  falls  much  more  steeply  between  the  begin- 
ning and  the  end  of  this  region  than  between  the  heart  and 
its  commencement.  In  the  veins  only  a  small  remnant  of 
resistance  remains  to  be  overcome,  and  the  lateral  pressure 
must  sink  again  rather  suddenly  about  the  end  of  the  capil- 
lary tract.  Fig.  42  shows  by  a  rough  diagram  the  manner 
in  which  the  pressure,  velocity  and  cross-section  probably 
change  from  part  to  part  of  the  vascular  system. 

The  Circulation  in  the  Veins. — The  slope  of  pressure,  as  we 
have  just  explained,  must  fall  rather  suddenly  near  the 
beginning  and  near  the  end  of  the  capillary  tract.  It  con- 
tinues falling  as  we  pass  along  the  veins,  till  the  heart  is 
again  reached.  In  the  right  heart,  and  in  the  thoracic 
portions  of  the  great  veins  which  enter  it,  the  pressure  may 
be  negative — that  is,  less  than  the  atmospheric  pressure. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    121 

And  since  nowhere  in  the  venous  system  is  the  pressure 
more  than  a  small  fraction  of  that  in  the  arteries,  its 
measurement  in  the  veins  is  correspondingly  difficult,  because 
any  obstruction  to  the  normal  flow  is  apt  to  artificially  raise 
the  pressure.  A  manometer  containing  some  lighter  liquid 
than  mercury,  such  as  water  or  a  solution  of  magnesium 
sulphate,  is  usually  employed,  in  order  that  the  difference  of 
level  may  be  as  great  as  possible.  In  the  sheep  the  pressure 
was  found  to  be  3  mm.  of  mercury  in  the  brachial,  and 
about  ii  mm.  in  the  crural  vein;  in  the  dog's  portal  vein 
about  10  mm. 

The  venous  pressure  being  so  low,  or,  in  other  words,  the  potential 
energy  which  the  systole  of  the  heart  imparts  to  the  blood  being  so 
greatly  exhausted  before  it  reaches  the  veins,  other  influences  begin 
here  appreciably  to  affect  the  blood- stream  : 

1.  Contraction  of  the  Muscles. — This  compresses  the  neighbouring 
veins,  and  since  the  blood  is  compelled  by  the  valves,  it  it  moves 
at  all,  to  move  towards  the  heart,  the  venous  circulation  is  in  this 
way  helped. 

2.  Aspiration   of  the  Thorax. — In    inspiration    the   intrathoracic 
pressure,  and  therefore  the  pressure  in  the  great  thoracic  veins,  is 
diminished,  and  blood  is  drawn  from  the  more  peripheral  parts  of  the 
venous  system  into  the  right  heart  (p.  250). 

3.  Aspiration  of  the  Heart. — When  the  heart,  after  its  contraction, 
suddenly  relaxes,  the  endocardiac  pressure  becomes  negative,  and 
blood   is  sucked  into  it,  just   as  when  the  indiarubber  ball  of  a 
syringe  is  compressed  and  then  allowed  to  expand.     But  we  cannot 
attribute  any  great  importance  to  this ;  and,  of  course,  it  is  only  the 
relaxation  of  the  right  ventricle  which  could  directly  affect  the  venous 
circulation. 

4.  Every  change  of  position  of  the   limbs,  as  in   walking,  aids 
the   venous   circulation  (Braune),  and   this   independently   of   the 
muscular  contraction.     When  the  thigh  of  a  dead  body  is  rotated 
outwards,  and  at  the  same  time  extended,  a  manometer  connected 
with  the  femoral  vein  shows  a  negative  pressure  of  5  to  10  mm.  of 
water.     When    the   opposite   movements   are   made,    the  pressure 
becomes  positive. 

It  follows  from  the  number  of  casually-acting  influences  O.  ~ 
which  affect  the  blood-flow  in  the  veins  that  it  cannot  be 
very  regular  or  constant.  We  have  seen  that  in  the  great 
arteries  there  is  a  considerable  variation  of  velocity  and  of 
pressure  with  every  beat  of  the  heart ;  and  although  this 
variation  is  absent  from  the  veins,  since  normally  the  pulse 
does  not  penetrate  into  them,  the  venous  flow  is,  never- 


122  A  MANUAL  OF  PHYSIOLOGY 

theless,  as  a  matter  of  fact,  more  irregular  than  the  arterial. 
So  that  if  it  is  difficult  to  give  a  useful  definition  of  the 
term  *  velocity  of  the  blood  '  in  the  case  of  the  arteries, 
it  is  still  more  difficult  to  do  so  in  the  case  of  the  veins. 
Where  voluntary  movement  is  prevented,  one  potent  cause 
of  variation  in  the  venous  flow  is  eliminated  ;  and  in 
curarized  animals  certain  observers  have  found  but  little 
difference  between  the  mean  velocity  in  the  veins  and  in  the 
corresponding  arteries.  Others  have  found  the  velocity  in 
the  veins  considerably  less,  which  is  indeed  what  we  should 
expect  from  the  fact  that  the  average  cross-section  of  the 
venous  system  is  greater  than  that  of  the  arterial  system. 

To  sum  up,  we  may  conclude  that,  upon  the  whole,  the 
blood  passes  with  gradually-diminishing  velocity  from  the 
left  ventricle  along  the  arteries  ;  it  is  greatly  and  somewhat 
suddenly  slowed  in  the  broad  and  branching  capillary  bed  ; 
but  the  stream  gathers  force  again  as  it  becomes  more  and 
more  narrowed  in  the  venous  channel,  although  it  never 
acquires  the  speed  which  it  has  in  the  aorta. 

To  complete  the  account  of  the  circulation  in  the  veins,  it 
must  be  added  that  in  some  healthy  persons,  but  more  fre- 
quently and  more  distinctly  in  cases  of  incompetence  of  the 
tricuspid  valve,  a  venous  pulse  may  be  seen  in  the  jugular 
vein  ;  but  this  pulse  travels  from  the  heart  against  the  blood- 
stream, not  with  it. 

The  Circulation-time. — Hering  was  the  first  who  attempted 
to  measure  the  time  required  by  the  blood,  or  by  a  blood- 
corpuscle,  to  complete  the  circuit  of  the  vascular  system. 
He  injected  a  solution  of  potassium  ferrocyanide  into  a  vein 
(generally  the  jugular),  and  collected  blood  at  intervals  from 
the  corresponding  vein  of  the  opposite  side.  After  the 
blood  had  clotted,  he  tested  for  the  ferrocyanide  by  addition 
of  ferric  chloride  to  the  serum.  The  first  of  the  samples 
that  gave  the  Prussian  blue  reaction  corresponded  to  the 
time  when  the  injected  salt  had  just  completed  the  circula- 
tion. 

Q  This  method  was  improved  by  Vierordt,  who  arranged  a  number 

of  cups  on  a  revolving  disc  below  the  vein  from  which  the  blood  was 
to  be  taken.  In  these  cups  samples  of  the  blood  were  received, 
and  the  rate  of  rotation  of  the  disc  being  known,  it  was  possible  to 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    123 

measure  the  interval  between  the  injection  and  appearance  of  the 
salt  with  considerable  accuracy.  Hermann  made  a  further  advance 
by  allowing  the  blood  to  play  upon  a  revolving  drum  covered  with  a 
paper  soaked  in  ferric  chloride,  and  by  using  the  less  poisonous 
sodium  ferrocyanide  for  injection. 

Even  as  thus  modified,  the  method  laboured  under  serious  defects. 
It  was  not  possible  to  make  more  than  a  single  observation  on  one 
animal,  at  least  without  allowing  a  considerable  interval  for  the 
elimination  of  the  ferrocyanide,  and,  further,  the  method  was  unsuited 
for  the  estimation  of  the  circulation  time  in  individual  organs.  In 
both  of  these  respects  the  more  recently  introduced  electrical  method 
presents  considerable  advantages  ;  for  by  its  aid  we  can  not  only 
obtain  satisfactory  measurements  of  the  circulation  time  in  such 
organs  as  the  lungs,  liver,  kidney,  etc.,  but  we  can  repeat  them  an 
indefinite  number  of  times  on  the  same  animal. 

A  cannula,  connected  with  a  burette  (or  a  Mariotte's  bottle,  or  a 
syringe),  containing  a  solution  of  sodium  chloride  (usually  a  1*5  to 
2  per  cent,  solution),  is  tied  into  a  vessel — say,  the  jugular  vein. 
Suppose  that  the  time  of  the  circulation  from  the  jugular  to  the 
carotid  is  required — that  is,  practically  the  time  of  the  lesser  or 
pulmonary  circulation.  A  small  portion  of  one  carotid  artery  is 
isolated,  and  laid  on  a  pair  of  hook-shaped  platinum  electrodes,* 
covered,  except  on  the  concave  side  of  the  hook,  with  a  layer  of 
insulating  varnish.  To  further  secure  insulation,  a  bit  of  very  thin 
sheet-indiarubber  is  slipped  between  the  artery  and  the  tissues. 
By  means  of  the  electrodes  the  piece  of  artery  lying  between  them, 
with  the  blood  that  flows  in  it,  is  connected  up  as  one  of  the  /* 
resistances  in  a  Wheatstone's  bridge  (p.  519).  The  secondary  coil 
of  a  small  inductorium,  arranged  for  giving  an  interrupted  current, 
and  with  a  single  Daniell  cell  in  its  primary,  is  substituted 
for  the  battery,  and  a  telephone  for  the  galvanometer,  according  to  „ 
Kohlrausch's  well-known  method  for  the  measurement  of  the  re- 
sistance of  electrolytes.  It  is  well  to  have  the  induction  machine 
set  up  in  a  separate  room  and  connected  to  the  resistance-box  by 
long  wires  so  that  the  noise  of  the  Neefs  hammer  may  be  inaudible. 
The  bridge  is  balanced  by  adjusting  the  resistances  until  the  sound 
heard  in  the  telephone  is  at  its  minimum  intensity,  the  secondary  coil 
being  placed  at  such  a  distance  from  the  primary  that  there  is  no 
sign  of  stimulation  of  muscles  or  nerves  in  the  neighbourhood  of 
the  electrodes  when  the  current  is  closed.  A  definite,  small  quantity 
of  the  salt  solution  is  now  allowed  to  run  into  the  vein  by  turning 
the  stop-cock  of  the  burette.  It  moves  on  with  the  velocity  of  the 
blood,  and  reaching  the  artery  on  the  electrodes  causes  a  diminution 
of  its  electrical  resistance  (p.  34).  This  disturbs  the  balance  of  the 
bridge,  and  the  sound  in  the  telephone  becomes  louder.  The  time 
from  the  beginning  of  the  injection  to  the  alteration  in  the  sound  is 

*  The  electrodes  can  easily  be  made  by  beating  out  one  end  of  a  piece 
of  thick  platinum  wire  to  a  breadth  cf  5  or  6  mm.,  and  then  bending  the 
flattened  part  into  a  hook. 


124  A  MANUAL  OF  PHYSIOLOGY 

the  circulation-time  between  jugular  and  carotid,  and  it  can  be  easily 
read  off  by  a  stop-watch.  Instead  of  the  telephone  a  galvanometer 
may  be  used,  the  equal  and  oppositely  directed  induction  shocks 
being  replaced  by  a  weak  voltaic  current  and  the  platinum  by  un- 
polarizable  electrodes  (p.  526).  But  this  is  somewhat  less  convenient, 
and  in  general  not  more  accurate. 

The  circulation-time  of  an  organ  like  the  kidney  can  be  measured 
by  adjusting  a  pair  of  electrodes  under  the  renal  artery  and  another 
under  the  renal  vein,  and  reading  off  the  interval  required  by  the 
salt  solution  to  pass  from  the  point  of  injection  first  to  the  artery 
and  then  to  the  vein.  The  difference  is  the  circulation-time  through 
the  kidney. 

For  certain  purposes,  and  particularly  for  measurements  on  small 
animals  like  the  rabbit,  or  on  organs  whose  vessels  are  too  delicate 
to  be  placed  on  electrodes  without  the  risk  of  serious  interference 
with  the  circulation,  another  method  may  be  employed  with  ad- 
vantage. It  depends  on  the  injection  of  a  pigment,  like  methylene 
blue,  which  at  first  overpowers  the  colour  of  the  blood  and  shows 
through  the  walls  of  the  bloodvessels,  but  is  soon  reduced  to  a 
colourless  substance,  methylene  white.  The  details  of  the  method 
are  given  in  the  Practical  Exercises  (p.  192). 

T  It  may  be  said  in  general  terms  that  in  one  and  the  same 

animal  the  time  of  the  lesser  circulation  is  short  as  compared  with 
the  total  circulation  -  time,  relatively  constant,  and  but  little 
affected  by  changes  of  temperature.  In  animals  of  the  same 
species  it  increases  with  the  size,  but  more  slowly,  and  rather  in 
proportion  to  the  increase  of  surface  than  to  the  increase  of  weight. 

Thus  a  dog  weighing  2  kilogrammes  had  an  average  pulmonary 
circulation  -  time  of  4*05  seconds,  while  that  of  a  dog  weighing 
ir8  kilos  was  87  seconds,  and  that  of  a  dog  with  a  body- weight  of 
18-2  kilos  only  10-4  seconds.  It  is  probable  that  in  a  man  the 
pulmonary  circulation-time  is  not  usually  much  less  than  1 2  seconds, 
nor  much  more  than  15  seconds. 

The  circulation  time  in  the  kidney,  spleen  and  liver  is 
relatively  long  and  much  more  variable  than  that  of  the 
lungs,  being  easily  affected  by  exposure  and  changes  of 
temperature  (increased  by  cold,  diminished  by  warmth). 

In  a  dog  of  13*3  kilos  weight  the  average  circulation-time 
of  the  spleen  was  10-95  seconds;  kidney,  13' 3  seconds; 
lungs,  8*4  seconds.  The  circulation-time  of  the  stomach  and 
intestines  is  (in  the  rabbit)  comparatively  short,  not  exceed- 
ing very  greatly  that  of  the  lungs,  but  it  is  lengthened  by 
exposure.  The  circulation-time  of  the  retina  and  that  of  the 
heart  (coronary  circulation)  are  the  shortest  of  all. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    125 

The  total  circulation-time  is  properly  the  time  required  for  the 
whole  of  the  blood  to  complete  the  round  of  the  pulmonary  and 
systemic  circulation.  But  there  are  many  routes  open  to  any  given 
particle  of  blood  in  making  its  systemic  circuit.  If  it  passes  from 
the  aorta  through  the  coronary  circulation  it  takes  an  exceedingly 
short  route.  If  it  passes  through  the  intestines  and  liver,  or  through 
the  kidney,  or  through  the  lower  limbs,  it  takes  a  long  route.  So 
that  to  determine  the  total  circulation-time  by  direct  measurement 


FIG.  43.— MEASUREMENT  OF  THE  PULMONARY  CIRCULATION -TIME  IN 
RABBIT  BY  INJECTION  OF  METHYLENE  BLUE. 

we  must  know  (i)  the  quantity  of  blood  that  passes  on  the  average 
by  each  path  in  a  given  time,  and  (2)  the  average  circulation-time  of 
each  path.  If  the  average  weight  of  blood  in  each  organ  be  repre- 

SCntCQ       Dy      7//-_      7//~.       W_         Ptr*     •        QnH       frHp>       d\7^rinr^      r»itv>n1o  f  I/-**-*  _   fiwii*c> 


*-•      \  **  /       •'"^      »*  »  V-'-lW-^W       \^li  V^U  J.CHJ.WI.1      LillJV^         \./t 

rage  weight  of  blood  in  each  organ  be  repre- 
^3,  etc. ;  and  the  average  circulation  -  times 
I  /  be  the  total  systemic  circulation-time  ;  then 

wiT»    Z£/2T>    W3T>  etc'>  will  represent  the  quantity  of  blood  passing 

1  2  *3 

through  each  organ  in  /  seconds,  since  in  the  average  circulation- 


i 

Z£/2T» 


v 

etc. 

t 


126  A  MANUAL  OF  PHYSIOLOGY 

time  of  an  organ  the  whole  of  the  blood  in  it  at  the  beginning  of 
the  period  of  observation  will  have  been  exchanged  for  fresh  blood. 
But  the  whole  of  the  blood  in  the  body,  which  we  may  call 
W,  passes  once  round  the  systemic  circulation  in  t  seconds.  There- 
fore, u\-  +  wz-  +  ws-,  etc.,  =  W.  In  this  equation  everything  can  be 

*i         *s       '  *z 

determined  by  experiment  except  /,  and  therefore  t  can  be  calculated. 
Adding  i  to  the  pulmonary  circulation-time,  we  arrive  at  the  total 
circulation-time. 

Although  our  experimental  data  are  as  yet  too  meagre  to  make  the 
calculation  more  than  a  rough  approximation,  it  appears  probable 
that  in  certain  animals  the  total  circulation-time  is  five  or  six  times 
as  great  as  the  pulmonary  circulation-time.  If  the  same  ratio  holds 
good  in  man,  the  total  circulation-time  is  unlikely  to  be  much  less 
than  a  minute  or  much  greater  than  a  minute  and  a  quarter.  We 
shall  see  directly  that  this  estimate  is  confirmed  by  data  derived 
from  a  different  source.  In  the  meantime,  we  may  use  it  provisionally 
to  calculate  the  work  done  by  the  heart.  Let  us  take  for  simplicity 
the  total  circulation-time  as  i  minute  in  a  yo-kilo  man,  the  quantity 
of  blood  as  5  J  kilos,  and  the  mean  pressure  in  the  aorta  as  200  mm. 
of  mercury.  Up  to  the  time  when  the  semilunar  valves  are  opened, 
the  work  done  by  the  left  ventricle  is  spent  in  raising  the  intra- 
ventricular  pressure  till  it  is  sufficient  to  overcome  the  pressure  in 
the  aorta.  If  a  vertical  tube  were  connected  with  the  left  ventricle, 
the  blood  would  rise  till  the  column  wasoof  the  same  weight  as  a 
column  of  mercury  of  equal  section  and  200  mm.  high.  This  column 
of  blood  would  be  about  2  56  metres  in  height.  If  a  reservoir  were 
placed  in  communication  with  the  tube  at  this  height,  a  quantity  of 
blood  equal  to  that  ejected  from  the  ventricle  would  at  each  systole 
pass  into  the  reservoir ;  and  the  work  which  the  blood  thus  collected 
would  be  capable  of  doing,  if  it  were  allowed  to  fall  to  the  level  of 
the  heart,  would  be  equal  to  the  work  expended  by  the  heart  in 
forcing  it  up.  Thus,  in  i  minute  the  work  of  the  left  ventricle  would 
be  equal  to  that  done  in  raising  5^  kilos  of  blood  to  a  height  of 
2*56  metres — that  is,  about  14  kilogramme-metres;  in  24  hours  it 
would  be,  say,  20,000  kilogramme-metres.  Taking  the  mean  pressure 
in  the  pulmonary  artery  at  one  third  of  the  aortic  pressure  (the 
estimates  of  different  observers  vary  from  one-third  to  one-sixth  in 
different  animals),  we  get  for  the  daily  work  of  the  right  ventricle 
about  7,000  kilogramme-metres.  The  work  of  the  two  ventricles  is 
thus  about  27,000  kilogramme-metres,  which  is  enough  to  raise  a 
weight  of  half  a  stone  from  the  bottom  of  the  deepest  mine  in  the 
world  to  the  top  of  its  highest  mountain,  or  to  raise  the  man  himself 
to  more  than  twice  the  height  of  the  spire  of  Strasburg  Cathedral. 
By  friction  in  the  bloodvessels  this  work  is  almost  all  changed  into 
its  equivalent  of  heat,  namely,  about  63,000  small  calories  (p.  479). 
Further,  since  the  contraction  of  the  heart  is  always  maximal  (p.  131), 
and  there  is  reason  to  believe  that  the  quantity  of  blood  ejected  at  a 
single  systole  by  the  left  ventricle  (being  dependent  upon  the  inflow 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    127 

from  the  pulmonary  veins,  and  therefore  upon  the  inflow  into  the 
right  side  of  the  heart  from  the  systemic  veins)  varies  widely,  some 
of  the  mechanical  effect  of  the  contraction  must  be  wasted  when 
the  quantity  is  less  than  the  ventricle  is  capable  of  expelling. 

Output  of  the  Heart. — If  5  J  kilos  of  blood  pass  through  the  heart 
in  i  minute  with  the  average  pulse-rate  of  72  per  minute,  the  quantity 

t  COO 

ejected  by  either  ventricle  with  every  systole  will  be ==76  grm., 

or  about  72  c.c.  This  is  much  less  than  the  amount  assigned  by 
Vierordt,  which  has  gained  the  greatest  vogue  in  physiological  text- 
books, but  all  recent  observers  who  have  directly  measured  the  out- 
put are  agreed  that  Vierordt's  estimate  is  too  high.  Thus,  in  a  series 
of  experiments  on  more  than  20  dogs,  ranging  in  weight  from  5  to 
nearly  35  kilos,  it  has  been  shown  that  the  output,  or  contraction 
volume,  as  it  is  sometimes  called,  of  the  left  ventricle  per  kilo  of 
body-weight  diminishes  as  the  size  of  the  animal  increases  ;  and  the 
relation  between  body-weight  and  output  is  such  that  in  a  man 
weighing  70  kilos  we  can  hardly  suppose  that  the  ventricle  discharges 
more  than  105  grm.  of  blood  per  second,  or  87  grm.  (80  c.c  )  per 
heart-beat  with  a  pulse-rate  of  72.  Putting  this  result  along  with 
that  deduced  from  the  circulation-time,  we  can  pretty  safely  conclude 
that  the  average  amount  of  blood  thrown  out  by  each  ventricle  at 
each  beat  is  not  more  than  70  or  80  c.c.  Zuntz,  from  the  quantity 
of  oxygen  absorbed  by  the  blood  in  the  lungs,  has  estimated  the 
output  at  60  c.c.  But  according  to  him  this  may  be  doubled  during 
severe  muscular  work,  when,  as  a  matter  of  fact,  by  the  aid  of  the 
X-rays  or  by  percussion  of  the  chest,  the  volume  of  the  heart  may 
be  shown  to  be  considerably  increased.  In  the  middle  of  last 
century,  Passavant  calculated  the  output  at  46*5  grm.,  which  is  almost 
certainly  too  low. 


The  Relation  of  the  Nervous  System  to  the  Circulation. 

So  far  we  have  been  considering  the  circulation  as  a  purely 
physical  problem.  We  have  spoken  of  the  action  of  the 
heart  as  that  of  a  force-pump,  and  perhaps  to  a  small  extent 
that  of  a  suction-pump  too.  We  have  spoken  of  the  blood- 
vessels as  a  system  of  more  or  less  elastic  tubes  through 
which  the  blood  is  propelled.  We  have  spoken  of  the  re- 
sistance which  the  blood  experiences  and  the  pressure  which 
it  exerts  in  this  system  of  tubes,  and  we  have  considered 
the  causes  of  this  resistance,  the  interpretation  of  this 
pressure,  and  the  physical  changes  in  the  vascular  system 
that  may  lead  to  variations  of  both.  But  so  far  we  have 
not  at  all,  or  only  incidentally  and  very  briefly,  dealt  with 


128  A  MANUAL  OF  PHYSIOLOGY 

the  physiological  mechanism  through  which  the  physical 
changes  are  brought  about.  We  have  now  to  see  that 
although  the  heart  is  a  pump,  it  is  a  living  pump ;  that 
although  the  vascular  system  is  an  arrangement  of  tubes, 
these  tubes  are  alive  ;  and  that  both  heart  and  vessels  are 
kept  constantly  in  the  most  delicate  poise  and  balance  by 
impulses  passing  from  the  central  nervous  system  along  the 
nerves. 

In  many  respects,  and  notably  as  regards  the  influence  of 
nerves  on  it,  we  may  look  upon  the  heart  as  an  expanded, 
thickened  and  rhythmically-contractile  bloodvessel,  so  that 
an  account  of  its  innervation  may  fitly  precede  the  descrip- 
tion of  vaso-motor  action  in  general. 

The  Relation  of  the  Heart  to  the  Nervous  System. — A  very 
simple  experiment  is  sufficient  to  prove  that  the  beat  of  the 
heart  does  not  depend  on  its  connection  with  the  central 
nervous  system,  for  an  excised  frog's  heart  may,  under 
favourable  conditions,  of  which  the  most  important  are  a 
moderately  low  temperature,  the  presence  of  oxygen  and  the 
prevention  of  evaporation,  continue  to  beat  for  days.  The 
mammalian  heart  also,  after  removal  from  the  body,  beats 
for  a  time,  and  indeed,  if  defibrinated  blood  be  artificially 
circulated  through  the  coronary  vessels,  for  several  hours. 
But  although  this  proves  that  the  heart  can  beat  when 
separated  from  the  central  nervous  system,  it  does  not 
prove  that  nervous  influence  is  not  essential  to  its  action, 
for  in  the  cardiac  substance  nervous  elements,  both  cells  and 
fibres,  are  to  be  found. 

The  Intrinsic  Nerves  of  the  Heart. — In  the  heart  of  the  frog 
numerous  nerve-cells  are  found  in  the  sinus  venosus,  espe- 
cially near  its  junction  with  the  right  auricle  (Remak's 
ganglion).  A  branch  from  each  vagus,  or  rather  from  each 
vago-sympathetic  nerve  (for  in  the  frog  the  vagus  is  joined  a 
little  below  its  exit  from  the  skull  by  the  sympathetic), 
enters  the  heart  along  the  superior  vena  cava  (pp.  173,  174). 

Running  through  the  sinus,  with  whose  ganglion  cells  the  true 
vagus  fibres,  or  some  of  them,  are  believed  to  make  physiological 
junction  (p.  141),  the  nerves  pursue  their  course  to  the  auricular 
septum.  Here  they  form  an  intricate  plexus,  studded  with  ganglion 
cells.  From  the  plexus  nerve  fibres  issue  in  two  main  bundl 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    129 

which  pass  down  the  anterior  and  posterior  borders  of  the  septum 
to  end  in  two  clumps  of  nerve-cells  (Bidder's  ganglia),  situated  at 
the  auriculo-ventricular  groove.  These  ganglia  in  turn  give  off 
fine  nerve-bundles  to  the  ventricle,  which  form  three  plexuses,  one 
under  the  pericardium,  another  under  the  endocardium,  and  a  third 
in  the  muscular  wall  itself,  or  myocardium.  From  the  last  of  these 
plexuses  numerous  non-medullated  fibres  run  in  among  the  muscular 
fibres  and  end  in  close  relation  with  them.  Similar  plexuses  of  nerve- 
fibres  exist  in  the  mammalian  ventricle.  But  while  a  few  scattered 
ganglion  cells  are  found  in  the  upper  part  of  the  ventricular  wall, 
neither  in  the  mammal  nor  in  the  frog  have  any  been  as  yet  demon- 
strated in  the  apical  half. 

Cause  of  the  Rhythmical  Beat  of  the  Heart. — It  was  long  sup- 
posed that  the  presence  of  ganglion  cells  was  the  clue  to  the 
explanation  of  the  automatic  contraction  of  the  heart,  and 
by  some  they  are  still  looked  upon  as  centres  from  which 
impulses  are  sent  out  at  regular  intervals  to  the  cardiac 
muscular  fibres.  Nor  on  a  superficial  view  are  arguments 
wanting  in  support  of  this  opinion.  We  divide,  in  the  frog, 
the  sinus  which  contains  ganglion  cells  from  the  lower 
portion  of  the  heart,  and  it  continues  to  pulsate.  We  cut 
off  the  apex,  which  contains  no  ganglion  cells  and  it  remains 
obstinately  at  rest.  Further,  if,  without  actually  cutting  off 
the  apex,  we  dissever  it  physiologically  from  the  heart  by 
crushing  a  narrow  zone  of  tissue  midway  between  it  and  the 
auriculo-ventricular  groove,  we  appear  to  abolish  for  ever  its 
power  of  rhythmical  contraction.  The  frog  may  live  for 
many  weeks,  but  in  general  the  apex  remains  in  permanent 
diastole.  It  can  be  caused  to  contract  by  an  artificial 
stimulus,  but  it  neither  takes  part  in  the  spontaneous  con- 
traction of  the  rest  of  the  heart,  nor  does  it  start  an  in- 
dependent beat  of  its  own.  What  can  be  simpler  than  to 
suppose  that  the  sinus  beats  because  it  has  ganglion  cells  in 
its  walls,  and  that  the  apex  refuses  to  beat  because  it  has 
none  ?  But  if  we  pursue  our  investigations  a  little  farther, 
we  shall  find  that  the  matter  is  more  complex.  Let  us 
inquire,  for  instance,  what  happens  to  the  auricles  and 
ventricle  of  the  frog's  heart  when  the  sinus  is  cut  off.  The 
answer  is  that,  as  a  rule,  while  the  sinus  goes  on  beating, 
the  rest  of  the  heart  comes  to  a  standstill,  in  spite  of  the 
numerous  ganglion  cells  in  the  auricular  septum  and  the 

9 


130  A  MANUAL  OF  PHYSIOLOGY 

auriculo-ventricular  groove.  Not  only  so,  but  if  the  ventricle 
be  now  severed  from  the  auricles  by  a  section  carried  through 
the  groove,  it  is  the  former,  poor  in  nerve-cells  though  it 
be,  which  will  usually  first  begin  to  beat.  We  shall  again 
have  to  discuss  this  experiment  (p.  142).  It,  at  any  rate, 
proves  this,  that  the  presence  of  ganglion  cells  is  not  the 
only  condition  on  which  the  power  of  automatic  rhythmical 
contraction  depends.  For  a  portion  of  the  heart  rich  in 
ganglion  cells  may,  under  certain  circumstances,  refuse  to 
beat.  The  converse  is  also  true  :  rhythmical  contraction, 
either  spontaneous  or  artificially  induced,  may  be  observed 
in  many  organs  that  are  free  from  nerve-cells,  or  in  which, 
at  least,  no  nerve-cells  have  ever  been  discovered.  The 
embryonic  heart,  for  instance,  beats  with  a  regular  rhythm 
^  at  a  time  when  as  yet  no  ganglion  cells  have  grown  into  its 
walls.  The  isolated  bulbus  aortse  in  the  frog,  which  seems  to 
contain  no  ganglion  cells,  and  even  the  tiniest  microscopic 
fragments  of  it,  will  pulsate  spontaneously.  A  portion  of 
the  apex  of  a  cat's  ventricle,  presumably  ganglion-free,  con- 
tinues for  a  considerable  time  to  beat  with  a  rhythm  of  its 
own  when  connected  with  the  rest  of  the  heart  by  nothing 
but  its  bloodvessels.  We  know,  further,  that  the  ganglion- 
free  apex  of  the  frog's  heart,  lifeless  as  it  seems  when  left 
to  itself,  can  be  caused  to  execute  a  long  and  regular  series 
of  pulsations  when  its  cavity  is  distended  with  defibrinated 
blood,  or  serum,  or  certain  artificial  nutritive  fluids,  or  even 
normal  saline  solution  ;  that  strips  of  the  ventricle  of  the 
tortoise,  also  free  from  ganglia,  can  be  made  to  beat  rhythmi- 
cally; that  the  rhythmical  contraction  of  the  smooth  muscle 
of  the  ureter  of  the  rabbit  and  dog  is  affected  by  distension 
much  as  that  of  the  cardiac  muscle  is  ;  and,  finally,  that 
even  ordinary  skeletal  muscle  can  contract  in  a  rhythmical 
manner  under  the  stimulus  of  a  certain  tension  and  in 
certain  saline  solutions. 

We  can  hardly  doubt,  in  view  of  such  facts — and  others  oi 
like  significance  might  easily  be  added — that  the  power  ol 
automatic  rhythmical  contraction  possessed  by  the  heart  is 
essentially  a  property  of  the  cardiac  muscle,  a  property 
which  belongs  also,  though  in  much  smaller  degree,  to 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     131 

muscular  tissue  in  other  parts  of  the  vascular  system,  e.g., 
in  the  central  artery  of  the  rabbit's  ear,  and  the  veins  of  the 
bat's  wing.  At  the  same  time  it  must  be  remembered  that 
full  and  formal  proof  of  the  myogenic  origin  of  the  cardiac 
beat  has  not  yet  been  given.  It  is  probable,  but  not  proven. 

We  have  seen  that  there  is  a  normal  order  or  sequence  in 
which  the  different  parts  of  the  heart  contract,  the  contrac- 
tion beginning  both  in  the  frog  and  in  the  mammal  at  the 
base,  and  travelling  more  or  less  rapidly  towards  the  apex. 
It  would  seem  that  the  muscular  tissue  of  the  part  of  the 
heart  in  which  the  beat  begins  has  a  higher  rhythmical  power 
than  the  rest  of  the  cardiac  muscle,  and  that  normally  the 
contraction  is  only  propagated,  not  originated,  by  the  lower 
portion  of  the  heart.  But  under  certain  conditions  the 
normal  sequence  can  be  reversed.  In  the  heart  of  the 
skate,  it  is  easy  by  stimulating  the  bulbus  arteriosus  to  -£-*-& 
cause  a  contraction  passing  from  bulbus  to  sinus.  Not  only 
may  the  normal  sequence  be  changed  in  the  entire  heart, 
but  any  part  of  the  heart  may  apparently  have  its  rhythmical 
power  exalted  by  appropriate  means,  so  that  it  can  be 
brought  to  beat  rhythmically  when  isolated  from  the  rest  of 
the  heart.  On  the  other  hand,  the  power  of  propagating  the 
contraction  may  be  artificially  interfered  with — increased  by 
heat,  diminished  by  cold,  abolished  by  pressure  or  fatigue. 
If,  e.g.,  a  frog's  heart  is  supported  by  a  clamp  fixed  in  the 
auriculo-ventricular  groove,  and  the  clamp  is  tightened  or 
the  ventricle  cooled,  while  the  auricle  is  at  the  ordinary  tem- 
perature, or  if  the  auricle  is  heated  while  the  ventricle  is 
at  the  ordinary  temperature,  only  every  second  or  third 
auricular  beat  will  be  followed  by  a  ventricular  beat  (p.  172). 

In  addition  to  its  marked  power  of  rhythmical  contraction, 
the  cardiac  muscle  is  distinguished  from  ordinary  skeletal 
muscle  by  other  peculiarities.  The  most  striking  of  these  is 
that  '  it  is  everything  or  nothing  with  the  heart ' ;  in  other 
words,  the  heart  muscle,  when  it  contracts,  makes  the  best 
effort  of  which  it  is  capable  at  the  time  ;  a  weak  stimulus,  if 
it  can  just  produce  a  beat,  causes  as  great  a  contraction  as 
a  strong  stimulus.  Another  peculiarity  is  that  a  true  tetanus 
of  the  cardiac  muscle  cannot  be  obtained  at  all,  or  only  under 

9—2 


132  A  MANUAL  OF  PHYSIOLOGY 

very  special  conditions.     When  the  ventricle  of  a  normally 
beating  frog's  heart  is  stimulated  by  a  rapid  series  of  induction 
shocks,  its  rate  is  generally  increased,  but  there  is  no  definite 
relation  between  the  number  of  stimuli  and  the  number  of 
beats.     Many  of  the  stimuli  are  ineffective.     In  the  same 
way  a  portion  of  the  heart,  such  as  the  apex  of  the  ventricle, 
when  stimulated  in  the  quiescent  condition  by  an  interrupted 
current,  responds  by  a  rhythmical  series  of  beats,  and  not  by 
a  tetanus.    It  is  evident  that  the  cardiac  muscle,  like  ordinary 
striped  muscle,  is  for  some  time  after  excitation  incapable 
of  responding  to  a  fresh  stimulus,  i.e.,  there  is  a  refractory 
period.     But  this    is  immensely  longer  in   cardiac  than  in 
skeletal  muscle.     When  the  phenomenon  is  analyzed,  it  is 
found  that  a  stimulus  falling  into  the  heart  muscle  between 
the    moment    at    which    the    contraction   begins   and    the 
moment  at  which  it  reaches  its  maximum,  produces  no  effect 
— is,  so  to  speak,  ignored.     When  the  stimulus  is  thrown  in 
at  any  point  between  the  maximum  of  the  systole  and  the 
beginning  of  the  next  contraction,  it  causes  what  is  called 
an  extra  contraction.     The  extra  contraction  is  followed  by 
a  longer  pause  than  usual — a  so-called  compensatory  pause 
— which  just  restores  the  rhythm,  so  that  the  succeeding 
systole  falls  in  the  curve  where  it  would  have  fallen  had  there 
been  no  extra  contraction  (Fig.  44).     The  refractory  period 
is  shorter  for  strong  than  for  weak  stimuli,  and  is  markedly 
diminished  by  raising  the  temperature  of  the  heart.     So 
that  stimulation  of  the  heated  heart  with  a  series  of  strong 
induction  shocks  may  cause  a  tetaniform  condition,  if  not  a 
typical  tetanus.     The  contraction  of  the  normally  beating 
heart  is  really  a  simple  contraction,  and  not  a  tetanus.     The 
capillary   electrometer    shows   only  the   electrical   changes 
corresponding  to  a  single  contraction  (p.  622)  ;  and  when 
the  nerve  of  a  nerve-muscle  preparation  is  laid  on  the  heart, 
the  muscle  responds  to  each  beat  by  a  simple  twitch,  and 
not  by  tetanus  (p.  179). 

Like  ordinary  skeletal  muscle,  the  cardiac  muscle  is  at  first 
benefited  by  contraction,  so  that  when  the  apex  is  stimulated 
at  regular  intervals,  each  contraction  is  somewhat  stronger 
than  the  preceding  one.  To  this  phenomenon  the  name  of 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     133 

the  staircase  or  '  treppe  '  has  been  given  from  the  appearance 
of  the  tracings  (p.  548). 

The  Extrinsic  Nervous  Mechanism  of  the  Heart. — While,  as 
we  have  seen,  the  essential  cause  of  the  rhythmical  beat  of 
the  heart  resides  in  the  tissue  of  the  heart  itself,  it  is  con- 
stantly affected  by  impulses  that  reach  it  from  the  central 
nervous  system.  These  impulses  are  of  two  kinds,  or,  rather, 
produce  two  distinct  effects :  inhibition,  or  diminution  in  the 
rate  or  force  of  the  heart-beat,  and  augmentation,  or  increase 
in  the  rate  or  force.  Both  the  inhibitory  and  the  augmentor 
impulses  arise  in  the  medulla  oblongata,  and  perhaps  a 


A  frog's  heart 
was  stimulated  at 
a  point  correspond- 
ing to  the  nick  in 
the  horizontal  line 
below  each  curve. 
In  i  and  2  there 
was  no  response  ; 
in  3  and  4  there 
was  an  extra  con- 
traction, succeeded 
by  a  compensatory 
pause. 


FIG.  44.— REFRACTORY  PERIOD  AND  COMPENSATORY  PAUSE  (MAREY). 

narrow  zone  of  the  neighbouring  portion  of  the  cord ;  and 
they  can  be  artificially  excited  by  stimulation  in  this 
region.  They  pursue  their  course  to  the  heart  by  fibres 
which  may  in  certain  animals  be  mingled  together,  but  are 
anatomically  distinct.  We  may,  therefore,  divide  the  ex- 
trinsic or  external  nervous  mechanism  of  the  heart  into  a 
cardio-inhibitory  centre  with  its  efferent  inhibitory  nerve- 
fibres,  and  a  cardio-augmentor  centre  with  its  efferent 
augmentor  nerve-fibres.  Both  of  those  centres,  as  we  shall 
see,  have  also  extensive  relations  with  afferent  nerve-fibres 
from  all  parts  of  the  body,  including  the  heart  itself. 

It  was  in  the  vagus  of  the  frog  that  inhibitory  nerves  were 
first  discovered  by  the  brothers  Weber  more  than  fifty  years 


134 


A  MANUAL  OF  PHYSIOLOGY 


ago,  and  even  now  our  knowledge  of  the  cardiac  nervous 
mechanism  is  more  complete  in  this  animal  than  in  any 
other.  We  shall,  therefore,  first  describe  the  phenomena  of 
inhibition  and  augmentation  as  we  see  them  in  the  heart  of 
the  frog,  and  then  pass  on  to  the  mammal 

In  the  frog  the  inhibitory  fibres  leave  the  medulla  oblongata  in  the 
vagus  nerve.     The  augmentor  fibres  come  off  from  the  upper  part  of 

the  spinal  cord  by  a  branch  from  the 
third  nerve  to  the  third  sympathetic 
ganglion,  and  thence  find  their  way 
along  the  sympathetic  cord  to  its 
junction  with  the  vagus,  in  which  they 
run,  mingled  with  the  inhibitory  fibres, 
down  to  the  heart. 

When  the  vago-sympathetic  in 
the  frog  or  toad  is  cut,  and  its 
peripheral  4end  stimulated,  the 
heart  in  the  vast  majority  of  cases 
is  stopped  or  slowed,  or  its  beat 
is  distinctly  weakened  without,  it 
may  be,  any  marked  slowing.  In 
other  words,  the  rate  at  which  the 
heart  was  working,  before  the 
stimulation,  is  greatly  diminished, 
or  reduced  to  zero.  Such  an 
effect,  a  diminution  of  the  rate  of 
working,  we  call  Inhibition.  What 
precise  form  the  inhibition  shall 
take,  whether  the  stoppage  shall 
be  complete  or  partial,  appears  to 

depend  partly  upon  the  strength  of  the  stimulus  used,  and 
partly  upon  the  state  of  the  heart  itself.  Some  hearts  it  may 
be  impossible  to  stop  with  weak  stimulation,  although  other 
signs  of  inhibition  may  be  distinct,  while  they  are  readily 
stopped  by  stronger  stimulation.  In  other  cases  the 
strongest  stimulation  may  not  produce  complete  standstill. 
Again,  a  heated  heart  may  be  more  readily  brought  to 
standstill  by  stimulation  of  the  vagus  than  a  heart  at  the 
ordinary  temperature  or  a  cooled  heart. 

But  there  are  other  points  of  importance  to  be  noted  in 


FIG.  45  (AFTER  FOSTER). — 
DIAGRAM  OF  EXTRINSIC 
NERVES  OF  FROG'S  HEART. 

Ill,  3rd  spinal  nerve  ;  AV, 
annulus  of  Vieussens  ;  X,  roots 
of  vagus  ;  IX,  glosso-pharyngeal 
nerve  ;  VS,  combined  vagus  and 
sympathetic  ;  i,  2,  and  3,  the  ist, 
2nd,  and  3rd  sympathetic  ganglia. 
The  dark  line  indicates  the  course 
of  the  sympathetic  fibres.  The 
arrows  show  the  direction  of  the 
augmentor  impulses. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     135 

regard  to  this  inhibition :  (i)  It  does  not  begin  for  a  little 
time  after  stimulation  has  begun.  In  other  words,  there  is 
a  distinct  latent  period ;  and  the  length  of  this  latent  period 
is  related  to  the  phase  of  the  heart's  contraction  at  which 
the  stimulus  is  thrown  in,  and  to  the  rate  at  which  the  heart 
is  beating.  As  a  general  rule,  the  heart  makes  at  least  one 
beat  before  it  stops. 

(2)  The  inhibition  does  not  continue  indefinitely,  even  if 
stimulation  of  the  nerve  is  kept  up.     Sooner  or  later,  and 


FIG.  46.— TRACING  FROM  FROG'S  HEART. 

A,  auricular,  V,  ventricular  tracing.  Sinus  stimulated  (primary  coil  70  mm.  from 
secondary).  Heart  at  temperature  ii'2°  C.  Complete  standstill.  The  time  tracing 
between  the  curves  marks  intervals  of  two  seconds. 

usually,  in  fact,  after  an  interval  of  a  few  seconds,  the  heart 
begins  again  to  beat  if  it  has  been  completely  stopped,  or  to 
quicken  its  beat  if  it  has  only  been  slowed,  or  to  strengthen 
it  if  the  inhibition  has  only  weakened  the  contraction, 
and  it  soon  regains  its  old  rate  of  working.  Not  only 
so,  but  very  often  there  follows  a  longer  or  shorter  period 
during  which  the  heart  works  at  a  greater  rate  than  it  did 
before  the  inhibition,  and  this  greater  rate  of  working  may 
be  manifested  by  increased  frequency  of  beat,  or  increased 


I36  A  MANUAL  OF  PHYSIOLOGY 

strength  of  beat,  or  by  both.  When  the  temperature  of  the 
heart  is  low,  increased  frequency;  when  it  is  high,  increased 
strength,  is  generally  seen  during  this  period  of  secondary 
augmentation.*  The  cause  of  this  secondary  augmentation, 
and  of  the  primary  augmentation  sometimes  seen  in  fresh 
preparations  and  often  in  hearts  that  have  been  long 
exposed  (Fig.  49),  excited  much  speculation  before  it  was 
known  that  sympathetic  fibres  existed  in  the  vagus.  There 
is  no  longer  any  doubt  that  it  is  due  to  the  stimulation  of 
these  accelerator  or,  as  it  is  better  to  call  them  (since  mere 
acceleration  is  not  the  only  consequence  of  their  stimula- 


FIG.  47. — FROG'S  HEART.     VAGUS  STIMULATED. 

Temperature  of  heart  8°  C. ,  78  mm.  between  the  coils.    Diminution  in  force  of  auricle 
and  ventricle,  but  not  complete  standstill.     Time  tracing  shows  two-second  intervals. 

tion),  augmentor  fibres  in  the  mixed  nerve.  For  (i)  excita- 
tion of  the  roots  of  the  vagus  proper  within  the  skull,  and 
therefore  above  the  junction  of  the  sympathetic  fibres, 
causes  no  secondary  augmentation,  or  very  little,  and  the 
inhibition  lasts  far  longer  than  when  the  mixed  trunk  is 
stimulated. 

(2)  Excitation  of  the  upper  or  cephalic  end  of  the  sym- 
pathetic cord  before  it  has  joined  the  vagus  causes,  after  a 

*  Augmentation  is  termed  '  secondary '  when  it  is  preceded  by  inhibi- 
tion, 'primary'  when  it  is  not  so  preceded. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH 


137 


relatively  long  latent  period,  marked  augmentation.  And  if 
the  contractions  of  the  heart  are  registered,  the  tracing  bears 
a  close  resemblance  to  the  curve  of  secondary  augmentation 
following  excitation  of  the  mixed  nerve  on  the  other  side 
with  an  equally  strong  stimulus  and  for  an  equal  time. 

(3)  When  the  vago-sympathetic  is  stimulated  weakly  there 
is  little  or  no  secondary  augmentation.  Now,  it  is  known 
that  the  augmentor  fibres  require 
a  comparatively  strong  stimulus 
to  cause  any  effect  when  they  are 
separately  excited,  whereas  a  weak 
stimulus  will  excite  the  inhibitory 
fibres. 

The  question  arises  at  this  point, 
why  it  is  that,  when  the  inhibitory 
and  augmentor  fibres  are  stimu- 
lated together  in  the  mixed  nerve 
(and  the  same  is  true  when  the 
sympathetic  on  one  side  and  the 
vagus  on  the  other  are  stimulated 
at  the  same  time),  the  inhibitory 
effect  always  comes  first,  when 
there  is  any  inhibitory  effect,  while 
the  augmentation  always  has  to 
follow.  The  answer  has  some- 
times been  given,  that  the  latent 
period  of  the  augmentor  fibres  is 
longer  than  that  of  the  inhibitory 

fibres.       But   although    this    is    Cer-       various   temperatures,    the    ordi- 

.    11  ,  .  nates  being  the  excess  of  the  rate 

tamly  the    Case,  the    answer    IS    in-       after,  over  that  before  stimulation. 

sufficient  For  the  period  of  post- 
ponement may  be  much  greater  than  the  latent  period  of 
the  sympathetic  fibres  when  stimulated  by  themselves.  The 
inhibition  apparently  runs  its  course  without  being  affected 
by  the  simultaneous  augmentor  effect,  which,  lying  latent 
until  the  end  of  the  inhibition,  then  bursts  out  and  com- 
pletes its  own  curve.  It  is  not  like  the  passing  of  two  waves 
through  each  other,  but  rather  like  the  stopping  of  one  wave 
until  the  other  has  passed  by.  It  seems  as  if  augmenta- 


FIG.  48. 

A  is  a  curve    representing   in 
an   experiment   the    rate    of    the 


rate  after  stimulation,  the  number 
of  beats  per  100"  being  laid  off 
along  the  vertical,  the  temperature 
of  the  hearth  along  the  horizontal 
axis.  C  is  a  curve  showing  the  ratio 
of  the  frequency  after,  to  that 
before  stimulation  of  the  sym- 


38 


A  MANUAL  OF  PHYSIOLOGY 


tion  cannot  develop  itself  in  the  presence  of  inhibition — at 
least,  until  the  latter  is  nearly  spent.  In  the  frog,  at  any 
rate,  the  two  processes  can  hardly  be  considered  as 
antagonistic,  in  the  sense  that  a  definite  amount  of 
augmentor  excitation  can  overcome  a  definite  amount  of 
inhibitory  excitation.  Nor  is  it  the  case  that  when  the 
heart  is  played  upon  at  the  same  time  by  impulses  of  both 


FIG.  49.— FROG'S  HEART. 


A,  auricular  ;  V,  ventricular  tracing.     Ventricle  beating  very  feebly.     Vagus  stimu- 
lated (60  mm.  between  coils).     Marked  augmentation  of  ventricular  beat. 

kinds,  it  pits  them  against  each  other  and  strikes  the 
balance  accurately  between  them.  It  is  possible,  however, 
that  when  the  inhibitory  fibres  are  very  weakly,  and  the 
augmentory  fibres  very  strongly  stimulated,  the  amount  of 
'inhibition  may  be  somewhat  diminished.  In  mammals,  on 
the  other  hand,  a  true  antagonism  seems  to  exist;  and 
stimulation  of  the  inhibitory  nerves  is  less  effective  when 
the  augrnentors  are  excited  at  the  same  time. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    139 


GTV'- 


In  mammals  (and  in  what  follows  we  shall  restrict  ourselves  to  the 
dog,  cat  and  rabbit,  as  it  is  in  these  animals  that  the  subject  has  been 
chiefly  studied)  the  inhibitory  fibres  run  down  the  vagus  in  the  neck 
and  reach  the  heart  by  its  cardiac  branches.  They  are  not,  however, 
generally  believed  to  be  derived  from  the  roots  of  the  vagus  itself,  but 
from  the  inner  branch  of  the  spinal  accessory,  which  joins  the  vagus. 
The  augmentor  fibres  leave  the  spinal  cord  in  the  anterior  roots  of  the 
second  and  third  thoracic  nerves,  and 
possibly  to  some  extent  by  the  fourth 
and  fifth.  Through  the  corresponding 
white  rami  communicantes  they  reach 
the  sympathetic  cord,  and  running 
up  through  the  stellate  ganglion  (first 
thoracic),  and  the  annulus  of  Vieussens, 
which  surrounds  the  subclavian  artery, 
to  the  inferior  cervical  ganglion,  they 
pass  off  to  the  heart  by  separate  *  ac- 
celerator '  branches,  taking  origin  either 
from  ihe  annulus  or  from  the  inferior 
cervical  ganglion. 

In  the  dog  the  vagus  and  cervical 
sympathetic  are,  in  the  great  majority 
of  cases,  contained  in  a  strong  common 
sheath,  and  pass  together  through  the 
inferior  cervical  ganglion.  After  open- 
ing this  sheath  they  may  with  care  be 
separated,  the  fibres  running  in  distinct 
strands,  and  not  mixed  together  as  in  FlG-  5°-— DIAGRAM  OF  CAR- 
the  vago-sympathetic  of  the  frog.  For  %£*%»*  ™E  D°° 
some  distance  below  the  superior  TT  TTT  .  . .  ,  .  , 

..  .      ,  II,  III,  second  and  third  dorsal 

Cervical    ganglion    the    cervical    Sympa-      nerves;    SA,    subclavian    artery; 
thetlC  is  not  connected  with  the  vagUS,      AV,  annulus  of  Vieussens  ;  ICG, 

and  here  the  nerves  may  be  separately    J."^0^  °2IJStthS??0i:    fi«t 

Stimulated   without   any   artificial    ISOla-      thoracic  or  stellate  ganglion  of  the 
tion,  but    the    electrodes   must   be  very      sympathetic  -^  2,  second   thoracic 

well  insulated,  as  the  available  length 


Ill 


fites 


Of  nerve  is  Small.  wards  the  heart ;  X,"  roots  of  vagus ; 

In  the  rabbit,  cat,  horse,  and  some  XI,  roots  of  spinal  accessory  ;JG, 

.1                           ,        ,                           j  jugular  ganglion;  G IV,  ganglion 

other  mammals,  the  vagus  and  sympa  Jtr~nci  Vagi  Tin.,  inhibitory  hbres 

thetic   run   a   separate   course   in   the  passing  off  towards  the  heart, 
neck. 


The  effects  of  stimulation  of  the  vagus  or  vago-sym- 
pathetic  in  the  mammal  are  very  much  the  same  as  in  the 
frog,  except  that  secondary  augmentation  is  far  less  marked 
or  altogether  absent,  and  that  in  the  mammal  the  inhibitory  (f^^ 
fibres  have  no  direct  action  on  the  ventricle.  It  indeed 
beats  more  slowly  when  the  auricle  is  slowed,  but  this  is 


140 


A  MANUAL  OF  PHYSIOLOGY 


only  because  in  the  normally  beating  heart  the  ventricle 
takes  the  time  from  the  auricle.  The  strength  of  the  ven- 
tricular contractions  is  not  at  all  diminished,  even  when  the 
auricle  is  beating  very  feebly  during  inhibition.  When  the 
auricle  is  completely  stopped,  which  does  not  occur  so 
readily  as  in  the  frog,  the  ventricle  also  stops  for  a  short 
time,  but  soon  begins  to  beat  again  with  an  independent 
rhythm  of  its  own.  In  the  frog  the  ventricle  is  directly 
affected  by  stimulation  of  the  vagus,  and  the  force  of  its 

beats  is  diminished 
independently  of 
the  inhibitory 
effects  in  the 
auricles  (Practical 
Exercises,  pp.  178, 

179)- 

Stimulation      of 

the  accelerator 
nerves  in  the  dog 
causes  an  increase 
in  the  force  of  both 
the  auricular  and 
ventricular  con- 
traction, and,  as  a 
rule,  in  addition, 
some  increase  in 
the  rate  of  the 
beat. 

As  to  the  nature 

of  the  physiological  linkage  between  the  cardiac  nerves  and  the 
muscular  tissue  of  the  heart  we  know  but  little.  It  has 
been  supposed  that  within  the  heart  itself  there  may  exist 
peripheral  nervous  mechanisms  which  mediate  between  the 
nerves  and  the  muscle.  We  have  already  given  reasons 
for  denying  to  the  ganglion  cells  any  important  share  in 
the  maintenance  of  the  rhythmical  beat,  but  we  have  not 
assigned  them  any  function.  It  has  been  suggested  that 
the  ganglia  may  act  as  local  inhibitory,  or  even  as  local 
augmentor,  centres.  Others,  however,  have  inclined  to  the 


FIG.  51. — BLOOD-PRESSURE  TRACING  (RABBIT). 

Vagus  stimulated  at  I.     Stimulus  stronger  in  B  than 
in  A  (Hiirthle's  spring  manometer). 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     141 

view  that  the  cells  on  the  course  of  nerve-fibres  in  the  heart 
are  rather  stations  where  the  fibres  lose  their  medulla,  and 
where  possibly  other  anatomical  changes  and  rearrangements 
occur,  than  important  intermediate  mechanisms  which 
essentially  modify  the  physiological  impulses  falling  into 
them,  and  shape  the  visible  results  that  follow  those  im- 
pulses. In  the  discussions  that  have  arisen  over  this 
question,  appeal  has  frequently  been  made  to  the  action  of 
certain  poisons  on  the  heart. 

Thus,  after  nicotine  has  been  injected  subcutaneously,  or 
painted  directly  on  the  heart  of  a  frog,  stimulation  of  the 
vago-sympathetic  causes  no  inhibition  ;  it  may  cause  aug- 
mentation. But  stimulation  of  the  junction  of  the  sinus 
and  auricle  still  causes  inhibition,  as  in  the  normal  heart. 
Curara,  conine,  and  other  drugs,  resemble  nicotine  in  this 
respect. 

Atropia  and  its  allies,  such  as  daturine,  not  only  abolish 
the  inhibitory  effect  of  stimulation  of  the  vagus  trunk,  but 
also  that  of  stimulation  of  the  junction  of  sinus  and  auricle. 

Muscarine,  a  poison  contained  in  certain  mushrooms 
(p.  174),  causes  diastolic  arrest  of  the  heart,  which,  when 
the  circulation  is  intact,  becomes  swollen  and  engorged 
with  blood.  This  action  takes  place  in  a  heart  already 
poisoned  with  nicotine  or  one  of  its  congeners,  but  not  in  a 
heart  under  the  influence  of  atropia  or  its  allies.  And  a  heart 
brought  to  standstill  by  muscarine  can  be  made  to  beat  again 
by  the  application  of  atropia,  although  not  by  nicotine. 

These  facts  may  be  explained  as  follows :  Nicotine 
paralyzes  not  the  very  ends  of  the  vagus,  but  the  ganglia 
through  which  its  fibres  pass.  Stimulation  of  the  sinus, 
which  is  practically  stimulation  of  the  vagus  fibres  between 
the  ganglion  cells  and  the  muscular  fibres,  is  therefore 
effective,  although  stimulation  of  the  nerve-trunk  is  not 
(Langley).  On  the  other  hand,  the  atropia  group  paralyzes 
the  nerve-endings  themselves,  so  that  neither  stimulation 
of  the  sinus  nor  of  the  nerve-trunk  can  cause  inhibition. 
Muscarine,  on  the  contrary,  stimulates  the  vagus  fibres 
between  the  nerve-cells  and  the  muscle,  or  the  actual  nerve- 
endings,  or  some  other  local  nervous  mechanism,  and  thus 


142  A  MANUAL  OF  PHYSIOLOGY 

keeps  the  heart  in  a  state  of  permanent  inhibition,  which  is 
removed  when  atropia  cuts  out  the  nerve-endings.  It  is 
quite  in  accordance  with  this,  that  muscarine  has  no  effect 
on  a  heart  whose  vagus  nerves,  as  occasionally  happens, 
have  no  inhibitory  power. 

Some  observers  have  supposed  that  although  muscarine  and  pilo- 
carpine  in  large  doses  do  act  on  the  nervous  structures  of  the  sinus, 
their  primary  and  chief  effect  is  to  depress  the  rhythmical  power  of 
the  muscle,  which  atropia,  on  the  other  hand,  increases  (Gaskell). 
And  this  view  gains  a  certain  amount  of  support  from  the  facts  that 
muscarine  and  atropia  act  very  much  in  the  same  way  on  the  heart  of 
the  mammalian  embryo  (rat,  rabbit,  etc.)  before  and  after  the  develop- 
ment of  its  intrinsic  nervous  system,  and  that  the  passage  of  an 
interrupted  current  through  the  heart  of  very  young  embryos  causes 
distinct  inhibition.  But,  on  the  other  hand,  muscarine  fails  to  affect 
the  heart  in  many  invertebrate  animals — for  instance,  in  the  Daphma 
(Pickering).  So  that  the  only  conclusion  to  which  it  is  possible  to 
come  is  that  we  do  not  as  yet  thoroughly  understand  either  the  mode 
of  action  of  these  substances  or  their  point  of  attack. 

Stannius'  Experiment.— Nor  can  much  more  be  said  of  another 
series  of  phenomena  that  are  intimately  related  to  our  present  subject, 
and  have  excited,  since  they  were  first  made  known  by  Stannius,  an 
enormous  amount  of  discussion.  The  chief  facts  of  this  classical 
experiment  we  have  already  mentioned  (p.  130),  and  they  are  also 
described  in  the  'Practical  Exercises'  (p.  175).  They  are  easy  to 
verify,  but  difficult  to  interpret.  To  Gaskell  and  his  followers  the 
most  probable  explanation  of  the  standstill  caused  by  the  first  ligature 
is  that  the  lower  portion  of  the  heart,  when  cut  off  from  the  sinus  in 
which  the  beat  normally  originates,  needs  some  time  for  the  develop- 
ment of  its  rhythmical  power  to  the  point  at  which  an  independent 
rhythm  can  be  maintained.  For  in  the  heart  of  the  tortoise,  in  which 
a  similar  temporary  standstill  of  the  auricles  and  ventricle  occurs 
when  the  former  are  detached  from  the  sinus,  the  circulation  of  a 
blood  solution  through  the  coronary  vessels  or  the  application  of 
atropia,  both  of  which,  according  to  Gaskell,  increase  the  rhythmical 
power  of  the  cardiac  muscle,  prevents  or  removes  the  standstill.  The 
effects  following  the  second  Stannius  ligature  are  supposed  to  be  due 
to  stimulation  of  the  muscular  tissue  by  the  ligature.  But  it  is  not 
easy  to  explain  why  the  second  ligature  should  stimulate  the  ventricle 
in  preference  to  the  auricles,  and  why  the  first  ligature  should 
apparently  not  stimulate  the  muscular  tissue  at  all.  Nor  does  the 
explanation  become  easier  if  we  suppose,  as  is  sometimes  done,  that 
it  is  the  Bidder's  ganglia  which  are  stimulated  by  the  ligature  or  by  the 
knife,  for  there  is  no  real  evidence  that  they  have  motor  functions. 

Another  view  is  that  the  first  ligature  stimulates  the  inhibitory 
mechanism  (vagus  fibres)  at  the  junction  of  the  sinus  and  right  auricle, 
a  position  in  which  it  is  specially  sensitive  to  stimuli.  This  causes 
inhibition  of  the  whole  of  the  heart  below  the  ligature.  The  second 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    143 

ligature  cuts  off  the  ventricle  from  the  inhibitory  impulses,   while 
leaving  the  auricle  still  under  their  influence. 

Nature  of  Inhibition  and  Augmentation. — So  far  we  have  been 
discussing  the  phenomena  of  inhibition  and  augmentation  as  ultimate 
facts.  We  have  not  attempted  to  go  behind  them,  nor  to  ask  what  it 
is  that  really  happens  when  inhibitory  impulses  fall  into  a  heart,  which 
from  the  first  days  of  embryonic  life  has  gone  on  beating  with  a  regular 
rhythm,  and  in  the  space  of  a  second  or  two  bring  it  to  a  standstill. 
The  question  cannot  fail  to  press  itself  upon  the  mind  of  anyone  who 
has  ever  witnessed  this  most  beautiful  of  physiological  experiments ; 
but  as  yet  there  is  no  answer  except  ingenious  speculations.  The 
most  plausible  of  these 
is  the  trophic  theory  of 
Gaskell,  who  sees  in  the 
vagus  a  nerve  which  so 
acts  upon  the  chemical 
changes  going  on  in  the 
heart  as  to  give  them  a 
trophic,  or  anabolic,  or 
constructive  turn,  and 
thus  to  lessen  for  the 
time  the  destructive 
changes  underlying  the 
muscular  contraction. 
The  augmentor  nerves, 
on  the  other  hand,  are 
supposed  to  exert  a 
katabolic  influence,  and 
to  favour  these  destruc- 
tive changes.  And  while, 
according  to  Gaskell,  FIG.  52.— FROG'S  HEART. 

the  natural  consequence        Sympathetic  stimulated  (30  mm.  between  the  coils). 
nf  inhihitinn    ic    a    Qtncrp  Temperature    12°.     Marked   increase  in   force.     Only 
a   Sia&e  auricular  tracjng  reproduced.     Time  trace,  two-second 
of    increased   efficiency  intervals, 
and  working  power  when 

the  inhibition  has  passed  away,  the  natural  complement  of  augmenta- 
tion is  a  temporary  exhaustion. 

But  it  must  be  remembered  that  this  distinction  is  not  as  yet  based 
upon  any  very  solid  foundation  of  actually-observed  and  easily- 
interpreted  facts,  while  to  some  of  the  facts  brought  forward  in  its 
favour  undue  importance  has  been  given.  For  instance,  a  positive 
electrical  variation  has  been  seen  in  the  quiescent  auricle  of  the 
tortoise  on  stimulating  the  vagus,  and  a  negative  variation  in  the 
quiescent  frog's  ventricle  on  stimulating  the  cardiac  sympathetic, 
neither  of  these  variations  apparently  being  accompanied  with  any 
sensible  mechanical  change.  It  has  been  argued  from  this  (on  the 
assumption  that  the  negative  variation  observed  when  most  excitable 
tissues,  muscle  and  nerve,  for  example,  are  stimulated,  is  the  ex- 
pression of  destructive  metabolic  changes  or  katabolism),  that  the 
vagus  has  the  power  of  causing  constructive  (anabolic)  changes,  and 


144  A  MANUAL  OF  PHYSIOLOGY 

the  augmentor  nerves  the  power  of  causing  destructive  (katabolic) 
changes,  apart  from  mechanical  effects.  But  all  that  we  really  know 
is  that  electrical  changes  and  chemical  changes  can  both  be  evoked 
in  living  tissues.  We  are  quite  ignorant  of  the  relation  between 
the  two. 


Normal  Excitation  of  the  Cardiac  Nervous  Mechanism. 
—We  have  now  to  inquire  how  this  elaborate  nervous 
mechanism  is  normally  set  into  action.  And  we  may  say  at 
once  that,  striking  as  are  the  effects  of  experimental  stimula- 
tion of  the  vagus  trunk  or  the  nervi  accelerantes  in  their 
course,  it  is  only  under  exceptional  circumstances  that  the 
efferent  nerve-fibres,  at  any  rate  before  they  have  entered  the 
heart,  can  be  directly  excited  in  the  intact  body.  In  certain 
cases  the  pressure  of  a  tumour  or  an  aneurism  on  the  nerve- 
trunks,  or,  in  the  case  of  the  accelerators,  the  progress  of 
a  pathological  change  in  the  sympathetic  ganglia  through 
which  the  fibres  pass,  has  been  thought  to  bring  about  by 
direct  stimulation  a  slowing  or  a  quickening  of  the  pulse.  In 
some  individuals  the  vagus  may  be  excited  by  compressing 
it  against  the  vertebral  column  or  against  a  bony  tumour  in 
the  neck.  But  it  is  from  the  cardio-inhibitory  and  cardio- 
augmentor  centres  in  the  medulla  oblongata  that  the  im- 
pulses which  regulate  the  activity  of  the  heart  are  normally 
discharged.  Inhibitory  impulses  seem  to  be  constantly 
passing  out  from  the  medulla,  for  section  of  both  vagi 
causes  almost  invariably  an  increase  in  the  rate  of  the 
heart,  at  least  in  mammals,  although  the  increase  is  less 
conspicuous  in  animals  like  the  rabbit,  whose  normal  pulse- 
rate  is  high,  than  in  animals  like  the  dog,  whose  pulse-rate  is 
comparatively  low.  Section  of  one  vagus  usually  causes  only 
a  comparatively  slight  increase,  for  the  other  is  able  of  itself 
to  control  the  heart.  It  is  not  known  whether  the  augmentor 
centre  in  like  manner  discharges  a  continuous  stream  of  im- 
pulses, or  is  only  roused  to  occasional  activity  by  special 
stimuli.  For  the  results  of  section  of  the  nervi  accelerantes, 
or  the  extirpation  of  the  inferior  cervical  and  stellate  ganglia, 
are  dubious  and  conflicting.  But  if  it  does  exert  a  tonic 
influence  on  the  heart,  this  is  far  feebler  than  the  tone  of 
the  inhibitory  centre.  As  to  the  nature  of  this  inhibitory 
tone,  and  the  manner  in  which  it  is  maintained,  we  know 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    145 

but  little.  It  may  be  that  the  chemical  changes  in  the 
nerve-cells  of  the  inhibitory  centre  lead  of  themselves  to  the 
discharge  of  impulses  along  the  inhibitory  nerves.  But 
there  is  some  evidence  that,  in  the  complete  absence  of 
stimulation  from  without,  the  activity  of  the  centre  would 
languish,  and  perhaps  be  ultimately  extinguished.  For 
when  the  greater  number  of  the  afferent  impulses  have  been 
cut  off  from  the  medulla  oblongata  by  a  transverse  section 
carried  through  its  lower  border,  division  of  the  vagi  pro- 
duces little  effect  on  the  rate  of  the  heart.  Be  this  as  it 
may,  we  know  that  the  activity  of  the  inhibitory  centre  is 
profoundly  influenced — and  that  both  in  the  direction  of  an 
increase  and  of  a  diminution — by  impulses  that  fall  into  it 
through  afferent  nerves  and  by  stimuli  directly  applied  to 
it.  And  we  may  assume  that  the  same  is  true  of  the 
augmentor  centre.  When,  for  instance,  the  central  end  of 
one  vagus  is  stimulated,  the  other  being  intact,  the  usual 
result  is  a  slowing  or  weakening  of  the  heart,  which,  how- 
ever, is  generally  less  marked  than  when  the  stimulation  is 
applied  to  the  peripheral  end  of  the  nerve.  But  sometimes 
the  heart  is  accelerated  without  any  trace  of  a  preceding 
inhibition. 

The  depressor  nerve,  a  branch  of  the  vagus,  which  is 
easily  found  in  the  rabbit  as  a  slender  nerve  running  quite 
close  to  the  sympathetic  in  the  neck,  and  a  little  to  its  inner 
side,  falls  into  the  same  category  with  the  vagus  itself  as 
regards  its  reflex  action  on  the  heart,  to  which  it  bears  a  most 
important  relation.  Stimulation  of  its  peripheral  end  has 
no  effect,  for  the  cardiac  fibres  which  it  carries  are  afferent, 
not  efferent.  But  excitation  of  its  central  end  causes  a 
marked  fall  of  blood-pressure  (p.  161),  accompanied  by,  but 
not  essentially  due  to,  a  distinct  slowing  of  the  heart.  If 
the  animal  is  not  under  the  influence  of  an  anaesthetic,  there 
may  also  be  signs  of  pain,  and  for  this  reason  the  depressor 
has  sometimes  been  spoken  of,  somewhat  loosely,  as  the 
sensory  nerve  of  the  heart.  The  abdominal  sympathetic 
(of  the  frog)  also  contains  afferent  fibres,  through  which 
reflex  inhibition  of  the  heart  can  be  produced  when  they 
are  excited  mechanically  by  a  rapid  succession  of  light 

10 


146  A  MANUAL  OF  PHYSIOLOGY 

strokes  on  the  abdomen  with  the  handle  of  a  scalpel 
(Goltz). 

On  the  other  hand,  when  the  central  end  of  an  ordinary 
peripheral  nerve  like  the  sciatic  is  excited,  the  common 
effect  is  pure  augmentation,  which  sometimes  perhaps 
develops  itself  with  greater  suddenness  than  when  the 
accelerator  nerves  are  directly  stimulated.  Occasionally, 
however,  the  augmentation  is  abruptly  followed  by  a  typical 
vagus  action.  Here  the  reflex  inhibitory  effect  seems  to 
break  in  upon  and  cut  short  the  reflex  augmentor  effect. 

These  examples  show  that  certain  afferent  nerves  are 
especially  related  to  the  cardio-inhibitory,  and  others  to  the 
cardio  augmentor,  centre,  or  at  least  that  the  central  con- 
nections of  some  nerves  are  such  that  inhibition  is  the 
usual  effect  of  their  reflex  excitation,  while  the  opposite  is 
the  case  with  other  nerves.  But  it  is  improbable  that  the 
effect  of  a  stream  of  afferent  impulses  reaching  the  cardiac 
centres  by  any  given  nerve  is  determined  solely  by  anato- 
mical relations.  The  intensity  and  the  nature  of  the 
stimulus  seems  also  to  have  something  to  do  with  the  result. 
For  when  ordinary  sensory  nerves  are  weakly  stimulated, 
augmentation  is  said  to  be  more  common  than  inhibition, 
and  the  opposite  when  they  are  strongly  stimulated.  And 
while  a  chemical  stimulus,  like  the  inhaled  vapour  of 
chloroform  or  ammonia,  causes  in  the  rabbit  reflex  inhibi- 
tion of  the  heart  through  the  fibres  of  the  trigeminus  that 
confer  common  sensation  on  the  mucous  membrane  of  the 
nose,  the  mechanical  excitation  of  the  sensory  nerves  of  the 
pharynx  and  oesophagus  when  water  is  slowly  sipped  causes 
acceleration.*  The  stimulation  of  the  nerves  of  special 
sense  is  followed  sometimes  by  the  one  effect  and  some- 
times by  the  other.  To  complete  the  catalogue  of  the 
nervous  channels  by  which  impulses  may  reach  the  cardiac 
centres  in  the  medulla,  we  may  add  that  there  must  be  an 
extensive  connection  between  them  and  the  cerebral  cortex, 
since  every  passing  emotion  leaves  its  trace  upon  the  curve 
of  cardiac  action.  It  is  a  remarkable  fact,  too,  and  one 

*  In  78  healthy  students  the  average  pulse-rate  (in  the  sitting  position) 
was  increased  from  73  to  85  per  minute  by  sipping  water. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    147      0  . 

that  can  only  be  explained  by  such  a  connection,  that 
although  in  the  vast  majority  of  individuals  the  will  has  no 
influence  whatever  on  the  rate  or  force  of  the  heart,  except, 
perhaps,  indirectly  through  the  respiration,  some  persons 
have  the  power,  by  a  voluntary  effort,  of  markedly  accelerat- 
ing the  pulse.  In  one  case  of  this  kind  it  was  noticed  that 
perspiration  broke  out  on  the  hands  and  other  parts  of  the 
body  when  the  heart  was  voluntarily  accelerated.  A  rise  of 
blood-pressure  due  to  constriction  of  the  vessels  has  also 
been  observed.  The  effort  cannot  be  kept  up  for  more  than 
a  short  time,  and  the  pulse-rate  quickly  goes  back  to  normal. 
It  has  been  recently  asserted  that  this  peculiar  power  is 
more  common  than  has  been  supposed,  and  that  where  it  is 
present  in  rudiment,  it  can  be  cultivated,  although  it  is  a 
dangerous  acquisition  (Van  de  Velde). 

As  an  example  of  the  direct  action  of  a  chemical  stimulus 
on  a  cardiac  centre,  we  may  cite  the  marked  inhibition  pro- 
duced by  injection  of  an  extract  of  the  suprarenal  capsule 
into  a  vein  (p.  475),  and  as  an  instance  of  the  direct  action 
of  a  physical  change,  the  slowing  of  the  heart  in  asphyxia  as 


the  blood-pressure  rises  (p.  163).  The  variation  in  the  pulse- 
rate  associated  with  changes  in  the  position  of  the  body, 
to  which  we  have  already  referred  (p.  96),  has  been  attri- 
buted to  direct  stimulation  of  the  inhibitory  centre  by  the 
increase  of  blood-pressure  in  the  medulla  oblongata  when  a 
person  who  has  been  standing  assumes  the  supine,  or  even 
the  sitting,  posture.  But  it  may  also  be  due  in  part  to 
changes  in  the  amount  of  muscular  contraction. 

Theoretically,  quickening  of  the  heart  might  be  caused 
either  by  a  diminution  in  the  inhibitory  tone  or  by  an 
increase  in  the  activity  of  the  augmentor  centre ;  and 
slowing  of  the  heart  might  be  due  either  to  a  diminution  in 
the  augmentor  tone,  if  such  exists,  or  to  an  increase  in  the 
activity  of  the  inhibitory  centre.  So  that  it  is  not  always 
easy  to  interpret  such  results  as  we  have  quoted  above. 
But  it  would  appear  that  under  ordinary  conditions  the  rate 
of  the  heart  is  mainly  regulated  by  the  inhibitory  centre, 
which,  within  a  considerable  range,  can  produce  variations 
in  either  direction.  The  augmentor  mechanism  is  perhaps 

10 — 2 


r\ 


148  A  MANUAL  OF  PHYSIOLOGY 

merely  auxiliary  to  the  inhibitory,  being  called  into  action 
only  in  emergencies. 

Vaso-motor  Nerves. — Just  as  the  muscular  walls  of  the  heart 
are  governed  by  two  sets  of  nerve-fibres,  a  set  which  keeps 
down  the  rate  of  working  and  a  set  which  may  increase  it, 
the  muscular  walls  of  the  vessels  are  under  the  control  of 
nerves  which  have  the  power  of  diminishing  their  calibre 
(vaso-constrictor),  and  of  nerves  which  have  the  power  of 
increasing  it  (vaso- dilator).  All  nerves  that  affect  the  calibre 
of  the  vessels,  whether  vaso-constrictor  or  vaso-dilator,  are 
included  under  the  general  name  vaso-motor.  These  vaso- 
motor  nerves,  like  the  augmentor  and  inhibitory  fibres  of 
the  heart,  are  connected  with  a  centre  or  centres,  which  in 
turn  are  in  relation  with  numerous  afferent  nerves.  So  far 
as  we  know  at  present,  vaso-motor  nerves  influence  chiefly 
the  small  arteries.  Although  nerve-fibres  have  been  seen 
surrounding  capillaries,  nothing  is  known  of  any  change  of 
lumen  occurring  in  these  vessels  as  a  direct  result  of  the 
action  of  nerves  going  to  them.  Nor  has  the  existence  of 
vaso-motor  nerves  for  veins,  except  the  portal  system,  been 
proved  up  to  this  time  by  any  clear  and  unambiguous  ex- 
periment, although  there  are  grounds  on  which  it  has  been 
argued  that  in  some  animals,  at  least,  the  nervous  system 
does  govern  the  calibre  or  '  tone  '  of  the  whole  venous  tract. 
These  grounds  will  be  mentioned  in  the  proper  place. 
Meanwhile,  before  describing  the  distribution  of  the  best- 
known  tracts  of  vaso-motor  fibres  and  defining  the  position 
of  the  vaso-motor  centres,  we  must  first  glance  at  the 
principal  methods  by  which  our  knowledge  of  this  subject 
has  been  attained. 

T.  (i)  In  superficial  and  translucent  parts  inspection  is  sufficient. 
Paling  of  the  part  indicates  constriction  :  flushing,  dilatation  of  the 
small  vessels.  This  method  has  been  much  used,  sometimes  in  con- 
junction with  (2)  in  such  parts  as  the  balls  of  the  toes  of  dogs  or  cats 
(when  there  is  little  or  no  pigment  present),  the  ear  of  the  rabbit,  the 
conjunctiva,  the  mucous  membrane  of  the  mouth  and  gums,  the  web 
of  the  frog,  the  wing  of  the  bat,  the  intestines,  uterus,  and  other 
internal  organs. 

(2)  Observation  of  changes  in  the  temperature  of  parts.  This 
method  has  been  chiefly  employed  in  investigating  the  vaso-motor 
nerves  of  the  limbs,  the  thermometer  bulb  being  fixed  between  the 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    149 

toes.  In  such  peripheral  parts  the  temperature  of  the  blood  is 
normally  less  than  that  of  the  blood  in  the  internal  organs,  because 
the  opportunities  of  cooling  are  greater.  The  effect  of  a  freer  cir- 
culation of  blood  (dilatation  of  the  arteries)  is  to  raise  the  tempera- 
ture ;  of  a  more  restricted  circulation  (constriction  of  the  arteries),  to 
lower  it. 

(3)  Measurement   of    the   blood-pressure.     If    we   measure    the     7*, 
arterial  blood-pressure  at  one  point,   and  find  that  stimulation  of 
certain  nerves  increases  it  without  affecting  the  action  of  the  heart, 

we  can  conclude  that  upon  the  whole  the  tone  of  the  small  vessels 
has  been  increased.  But  we  cannot  tell  in  what  region  or  regions 
the  increase  has  taken  place ;  nor  can  we  tell  whether  it  has  not  been 
accompanied  by  diminution  of  tone  in  other  tracts. 

But  if  we  measure  simultaneously  the  blood-pressure  in  the  chief 
artery  and  chief  vein  of  a  part  such  as  a  limb,  we  can  tell  from  the 
changes  caused  by  section  or  stimulation  of  nerves  whether,  and  in 
what  sense,  the  tone  of  the  small  vessels  within  this  area  has  been 
altered.  For  example,  if  we  found  that  the  lateral  pressure  in  the 
artery  was  diminished,  while  at  the  same  time  it  was  increased  in  the 
vein,  we  should  know  that  the  '  resistance  '  between  artery  and  vein 
had  been  lessened,  and  that  the  blood  now  found  its  way  more 
readily  from  the  artery  into  the  vein.  If,  on  the  other  hand,  the 
venous  pressure  was  diminished,  and  the  arterial  pressure  simul- 
taneously increased,  we  should  have  to  conclude  that  the  vascular 
resistance  in  the  part  was  greater  than  before.  If  the  pressure  both 
in  artery  and  vein  was  increased,  we  could  not  come  to  any  conclu- 
sion as  to  local  changes  of  resistance  without  knowing  how  the 
general  blood-pressure  had  varied. 

It  is  also  sufficient  to  measure  the  blood-pressure  simultaneously 
at  two  points  of  the  arterial  path  by  which  blood  reaches  the  part, 
provided  that  there  is  a  distinct  difference  in  the  pressure  at  the  two 
points.  The  ratio  of  the  two  pressures  will  not  be  altered  by  any 
general  change  of  blood-pressure  due  to  changes  in  the  action  of  the 
heart ;  any  alteration  in  the  ratio  will  indicate  a  change  in  the  peri- 
pheral vascular  resistance  in  the  part  beyond  the  more  distal  of  the 
two  manometers. 

On  this  principle,  Hiirthle  has  studied  the  changes  in  the  circula-    - 
tion  of  the  brain  by  inserting  manometers  into  the  central  end  of  the 
divided  common  carotid  and    the  peripheral   end  of   the  internal 
carotid.     The  former  shows  the  lateral  pressure  in  the  aorta,  the 
latter  that  in  the  circle  of  Willis. 

(4)  The  measurement  of  the  velocity  of  the  blood  in  the  vessels 
of  the  part.     This  may  be  done  by  the  stromuhr  or  dromograph,  or 
by  allowing  the  blood  to  escape  from  a  small  vein  and  measuring  the 
outflow  in  a  given  time,  or,  without  opening  the  vessels,  by  estimating 
the  circulation  time  (p.  123).     When  changes  in  the  general  arterial 
pressure  are  eliminated,  slowing  of  the  blood-stream  through  a  part 
corresponds  to  increase  of  vascular  resistance  in  it ;  increase  in  the 
rate  of  flow  implies  diminished  vascular  resistance.     Sometimes  the 
red  colour  of  the  blood  issuing  from  a  cut  vein,  and  the  visible  pulse 


150  A  MANUAL  OF  PHYSIOLOGY 

in  the  stream,  indicate  with  certainty  that  the  vessels  of  the  organ 
have  been  dilated. 

(5)  Alterations  in  the  volume  of  an  organ  or  limb  are  often  taken 
as  indications  of  changes  in  the  calibre  of  the  small  vessels  in  it. 
We  have  already  seen  how  these  alterations  are  recorded  by  means 
of  a  plethysmograph  (p.  116).     The  brain  is  enclosed  in  the  skull  as 
in  a  natural  plethysmograph,   and  changes  in   its  volume  may  be 
registered  by  connecting  a  recording  apparatus  with  a  trephine  hole. 

(6)  For   the   separation   of  the   effects   of  stimulation   of  vaso- 
constrictor and  vaso-dilator  fibres  when  they  are  mingled  together,  as 
is  the  case  in  many  nerves,  advantage  is  taken  of  certain  differences 
between  them.     For  example,  the  vaso-constrictors  degenerate  sooner 
than  the  vaso  dilators  when  cut  off  from  the  nerve-cells  to  which  they 
belong.     So  that  if  a  nerve  is  divided,  and  some  days  allowed  to 


FIG.  53. — PLETHYSMOGRAMS  (HIND  LIMB  OF  CAT). 

To  be  read  from  right  to  left.  On  the  left  hand  is  shown  the  effect  of  slow  stimula- 
tion of  the  sciatic  (i  per  second) ;  on  the  right  hand  the  effect  of  rapid  stimulation 
(64  per  second). 

elapse  before  stimulation,  only  the  dilators  will  be  excited.  The 
vaso-dilators  are  more  sensitive  to  weak  stimuli  repeated  at  long 
intervals  than  to  strong  and  frequent  stimuli,  and  the  opposite  is  true 
of  the  constrictors.  When  a  nerve  containing  both  kinds  of  fibres  is 
heated,  the  excitability  of  the  vaso-constrictors  is  increased  in  a 
greater  degree  than  that  of  the  dilators ;  when  the  nerve  is  cooled, 
the  dilators  preserve  their  excitability  at  a  temperature  at  which  the 
constrictors  have  ceased  to  respond  to  stimulation  (Fig.  53). 

The  Chief  Vaso-motor  Nerves. — The  first  discovery  of  vaso- 
motor  nerves  was  made  in  the  cervical  sympathetic.  When 
this  nerve  is  cut,  the  corresponding  side  of  the  head,  and 
especially  the  ear,  become  greatly  injected  owing  to  the 
dilatation  of  the  vessels.  This  experiment  can  be  very 
readily  performed  on  the  rabbit,  and  the  changes  are  most 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    151 

easily  followed  in  an  albino.  The  ear  on  the  side  of  the  cut 
nerve  is  redder  and  hotter  than  the  other ;  the  main  arteries 
and  veins  are  swollen  with  blood,  and  many  vessels  formerly 
invisible  come  into  view.  The  slow  rhythmical  changes  of 
calibre,  which  in  the  normal  rabbit  are  very  characteristically 
seen  in  the  middle  artery  of  the  ear,  disappear  for  a  time  after 
section  of  the  sympathetic,  although  they  ultimately  again 
become  visible  (Practical  Exercises,  p.  189). 

Stimulation  of  the  cephalic  end  of  the  cut  sympathetic 
causes  a  marked  constriction  of  the  vessels  and  a  fall  of 
temperature  on  the  same  side  of  the  head.  From  these 
facts  we  know  that  the  cervical  sympathetic  in  mammals 
contains  vaso-constrictor  fibres  for  the  side  of  the  head  and 
ear,  and  that  these  fibres  are  constantly  in  action.  Certain 
parts  of  the  eye,  and  the  salivary  glands,  larynx,  resophagus, 
and  thyroid  gland,  are  also  supplied  with  vaso-motor  (con- 
strictor) nerves  from  the  cervical  sympathetic. 

It  has  been  asserted  that  the  cervical  sympathetic  con- 
tains  vaso-constrictor  fibres  for  the  corresponding  half  of  the 
brain  and  its  membranes,  although  fibres  of  this  kind  also* 
reach  it  by  other  routes  ;  but  this  has  been  disputed,  and 
some  observers  have  even  gone  so  far  as  to  deny  that  the 
vessels  of  the  brain  have  any  vaso-motor  nerves  (Roy  and 
Sherrington).  To  say  the  least,  their  existence  must  still  be 
regarded  as  '  not  proven,'  although  nerve-fibres  may  be  seen 
in  and  around  the  walls  of  the  cerebral  bloodvessels  (Huber), 
and  it  is  difficult  to  believe  that  these  have  not  a  vaso-motor 
function.  That  the  nerve  contains  some  dilator  fibres  seems 
proved  by  the  fact  that  stimulation  of  the  cephalic  end  in 
the  dog  causes  flushing  of  the  mucous  membrane  of  the 
mouth  on  the  same  side.  The  vaso-motor  fibres  of  the  head 
run  up  in  the  cervical  sympathetic,  and  then  pass  into  various 
cerebral  nerves,  of  which  the  fifth  or  trigeminus  is  the  most 
important. 

The  trigeminus  nerve  contains  vaso-constrictor  nerves  for 
various  parts  of  the  eye  (conjunctiva,  sclerotic,  iris),  and  for 
the  mucous  membrane  of  the  nose  and  gums,  and  section  of 
it  is  followed  by  dilatation  of  the  vessels  of  these  regions. 
The  lingual  branch  of  the  trigeminus  supplies  vaso-motor 


152  A  MANUAL  OF  PHYSIOLOGY 

fibres  to  the  tongue,  and  apparently  both  vaso-constrictor 
and  vaso-dilator. 

In  some  animals,  the  rabbit  for  instance,  the  ear  derives 
part  of  its  vaso-motor  supply  directly  from  the  cerebro- 
spinal  system,  through  the  great  auricular  nerve,  as  well  as 
through  the  cervical  sympathetic. 

Another  great  vaso-motor  tract,  the  most  influential  in 
the  body,  is  contained  in  the  splanchnic  nerves,  which  govern 
the  vessels  of  many  of  the  abdominal  organs.  Section  of 
these  nerves  causes  an  immediate  and  sharp  fall  of  arterial 
pressure.  The  intestinal  vessels  are  dilated  and  overfilled 
with  blood.  As  a  necessary  consequence  of  their  immense 
capacity,  the  rest  of  the  vascular  system  is  underfilled,  and 
the  blood-pressure  falls  accordingly.  Stimulation  of  the 
peripheral  end  of  the  splanchnic  nerves  causes  a  great  rise 
of  blood-pressure,  owing  to  the  constriction  of  vessels  in 
the  intestinal  area.  We  therefore  conclude  that  in  the 
splanchnics  there  are  vaso-motor  fibres  of  the  constrictor 
type,  and  that  impulses  are  constantly  passing  down  them 
to  maintain  the  normal  tone  of  the  vascular  tract  which 
they  command.  The  presence  of  dilator  fibres  (for  the 
intestines  and  the  kidney,  for  example)  has  also  been 
demonstrated  in  the  splanchnic  nerves,  although  the  con- 
strictors predominate,  and  special  methods  have  to  be 
employed  for  the  detection  of  the  dilators. 

The  same  is  true  of  the  nerves  of  the  extremities,  which 
certainly  contain  vaso-dilator  fibres  in  addition  to  vaso- 
constrictors, although  the  difficulty  of  demonstrating  the 
presence  of  the  former  is  fully  as  great  as  it  is  in  the 
splanchnics.  For  the  investigation  is  complicated  by  the 
fact  that  such  nerves  as  the  sciatic  supply  with  vaso-motor 
fibres  two  leading  tissues — skin  and  muscle  ;  and  these  are 
not  necessarily  affected  in  the  same  direction  or  to  the  same 
extent  by  stimulation  of  their  vaso-motor  fibres.  The  vaso- 
constrictors under  ordinary  conditions  preponderate,  so  that 
section  of  the  sciatic  or  the  brachial  is  generally  followed  by 
flushing  of  the  balls  of  the  toes  and  rise  of  temperature, 
stimulation  by  paling  and  fall  of  temperature.  By  taking 
advantage,  however,  of  the  unequal  excitability  of  dilators 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     153 

and  constrictors  in  a  degenerating  nerve,  and  of  the  differ- 
ences between  the  two  kinds  of  fibres  in  their  reaction  to 
electrical  stimuli  (p.  150),  it  has  been  shown  that  vaso- 
dilators are  also  present,  and  come  to  the  front  when 
the  conditions  are  rendered  favourable  for  them  and  un- 
favourable for  the  constrictors. 

The  vaso-motor  fibres  for  the  fore-limb  (dog)  issue  from  the  cord 
in  the  anterior  roots  of  the  third  to  the  eleventh  dorsal  nerves,  and 
for  the  hind-limb  in  the  anterior  roots  of  the  eleventh  dorsal  to  the 
third  lumbar.  Stimulation  of  most  of  these  roots  causes  constriction 
of  the  vessels,  but  stimulation  of  the  eleventh  dorsal  may  cause 
dilatation  (Bayliss  and  Bradford). 

The  Vaso-motor  Nerves  of  Muscle. — When  the  motor  nerve 
of  the  thin  mylo-hyoid  muscle  of  the  frog,  which  can  be 
observed  under  the  microscope,  is  cut,  the  vessels  are  seen 
to  dilate.  On  stimulation  of  the  peripheral  end  of  the  cut 
nerve  they  dilate  still  more,  and  this  effect  is  not  abolished 
when  contraction  of  the  muscle  is  prevented  by  a  dose  of 
curara  insufficient  to  paralyze  the  vaso-motor  nerves 
(Gaskell).  The  dilatation  on  section  of  the  nerve  has  been 
held  to  indicate  the  existence  in  it  of  vaso-constrictor  fibres, 
and  the  dilatation  on  stimulation  of  the  nerve,  the  existence 
of  a  larger  number  of  vaso-dilators,  which  overcome  the 
constrictors  when  both  are  excited.  And  it  has  been  argued 
that  this  is  of  use  to  the  contracting  muscle,  which  requires 
a  free  flow  of  blood  to  supply  it  with  food  materials  and  to 
carry  off  its  waste  products.  The  average  flow  of  blood 
through  a  mammalian  muscle  is  also  increased  during  con- 
traction, apart  from  the  initial  increase  due  to  the  com- 
pression of  the  muscular  veins.  The  outflow  of  blood  from 
the  main  vein  of  one  of  the  muscles  used  in  mastication  in 
the  horse  was  found  to  be  three  times  as  great  during 
voluntary  work  with  it  (in  chewing)  as  in  rest.  And  although 
no  increase  in  the  blood-flow  through  the  skeletal  muscles  of 
a  completely  curarized  mammal  has  ever  been  satisfactorily 
demonstrated,  we  can  hardly  doubt  that  they  are  provided 
with  vaso-dilator  fibres,  and  more  scantily  with  vaso-con- 
strictors.  The  existence  in  the  vagus  of  vaso-constrictor 
fibres  for  the  coronary  arteries  of  the  heart  has  also  been 


154  A  MANUAL  OF  PHYSIOLOGY 

asserted  (Porter).  It  has  been  suggested  that  the  muscular 
vessels  are  widened  in  contraction,  not  through  vaso-motor 
nerves,  but  by  the  direct  action  of  the  acid  products  of  the 
active  muscle  itself,  since  it  has  been  found  that  very  dilute 
acids  (lactic  acid,  e.g.)  cause  general  dilatation  of  the  small 
vessels.  A  similar  explanation  has  been  extended  to  the 
dilatation  of  the  vessels  of  the  brain  during  cerebral  activity 
by  some  of  those  who  deny  the  existence  of  vaso-motor 
nerves  for  that  organ.  But  this  ingenious  speculation  rests 
upon  a  very  narrow  basis  of  fact. 

Vaso-motor  Nerves  of  the  Lungs. — There  has  been  much 
discussion  as  to  the  course,  and  even  as  to  the  existence,  of 
vaso-motor  fibres  for  the  lungs.  The  problem  is  perhaps  the 
most  difficult  in  the  whole  range  of  vaso-motor  topography, 
for  the  pulmonary  circulation  is  so  related  to  other  vascular 
tracts,  that  changes  produced  in  the  vessels  of  distant 
organs  by  the  stimulation  or  section  of  nerves  may  affect 
the  quantity  of  blood  received  by  the  right  side  of  the  heart, 
and  therefore  the  quantity  propelled  through  the  lungs  and 
the  pressure  in  the  pulmonary  artery.  All  that  we  really 
know  is  that  the  lungs  are  supplied  with  vaso-constrictor 
fibres,  although  in  all  probability  less  richly  than  most  other 
organs.  Some  of  these  fibres  appear  to  pass  out  from  the 
upper  half  of  the  dorsal  spinal  cord  (Bradford  and  Dean), 
but  perhaps  others  reach  their  destination  by  the  vagus. 

In  most  of  the  peripheral  nerves  vaso-dilator  fibres  are 
mingled  with  vaso-constrictors ;  but  in  certain  situations, 
for  an  anatomical  reason  that  will  be  mentioned  presently, 
nerves  exist  in  which  the  only  vaso-motor  fibres  are  of  the 
dilator  type.  Of  these,  the  most  conspicuous  examples  are 
the  chorda  tympani  and  the  nervi  erigentes ;  and,  indeed,  it 
was  in  the  chorda  that  vaso-dilators  were  first  discovered  by 
Bernard.  The  chorda  tympani  contains  vaso-dilator  and 
secretory  fibres  for  the  submaxillary  and  sublingual  salivary 
glands.  With  the  secretory  fibres  we  have  at  present 
nothing  to  do ;  and  the  whole  subject  will  have  to  be 
returned  to,  and  more  fully  discussed  in  Chapter  IV.  But 
a  most  marked  vascular  change  is  produced  by  stimulation 
of  the  peripheral  end  of  the  divided  chorda  tympani  nerve. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     155 

The  glands  flush  red ;  more  blood  is  evidently  passing 
through  their  vessels.  Allowed  to  escape  from  a  divided 
vein,  the  blood  is  seen  to  be  of  bright  arterial  colour  and 
shows  a  distinct  pulse.  The  small  arteries  have  been  dilated 
by  the  action  of  the  vaso-motor  fibres  in  the  nerve.  The 
resistance  being  thus  reduced,  the  blood  passes  in  a  fuller 
and  more  rapid  stream  through  the  capillaries  into  the 
veins,  and  on  the  way  there  is  not  time  for  it  to  become 
completely  venous.  These  vaso-dilator  fibres  are  apparently 
not  in  constant  action,  for  section  of  the  nerve,  as  a  rule, 
produces  little  or  no  change.  Vaso-constrictor  fibres  pass 
to  the  salivary  glands  from  the  cervical  sympathetic,  along 
the  arteries,  and  stimulation  of  that  nerve  causes  narrowing 
of  the  vessels  and  diminution  of  the  blood-flow,  sometimes 
almost  to  complete  stoppage. 

The  nervi  erigentes  are  the  nerves  through  which  erection 
of  the  penis  is  caused.  When  they  are  divided  there  is  no 
effect,  but  stimulation  of  the  peripheral  end  causes  dilatation 
of  the  vessels  of  the  erectile  tissue  of  the  organ,  which 
becomes  overfilled  with  blood.  During  stimulation  of  these 
nerves,  the  quantity  of  blood  flowing  from  the  cut  dorsal 
vein  of  the  penis  may  be  fifteen  times  greater  than  in  the 
absence  of  stimulation.  It  spurts  out  in  a  strong  stream, 
and  is  brighter  than  ordinary  venous  blood  (Eckhard). 
Stimulation  of  the  peripheral  end  of  the  nervus  pudendus 
causes  constriction  of  the  vessels  of  the  penis,  so  that  it 
contains  vaso-constrictor  fibres  which  are  the  antagonists  of 
the  nervi  erigentes. 

Vaso-motor  Nerves  of  Veins.  —  Like  arteries,  veins  have 
plexuses  of  nerve -fibres  in  their  walls,  and  contract  in 
response  to  various  stimuli.  In  some  cases,  e.g.,  in  the  wing 
of  the  bat,  rhythmical  contractions  of  the  veins  are  strikingly 
displayed,  but  they  do  not  seem  to  depend  on  the  nervous 
system,  as  they  persist  after  section  of  the  brachial  nerves. 
But  up  to  a  very  recent  date  there  was  no  clear  proof  of 
the  existence  of  vaso-motor  nerves  for  veins.  In  1892, 
however,  Mall  showed  that  vaso-constrictor  fibres  for  the 
portal  vein  exist  in  the  splanchnic  nerves.  When  these  were 
stimulated,  after  the  disturbing  effect  of  changes  in  the 


156  A  MANUAL  OF  PHYSIOLOGY 

circulation  through  the  intestines  had  been  eliminated  by 
compression  of  the  aorta  in  the  thorax,  an  actual  shrinking 
of  the  vein  could  be  observed.  The  fibres  appear  to  issue 
from  the  spinal  cord  by  the  anterior  roots  of  the  third  to 
the  eleventh  dorsal  nerves,  but  chiefly  in  the  fifth  to  the 
ninth  dorsal  (Bayliss  and  Starling).  When  the  liver  is 
enclosed  in  a  plethysmograph  of  special  construction,  and 
the  central  end  of  an  ordinary  sensory  nerve,  like  the  sciatic, 
excited,  reflex  vaso-constriction  takes  place  in  the  portal 
area,  the  volume  of  the  organ  diminishes,  and  the  blood- 
pressure  rises  in  the  portal  vein  (Fransois-Franck  and 
Hallion). 

The  vena  portae  and  its  branches  are  in  the  physiological 
sense  arteries  rather  than  veins,  since  they  break  up  into 
capillaries,  and  it  was  to  be  expected  that  the  regulation  of 
the  blood-flow  in  them  would  be  carried  out  in  the  same 
way  as  in  ordinary  arteries,  namely,  by  means  of  vaso-motor 
nerves.  But  we  must  not,  without  special  proof,  extend  the 
results  obtained  in  the  portal  system  to  ordinary  veins.  A 
certain  amount  of  evidence,  however,  exists  that  even  such 
veins  as  those  of  the  extremities  are  supplied  with  vaso- 
constrictor fibres.  After  ligation  of  the  crural  artery, 
stimulation  of  the  peripheral  end  of  the  sciatic  has  been 
seen  to  cause  contraction  of  the  crural  vein  (Thompson). 

Course  of  the  Vase-motor  Nerves. — In  the  dog  the  vaso-con- 
strictors  pass  out  as  fine  medullated  fibres  (1*8  to  3*6  //,  in 
diameter)  in  the  anterior  roots  of  the  second  dorsal  to  about 
the  second  lumbar  nerves  (Gaskell).  They  proceed  by  the 
white  rami  communicantes  to  the  lateral  sympathetic 
ganglia,  where,  or  in  more  distal  ganglia  such  as  the  inferior 
mesenteric,  they  lose  their  medulla,  and  their  axis-cylinder 
processes  (Chap.  XII.)  break  up  into  fibrils  that  come  into 
close  relation  with  the  nerve-cells  of  the  ganglia.  These 
ganglion  cells  in  their  turn  send  off  axis-cylinder  processes, 
which,  acquiring  a  neurilemma,  become  non-medullated  nerve 
fibres,  and  now  pass  by  various  routes  to  their  final  destina- 
tion, the  unstriped  muscular  fibres  of  the  bloodvessels. 
Their  course  to  the  head  has  been  already  described.  To 
the  limbs  they  are  distributed  in  the  great  nerves  (brachial 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     157 

plexus,  sciatic,  etc.),  which  they  reach  from  the  sympathetic 
ganglia  by  the  grey  rami  communicantes. 

The  outflow  of  vaso-dilator  fibres,  which  also  takes  place 
through  the  anterior  roots,  does  not  seem  to  be  restricted  to 
any  particular  part  of  the  cord,  although  their  existence  has 
been  most  clearly  demonstrated  in  nerves  springing  from  those 
regions  of  the  cerebro-spinal  axis  from  which  vaso-constrictor 
fibres  do  not  arise,  and  where,  therefore,  we  have  not  to 
contend  with  the  difficulty  and  doubt  of  mixed  effects. 
Some  even  emerge  in  the  roots  of  origin  of  certain  of  the 
cranial  nerves,  as  the  trigeminus,  although  many  of  the 
vaso-dilator  fibres  contained  in  the  trunk  of  this  nerve 
distal  to  the  Gasserian  ganglion  are  derived  from  the  cervical 
sympathetic,  and  originally  come  off  from  the  upper  dorsal 
portion  of  the  spinal  cord.  The  vaso-dilators  appear  upon 
the  whole  to  pursue  much  the  same  course  towards  the 
periphery  as  the  vaso-constrictors,  although  they  often  run 
for  a  greater  distance  after  leaving  the  cord  without 
losing  their  medulla.  But  eventually  they  too  come  into 
relation  with  ganglion  cells,  sometimes  scattered  along  their 
course,  or  lying  near  or  in  the  organs  to  which  they  are 
distributed  ;  and  as  in  the  case  of  the  vaso-constrictors, 
these  ganglion  cells  with  their  axis-cylinder  processes  con- 
tinue the  nervous  path  to  the  periphery.  It  is  believed  that 
every  vaso-motor  fibre  is  interrupted  by  one,  and  only  by 
one,  ganglion  cell  between  the  cord  and  the  bloodvessels. 

Effect  of  Nicotine  on  Nerve-cells. — A  method  which  has  been 
found  most  fruitful  in  studying  the  relations  of  sympathetic  ganglion 
cells  to  the  vaso-motor  fibres,  as  well  as  to  the  pilo-motor*  and 
secretory  fibres  which  in  certain  situations  are  so  intricately  mingled 
with  them,  must  here  be  mentioned.  It  depends  upon  the  fact  that 
when  a  suitable  dose  of  nicotine  (10  milligrammes  in  a  cat)  is  in- 
jected into  a  vein,  or  a  solution  is  painted  on  a  ganglion  with  a 
brush,  the  passage  of  nerve-impulses  through  the  ganglion  is  blocked 
for  a  time  (Langley).  The  seat  of  the  *  block '  is  probably  the  felt- 
work  of  fibrils  in  which  the  central  nerve-fibres  terminate  around  the 
ganglion  cells  (Cushny  and  Huber).  The  nerve-fibres  peripheral  to 
the  ganglion  are  not  affected.  The  question  whether  efferent  fibres 
are  connected  with  nerve-cells  between  a  given  point  and  their 

*  Pilo-motor  nerves  supply  the  smooth  arrector  pili  muscles,  whose 
contraction  causes  the  hair  to  '  stand  on  end.' 


158  A  MANUAL  OF  PHYSIOLOGY 

peripheral  distribution  can,  therefore,  be  answered  by  observing 
whether  any  effect  of  stimulation  is  abolished  by  nicotine.  If,  for 
instance,  the  excitation  of  a  nerve  caused  constriction  of  certain 
bloodvessels  before,  and  has  no  effect  after,  the  application  of 
nicotine  to  a  ganglion,  its  vaso- con  stricter  fibres,  or  some  of  them, 
must  be  connected  with  nerve-cells  in  that. ganglion. 

We  have  thus  traced  the  vaso-motor  nerves  from  the 
cerebro-spinal  axis  to  the  bloodvessels  which  they  control ; 
it  still  remains  to  define  the  portion  of  the  central  nervous 
system  to  which  these  scattered  threads  are  related,  which 
holds  them  in  its  hand  and  acts  upon  them  as  the  needs  of 
the  organism  may  require. 

Vaso-motor  Centres. — Now,  experiment  has  shown  that  there 
is  one  very  definite  region  of  the  spinal  bulb  which  has  a  most 
intimate  relation  to  the  vaso-motor  nerves.  If  while  the  blood- 
pressure  in  the  carotid  is  being  registered,  say,  in  a  curarized 
rabbit,  the  central  end  of  a  peripheral  nerve  like  the  sciatic 
is  stimulated,  the  pressure  rises  so  long  as  the  bulb  is  intact, 
this  rise  being  largely  due  to  the  reflex  constriction  of 
the  vessels  in  the  splanchnic  area.  If  a  series  of  trans- 
verse sections  be  made  through  the  brain,  the  rise  of 
pressure  caused  by  stimulation  of  the  sciatic  is  not  affected 
till  the  upper  limit  of  the  bulb  is  almost  reached.  If  the 
slicing  is  still  carried  downwards,  the  blood-pressure  sinks, 
and  the  rise  following  stimulation  of  the  sciatic  becomes  less 
and  less.  When  the  medulla  has  been  cut  away  to  a  certain 
level,  only  an  insignificant  rise  or  none  at  all  can  be  obtained. 
The  portion  of  the  medulla  the  removal  of  which  exerts  an 
influence  on  the  blood-pressure,  and  its  increase  by  reflex 
stimulation,  extends  from  a  point  4  to  5  mm.  above  the 
point  of  the  calamus  scriptorius  to  within  I  to  2  mm.  of  the 
corpora  quadrigemina  (Owsjannikow).  Other  observers  give 
narrower  limits.  Stimulation  of  the  medulla  causes  a  rise, 
destruction  of  this  portion  of  it  a  fall,  of  general  blood- 
pressure.  There  is  evidently  in  this  region  a  nervous 
'  centre '  so  intimately  related,  if  not  to  all  the  vaso-motor 
nerves,  at  least  to  such  very  important  tracts  as  to  deserve 
the  name  of  a  vaso-motor  centre.  Experiment  has  shown 
that  this  is  much  the  most  influential  centre,  and  it  is 
usually  called  the  chief  or  general  vaso-motor  centre.  But 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     159 

there  are  subsidiary  centres  all  along  the  cord,  and  while  a 
very  large  number  of  the  constrictor  fibres  are  related  to  the 
chief  centre  in  the  medulla,  some  are  either  normally  under 
the  control  of  subordinate  centres,  or  may  in  special  circum- 
stances come  to  be  dominated  by  them. 

Thus,  in  the  frog  it  is  possible  to  go  on  destroying  more  O . 
and  more  of  the  cord  from  above  downwards,  and  still  to 
obtain  reflex  vaso-motor  effects,  as  seen  in  the  vessels  of 
the  web,  by  stimulating  the  central  end  of  the  sciatic  nerve. 
Although  these  effects  indeed  diminish  in  amount  as  the 
destruction  of  the  cord  proceeds,  yet  a  distinct  change  can 
be  caused  when  only  a  small  portion  of  the  cord  remains 
intact. 

Similarly,  in  the  mammal  evidence  has  been  obtained  of 
the  existence  of  'centres'  at  various  levels  of  the  cord, 
capable  of  acting  as  vaso-motor  centres  after  the  chief 
centre  in  the  bulb  has  been  cut  off.  For  example,  after 
section  of  the  cord  at  the  upper  limit  of  the  lumbar  region, 
erection  of  the  penis,  which  is  known  to  be  due  to  a  reflex 
dilatation  of  its  arteries  through  the  nervi  erigentes,  can  still 
be  caused  by  mechanical  stimulation  of  the  glans  penis,  so 
long  as  the  afferent  fibres  of  the  reflex  arc  contained  in  the 
nervus  pudendus  are  intact.  Destruction  of  the  lumbar 
cord  abolishes  the  effect.  It  is  impossible  to  avoid  the  con- 
clusion that  a  vaso-dilator  or  erection  centre,  which  is  in 
relation  on  the  one  hand  with  the  nervi  erigentes,  and  on 
the  other  with  the  nervus  pudendus,  exists  in  the  lower 
portion  of  the  spinal  cord.  Vaso-motor  centres  for  the 
hind-limbs  have  also  been  located  in  the  same  region.  And 
such  centres  appear  to  exist  even  beyond  the  limits  of  the 
central  nervous  system.  For  when  the  lower  portion  of 
the  cord  is  completely  destroyed,  the  dilatation  of  the 
vessels  of  the  hind-limbs,  which  is  at  first  so  conspicuous, 
passes  away  after  a  time  ;  and  the  only  plausible  explanation 
seems  to  be  that  the  functions  of  vaso-motor  centres  have 
been  assumed  by  some  of  the  peripheral  (sympathetic) 
ganglia  (Goltz  and  Ewald). 

Of  the  anatomical  relations  of  the  nerve-cells  that  make  up  the      0 
bulbar  and  spinal  vaso-motor  centres,  little  more  is  known  than  may 


160  A  MANUAL  OF  PHYSIOLOGY 

be  deduced  from  the  physiological  facts  we  have  been  reciting.  It 
has  been  surmised  that  certain  cells  of  small  size  scattered  up  and 
down  the  cord  in  the  anterior  horn  and  intermedio-lateral  tract,  and 
cropping  out  also  in  the  bulb,  are  vaso-motor  cells.  It  must  be 
assumed  that  their  axis-cylinder  processes  are  connected  with  the 
vaso-motor  fibres  which  we  have  already  discovered  emerging  from 
the  brain  in  certain  cranial  nerves  and  from  the  cord  in  the  anterior 
spinal  roots.  And,  indeed,  there  is  reason  to  believe  that,  in  the  case 
of  the  spinal  vaso-motor  cells  at  any  rate,  the  connection  is  made 
without  the  intervention  of  any  other  nerve-cells,  and  that  the  axis- 
cylinders  of  these  vaso-motor  fibres  are  the  axis-cylinder  processes  of 
the  vaso-motor  cells.  So  that  the  simplest  efferent  path  along  which 
vaso-motor  impulses  can  pass  may  be  considered  as  built  up  of  two 
neurons,  one  with  its  cell-body  in  the  central  nervous  system,  and  the 
other  in  a  sympathetic  ganglion.  But  since  it  would  appear  that  the 
spinal  vaso-motor  centres  are  under  the  control  of  the  chief  centre 
in  the  bulb,  it  is  necessary  to  suppose  that  the  axis-cylinder  processes 
of  some  of  the  cells  of  the  bulbar  centre  come  into  relation  with  the 
spinal  vaso-motor  cells,  and  that  impulses  passing,  let  us  say,  from 
the  bulb  to  the  vessels  of  the  leg,  would  have  to  traverse  three 
neurons  (see  Chap.  XIL). 

Vaso-motor  Reflexes. — We  have  already  seen  that  the 
cardiac  centres  are  constantly  influenced  by  afferent  im- 
pulses, and  that  in  the  direction  either  of  augmentation  or 
inhibition.  The  vaso-motor  centre  in  the  bulb  is  equally 
sensitive  to  such  impulses.  They  reach  it  for  the  most  part 
along  the  same  nerves,  and  by  increasing  or  diminishing  its 
tone  cause  sometimes  constriction  and  sometimes  dilatation 
of  the  vessels,  the  result  depending  partly  upon  the  anato- 
mical connection  of  the  afferent  fibres,  but  apparently  in 
part  also  upon  the  state  of  the  centre. 

Of  the  afferent  nerves  that  cause  vaso-dilatation,  the  most 
important  is  the  depressor,  whose  reflex  inhibitory  action  on 
the  heart  has  been  alreaSy  described.  The  fall  in  the 
arterial  pressure  is  due  chiefly,  not  to  the  inhibition  of  the 
heart,  but  to  the  inhibition  of  the  portion  of  the  vaso-motor 
centre  that  presides  over  the  great  area  ruled  by  the 
splanchnic  nerves,  and  the  consequent  dilatation  of  the 
vessels  of  the  abdominal  viscera.  For  if  these  nerves  have 
been  previously  cut,  stimulation  of  the  depressor  is  ineffective, 
while  it  produces  its  usual  result  after  section  of  the  vagi. 
It  has  been  suggested  that  the  function  of  the  depressor  is 
to  act  as  an  automatic  check  upon  the  blood-pressure  in  the 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH    161 


interest  of  the  heart,  its  terminations  in  the  ventricular  wall 
being  mechanically  stimulated  when  the  pressure  tends  to 
rise  towards  the  danger  limit.  In  rare  cases,  efferent  inhi- 
bitory fibres  for  the  heart  have  been  found  in  the  depressor 
of  the  rabbit. 

Many  of  the  peripheral  nerves  contain  fibres  whose 
stimulation  is  followed  by  dilatation  of  the  bloodvessels  in 
special  regions,  usually  the  areas  to  which  they  are  them- 
selves distributed,  accompanied  by  constriction  of  distant 
and,  it  may  be,  more  extensive  vascular  tracts.  Thus,  the 
usual  local  effect  of  stimulating  the  afferent  fibres  of  the 


FIG.  54. — DIAGRAM  OF  DE- 
PRESSOR NERVE  IN  RABBIT. 


X,  vagus;  SL,  superior  laryn-     Fl(J    55._BLOOD-PRESSURE  TRACING  (RABBIT) 
.geal  branch  of  vagus;   D,  de-  JJ        m™™™  MAM™*-™^  \ 


vagus 

pressor  fibres.  The  arrows  show 
the  course  of  the  impulses  that 
affect  the  blood-pressure. 


MANOMETER.) 

Central  end  of  depressor  stimulated  at  i  ;  stimula- 
tion stopped  at  2.     Time  trace  seconds. 


Jowestjhree  thprjidcjierves,  injwhpse  anterior  roots. run  the 
vaso-motor  fibres  for  the  kidney,  is  a  dilatation  of  the  renal 
vessels  (Bradford),  and  the  usual  local  effect  of  stimulating 
the  infra-orbital  or_supra-orbital  nerve  a  dilatation  of  the 
external  maxillary  artery.  But  the  general  effect  in  both 
cases  is  vaso-constriction  in  other  regions  of  the  body, 
which  more  than  compensates  the  local  dilatation,  so  that 
the  arterial  blood-pressure  rises.  It  is  not  difficult  to  see 
that  both  of  these  changes  render  it  easier  for  the  part  to 
obtain  an  increased  supply  of  blood. 

II 


i62  A  MANUAL  OF  PHYSIOLOGY 

The  kind  of  stimulus  seems  to  have  something  to  do  with 
the  direction  of  the  reflex  vaso-motor  change,  for  while 
electrical  stimulation  of  every  muscular  nerve,  even  of  the 
very  finest  twigs  that  can  be  isolated  and  laid  on  electrodes, 
provokes  always,  whether  the  shocks  follow  each  other 
rapidly  or  slowly,  a  rise  of  general  blood-pressure,  mechanical 
stimulation  of  a  muscle,  as  by  kneading  or  massage,  causes 
a  fall.  The  condition  of  the  afferent  fibres  also  exerts  an 
influence.  For  example,  excitation  of  the  central  end  of  a 
sciatic  nerve  that  has  been  cooled  is  followed  by  vaso- 
dilatation  and  fall  of  pressure,  the  opposite  of  the  ordinary 
result.  These  and  similar  facts  have  led  to  the  idea  that 
most  afferent  nerves  contain  two  kinds  of  fibres,  whose 
stimulation  can  affect  the  activity  of  the  vaso-motor  centres, 
'  reflex  vaso-constrictor,'  or  *  pressor '  fibres,  and  *  reflex 
vaso-dilator,'  or  '  depressor '  fibres.  The  branch  of  the 
vagus,  however,  to  which  the  name  *  depressor  '  has  been 
specially  given,  is  the  only  peripheral  nerve  the  excitation  of 
which  is  in  all  circumstances  followed  by  a  general  diminu- 
tion of  arterial  pressure.  If  specific  '  depressor  '  fibres  exist 
elsewhere,  they  are  so  mingled  with  '  pressor '  fibres  that 
their  action  is  masked  when  both  are  stimulated  together. 
The  state  of  the  vaso-motor  centre  is  a  third  factor,  which 
has  some  importance  in  determining  the  result  of  reflex 
vaso-motor  stimulation.  For  instance,  in  an  animal  deeply 
anaesthetized  with  chloroform  or  chloral,  excitation  of  an 
ordinary  sensory  nerve  may  cause,  not  a  rise,  but  a  fall  of 
blood-pressure. 

An  interesting  illustration  of  the  reciprocal  relation 
between  different  parts  is  found  in  the  opposite  behaviour  o 
the  vessels  of  the  skin  and  those  of  the  internal  organs 
which  is  often  observed  during  reflex  stimulation  of  th 
vaso-motor  centres.  For  example,  stimulation  of  the  cut  enc 
of  the  sciatic  causes,  as  we  have  already  seen,  a  notable  risi 
in  the  blood-pressure  and  extensive  vaso-constriction.  Thi 
certainly  involves  the  splanchnic  area  ;  but  superficial  parts 
as  the  lips,  may  be  seen  to  be  flushed  with  blood.  Ii 
asphyxia,  when  the  vaso-motor  centres  are  directly  stimu 
lated  by  the  venous  blood,  this  antagonism  is  still  bette 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     163 

marked :  the  cutaneous  vessels  are  widely  dilated  and 
engorged,  the  face  is  livid,  but  the  abdominal  organs  are 
pale  and  bloodless  (Heidenhain).  The  blood-pressure  rises 
rapidly,  reaches  a  maximum,  and  then  gradually  falls  as  the 
vaso-motor  centre  becomes  paralyzed  (Figs.  56  and  57). 

These  facts  enable  us  to  some  extent  to  understand  the  ~7~, 
manner  in  which  the  distribution  of  the  blood  is  adjusted  to 
the  requirements  of  the  different  parts  of  the  body,  so  that 
to  a  certain  degree  of  approximation  no  organ  has  too  much, 
and  none  too  little.  The  blood-supply  of  the  organs  is 
always  shifting  with  the  calls  upon  them.  Now,  it  is  the 
actively-digesting  stomach  and  the  actively-secreting  glands 
of  the  alimentary  tract  which  must  be  fed  with  a  full  stream 


FIG.  56. — RISE  OF  BLOOD-PRESSURE  IN  ASPHYXIA  (IN  RABBIT). 

Respiration  stopped  at  i.  Interval  between  2  and  3  (not  reproduced)  44  seconds, 
during  which  the  blood-pressure  steadily  rose.  At  4,  respiration  resumed.  Time 
tracing  marks  seconds. 

of  blood,  to  supply  waste  and  to  carry  away  absorbed  nutri- 
ment. Again,  it  is  the  working  muscles  of  the  legs  or  of  the 
arms  that  need  the  chief  blood-supply.  But  wherever  the 
call  may  be,  the  vaso-motor  mechanism  is  able,  in  health, 
to  answer  it  by  bringing  about  a  widening  of  the  small 
arteries  of  the  part  which  needs  more  blood,  and  a  compen- 
satory narrowing  of  the  vessels  of  other  parts  whose  needs 
are  not  so  great. 

It  is  also  through  the  vaso-motor  system,  and  especially 
by  the  action  of  that  portion  of  it  which  governs  the 
abdominal  vessels,  and  of  the  nerves  that  regulate  the  work 
of  the  heart,  that  in  animals  to  which  the  upright  position 

II — 2 


164  A  MANUAL  OF  PHYSIOLOGY 

is  normal  (monkey)  and  in  man  the  influence  of  changes  of 
posture  on  the  circulation  is  almost  completely  compensated.* 
The  pressure  in  the  upper  part  of  the  human  brachial  artery 
has  been  measured  by  a  special  form  of  sphygmo-manometer, 
first   in  the  horizontal  and  then  immediately  afterward  ii 
the  standing  posture,  and  in  health  it  has  been  found  t< 
remain   practically   unchanged.      But    if    the    person   was 
over-worked   or   out  of  sorts,  the   compensation  was   les 
complete.      In   such  animals  as   the  rabbit   this   compen- 
sation is  totally  inefficient.     When  a  domesticated  rabbit, 
which  has   been  kept   in  a  hutch,  is   suspended  vertical!] 
with  the  feet  down,  the   blood  drains  into  the  abdomim 
vessels,    syncope,  speedily   ensues,   and   in    a   period   thai 
ranges   from   less  than  a   quarter  to  three-quarters   of  ai 
hour  the  animal  dies  in  the  convulsions  of  acute  cerebral 
anaemia   (Salathe*,   Hill).     The  head-down   position  has  n( 
ill  effects.     In  wild  rabbits,  whose  abdominal  wall  is  more 
tense    and    elastic,   these    fatal   symptoms   are   not   easil; 
produced,  and  the  same  is  true  of  cats  and  dogs.     But  in 
all   animals,  when   the  compensation    is   destroyed,   as   in 
paralysis  of  the  vaso-motor  centre  by  chloroform,  the  cir- 
culation may  be  profoundly  influenced  by  the  position  of  the 
body :  elevation  of  the  head  may  lead  to  cerebral  anaemia, 
syncope,  and  even  death;  elevation  of  the  legs,  and  par- 
ticularly the  abdomen,  may  restore  the  sinking  pulse  by 
filling  the  heart  and  the  vessels  of  the  brain.     If  a  chloralized 
dog  be  fastened  on  a  board  which  can  be  rotated  about  a 

*  Two  factors  may  be  distinguished  in  the  blood-pressure,  the  hydro- 
static and  the  hydrodynamic  elements.  The  hydrostatic  portion  of  the 
pressure  is  due  to  the  weight  of  the  column  of  blood  acting  on  the  vessel ; 
the  hydrodynamic  portion  of  the  pressure  is  due  to  the  work  of  the  heart. 
If  a  dog  be  securely  fastened  to  a  holder  arranged  in  such  a  way  that  the 
animal  can  be  placed  vertically,  with  the  head  up  or  down,  and  the  mean 
blood-pressure  in  the  crural  artery  be  measured  in  the  two  positions,  there 
will  be  a  considerable  difference.  For  when  the  legs  are  uppermost  the 
heart  has  to  overcome  the  weight  of  the  column  of  blood  rising  above  it 
to  the  crural  artery  ;  when  the  head  is  uppermost  the  action  of  the  heart 
is  reinforced  by  the  weight  of  the  blood.  And  if  no  change  were  produced 
in  the  action  of  the  heart,  or  in  the  general  resistance  of  the  vascular  path, 
by  the  change  of  position,  this  difference  would  be  equal  to  the  pressure 
of  a  column  of  blood  twice  as  high  as  the  straight-line  distance  between 
the  cannula  and  the  point  of  the  arterial  system  at  which  the  pressure  is 
the  same  with  head  up  as  with  head  down  (indifferent  point). 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     165 

horizontal  axis  passing  under  the  neck,  the  blood-pressure 
in  the  carotid  artery  falls  greatly  when  the  animal  is  made 
to  assume  the  vertical  position  with  the  head  up,  and  either 
rises  a  little  or  remains  relatively  unchanged  when  the  head 
is  made  to  hang  down.  So  great  may  the  fall  of  pressure  be 
in  the  former  position  that  death  may  occur  if  it  be  long 
maintained  (Practical  Exercises,  p.  187). 

Finally,  it  is  in  virtue  of  the  amazing  power  of  accommoda-    77 
tion  possessed  by  the  vascular  system,  as  controlled  by  the 
vaso-motor   and  cardiac  nerves,  that  so  long  as  these  are 


I    I    I    1      (    I    I    I    I    I    1    i    I    I  1    I    I    I    t    I    I     I  r  I 


FIG.  57.— BLOOD-PRESSURE  TRACING  FROM  A  DOG  POISONED  WITH  ALCOHOL. 
;  The  respiratory  centre  being  paralyzed,  respiration  stopped,  and  the  typical  rise  of 
blood-pressure  in  asphyxia  took  place.  The  pressure  had  again  fallen,  and  total 
I  paralysis  of  the  vaso-motor  centre  was  near  at  hand,  when  at  A  the  animal  made  a 
single  respiratory  movement.  The  quantity  of  oxygen  thus  taken  in  was  enough 
to  restore  the  vaso-motor  centre,  and  the  blood-pressure  again  rose.  This  was  re- 
peated five  or  six  times. 

not  disabled  the  total  quantity  of  blood  may  be  greatly 
diminished  or  greatly  increased,  without  endangering  life, 
or  even  causing  more  than  a  transient  alteration  in  the 
arterial  pressure.  It  is  not  until  at  least  a  quarter  of  the 
.blood  has  been  withdrawn  that  there  is  any  notable  effect 
on  the  pressure,  for  the  loss  is  quickly  compensated  by  an 
increase  in  the  activity  of  the  heart  and  a  constriction  of 
the  small  arteries.  An  animal  may  recover  after  losing  con- 
siderably more  than  half  its  blood.*  Conversely,  the  volume 

*  It  is  not  usually  possible  to  obtain  quite  two-thirds  of  the  total  blood 
:>y  bleeding  a  dog  from  an  artery  like  the  carotid. 


1 66  A  MANUAL  OF  PHYSIOLOGY 

of  the  circulating  liquid  may  be  almost  doubled  by  the  in- 
jection of  blood  or  normal  saline  solution  without  causing 
death,  and  increased  by  50  per  cent,  without  any  marked 
increase  in  the  pressure.  The  excess  is  promptly  stowed 
away  in  the  dilated  vessels,  especially  those  of  the  splanchnic 
area ;  the  water  passes  rapidly  into  the  lymph,  and  is  then 
more  gradually  eliminated  by  the  kidneys. 

From  these  facts  we  can  deduce  the  practical  lesson, 
that  blood-letting,  unless  copious,  is  useless  as  a  means  of 
lowering  the  general  arterial  pressure,  while  it  need  not  be 
feared  that  transfusion  of  a  considerable  quantity  of  blood, 
or  of  salt  solution,  in  cases  of  severe  haemorrhage  will 
dangerously  increase  the  pressure.  And  from  the  physio- 
logical point  of  view  the  term  '  haemorrhage  '  includes  more 
than  it  does  in  its  ordinary  sense.  For  as  dirt  to  the 
sanitarian  is  '  matter  in  the  wrong  place,'  haemorrhage  to 
the  physiologist  is  blood  in  the  wrong  place.  Not  a  drop  of 
blood  may  be  lost  from  the  body,  and  yet  death  may  occur 
from  haemorrhage  into  the  pleural  or  the  abdominal  cavity, 
into  the  stomach  or  intestines.  Not  only  so,  but  a  man 
may  bleed  to  death  into  his  own  bloodvessels  ;  in  shock,  as 
well  as  in  ordinary  fainting  or  syncope,  the  blood  which 
ought  to  be  circulating  through  the  brain,  heart  and  lungs 
may  stagnate  in  the  dilated  vessels  of  the  splanchnic  area. 

0,  The  Lymphatic  Circulation. — As  has  already  been  mentioned, 
some  of  the  constituents  of  the  blood,  instead  of  passing  back  to 
the  heart  from  the  capillaries  along  the  veins,  find  their  way  by 
a  much  more  tedious  route  along  the  lymphatics.  The  blood- 
capillaries  are  everywhere  in  very  intimate  relation  with  lymph- 
capillaries,  which  are  simply  irregular  spaces,  more  or  less  completely 
lined  with  epithelioid  cells,  in  the  connective-tissue  that  everywhere 
accompanies  and  supports  the  bloodvessels.  The  constituents  of  the 
blood-plasma  are  filtered  through,  or,'  as  some  say,  secreted  by  the 
capillary  walls  into  the  lymph  spaces,  and  there  form  the  clear  liquid 
known  as  lymph,  from  which  the  cells  of  the  tissues  take  up  food, 
and  into  which  they  discharge  waste  products.  The  lymph  spaces 
are  connected  with  more  regular  lymphatic  vessels,  with  lymphatic 
glands  at  intervals  on  their  course.  These  fall  into  larger  trunks, 
and  finally  the  greater  part  of  the  lymph  reaches  the  blood  again  by 
the  thoracic  duct,  which  opens  into  the  venous  system  at  the  junction 
of  the  left  subclavian  and  internal  jugular  veins.  The  lymph  from 
the  right  side  of  the  head  and  neck,  the  right  extremity,  and  the 
right  side  of  the  thorax  with  its  viscera,  is  collected  by  the  right 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH     167 

lymphatic  duct,  which  opens  at  the  junction  of  the  right  subclavian 
and  internal  jugular  veins.  The  openings  of  both  ducts  are  guarded 
by  semilunar  valves,  which  prevent  the  reflux  of  blood  from  the 
veins.  Serous  cavities  like  the  pleural  sacs  are  really  large  lymph 
spaces,  and  they  are  connected  through  small  openings,  called 
stomata,  with  lymphatic  vessels. 

The  rate  of  flow  of  the  lymph  in  the  thoracic  duct  is  very  small 
compared  with  that  of  the  blood  in  the  arteries — only  about  4  mm. 
per  second,  according  to  one  observer.  Nevertheless,  a  substance 
injected  into  the  blood  can  be  detected  in  the  lymph  of  the  duct  in 
four  to  seven  minutes  (Tschirwinsky).  The  factors  which  contribute 
to  the  maintenance  of  the  lymph  flow  are : 

(1)  The  pressure  under  which  it  passes  from  the  capillaries  into 
the  lymph  spaces.    The  pressure  in  the  thoracic  duct  of  a  horse  may 
be  as  high  as  1 2  mm.  of  mercury ;  in  the  dog  it  may  be  less  than 
i  mm.     The  difference  is  probably  due,  in  part  at  least,  to  a  differ- 
ence in  the  experimental  conditions,  dogs  being  usually  anaesthetized 
for  such   measurements,  horses  not.     The  pressure  in   the  lymph 
spaces  must,  of  course,  be  higher  than  in  the  thoracic  duct,  how 
much  higher  we  do  not  know. 

(2)  The  contraction  of  muscles   increases  the   pressure  of   the 
lymph  by  compressing  the  channels  in  which  it  is  contained,  and 
the  valves,  with  which  the  lymphatics  are  even  more  richly  provided 
than  the  veins,  hinder  a  backward  and  favour  an  onward  flow.     The 
contractions  of  the  intestines,  and  especially  of  the  villi,  are  an  im- 
portant aid  to  the  movement  of  the  chyle.     By  the  contraction  of 
the  diaphragm,  substances  may  be  sucked  from  the  peritoneal  cavity 
into  the  lymphatics  of  its  central  tendon,  through  the  stomata  in  the 
serous  layer  with  which  its  lower  surface  is  clad.     It  is  even  possible 
by  passive  movements  of  the  diaphragm  in  a  dead  rabbit  to  inject 
its  lymphatics  with  a  coloured  liquid  placed  on  its  peritoneal  surface. 
Passive  movements  of  the  limbs  and  massage  of  the  muscles  are  also 
known  to  hasten  the  sluggish  current  of  the  lymph,  and  are  some- 
times employed  with  this  object  in  the  treatment  of  disease. 

(3)  The  movements  of  respiration  aid  the  flow.     At  every  inspira- 
tion the  pressure  in  the  great  veins  near  the  heart  becomes  negative, 
and  lymph  is  sucked  into  them. 

(4)  In  some  animals   rhythmically-contracting  muscular  sacs  or 
hearts  exist  on  the  course  of  the  lymphatic  circulation.     The  frog 
has  two  pairs,  an  anterior  and  a  posterior,  of  these  lymph  hearts,  which 
pulsate,  although  not  with  any  great  regularity,  at  an  average  rate  of 
sixty  to  seventy  beats  a  minute,  and  appear  to  be  governed  by  motor 
and  inhibitory  centres  situated  in  the  spinal  cord.     Such  hearts  are 
also  found  in  reptiles.    It  is  possible  that  in  animals  without  localized 
lymph  hearts  the  smooth  muscle,  which  is  so  conspicuous  an  element 
in  the  walls  of  the  lymphatic  vessels,  may  aid  the  flow  by  rhythmical 
contractions. 


168  A  MANUAL  OF  PHYSIOLOGY 


PRACTICAL  EXERCISES  ON  CHAPTER  II. 

1.  Microscopic  Examination  of  the  Circulating  Blood. — (i)  Take 
a  tadpole  and  lay  it  on  a  glass  slide.     Cover  the  tail  with  a  large 
cover-slip,  and  examine  it  with  the  low  power  (Leitz,  oc.  III.,  obj.  3). 
Generally  the  tail  will  stick  so  closely  to  the  slide,  and  the  animal  will 
move  so  little,  that  a  sufficiently  good  view  of  the  circulation  can  be 
obtained.     If  there  is  any  trouble,  destroy  the  brain  with  a  needle. 

Observe  the  current  of  the  blood  in  arteries,  capillaries  and  veins. 
An  artery  may  be  easily  distinguished  from  a  vein  by  looking  for  a 
place  at  which  the  vessel  bifurcates.  In  veins  the  blood  flows  in  the 
two  branches  of  the  fork  towards  the  point  of  bifurcation,  in  arteries 
away  from  it. 

Sketch  a  part  of  a  field. 

To  Pith  a  Frog, — Wrap  the  animal  in  a  towel,  bend  the  head 
forwards  with  the  index-finger  of  one  hand,  feel  with  the  other  for  the 
depression  at  the  junction  of  the  head  and  backbone,  and  push  a 
narrow-bladed  knife  right  down  in  the  middle  line.  The  spinal  cord 
will  thus  be  divided  with  little  bleeding.  Now  push  into  the  cavity 
of  the  skull  a  piece  of  pointed  lucifer  match.  The  brain  will  thus 
be  destroyed.  The  spinal  cord  can  be  destroyed  by  passing  a  blunt 
needle  down  inside  the  vertebral  canal. 

(2)  Take  a  frog  and  pith  its  brain  only,  inserting  a  match  to  prevent 
bleeding.  Pin  the  frog  on  a  plate  of  cork  into  one  end  of  which  a 
glass  slide  has  been  fastened  with  sealing-wax.  Lay  the  web  of  one 
of  the  hind-legs  on  the  glass  and  gently  separate  two  of  the  toes,  if 
necessary  by  threads  attached  to  them  and  secured  to  the  cork  plate. 
Put  the  plate  on  the  microscope-stage  and  fasten  by  the  clips  (see 
pp.  26,  107). 

2.  Anatomy  of  the  Frog's  Heart. — Expose  the  heart  of  a  pithed 
frog  by  pinching  up  the  skin  over  the  abdomen  in  the  middle  line, 
dividing  it  with  scissors  up  to  the  lower  jaw,  and  then  cutting  through 
the  abdominal  muscles  and  the  bony  pectoral  girdle.     The  external 
abdominal  vein,  which  will  be  observed  on  reflecting  the  skin,  can 
be  easily  avoided.     The  heart  will  now  be  seen  enclosed  in  a  thin 
membrane,  the   pericardium,  which   should   be   grasped  with  fine- 
pointed  forceps  and  freely  divided.    Connecting  the  posterior  surface 
of  the  heart  and  the  pericardium  is  a  slender  band  of  connective 
tissue,  the  fraenum.     A  silk  ligature  may  be  passed  around  this  with 
a  threaded  curved  needle  and  tied,  and  then  the  fraenum  may  be 
divided  posterior  to  the  ligature.    The  anatomical  arrangement  of  the 
various  parts  of  the  heart  should  now  be  studied.     Note  the  single 
ventricle  with  the  bulbus  arteriosus,  the  two  auricles,  and  the  sinus 
venosus,  turning  the  heart  over  to  see  the  latter  by  means  of  the 
ligature.     Observe  the  whitish  crescent  at  the  junction  of  the  sinus 
venosus  and  the  right  auricle  (Fig.  58). 

3.  The  Beat  of  the  Heart. — Note  that  the  auricles  beat  first,  and 
then  the  ventricle.    The  ventricle  becomes  smaller  and  paler  during  its 
systole,  and  blushes  red  during  diastole.     Count  the  number  of  beats 
of  the  heart  in  a  minute.     Now  excise  the  heart,  lifting  it  by  means 


PRACTICAL  EXERCISES 


169 


of  the  ligature,  and  taking  care  to  cut  wide  of  the  sinus  venosus. 
Place  the  heart  in  a  small  porcelain  capsule  on  a  little  blotting-paper 
moistened  with  normal  saline.  Observe  that  it  goes  on  beating. 
Put  a  little  ice  or  snow  in  contact  with  the  heart,  and  count  the 
number  of  beats  in  a  minute.  The  rate  is  greatly  diminished.  Now 
remove  the  ice  and  blotting-paper,  cover  the  heart  with  normal 
saline,  and  heat,  noting  the  temperature  with  a  thermometer.  Observe 
that  the  heart  beats  faster  and  faster  as  the  temperature  rises.  At 
40°  C.  to  43°  C.  it  stops  beating  in  diastole  (heat  standstill).  Now 
at  once  pour  off  the  heated  liquid,  and  run  in  some  cold  normal 
saline.  The  heart  will  begin  to  beat  again. 

4.  Cut  off  the  apex  of  the  ventricle  a  little  below  the  auriculo- 
ventricular  groove.     The  auricles,  with  the  attached  portions  of  the 
ventricle,  go  on  beating.     The  apex  does  not  contract  spontaneously, 
but  can  be  made  to 

beat  by  stimulating 
it  mechanically  (by 
pricking  it  with  a 
needle)  or  electrically. 
Divide  the  still  con- 
tracting portion  of 
the  heart  by  a  longi 
tudinal  incision.  The 
two  halves  go  on 
beating. 

5.  Heart -tracings. 
— (i)  Fasten  a  myo- 
graph-plate  (Fig.  59) 
on  a  stand.     Take  a 
long  light  lever  con- 
sisting of  a  Straw  or     ventricle  .  d>  bulbus  arteriosus ;  e,  f,  aortse  ;  g,  sinus 
a  piece  of  thin  chip,     venosus. 

armed    at    one    end 

with  a  writing-point  of  parchment-paper,  supported  near  the  other 
end  by  a  horizontal  axis,  and  pierced  not  far  from  the  axis  by 
a  needle  carrying  on  its  point  a  small  piece  of  cork  or  a  ball  of 
sealing-wax.  A  counterpoise  is  adjusted  on  the  short  arm  of  the 
lever  in  the  form  of  a  small  leaden  weight.  Cover  a  drum  with 
glazed  paper  and  smoke  it.  The  paper  must  be  put  on  so  tightly 
that  it  will  not  slip.  To  smoke  the  drum,  hold  it  by  the  spindle 
in  both  hands  over  a  fish-tail  burner,  depress  the  drum  in  the 
flame,  and  rotate  rapidly  Avoid  putting  on  a  heavy  coating  of 
smoke,  as  a  more  delicate  tracing  is  obtained  when  the  paper  is 
lightly  smoked  The  speed  of  the  drum  can  be  varied  by  putting 
in  or  taking  out  a  small  vane.  Arrange  an  electro-magnetic  time- 
marker  for  writing  seconds  (Fig.  60).  Pith  a  frog  (brain  only), 
expose  the  heart,  and  put  under  it  a  cover-slip  to  give  it  support.  Pin 
the  frog  on  the  myograph-plate,  and  adjust  the  foot  of  the  lever  so  that 
it  rests  on  the  ventricle  or  the  auriculo-ventricular  junction.  Bring 
the  writing-point  of  the  lever  and  that  of  the  time-marker  vertically 


FIG.  58.— FROG'S  HEART  WITH  STANNIN'S  LIGA- 
TURES IN  POSITION  (CYON). 

Anterior  surface  of  heart  shown  on  the  left,  posterior 
surface  on  the  right,     a,  right  auricle  ;  b,  left  auricle  ;  c. 


i;o  A  MANUAL  OF  PHYSIOLOGY 

under  each  other  on  the  surface  of  the  drum.  Set  off  the  drum  at 
the  slow  speed  (say,  a  centimetre  a  second).  When  the  lever  rests 
on  the  auriculo-ventricular  junction,  the  part  of  the  tracing  corre- 
sponding to  the  contraction  of  the  heart  will  be  broken  into  two 


FIG.  59. — ARRANGEMENT  FOR  OBTAINING  A  HEART  TRACING  FROM  A  FROG. 

portions,  representing  the  systole  of  the  auricles  and  ventricle  re- 
spectively. Cut  the  paper  off  the  drum  with  a  knife  and  carry  it 
to  the  varnishing-trough,  holding  the  tracing  by  the  ends  with  both 


FIG.  60. — ELECTRO-MAGNETIC  TIME-MARKER  CONNECTED  WITH  METRONOME. 

The  pendulum  of  the  metronome  carries  a  wire  which  closes  the  circuit  when  it  dips 
into  either  of  the  mercury  cups,  Hg. 

hands,  smoked  side  up.  Immerse  the  middle  of  it  in  the  varnish, 
draw  first  one  end  and  then  the  other  through  the  varnish,  let  it 
drip  for  a  minute  into  the  trough,  and  fasten  it  up  with  a  pin  to 
dry. 

(2)   Heart    Tracing,   with  Simultaneous  Record  of  Auricular  and 


PRACTICAL  EXERCISES 


171 


Ventricular  Contractions. — (a)  For  this  purpose  two  levers  may  be 
arranged,  one  resting  on  the  auricle,  the  other  on  the  ventricle,  the 
writing  points  being  placed  in  the  same  vertical  straight  line  on  the 
drum.  A  convenient  form  of  apparatus  is  shown  in  Fig.  61. 

(1)}  Gaskell's  Method  (a  modification  of). — Attach  a  silk  ligature  to 
the  very  apex  of  the  ventricle.  Divide  the  fnenum,  cut  the  aorta 
across  close  to  the  bulbus,  pinch  up  a  tiny  portion  of  the  auricle  and 
ligature  it.  Remove  the  intestines,  liver,  lungs,  etc.,  care  being  taken 
in  cutting  away  the  liver  not  to  injure  the  sinus.  Then  remove  the 
lower  jaw,  and  cut  away  the  whole  of  the  body  except  the  head,  part 
of  the  oesophagus,  and  the  tissue  connecting  it  with  the  heart.  Fix 
the  head  in  a  clamp  sliding  on  an  ordinary  stand.  The  heart  is  held 
at  the  auriculo-ventricular  junction  in  a  Gaskell's  clamp  supported  on 


„,-"•"* 

•**7— -» 


FIG.   61.— APPARATUS    FOR    OBTAINING   A    SIMULTANEOUS   TRACING   OF 
AURICULAR  AND  VENTRICULAR  CONTRACTIONS. 

a  separate  stand.  The  thread  connected  with  the  ventricle  is  brought 
round  a  pulley  and  attached  to  a  lever  above  the  heart.  The 
auricle  is  connected  with  another  lever.  The  writing  points  of 
the  two  levers  are  arranged  in  a  vertical  line  on  the  drum.  The 
small  pulley  must  be  oiled  from  time  to  time  to  lessen  the  friction 
(Fig.  62). 

6.  Dissection  of  the  Vagus  and  Cardiac  Sympathetic  Nerves  in 
the  Frog.— (i)  Put  the  tissues  in  the  region  of  the  neck  on  the 
stretch  by  passing  into  the  gullet  a  narrow  test-tube  or  a  thick  glass 
rod  moistened  with  water,  and  by  pinning  apart  the  anterior  limbs. 
Expose  the  heart  by  cutting  through  the  pectoral  girdle  in  the  way 
described  in  2  (p.  168).  On  clearing  away  a  little  connective  tissue 
and  muscle  with  a  seeker,  three  large  nerves  will  come  into  view. 
The  upper  is  the  glosso-pharyngeal,  the  lower  the  hypoglossal  ;  the 


172 


A  MANUAL  OF  PHYSIOLOGY 


vagus  crosses  diagonally  between  them  (Fig.  63).  Above  the  vagus 
trunk,  running  parallel  to  it,  and  separated  from  it  by  a  thin  muscle 
and  a  blood-vessel  (the  carotid  artery),  lies  its  laryngeal  branch.  The 
vagus  should  be  traced  up  to  the  ganglion  situated  on  it  near  its  exit 
from  the  skull. 

(2)  Then   cut  away  the   lower  jaw,  dividing  and  reflecting  the 
membrane  covering  the  roof  of  the  mouth.     At  the  junction  of  the 


FIG.  62. — ARRANGEMENT  FOR  RECORDING  AURICULAR  AND  VENTRICULAR 
CONTRACTIONS  (AND  STUDYING  THE  INFLUENCE  OF  TEMPERATURE  ON 
THE  HEART). 

C,  clamp  holding  the  heart  at  the  auriculo-ventricular  groove.  P,  pulley  round 
which  a  thread  attached  to  the  apex  of  the  ventricle  passes  to  the  lever  L/;  L,  lever 
connected  with  auricle.  (The  rest  of  the  arrangement  is  for  studying  the  influence  of 
temperature  on  the  heart  and  its  nerves,  G  being  a  vessel  filled  with  normal  saline 
solution  in  which  the  heart  is  immersed  ;  R.  an  inflow  tube  from  a  reservoir  containing 
salt  solution  at  the  temperature  required ;  O',  an  outflow  tube  by  which  G  may  be 
emptied  into  the  beaker  B' ;  O,  a  tube  passing  to  the  beaker  B  to  prevent  overflow  from 
G;  T,  a  thermometer.) 

skull  and  the  backbone  will  be  seen  on  each  side  the  levator  anguli 
scapulae  muscle  (Fig.  64).  Remove  this  muscle  carefully  with  fine 
forceps.  Clear  away  a  little  connective  tissue  lying  just  over  the  upper 
cervical  vertebras,  and  the  sympathetic  chain,  with  its  ganglia,  will 
be  seen.  Pass  a  fine  silk  thread  beneath  the  sympathetic  about  the 
level  of  the  large  brachial  nerve,  by  means  of  a  sewing-needle  which 
has  been  slightly  bent  in  a  flame  and  fastened  in  a  handle.  Tie  the 


PRACTICAL  EXERCISES 


173 


Glass  rod    jj 


Larynqeal 
\  branch  cf 
X  Vagus 


ligature,  divide  the  sympathetic  below  it,  and  isolate  it  carefully  with 
fine  scissors  up  to  its  junction  with  the  vagus  ganglion. 

Batteries. — To  setup  a  Daniell  Cell — Fill  the  porous  pot  (Fig.  143, 
p.  5 1 7)  previously  well  soaked  in  water,  with  dilute  sulphuric  acid(i  part 
of  commercial  acid  to  10  or  15  parts  of  water)  to  within  i  \  inches  of 
the  brim,  and  place  in 
it  the  piece  of  amalga- 
mated zinc.  If  the 
zinc  is  not  properly 
amalgamated,  leave 
it  in  the  pot  for  a 
minute  or  two  to 
clean  its  surface. 
Then  lift  it  out,  pour 
over  it  a  little  mer- 
cury, and  rub  the 
mercury  thoroughly 
over  it  with  a  cloth. 
Put  the  pot  into  the 
outer  vessel,  which 
contains  the  copper 
plate,  and  is  filled 
with  a  saturated  solu- 
tion of  sulphate  of 
copper,  with  some 
undissolved  crystals 
to  keep  it  saturated. 
After  using  the 
Daniell,  it  must 
always  be  taken  down. 
The  outer  pot  is  left 
with  the  copper  plate  FlG>  6^-THE  RELATIONS  OF  THE  VAGUS  IN  THE 
and  the  sulphate  solu-  FROG. 

tion  in  it.   The  zinc  is 

washed  and  brushed  bright.     The  sulphuric  acid  is  poured  into  the 
stock  bottle,  and  the  porous  pot  put  into  a  large  jar  of  water  to  soak. 

The  Bichromate  Cell  contains  only  one  liquid — a  mixture  of  i  part 
of  sulphuric  acid  with  4  parts  of  a  10  per  cent,  solution  of  potassium 
bichromate.  In  this  is  placed  one,  or  in  some  forms  two,  carbon 
plates  and  a  plate  of  amalgamated  zinc.  After  using  the  battery, 
take  the  zinc  out  of  the  liquid. 

The  Leclanche  battery  consists  of  a  porous  pot  filled  with  a 
mixture  of  manganese  dioxide  and  carbon  packed  around  a  carbon 
plate,  which  forms  the  positive  pole.  The  pot  stands  in  an  outer 
jar  of  glass  filled  with  a  saturated  solution  of  ammonium  chloride, 
into  which  dips  an  amalgamated  zinc  rod,  which  constitutes  the 
negative  pole. 

7.  Stimulation  of  the  Vagus  in  the  Frog. — Make  the  same 
arrangements  as  in  5(1)  (p.  169),  but,  in  addition,  set  up  an  induction 
machine  arranged  for  an  interrupted  current  (Fig.  65),  with  a  Daniell, 


174 


A  MANUAL  OF  PHYSIOLOGY 


a  bichromate,  or  a  Leclanche  cell  in  the  primary  circuit,  which 
should  also  include  a  simple  key.  Insert  a  short-circuiting  key 
in  the  secondary  circuit.  Attach  the  electrodes  to  the  short-cir- 
cuiting key,  push  the  secondary  coil  up  towards  the  primary  until  the 
shocks  are  distinctly  felt  on  the  tongue  when  the  Neef  s  hammer  is 
set  going  and  the  short-circuiting  key  opened.  Pith  the  brain  of  a 
frog,  expose  the  heart,  dissect  out  the  vagus  on  one  side,  ligature  it 
as  high  up  as  possible,  and  divide  above  the  ligature.  Fasten  the 
electrodes  on  the  cork  plate  by  means  of  an  indiarubber  band,  and 

lay  the  vagus  on  them. 
Set  the  drum  off  (at  slow 
speed).  After  a  dozen 
heart-beats  have  been  re- 
corded, stimulate  the  vagus 
for  two  or  three  seconds  by 
opening  the  short-circuiting 
key.  If  the  nerve  is  active, 
the  heart  will  be  slowed, 
weakened, or  stopped.  In 
the  last  case  the  lever  will 
trace  an  unbroken  straight 
line  ;  but  even  if  the  stimu- 
lation is  continued  the 
beats  will  again  begin. 

8.  Stimulation  of  the 
Junction  of  the  Sinus  and 
Auricles.  — After  a  suf- 
ficient number  of  the  obser- 
vations described  in  7  have 
been  taken  with  varying 
time  and  strength  of  stimu- 
lation, take  the  writing- 
points  off  the  drum,  apply 
the  electrodes  directly  to 
the  crescent  at  the  junction 
of  the  sinus  venosus  with 
the  right  auricle,  and 
stimulate.  The  heart  will 
be  affected  very  much  in 
the  same  way  as  by  stimula- 
tion of  the  vagus,  except  that  during  the  actual  stimulation  its  beats 
may  be  quickened  and  the  inhibition  may  only  begin  after  the 
electrodes  have  been  removed  (Fig.  46,  p.  135). 

9.  Effect  of  Muscarine  and  Atropia. — Paint  on  the  sinus  venosus 
with  a  small  camel's-hair  brush  a  very  dilute  solution  of  muscarine. 
The  heart  will  soon  be  seen  to  beat  more  slowly,  and  will  ultimately 
stop  in  diastole.  Now  apply  a  dilute  solution  of  sulphate  of  atropia 
to  the  sinus.  The  heart  will  again  begin  to  beat.  Stimulation  of 
the  vagus  will  now  cause  no  inhibition  of  the  heart,  because  its 
endings  have  been  paralyzed  by  atropia.  (Muscarine  has  also  been 


FIG.  64.— RELATION  OF  THE  SYMPATHETIC 
TO  THE  VAGUS  IN  THE  FROG. 

i,  2,  3,  4  are  spinal  nerves. 


PRACTICAL  EXERCISES  175 

applied  to  the  heart,  but  it  could  be  shown  by  a  separate  experiment 
that  atropia  by  itself  has  the  same  effect  on  the  vagus  endings.) 
(P.  141.) 

10.  Stannius'  Experiment. — Pith  a  frog.     Expose  the  heart  in  the 
way  described  under  2  (p.  168).     Ligature  the  fraenum  with  a  fine  silk 
thread,  and  use  the  thread  to  manipulate  the  heart.     With  a  curved 
needle   pass  a  moistened  silk   thread  between  the  aorta   and  the 
superior  vena  cava,  and  tie  it  round  the  junction  of  the  sinus  and 
right  auricle  (Fig.  58).    The  auricles  and  ventricle  stop  beating  as  soon 
as  the  ligature  is  tightened.    The  sinus  venosus  goes  on  beating.    Now 
separate  the  ventricle  from  the  rest  of  the  heart  by  an  incision  through 
the  auriculo-ventricular  groove,  or  tie  a  second  ligature  in  the  groove. 
The  ventricle  begins  to  beat  again,  the  auricle  remaining  quiescent 
in  diastole  (p.  142).     Occasionally  both  auricle  and  ventricle,  or  only 
the  auricle,  may  begin  to  beat. 

11.  Stimulation  of  Cardiac  Sympathetic  Fibres  in  the  Frog. — 
(i)  In  the  vago-sympathetic  after  the  inhibitory  fibres  have  been  cut  out.  by 
atropia. — Arrange  everything  as  in  7  (p.  173).     Assure  yourself,  by 


FIG.  65. — ARRANGEMENT  OF  INDUCTION  MACHINE  FOR  TETANUS. 
B,  battery  ;  K,  simple  key  ;  P,  primary  coil ;  S,  secondary  coil. 

stimulating  the  vagus,  that  it  inhibits  the  heart,  and  take  a  tracing 
during  stimulation.  Then  paint  a  dilute  solution  of  atropia  on  the 
sinus.  Stimulation  of  the  vagus,  which  is  really  the  vago-sympathetic 
(see  Fig.  64),  will  now  cause,  not  inhibition,  but  augmentation  (increase 
in  rate  or  force,  or  both),  since  the  endings  of  the  inhibitory  fibres 
have  been  paralyzed  by  atropia.  The  strength  of  the  stimulating 
current  required  to  bring  out  a  typical  augmentor  effect  is  greater  than 
that  needed  to  stimulate  the  inhibitory  fibres.  Take  a  tracing  to  show 
augmentation  produced  by  stimulating  the  nerve. 

(2)  By  direct  stimulation  of  the  cervical  sympathetic. — Make  the 
same  arrangements  as  in  n  (i),  but,  instead  of  isolating  the  vagus, 
dissect  out  the  sympathetic  on  one  side  in  the  manner  described  in 
6  (2)  (p.  172),  and  do  not  apply  atropia  to  the  heart.  Lay  the  upper 
(cephalic)  end  of  the  sympathetic  on  very  fine  and  well-insulated 
electrodes,  and  stimulate.  (To  insulate  electrodes  the  points  may 
be  covered  with  melted  paraffin.  When  the  paraffin  has  cooled,  a 
narrow  groove,  just  sufficient  to  lay  bare  the  wires  on  the  upper  side, 
is  made  in  it,  and  the  nerve  is  laid  in  this  groove.)  (Fig.  52,  p.  143.) 


i;6  A  MANUAL  OF  PHYSIOLOGY 

Experiments  7,  n  ^i)  and  n  (2)  will  be  rendered  more  exact 
by  connecting  a  second  electro-magnetic  signal  with  a  Pohl's  com- 
mutator without  cross- wires  (Fig.  66),  in  such  a  way  that  the  circuit 
is  interrupted  at  the  instant  when  stimulation  begins. 

12.  The  Action  of  the  Mammalian  Heart. — Inject  under  the 
skin  of  a  dog  (preferably  a  small  one)  i  cc.  of  a  2  per  cent,  solution 
of  morphia  hydrochlorate  for  every  kilogramme  of  body-weight.  As 
soon  as  the  morphia  has  taken  effect  (in  15-30  minutes),  fasten  the 
animal  back  down  on  a  holder  (as  in  Fig.  100),  pushing  the  mouth- 


FIG.  66. — ARRANGEMENT  FOR  RECORDING  THE  BEGINNING  AND  END  Of 
STIMULATION. 

C,  Pohl's  commutator  without  cross-wires  ;  B,  battery  in  circuit  of  primary  coil  P  ; 
B',  battery  in  circuit  of  electro-magnetic  signal  T  ;  K,  simple  key  in  primary  circuit ; 
S,  secondary  coil.  When  the  bridge  of  the  commutator  is  tilted  into  the  position 
shown  in  the  figure,  the  primary  circuit  is  closed  and  the  circuit  of  the  signal  broken. 

pin  behind  the  canine  teeth  and  screwing  the  nut  home.*     In  the 
meantime  select  a  tracheal  cannulaf  of  suitable  size,  and  get  ready 

*  A  simple  but  efficient  and  convenient  holder  for  a  dog  may  be 
easily  constructed  as  follows.  Take  a  board  of  the  length  required  (2%  to 
6  feet,  according  to  the  size  of  the  dog).  At  one  end  fasten  two  short 
upright  wooden  pins,  4  to  6  inches  apart.  These  are  pierced  from  side  to 
side  with  four  or  five  holes  at  different  heights.  An  iron  pin  passing 
behind  the  canine  teeth  of  the  animal  through  two  corresponding  holes 
in  the  uprights,  and  tied  over  the  muzzle  by  a  cord  arranged  in  a  figure 
of  eight,  secures  the  head.  For  a  large  dog  an  upper  pair  of  holes  is 
used,  for  a  small  dog  a  lower  pair.  The  feet  are  fastened  by  cords  to 
staples  inserted  into  the  sides  of  the  board,  the  fore-legs  being  drawn  tail- 
wards  for  all  operations  on  the  neck  or  head,  headvvards  for  operations  on 
the  thorax.  A  rabbit-holder  can  be  made  in  exactly  the  same  way. 

f  A  tracheal  cannula  is  easily  made  by  heating  a  piece  of  glass  tubing, 
about  6  inches  long,  a  short  distance  from  one  end,  and  drawing  it  out 
slightly  so  as  to  form  a  '  neck.'  The  tubing  is  then  bent  about  its  middle 
to  an  obtuse  angle,  and  the  end  next  the  neck  is  ground  obliquely  on  a 
stone.  The  diameter  of  the  cannula  should  be  about  the  same  as  that  of 
the  trachea  into  which  it  is  to  be  inserted  by  its  oblique  end. 


PRACTICAL  EXERCISES  177 

instruments  for  dissection — one  or  two  pairs  of  artery-forceps,  a  pair 
of  artery-clamps  (bulldog  pattern),  two  or  three  glass  cannulae  of 
various  sizes  for  bloodvessels,  ten  strong  waxed  ligatures,  sponges, 
hot  water,  a  towel  or  two,  and  a  pair  of  bellows  to  be  connected  with 
the  tracheal  cannula  when  the  chest  is  opened.  Arrange  an  in- 
duction-coil and  electrodes  for  a  tetanizing  current  (Fig.  65,  p.  175). 
With  scissors  curved  on  the  flat  clip  away  the  hair  from  the  front  of 
the  neck  and  the  anterior  surface  of  one  thigh  below  Poupart's 
ligament.  Put  the  hair  carefully  away,  and  remove  all  the  loose 
hairs  with  a  wet  sponge  so  that  they  may  not  get  into  the  wounds. 
If  the  animal  is  not  fully  anaesthetized,  give  ether.  Insert  a  glass 
cannula,  which  should  have  a  piece  of  indiarubber-tubing  2  to  3 
inches  in  length  on  its  wide  end,  into  the  central  end  of  the  femoral 
vein.  Feel  for  the  femoral  artery,  cut  down  over  it,  and  with  forceps 
or  a  blunt  needle  separate  the  femoral  vein  from  it  for  about  an  inch. 
Pass  two  unwaxed  ligatures  under  the  vein,  and  tie  a  loose  loop  on 
each.  Put  a  pair  of  bulldog  forceps  on  the  vein  between  the  liga- 
tures and  the  heart.  Now  tie  the  lower  (distal)  ligature,  and  cut  one 
end  short.  The  piece  of  vein  between  it  and  the  bulldog  forceps  is 
thus  distended  with  blood,  and  this  facilitates  the  next  step.  With 
fine-pointed  scissors  make  a  snip  in  the  wall  of  the  vein.  The 
cannula  is  now  pushed  through  the  slit  in  the  vein,  and  the  upper 
ligature  tied  firmly  round  its  neck.  By  the  aid  of  a  pipette,  made  by 
drawing  a  piece  of  glass  tubing  out  to  a  long  point,  the  cannula  and 
rubber  tube  are  then  completely  filled  with  normal  saline  solution. 
Be  sure  to  pass  the  point  of  the  pipette  right  down  to  the  point  of 
the  cannula,  so  as  to  dislodge  any  bubble  of  air  that  may  tend  to 
cling  there.  Then,  holding  up  the  open  end  of  the  rubber  tube, 
close  it,  without  allowing  any  air  to  enter,  by  means  of  a  screw  clamp 
or  bulldog  forceps,  or  a  small  piece  of  glass  rod.  i  or  2  cc.  of 
the  2  per  cent,  solution  of  morphia  may  be  injected  from  time  to 
time,  when  necessary,  by  pushing  the  needle  of  the  hypodermic 
syringe  through  the  rubber  tube.  When  the  needle  is  withdrawn  the 
little  hole  closes  completely,  and  nothing  escapes  from  the  cannula. 

To  put  a  Cannula  in  the  Trachea. — The  hair  having  been  clipped 
in  the  middle  line  of  the  neck  and  the  skin  shaved,  a  mesial  incision 
is  to  be  made,  beginning  a  little  below  the  cricoid  cartilage,  which 
can  be  felt  with  the  finger.  The  trachea  is  then  cleared  from  its 
attachments  by  forceps  or  a  blunt  needle,  and  two  strong  ligatures 
are  passed  beneath  it.  A  single  loop  is  placed  on  each  of  those, 
but  is  not  drawn  tight.  Raising  the  trachea  by  means  of  the  upper 
ligature,  the  student  makes  a  longitudinal  incision  through  two  or 
three  of  the  cartilaginous  rings,  inserts  the  cannula,  and  ties  the 
lower  ligature  firmly  around  its  neck.  It  is  well  also,  though  not 
necessary,  to  now  tie  the  upper  ligature,  and  additional  security  may 
be  obtained  by  tying  together  the  ends  of  the  two  ligatures  around 
the  cannula. 

Clip  off  the  hair  on  each  side  of  the  sternum.  Make  an  incision 
on  each  side  through  the  skin  and  down  to  the  costal  cartilages  about 
2  inches  from  the  edge  of  the  breast-bone,  and  long  enough  to 

12 


178  A  MANUAL  OF  PHYSIOLOGY 

expose  about  four  costal  cartilages  (say,  3rd  to  6th).  With  a  curved 
needle  pass  waxed  ligatures  round  the  cartilages,  and  tie  firmly  to 
compress  the  intercostal  vessels.  Then  pass  a  waxed  ligature  under 
the  upper  portion  of  the  sternum,  and  tie  it  very  tightly  round  that 
bone  so  as  to  occlude  the  internal  mammary  arteries.  The  bellows 
should  now,  or  earlier  if  any  symptoms  of  impeded  respiration  have 
appeared,  be  connected  with  one  end  of  the  horizontal  limb  of  a 
glass  T-piece,  the  other  end  of  which  is  similarly  connected  with  the 
tracheal  cannula.  The  stem  of  the  T-piece  is  provided  with  a  short 
piece  of  rubber  tubing,  which,  when  artificial  respiration  is  being 
carried  on,  is  to.  be  alternately  closed  and  opened — closed  during 
inflation  of  the  lungs,  and  opened  when  the  air  is  to  be  allowed  to 
escape  from  them.  Ether  may,  if  necessary,  be  administered  by 
passing  this  short  tube  through  one  neck  of  a  Woulff  s  bottle  con- 
taining the  anaesthetic,  and  alternately  compressing  and  opening  it  as 
described.  If  the  cannula  has  a  side-opening,  as  is  usually  the  case 
with  metal  cannula?,  the  T-piece  may  be  dispensed  with.  One 
student  should  take  sole  charge  of  the  artificial  respiration,  which 
ought  to  be  begun  as  soon  as  the  chest  has  been  opened,  and  con- 
tinued at  the  rate  of  about  twenty  inflations  per  minute.  The  costal 
cartilages  and  sternum  are  rapidly  cut  through  with  strong  scissors 
just  on  the  sternal  side  of  the  ligatures,  and  the  sternum  is  divided 
below  its  ligature,  the  artificial  respiration  being  suspended  for  an 
instant,  as  each  cut  is  made,  to  avoid  wounding  the  lungs.  The 
lower  part  of  the  sternum  is  turned  down  like  the  lid  of  a  box,  tied 
out  of  the  way  or  cut  off  altogether,  and  the  heart,  enclosed  in  the 
pericardium,  comes  into  view.  If  the  ligature  round  the  sternum  has 
not  properly  compressed  the  internal  mammary  arteries,  haemorrhage 
from  the  central  ends  may  now  occur.  In  this  case  they  must  be 
seized  with  artery-forceps  and  ligatured.  A  cotton  thread  is  now 
passed  with  a  suture-needle  through  each  side  of  the  pericardium, 
which  is  then  stitched  to  the  chest-wall  and  opened.  The  following 
observations  and  experiments  should  now  be  made : 

(a)  Note  the  various  portions  of  the  heart,  right  and  left  ventricles, 
right  and  left  auricles,  with  the  auricular  appendices.     Feel  the  heart 
with  the  hand,  and  observe  that  the  right  ventricle  is  softer  and  has 
thinner  walls  than  the  left,  and  that  the  auricles  are  softer  than  the 
ventricles.     Note  how  all  the  parts  of  the  heart  harden  in  the  hand 
during  systole  and  soften  during  diastole  (pp.  74-76). 

(b)  Dissect  out  the  vago-sympathetic  on  one  side  in  the  neck  of 
the  dog.     The  guide  to  the  nerve  is  the  carotid  artery.     These  two 
structures  and  the  internal  jugular  vein  lie  side  by  side  in  a  common 
sheath.     Feel  for  the  artery  a  little  external  to  the  trachea,  cut  down 
on  it,  open  the  sheath,  isolate  the  vago-sympathetic  for  about  an 
inch,  pass  two  ligatures  under  it,  tie  them,  and  divide  between  the 
ligatures.     The  peripheral  and  central  end  of  the  nerve  may  now  be 
successively  stimulated.     Stimulation  of  the  peripheral  end  causes 
slowing  of  the  heart  or  stoppage  in  diastole.     Feel  that  it  softens 
when  it  stops.     It  soon  begins  to  beat  again.     Stimulation  of  the 
central  end  of  the  vago-sympathetic  may  or  may  not  cause  inhibition. 


PRACTICAL  EXERCISES  179 

If  it  does,  expose  the  other  vago-sympathetic,  divide  it,  and  repeat 
the  stimulation  of  the  central  end.  There  will  now  be  no  inhibition 
of  the  heart.  Incidentally  it  may  be  seen  that  stimulation  of  the 
central  end  of  the  vago-sympathetic  causes  strong,  though,  of  course, 
with  opened  chest,  abortive,  respiratory  movements. 

(f)  Pith  a  frog  (brain  and  cord),  dissect  out  the  sciatic  nerve  on 
one  side  up  to  the  sacral  plexus.     Cut  off  the  whole  leg.     Drop  the 
cut  end  of  the  nerve  on  the  heart,  and  hold  the  preparation  so  that 
the  nerve  touches  the  heart  also  by  its  longitudinal  surface.      At 
each  cardiac  beat  the   nerve   is   stimulated   by  the  action  current 
(Chap.  XL),  and  the  muscles  of  the  leg  contract. 

(d)  Raise  the  board  so  that  the  head  of  the  animal  is  down  and 
the  hind-feet  up,  and  note  whether  there  is  any  effect  on  the  action 
and  filling  of  the  heart.     Repeat  the  observation  with  head  up  and 
feet  down. 

(e)  Compress  the  aorta  with  the  fingers,  and  observe  the  effect  on 
the  degree  of  dilatation  of  the  various  cavities  of  the  heart.     Repeat 
the    experiment   with    the    inferior   vena   cava,    and   compare    the 
results. 

(/)  Stop  the  artificial  respiration,  and  observe  the  changes  which 
take  place  in  the  auricles  and  ventricles,  comparing  particularly  the 
right  side  of  the  heart  with  the  left.  Before  the  heart  has  stopped 
beating,  recommence  the  artificial  respiration. 

(g)  When  the  heart  is  again  beating  with  a  fair  degree  of  regularity 
and  strength,  make  a  small  penetrating  wound  with  a  scalpel  in  the 
left  ventricle.     Observe  the  course  of  the  haemorrhage,  and  note 
especially  the  difference  in  systole  and  diastole. 

(h)  Lay  the  electrodes  on  the  heart,  and  stimulate  it  with  a  strong 
interrupted  current.  The  character  of  the  contraction  soon  becomes 
profoundly  altered.  Shallow  irregular  contractions  flicker  over  the 
surface,  with  a  kind  of  simmering  movement  suggestive  of  a  boiling 
pot  (delirium  cordis,  fibrillar  contraction).  Now  kill  the  animal  by 
stopping  the  artificial  respiration.  Observe  how  long  the  heart 
continues  to  beat,  and  which  of  its  divisions  stops  last. 

(i)  Make  a  dissection  of  the  cervical  sympathetic  up  to  the  superior 
•cervical  ganglion,  and  down  through  the  inferior  cervical  ganglion  to 
the  stellate  or  first  thoracic  ganglion.  Make  out  the  annulus  of 
Vieussens  and  the  cardiac  sympathetic  (accelerator)  branches  going 
-off  from  the  annulus  or  the  inferior  cervical  ganglion  to  the  cardiac 
plexus  (Fig.  50,  p.  139). 

13.  Action  of  the  Valves  of  the  Heart. —  (i)  Study  the  action  of 
the  valves  of  the  ox-heart  in  the  artificial  scheme.  Connect  the  ox- 
heart  provided  with  the  pump  P  and  bottle  B,  as  shown  in  Fig.  67. 
The  cavity  of  the  heart  is  illuminated  by  means  of  a  small  electric 
lamp,  the  wires  of  which  pass  in  at  A.  When  the  piston  of  the  pump 
is  pushed  down,  water  is  forced  through  the  aorta  D  along  the  tube 
T  into  the  bottle,  and  flows  back  again  into  the  left  auricle  by  the 
tube  T'.  During  each  stroke  of  the  pump  the  auriculo-ventricular 
valve  is  seen  through  the  glass  disc  inserted  into  C  to  close,  and  the 
semilunar  valve  is  seen  through  the  glass  in  D  to  open.  When 

12 — 2 


i8o 


A  MANUAL  OF  PHYSIOLOGY 


the  piston  is  raised,  the  semilunar  valve  is  seen  to  be  closed  and  the 
auriculo-ventricular  valve  to  be  opened.  For  comparison  a  human 
heart  with  a  valvular  lesion  might  be  used. 


FIG.  67. — ARRANGEMENT  TO  ILLUSTRATE  ACTION  OF  CARDIAC  VALVES  m 
THE  HEART  OF  AN  Ox  (GAD). 

C,  glass  window  in  left  auricle ;  D,  window  in  aorta  ;  E,  tube  inserted  through  apex 
of  heart  into  left  ventricle  and  connected  with  pump  P ;  A,  side  tube  on  E,  through 
which  wires  are  connected  with  a  tiny  incandescent  lamp  in  the  ventricle  ;  W,  water 
in  bottle  B  ;  T,  T  tubes. 

(2)  With  the  sheep's  or  dog's  heart  provided,  perform  the  following 
experiments : 


PRACTICAL  EXERCISES 


181 


(a)  Open  the  pericardium  and  notice  how  it  is  reflected  around 
the  great  vessels  at  the  base  of  the  heart.  Distinguish  the  pulmonary 
artery,  the  aorta,  the  superior  and  inferior  venae  cavaa,  and  the  pul- 
monary veins.  The  trachea  and  portions  of  the  lungs  may  also  be 
attached.  If  so,  remove  them  carefully  without  injuring  the  heart. 

(£)  Take  two  wide  glass  tubes,  drawn  slightly  into  a  neck  at  one 
end.  One  of  the  tubes  should  be  about  10  cm.  long,  and  the  other 
about  50  cm.  Tie  the  short  tube  A  firmly  by  its  neck  into  the 
superior  vena  cava,  the  long  tube  B  into  the  pulmonary  artery. 
Ligature  the  inferior  vena  cava.  Connect  A  by  a  small  piece  of  rubber 
tubing  with  a  funnel  supported  in  a  ring  on  a  stand.  Pour  water  into 
the  funnel  till  the  right  side  of  the  heart  is  full.  It  will  escape  from 
the  left  azygos  vein,  which  must  be  tied.  Put  on  any  additional 
ligatures  that  may  be  needed  to  render  the  heart  water-tight.  Support 
B  in  the  vertical  position  by  a  clamp.  Fill  the  funnel  with  water, 
and  it  will  rise  in  B  to  the  same  level  as  in  the  funnel.  Now  com- 
press the  right  ventricle  with  the  hand,  and  the  water  will  rise  higher, 
in  B.  Relax  the  pressure,  and  notice  that  the  water  remains  at  the 
higher  level  in  B,  being  prevented  by  the  semilunar  valves  from 


The  valves  are  supposed  to 
be  viewed  from  above,  the 
auricles  having  been  partially 
removed.  A,  aorta  with  semi- 
lunar  valve ;  Dt  position  of 
corpora  Arantii ;  P,  pulmonary 
artery ;  B,  wall  of  left  auricle  ; 
M,  mitral  valve,  with  i  and  2 , 
its  posterior  and  anterior  seg- 
ments ;  C,  wall  of  right  auricle ; 
T,  tricuspid  valve,  with  i,  its 
posterior,  2,  its  anterior,  and 
3,  its  external  segment. 


FIG.  68. — DIAGRAM  OF  VALVES  OF  HEART. 

flowing  back  into  the  ventricle.  By  alternately  compressing  the 
ventricle  and  allowing  it  to  relax,  water  can  be  pumped  into  B  till  it 
escapes  from  its  upper  end,  and  if  this  is  so  curved  that  the  water 
falls  into  the  funnel,  a  '  circulation '  which  imitates  that  of  the  blood 
can  be  established.  Note  that  during  the  pumping  the  sinuses  of 
Valsalva,  behind  the  semilunar  valves  at  the  origin  of  the  pulmonary 
artery,  become  prominent. 

(c)  Take  out  B  and  tear  out  one  of  the  segments  of  the  semilunar 
valve.  Replace  B,  and  notice  that  while  compression  of  the  ventricle 
has  the  same  effect  as  before,  the  water  no  longer  keeps  its  level  on 
relaxation,  but  regurgitates  into  the  ventricle.  This  illustrates  the 
condition  known  as  insufficiency  or  incompetence  of  the  valves.  But 
if  the  injury  is  not  too  extensive,  it  is  still  possible,  by  more 
vigorously  and  more  rapidly  compressing  the  heart,  to  pump  water 
into  the  funnel.  This  illustrates  the  establishment  of  compensation 
in  cases  of  valvular  lesion. 


182  A  MANUAL  OF  PHYSIOLOGY 

(d)  Now  remove  both  tubes.     Tie  the  pulmonary  artery.     Cut 
away  the   greater  part  of  the  right  auricle.     Pour  water  into  the 
auriculo-ventricular  orifice,  and   notice   that   the   segments  of   the 
tricuspid  valve  are  floated  up  so  as  to  close  the  orifice.     Invert  the 
heart,  and  the  ventricle  will  remain  full  of  water.     Open  the  right 
ventricle  carefully,  and  study  the  papillary  muscles,  and  the  chordae 
tendineae,  noting  that  the  latter  are  inserted  into  the  lower  surface  of 
the  segments  of  the  tricuspid  valve,  as  well  as  into  their  free  edges. 

(e)  Repeat  (b\  (c),  and  (d)  on  the  left  side  of  the  heart,  tying  tube 
B  into  the  aorta  as  far  from  the  heart  as  possible,  and  A  into  the  left 
auricle. 

(/)  Separate  the  aorta  from  the  left  ventricle,  cutting  wide  of  its 
origin  so  as  not  to  injure  the  semilunar  valves,  and  tie  a  short  wide 
tube  into  its  distal  end.  Fill  the  tube  with  water,  and  notice  that 
the  valves  support  it.  Cut  open  the  aorta  just  between  two  adjacent 
segments  of  the  valve,  and  notice  the  pockets  behind  the  segments, 
and  how  they  are  related  to  each  other,  and  connected  to  the  wall  of 
the  vessel. 

14.  Sounds   of  the  Heart. — (d)  In  a  fellow-student   notice   the 
position  of  the  cardiac  impulse,  the  chest  being  well  exposed.     Use 
both  a  binaural  and  a  single-tube  stethoscope.    Place  the  chest-piece 
of  the  stethoscope  over  the  impulse,  and  make  out  the  two  sounds 
and  the  pause,     (b]  With  the  hand  over  the  radial  or  brachial  artery, 
try  to  determine  whether  the  beat  of  the  pulse  is  felt  in  the  period 
of  the  sounds  or  of  the  pause,     (c)  Listen  with  the  stethoscope  over 
the  junction  of  the  second  right  costal  cartilage  with  the  sternum, 
and  compare  the  relative  intensity  of  the  two  sounds  as  heard  here 
with  their  relative  intensity  as  heard  over  the  cardiac  impulse. 

15.  Cardiogram. — Smoke  a  drum,  and  arrange  a  recording  tambour 
and  a  time-marker  beating  half  or  quarter  seconds  to  write  on  it 
(Fig.  60,  p.  170).  Apply  the  button  of  a  cardiograph  (Fig.  18,  p.  79)over 
your  own  cardiac  impulse,  and  fasten  it  round  the  body  by  the  bands 
attached  to  the  instrument.     Connect  the  cardiograph  by  an  india- 
rubber  tube  with  a  recording  tambour.    Set  the  drum  off  at  a  fast  speed, 
take  a  tracing,  and  varnish  it.     Compare  with  Fig.  19  (p.  So),  and 
measure  out   the  time-value  of  the  various  events  in   the  cardiac 
revolution  as  indicated  on  the  cardiogram. 

For  the  cardiograph,  a  small  glass  funnel,  the  stem  of  which  is 
connected  with  the  recording  tambour,  may  be  substituted,  the  broad 
end  of  the  funnel  being  pressed  over  the  apex-beat. 

1 6.  Sphygmographic  Tracings. — Attach  a  Marey's  sphygmograph 
(Fig.  26,  p.  90)  to  the  arm.     Fasten  a  smoked  paper  on  the  plate  D. 
Apply  the  pad  C  of  the  sphygmograph  to  the  wrist  over  the  point 
where  the  pulse  of  the  radial  artery  can  be  most  distinctly  felt.     Adjust 
the  pressure  by  moving  the  screw  G.     The  writing-point  of  the  lever 
E  will  rise  and  fall  with  every  pulse-beat    When  everything  is  satis- 
factorily arranged,  set  off  the  clockwork  which  moves  the  plate  D, 
and  a  pulse-tracing  will  be  obtained.     Study  the  changes  which  can 
be  produced  in  the  pulse  curve — (a)  by  altering  the  position  of  the 
body  (sitting,  standing,  and  lying  down) ;  (b)  by  exercise ;  (c)  by  in- 


PRACTICAL  EXERCISES 


183 


halation  of  2  drops  of  amyl  nitrite  poured  on  a  handkerchief;  (d)  by 
raising  the  arm  above  the  head  and  letting  it  hang  at  the  side  ;  (e)  by 
compression  of  the  brachial  artery  at  the  bend  of  the  elbow ;  (/)  by 
altering  the  pressure  of  the  pad.  Varnish  the  tracings  after  marking 
on  them  the  conditions  underwhich 
they  were  obtained. 

A  Dudgeon's  sphygmograph  may 
also  be  employed.  Or  a  small  glass 
funnel  connected  with  a  recording 
tambour  may  be  pressed  over  the 
carotid  artery.  The  lever  of  the 
tambour  writes  on  a  drum,  on  which 
at  the  same  time  half  or  quarter 
seconds  are  marked  by  an  electro- 
magnetic signal. 

17.  Plethysmographic  Tracings. 
— Connect  the  vessel  C  (Fig.  39, 
p.  1 1 6)  with  B,  place  the  arm  in  it, 
and  adjust  the  indiarubber  band 
to  make  a  watertight  connection. 

Support  C  so  that  the  arm  rests  easily  within  it,  and  fill  it  with  water 
at  body  temperature.     Adjust  a  writing-point,  carried  by  the  float  A, 


FIG.  69.— EFFECT  OF  EXERCISE  ON 
THE  PULSE  (MAREY). 

Upper  tracing,  normal ;  lower  tracing, 
after  running. 


FIG.  70. — EFFECT  OF  AMYL  NITRITE  ON  THE 

PULSE  (MAREY). 

Upper  tracing,  normal ;  lower,  after  inhalation 
of  amyl  nitrite. 


FIG.  71. — PULSE -TRACINGS 
FROM  DIFFERENT  ARTERIES. 
T,  temporal ;  JR,  radial ;  P, 
artery  of  foot.     (v.  Frey.) 


to  write  on  a  drum,  and  close  the  upper  tubulure  of  C  with  a  cork. 
The  quantity  of  blood  in  the  arm  is  increased  with  every  systole  of 
the  left  ventricle,  diminished  in  diastole.  The  float  will  therefore  rise 
when  the  ventricle  contracts,  and  sink  when  it  relaxes.  Or  C  may  be 


1 84 


A  MANUAL  OF  PHYSIOLOGY 


connected  by  a  rubber  tube  with  a  recording  tambour  writing  on  the 
drum.  No  water  must  get  into  the  tambour,  and  it  is  well  to  insert 
a  piece  of  glass  tubing  in  the  connection  between  it  and  the  plethysmo- 
graph,  so  that  it  may  be  seen  when  the  water  is  rising  too  high.  Adjust 
a  time-marker  to  write  half  or  quarter  seconds  (Fig.  60,  p.  170). 

(1)  Take  tracings  with  arm  (a)  horizontal,  (b)  hanging  down. 

(2)  With  the  arm   horizontal,  take   tracings  to  show  the   effect 
(a)  of  closing  and  opening  the  fist  inside  the  plethysmograph  ;  (b)  of 
applying  a  tight  bandage  round  the  arm  a  little  way  above  the  india- 
rubber  band  ;  (c)  of  inhaling  2  drops  of  amyl  nitrite. 


FIG.  72. — PLETHYSMOGRAPH  (CYON). 

M,  balanced  test-tube,  in  communication  with  D.  When  water  passes  from  vessel 
D  to  M,  or  from  M  to  D,  M  moves  down  or  up,  and  its  movements  are  recorded  by 
the  writing-point  N.  M  is  steadied  by  the  liquid  in  P,  into  which  it  dips. 

1 8.  Pulse-rate. — (i)  Count  the  radial  pulse  for  a  minute  in  the 
sitting,  supine,  and  standing  positions.  Use  a  stop-watch,  setting  it 
off  on  a  pulse-beat  and  counting  the  next  beat  as  one.  Make  three 
observations  in  each  position. 

(2)  Count  the  pulse  in  a  person  sitting  at  rest,  and  then  again  in 
the  sitting  position  immediately  after  active  muscular  exertion.     Note 
how  long  it  takes  before  the  pulse-rate  comes  back  to  normal. 

(3)  Count  the  pulse  in  a  person  sitting  at  rest.     Repeat  the  obser- 
vation while  water  is  being  slowly  sipped,  and  note  any  change. 


PRACTICAL  EXERCISES  185 

(4)  With  one  hand  over  the  thorax  of  a  rabbit,  count  its  pulse. 
Then  notice  the  effect  (a)  of  suddenly  closing  its  nostrils,  (^)  of 
bringing  a  small  piece  of  cotton-wool  sprinkled  with  ammonia  or 
chloroform  in  front  of  the  nose  (reflex  inhibition  of  the  heart}. 

19.  Blood-pressure  Tracing. — (a)  Put  a  dog  under  morphia  (p.  58). 
Set  up  an  induction-machine  arranged  for  an  interrupted  current 
(Fig.  65,  p.  175).  Fill  the  U-shaped  manometer-tube  (if  this  has  not 
already  been  done)  with  clean  mercury  to  the  height  of  10  to  12  c.m. 
in  each  limb.  Then,  tilting  the  tube  carefully,  fill  the  proximal  limb 
(i.e.,  the  limb  which  is  to  be  connected  with  the  bloodvessel)  with  a 
saturated  solution  of  sodium  carbonate  or  a  25  per  cent,  solution  of 
magnesium  sulphate.  This  is  easily  done  by  means  of  a  pipette 
furnished  with  a  long  point.  Now  attach  a  strong  rubber  tube  to 
the  proximal  end  of  the  manometer,  and  fill  it  also  with  the  solution. 
All  air  must  be  got  out  of  the  manometer  and  its  connecting-tube. 
Blow  into  the  rubber  tube  so  as  to  cause  a  difference  of  about 
10  cm.  in  the  height  of  the  mercury  in  the  two  limbs  of  the  mano- 
meter, and,  without  releasing  the  pressure,  clamp  the  tube  with  a 
pinchcock  or  screw  clamp  (Fig.  28,  p.  99). 

Now  smoke  a  drum,  and  arrange  the  writing-point  of  the  mano- 
meter-float so  that  it  will  write  on  it.  Suspend  a  small  weight  by  a 
piece  of  silk  thread  from  a  support  attached  to  the  stand  of  the 
drum  so  that  it  hangs  down  outside  of  the  writing-point  of  the 
manometer-float  and  always  keeps  it  in  contact  with  the  smoked 
surface  without  undue  friction.  A  piece  of  glass  rod  drawn  out  to  a 
fine  thread  in  the  blowpipe  flame  answers  very  well.  In  the  same 
vertical  line  below  the  writing-point  of  the  float,  adjust  the  writing- 
point  of  a  time-marker  beating  seconds  (Fig.  60,  p.  170). 

Next,  fasten  the  animal  on  a  holder,  back  down.  Give  ether  and 
insert  a  tracheal  cannula  (p.  177).  (The  tracheal  cannula  is  not 
absolutely  required  for  the  experiment,  but  it  is  convenient,  as  the 
animal  is  more  under  control,  and  artificial  respiration  can  be  begun 
at  any  moment,  should  this  be  necessary.)  Insert  a  glass  cannula, 
armed  with  a  short  piece  of  rubber  tubing,  into  the  central  (cardiac) 
end  of  the  carotid  artery  (p.  58).  Leaving  the  bulldog  forceps  on 
the  artery,  fill  the  cannula  and  tube  .with  the  magnesium  sulphate  or 
sodium  carbonate  solution.  Slip  the  rubber  tube  over  a  short  glass 
connecting-tube.  Fill  this  also  with  the  solution,  and  connect  it 
with  the  manometer-tube,  seeing  that  both  are  quite  full  of  liquid, 
so  that  no  air  may  be  enclosed.  Now  take  off  the  'bulldog  forceps, 
and  allow  the  drum  to  revolve  at  slow  speed.  The  writing-point  of 
the  manometer- float  will  trace  a  curve  showing  an  elevation  for  each 
heart-beat,  and  longer  waves  due  to  the  movements  of  respiration. 

(b]  Now  isolate  the  vago-sympathetic  nerve  in  the  neck.    Ligature 
doubly,  and  cut  between  the  ligatures.     Stimulate  first  the  peripheral 
(lower)  and  then  the  central  (upper)  end,  and  note  the  effect  on  the 
blood-pressure  curve. 

(c)  Expose  and  divide  the  other  vago-sympathetic  while  a  tracing 
is  being  taken.     Again  stimulate  the  central  end  of  the  nerve,  and 
observe  whether  there  is  any  effect. 


186 


A  MANUAL  OF  PHYSIOLOGY 


(d)  Expose  the  sciatic  nerve  in  one  leg.  This  is  very  easily  done 
as  follows.  The  leg  having  been  loosened  from  the  holder,  the  foot 
is  seized  by  one  hand  and  lifted  straight  up,  so  as  to  put  the  skin 
of  the  thigh  on  the  stretch.  An  incision  is  now  made  in  the 
middle  line  on  the  posterior  aspect  of  the  thigh,  the  skin  and  sub- 
cutaneous tissue  being  divided  at  one  sweep.  The  muscles  are 
separated  in  the  line  of  the  incision  with  the  fingers,  and  the  sciatic 
nerve  comes  into  view  lying  deeply  between  them.  Place  a  double 
ligature  on  it,  and  divide  between  the  ligatures.  Stimulate  the  upper 
(central  end) ;  the  blood-pressure  probably  rises,  and  the  heart  may 


FIG.  73.— BLOOD-PRESSURE  TRACING  FROM  A  DOG.     STIMULATION  OF 
CENTRAL  AND  PERIPHERAL  ENDS  OF  VAGUS. 

The  other  vagus  was  intact.  Stimulation  of  the  peripheral  end  caused  stoppage  of 
the  heart  and  a  marked  fall  of  pressure.  Stimulation  of  the  central  end  produced  a 
great  rise  of  pressure,  with,  perhaps,  a  slight  acceleration  of  the  heart. 

be  accelerated.  Stimulate  the  peripheral  end  of  the  nerve ;  there  is 
little  change  in  the  blood-pressure  and  none  in  the  rate  of  the  heart. 

(e)  Note,  incidentally,  that  stimulation  of  the  central  end  of  the 
sciatic  or  the  upper  (cephalic)  end  of  the  vago-sympathetic  may 
cause  increase  in  the  rate  and  depth  of  the  respiratory  movements. 
Dilatation  of  the  pupil  may  also  be  caused  by  stimulation  of  the 
upper  end  of  the  vago-sympathetic  through  the  sympathetic  fibres 
that  supply  the  iris. 

(/)  Again,  stimulate  the  peripheral  end  of  one  vagus,  or  of  both 
at  the  same  time,  while  a  tracing  is  being  taken,  and  see  how  long  it 


PRACTICAL  EXERCISES  187 

is  possible  to  keep  the  heart  from  beating.     Sometimes  in  the  dog 
inhibition  can  be  kept  up  so  long  that  the  animal  dies. 

(g)  Close  the  tracheal  cannula  so  that  air  can  no  longer  enter  the 
lungs.  In  a  very  short  time  the  blood-pressure  curve  begins  to  rise 
(rise  of  asphyxia).  After  some  minutes  the  pressure  falls,  and  finally 
becomes  zero ;  i.e.,  the  level  of  the  mercury  is  the  same  in  the  two 
limbs  of  the  manometer  (or,  rather,  the  mercury  in  the  distal  limb  is 
higher  than  that  in  the  proximal  limb  by  the  amount  needed  to 
exactly  balance  the  pressure  of  the  column  of  sodium  carbonate  in 
the  latter).  Disconnect  the  arterial  cannula  from  the  manometer, 
and  allow  the  writing-point  to  trace  a  horizontal  straight  line  (line  of 
zero  pressure)  on  the  drum  (Figs.  56  and  57). 

20.  The  Influence  of  the  Position  of  the  Body  on  the  Blood- 
pressure. — Inject  into  the  rectum  of  a  dog  3  to  4  grammes  of 
chloral  hydrate  dissolved  in  a  little  water.  See  that  it  does  not  run 
out  again  immediately  after  injection.  In  ten  minutes  anaesthetize  the 
animal  fully  with  the  mixture  of  equal  parts  of  alcohol,  chloroform  and 
ether,  known  as  the  ACE  mixture,  or  with  chloroform,  and  tie  it  very 
securely,  back  downward,  on  a  board  which  can  be  rotated  around  a 
horizontal  axis,  corresponding  in  position  to  the  point  at  which  the 
cannula  is  to  be  inserted.*  Set  up  a  drum  and  manometer  as  in  19 
(p.  185),  but  with  a  rubber  connecting-tube  of  such  length  as  will 
allow  free  rotation  of  the  board.  Insert"  a  cannula  into  the  central 
end  of  the  carotid  artery  at  a  point  immediately  above  the  axis  of 
rotation  of  the  board,  and  connect  it  with  the  manometer,  (a)  Take 
a  blood-pressure  tracing  with  the  board  horizontal,  (b]  Whilst  the 
tracing  is  being  taken,  rotate  the  board  so  that  the  position  of  the 
animal  becomes  vertical,  with  the  feet  down.  Mark  on  the  tracing 
the  moment  when  the  change  of  position  takes  place.  The  pressure 
falls.  Replace  the  dog  in  the  horizontal  position.  The  manometer 
regains  its  former  level.  Now  rotate  the  board,  till  the  animal  is  again 
vertical,  but  with  feet  up  and  head  down,  and  observe  the  effect  on 
the  blood-pressure.  The  respiratory  variations  are  greater  with  feet 
down  than  with  head  down.  Notice  in  both  cases  whether  there  is 
any  change  in  the  rate  of  the  heart,  (c)  Take  the  board  off  the 
stands,  lay  it  on  a  table,  expose  the  femoral  artery,  and  insert  a 
cannula  into  it.  Shift  the  axis  so  that  it  now  lies  below  this  cannula. 
Replace  the  board  on  the  stands,  and  repeat  (a)  and  (b).  The  fall 
of  pressure  will  now  take  place  in  the  head-down  position.! 

*  A  simple  arrangement  for  this  purpose  is  a  board  with  a  number  of 
staples  fastened  in  pairs  into  its  lower  surface,  so  that  an  iron  rod  can  be 
pushed  through  any  pair,  and  form  a  horizontal  axis  at  right  angles  to 
the  length  of  the  board.  The  dog  having  been  tied  down,  the  rod  is 
pushed  through  the  pair  of  staples  corresponding  to  the  position  of  the 
cannula  in  the  artery  that  is  to  be  connected  with  the  manometer.  The 
projecting  ends  of  the  rod  rest  in  two  ordinary  clamp-holders,  fastened  at 
a  convenient  height  on  two  strong  stands,  whose  bases  are  clamped  to  the 
end  of  a  table.  The  other  end  of  the  board  is  supported  by  a  piece  of 
wood  that  rests  on  the  floor,  and  can  be  removed  when  the  board  is  to  be 
rotated. 

t  In    1 6   dogs   the  fall  of  pressure  in  the  carotid   in   the  feet-down 


i88  A  MANUAL  OF  PHYSIOLOGY 

21.  Effects    of   Haemorrhage    and    Transfusion    on  the  Blood- 
pressure. — Anaesthetize  a  dog  with  morphia  and  ether,  and  insert  a 
cannula   into   the    carotid  artery,    another   into   one   femoral   vein 
(p.  177),  and  a  third  into  the  femoral  artery  on  the  opposite  side. 
Connect  the  first  cannula  with  a  manometer,  arranged  to  write  on 
a  drum  as  in  experiment  19  (p.   185).     Take  the  bulldog  off  the 
carotid,  and  measure  the  difference  in  the  level  of  the  mercury  in  the 
two  limbs  of  the  manometer  with  a  millimetre  scale. 

(1)  (a)  While  a  tracing  is  being  taken,  draw  off  about  10  c.c.  of 
blood  from  the  femoral  artery,  and  observe  whether  there  is  any 
effect  on  the  tracing.     Mark  on  the  tracing  the  moment  when  the 
removal  of  the  blood  begins  and  ends. 

(b)  Repeat  (a),  but  run  off  about  100  c.c.  of  blood,  and  let  this  be 
immediately  defibrinated.  Then  draw  off  portions  of  100  c.c.  at 
short  intervals  until  a  distinct  fall  of  blood-pressure  has  been  pro- 
duced. All  the  samples  of  blood  should  be  defibrinated. 

(2)  (a)  Now,  while  a  tracing  is  being  taken,  inject  the  whole  of 
the  defibrinated  blood  slowly  through  the  cannula  in  the  femoral 
vein  by  means  of  a  funnel  supported  by  a  stand  at  such  a  height  that 
the  blood  runs  in  easily.     A  stopcock  should  be  introduced  in  the 
connection  between  the  funnel  and  the  cannula,  and  this  should  be 
closed  before  the  funnel  is  quite  empty,  so  as  to  obviate  any  risk  of 
air  getting  into  the  vein.     Of  course,  the  cannula  and  connecting- 
tubes  must  all  be  freed  from  air  before  injection  is  begun.     Again, 
measure  the  difference  in  the  level  of  the  mercury  in  the  manometer 
and   compare   the    pressure   with    that   observed  before   the    first 
haemorrhage. 

(b)  Inject  into  the  vein,  while  a  tracing  is  being  obtained,  about 
too  c.c.  of  normal   saline  solution   heated  to  40°  C.,  and  go  on 
injecting  portions  of  100  c.c.  until  a  distinct  rise  of  pressure  has  taken 
place,  keeping  a  record  of  the  total  amount  injected,  and  marking  the 
time  of  each  injection  on  the  curve. 

(c)  After  an  interval  of  thirty  minutes,  again  measure  the  height  of 
the  mercury  in  the  manometer.     Then  bleed  the  dog  to  death  while 
a  tracing  is  being  recorded. 

22.  The  Influence  of  Albumoses  on  the   Blood-pressure — Albu- 
mose  (*  Peptone  ')  Plasma. — Set  up  the  apparatus  for  taking  a  blood- 
pressure  tracing  as  in  experiment  19,  but  omit  the  induction  coil. 
Weigh  a  dog.      Dissolve  0*5  gramme  Witte's  'peptone'  for  every 
kilo  of  body-weight  in  ten  times  its  weight  of  normal  saline  solution. 
Anaesthetize  the  dog  wich  morphia  and  ether  or  ACE  mixture.     Put 
cannulae  into  the  central  end  of  one  carotid,  of  one  crural  artery,  and 
of  the  crural  vein  on  the  opposite  side.     Connect  the  carotid  with 
the  manometer,  and  the  femoral  vein  with  a  burette  or  large  syringe 
containing  all  the  peptone  solution  except  15  drops,  which  are  put 

position  varied  from  12  to  100  mm.  of  mercury  ;  average  fall,  44.4  mm. 
In  12  out  of  the  16  animals  the  rise  of  pressure  in  the  head-down  position 
varied  from  2  to  36  mm. ;  in  I  there  was  no  change..;  in  3  there  was  a  fall 
of  5  to  24  mm. 


PRACTICAL  EXERCISES  189 

into  a  test-tube  labelled  A.  Take  care  that  the  connecting-tube  and 
cannula  are  free  from  air.  Label  another  test-tube  B.  Run  into 
both  test-tubes  about  5  c.c.  of  blood  from  the  femoral  artery,  and  set 
them  aside.  Now  commence  to  take  a  blood-pressure  tracing,  and 
while  it  is  going  on  quickly  inject  the  peptone  solution.  Notice  the 
effect  on  the  tracing.  The  pressure  falls  owing  largely  to  a  dilatation 
of  the  small  arteries  through  the  direct  action  of  the  peptone  on  their 
muscular  tissue  or  on  the  endings  of  the  vaso-motor  nerves.  As 
soon  as  the  injection  is  finished,  draw  off  a  sample  of  5  c.c.  of  blood 
into  a  test-tube  labelled  C,  and  let  it  stand.  In  ten  minutes  collect 
three  further  samples  of  5  c.c.,  D,  E,  and  F,  and  a  large  one,  G  ;  in 
half  an  hour  another  set  of  three  small  samples,  and  at  as  long  an 
interval  as  possible  thereafter  three  more.  Add  to  E  15  drops  of  a 
2  per  cent,  solution  of  calcium  chloride,  to  F  5  c.c.  of  a  solution  of 
fibrin  ferment  containing  some  calcium  chloride,  and  put  D,  E,  and 
F  into  a  water-bath  at  40°.  Treat  the  other  sets  of  small  samples  in 
the  same  way,  and  also  the  plasma  obtained  by  centrifugalising  G. 
Note  how  long  each  specimen  takes  to  clot,  and  report  your  results.* 


FIG.  74. — EFFECT  OF  INJECTION  OF  PEPTONE  ON  THE  BLOOD-PRESSURE 
IN  A  DOG.    (TO  BE  READ  FROM  RIGHT  TO  LEFT.) 

23.  Effect  of  Suprarenal  Extract  on  the  Blood-pressure. — See 
p.  604. 

24.  Section  and  Stimulation  of  the  Cervical  Sympathetic  in  the 
Eabbit. — Weigh  out  f  gramme  chloral  hydrate.     Dissolve  in  as  small 
a  quantity  of  water  as  possible,  and  inject  into  the  rectum  of  a  rabbit, 
preferably  an  albino.     Half  a  gramme  is  sufficient  for  a  small  rabbit. 
Put  a  pair  of  bulldog  forceps  on  the  anus  to  prevent  escape  of  the 
solution.      Set  up   an  induction   coil   arranged   for  an  interrupted 
current  (Fig.  65,  p.  175),  and  connect  it  through  a  short-circuiting 

*  Sometimes  the  injection  of  peptone  hastens  coagulation  instead  of 
hindering  it.  It  has  been  asserted  that  this  is  only  the  case  when  small 
doses  are  used  (less  than  0*02  gramme  per  kilo  of  body -weight).  But  in  2 
dogs  out  of  1 1  a  dose  of  0-5  gramme  per  kilo  has  been  seen  to  hasten  coagu- 
lation, and  in  i  out  of  12  to  leave  it  unaffected  ;  in  the  other  9  coagulation 
was  markedly  retarded.  The  blood-pressure  always  fell,  the  amount  of 
the  fall  varying  from  81  to  21  mm.  of  mercury  (average,  60  mm.).  It 
sometimes  returned  to  normal  in  twenty  to  thirty  minutes,  but  usually 
required  a  longer  time. 


£90  A  MANUAL  OF  PHYSIOLOGY 

key  with  electrodes.  The  preparations  necessary  for  an  operation 
with  antiseptic  precautions  are  supposed  to  have  been  previously 
made — the  instruments,  sponges,  and  ligatures  boiled  in  water ;  the 
instruments  then  immersed  in  a  5  per  cent,  solution  of  carbolic  acid, 
the  sponges  and  ligatures  in  corrosive  sublimate  solution  (0*1  per 
cent.).  The  hands  are  to  be  thoroughly  washed,  with  diligent  use  of 
the  nail-brush,  in  soap  and  water  before  the  cutting  operation  begins, 
and  then  soaked  in  the  corrosive  sublimate  solution. 

Fasten  the  rabbit  on  a  holder,  back  downwards,  as  in  Fig.  43.  Clip 
off  the  hair  on  the  anterior  surface  of  the  neck.  Remove  loose  hairs 
with  a  wet  sponge,  shave  the  neck,  and  wash  it  thoroughly,  first  with 
soap  and  water,  and  then  with  corrosive  sublimate.  Give  ether  if 
necessary.  Make  a  longitudinal  incision  in  the  middle  line  over  the 
trachea,  beginning  a  little  below  the  thyroid  cartilage  and  extending 
downwards  for  an  inch  and  a  half.  Feel  for  the  carotid  artery, 
expose,  and  raise  it  up.  Two  nerves  will  now  be  seen  coursing  beside 
the  artery.  The  larger  is  the  vagus,  the  smaller  the  sympathetic. 
A  third  and  much  finer  nerve  (the  depressor,  or  superior  cardiac 
branch  of  the  vagus)  may  also  be  seen  in  the  same  position,  but  the 
student  should  neglect  this  for  the  present.  Get  as  little  as  possible 
of  the  antiseptic  solutions  in  the  wound  till  your  observations  have 
been  completed,  as  the  nerves  may  be  injured  by  them.  Also  keep 
the  animal  warm  by  covering  it  with  a  cloth,  and  do  not  handle  or 
wet  its  ears.  Pass  a  ligature  under  the  sympathetic,  and  tie  it,  the 
ear  being  held  up  to  the  light  while  this  is  being  done,  so  that  its 
vessels  may  be  clearly  seen.  A  transient  constriction  of  the  arteries 
may  be  seen  at  the  moment  when  the  nerve  is  ligatured.  This  is 
due  to  stimulation  of  the  vaso-constrictor  fibres.  Then  follows  a 
marked  dilatation  of  the  bloodvessels,  due  to  paralysis  of  these  fibres. 
The  ear  is  flushed  and  hot.  Note  also  that  the  pupil  is  probably 
narrower  on  the  side  on  which  the  nerve  has  been  tied.  On  stimula- 
tion of  the  upper  (cephalic)  end  of  the  sympathetic  with  the  electrodes, 
the  vessels  are  markedly  constricted,  the  ear  becomes  pale  and 
cold,  and  the  pupil  dilates.  Cut  out  the  ligature,  wash  the  wound 
thoroughly  with  corrosive  sublimate,  and  close  it,  the  muscles  being 
first  brought  together  by  a  row  of  interrupted  sutures,  and  then  the 
skin  by  another  row.  Since  it  is  difficult,  if  not  impossible,  to 
thoroughly  disinfect  the  hair-follicles,  and  a  suture  passed  through 
a  septic  follicle  is  apt  to  give  rise  to  suppuration,  subcutaneous 
stitches — i.e.,  stitches  passed  by  a  curved  needle  through  the  deep 
layer  of  the  skin  without  coming  through  to  the  surface — may  be 
employed.  The  wound  is  to  be  protected  by  a  coating  of  collodion. 
No  other  dressing  is  required.  The  animal  is  now  removed  from  the 
holder  and  put  back  to  its  hutch.  The  student  must  examine  it  at 
least  once  a  day  for  the  next  week,  and  study  the  differences  between 
the  two  ears  (p.  151)  and  the  two  pupils. 

25.*  Stimulation  of  the  Depressor  Nerve  in  the  Rabbit. — Set  up 
the  apparatus  for  a  blood-pressure  tracing  as  described  in  19  (p.  185). 
Arrange  an  induction  coil  and  electrodes  for  an  interrupted  current. 
*  This  experiment  is  only  suitable  for  advanced  students. 


PRACTICAL  EXERCISES 


191 


Anaesthetize  a  rabbit  with  \  gramme  chloral  hydrate,  and  if  neces- 
sary with  ether.  For  blood-pressure  experiments  only  small  doses  of 
chloral  hydrate  or  chloroform  can  be  given,  as  they  affect  the  vaso- 
motor  centre.  Put  the  animal  on  the  holder.  Insert  a  cannula  in 
the  trachea  and  another  cannula  in  the  central  end  of  the  carotid 
artery.  Isolate  the  depressor  nerve.  Put  double  silk  ligatures  on  it, 
and  divide  between  them.  Connect  the  cannula  in  the  carotid  with 


FIG.  75. — ARTIFICIAL  SCHEME  TO  ILLUSTRATE  A  METHOD  OF  MEASURING 
THE  CIRCULATION-TIME. 

B,  bottle  containing  water,  the  rate  of  outflow  of  which  is  regulated  by  screw  clamp 
S,  syringe  filled  with  methylene-blue  solution,  connected  with  T- piece  A  ;  M,  beaker 
containing  methylene-blue  solution ;  b,  c,  screw-clamps ;  C,  T-piece,  inserted  in  the 
course  of  the  flexible  tube  E,  and  connected  with  the  glass  tube  T,  which  is  filled  with 
beads  ;  F,  outflow  tube.  The  clamp  c  having  been  closed  and  b  opened,  the  syringe  is 
filled  with  the  methylene-blue  solution,  b  is  then  closed,  c  opened,  and  a  definite 
quantity  of  the  solution  injected  into  the  system.  The  time  from  the  beginning  of 
injection  till  the  appearance  of  the  blue  at  G  is  measured  with  the  stop-watch. 

e  manometer  and  take  a  blood-pressure  tracing.  Stimulate  the 
ntral  (upper)  end  of  the  depressor.  A  marked  fall  of  blood- 
ressure,  accompanied  with  a  slowing  of  the  heart,  will  be  obtained 
(Fig.  55).  Stimulate  the  peripheral  (lower)  end  ;  no  effect.  Divide 
both  vagi,  and  again  stimulate  the  central  end  of  the  nerve.  The 
blood-pressure  again  falls,  but  there  is  no  alteration  in  the  rate  of  the 


192  A  MANUAL  OF  PHYSIOLOGY 

heart  (p.  160).  Close  the  tracheal  cannula,  and  obtain  another 
tracing,  showing  the  effect  of  asphyxia  (Fig.  56,  p.  163). 

Autopsy. — Dissect  the  nerve  that  has  been  stimulated,  up  to  the 
origin  of  the  superior  laryngeal  branch  of  the  vagus,  to  make  sure 
that  it  is  the  depressor  (Fig.  54,  p.  161). 

26.  Determination  of  the  Circulation-time. — (a)  Begin  with  an 
artificial  scheme  (Fig.  75).  Fill  the  syringe  with  a  0*2  per  cent, 
solution  of  methylene  blue.  Allow  the  water  to  flow  from  the  bottle 
by  loosening  the  clamp.  Inject  a  definite  quantity  of  the  methylene- 
blue  solution,  and  with  a  stop-watch  observe  how  long  it  takes  to 
pass  from  the  point  of  injection  to  the  end  of  the  glass  tube  filled 
with  beads.  Make  ten  readings  of  this  kind  and  take  the  mean. 
Then  raise  the  bottle  so  as  to  increase  the  rate  of  flow  of  the  water, 
and  repeat  the  observations.  The  '  circulation-time '  will  be  found 
to  be  diminished.  This  corresponds  to  an  increase  of  blood-pressure 
due  to  increased  activity  of  the  heart  without  change  in  the  calibre 
of  the  bloodvessels.  Next,  leaving  the  bottle  in  its  present  position, 
diminish  the  outflow  by  tightening  the  clamp ;  the  circulation-time 
will  be  increased.  This  corresponds  to  an  increase  of  blood-pressure 
due  to  diminution  in  the  calibre  of  the  small  arteries. 

(b)  Fill  the  syringe*  with  methylene-blue  solution  (0-2  per  cent,  in 
normal  saline),  as  in  (a}.  Keep  the  solution  warmed  to  40°  C.  by 
immersing  the  small  beaker  containing  it  in  a  water-bath,  or  heating 
over  a  bunsen  with  a  small  flame.  Weigh  a  rabbit,  and  inject 
f  gramme  chloral  into  the  rectum.  Fasten  it  on  a  holder,  back 
downwards  (Fig.  43,  p.  125).  Clip  off  the  hair  on  the  front  of  the 
neck,  and  after  giving  ether  if  the  animal  shows  the  least  sign  of 
pain,  make  an  incision  i  J  inches  long  in  the  middle  line,  beginning 
a  little  way  below  the  cricoid  cartilage.  Reflect  the  skin  and  isolate 
the  external  jugular  vein,  which  is  quite  superficial.  Carefully 
separate  about  f  inch  of  the  vein  from  the  surrounding  tissue,  and 
pass  two  ligatures  under  it,  but  do  not  tie  them.  Compress  the 
vein  with  a  pair  of  bulldog  forceps  between  the  heart  and  the 
ligatures.  Now  tie  the  uppermost  of  the  two  ligatures  (that  next  the 
head),  but  only  put  a  single  loose  loop  on  the  other.  The  piece 
of  vein  between  the  upper  ligature  and  the  bulldog  is  now  dis- 
tended with  blood.  With  fine-pointed  scissors  make  a  small  slit  in 
the  vein,  taking  great  care  not  to  divide  it  completely,  insert  the 
cannula,  and  tie  the  loose  ligature  firmly  over  its  neck.  Fill  the 
cannula  and  the  small  piece  of  rubber  tubing  attached  to  it  with 
normal  saline  by  means  of  a  pipette  with  a  long  point.  Expose  the 
carotid  on  the  other  side,  isolate  it  for  f  inch,  clear  it  carefully  from 
its  sheath,  slip  under  it  a  strip  of  thin  sheet  indiarubber,  and  between 
this  and  the  artery  a  little  piece  of  white  glazed  paper.  Connect 

*  A  burette,  sloped  so  as  to  make  a  small  angle  with  the  horizontal, 
may  be  substituted  for  the  syringe.  The  burette  is  supported  on  a  stand 
at  such  a  height  that  the  methylene-blue  solution  runs  without  great  force 
into  the  jugular  (say  10-15  cm.  above  the  level  of  the  cannula).  The 
danger  of  producing  an  abnormal  result  by  suddenly  raising  the  pressure 
in  the  right  side  of  the  heart  is  thus  avoided. 


PRACTICAL  EXERCISES  193 

the  cannula  in  the  jugular  with  the  T-piece  attached  to  the  syringe. 
Care  must  be  taken  that  no  air  remains  in  the  cannula  or  its  con- 
necting-tube, as  an  animal  not  unfrequently  dies  instantaneously  when 
a  bubble  of  air  is  injected  into  the  right  heart. 

Now  take  off  the  bulldog  from  the  vein,  and  make  a  series  of 
observations  on  the  pulmonary  circulation-time.  The  animal  must 
be  so  placed  that  a  good  light  falls  on  the  carotid.  If  necessary,  the 
light  of  a  gas-flame  may  be  concentrated  on  it  by  a  lens.  The 
student  holds  the  stop-watch  in  one  hand,  and  injects  a  measured 
quantity  of  the  methylene-blue  solution  with  the  other.  Uniformity 
in  the  quantity  injected  is  secured  by  fastening  on  the  piston  of  the 
syringe  a  screw-clamp,  which  stops  the  piston  at  the  desired  point. 
The  observation  consists  in  setting  off  the  watch  at  the  moment  when 
injection  begins  and  stopping  it  when  the  blue  appears  in  the  carotid. 
After  each  injection  the  screw-clamp  or  pinchcock  on  the  tube  con- 
nected with  the  cannula  must  be  tightened,  the  other  opened,  and 
the  syringe  refilled.  Great  care  must  be  taken  never  to  open  the  two 
clamps  at  the  same  time,  as  in  that  case  blood  may  regurgitate  through 
the  jugular  and  fill  the  syringe,  or  methylene  blue  may  be  sucked 
into  the  circulation.  As  many  observations  as  possible  should  be 
taken,  and  the  mean  determined.  The  circulation-time  observed  is 
approximately  that  of  the  lesser  circulation,  the  time  taken  by  the 
blood  to  pass  from  the  left  ventricle  to  the  carotid  being  negligible. 
The  specific  gravity  of  the  blood  may  also  be  tested  at  the  beginning 
and  end  of  the  experiment  by  Hammerschlag's  method  (p.  57). 

Autopsy. — Observe  particularly  the  state  of  the  lungs,  whether  the 
bladder  is  distended  or  not,  and  whether  any  of  the  serous  cavities 
or  the  intestines  contain  much  liquid  ;  so  as  to  determine,  if  possible, 
by  what  channel  the  water  injected  into  the  blood  may  have  been 
eliminated.  Notice  the  distribution  of  the  methylene  blue  in  such 
organs  as  the  kidneys  and  the  muscles  immediately  after  death,  and 
notice  that  the  blue  colour  becomes  more  pronounced  after  exposure 
for  a  time  to  the  air.  Make  a  longitudinal  section  through  a  kidney, 
and  observe  that  the  pigment  is  found  especially  in  the  cortex  and 
around  the  pelvis  at  the  apices  of  the  pyramids,  or  it  may  be  only  in  the 
cortex.  The  urine  is  greenish.  If  some  methylene  blue  has  been 
injected  after  the  heart  ceased  to  beat,  the  bloodvessels,  particularly 
in  the  mesentery,  may  be  beautifully  mapped  out  by  the  pigment. 
This  is  not  the  case  if  the  last  injection  took  place  before  death, 
since  the  blue  is  rapidly  reduced  by  living  tissues. 


CHAPTER    III. 
RESPIRATION. 

RESPIRATION  in  its  widest  sense  is  the  sum  total  of  the 
processes  by  which  the  ultimate  elements  of  the  body  gain 
the  oxygen  they  require,  and  get  rid  of  the  carbon  dioxide 
they  produce. 

Comparative. — In  a  unicellular  organism  no  special  mechanism  of 
respiration  is  needed ;  the  oxygen  diffuses  in,  and  the  carbon  dioxide 
diffuses  out,  through  the  general  surface.  The  simple  wants  of  such 
multicellular  animals  as  the  ccelenterates,  the  group  to  which  the  sea- 
anemone  belongs,  are  also  supplied  by  diffusion  through  the  ectoderm 
from  and  into  the  surrounding  water,  and  through  the  endoderm  from 
and  into  the  contents  of  the  body-cavity  and  its  ramifications. 

But  in  animals  of  more  complex  structure  special  arrangements 
become  necessary,  and  respiration  is  divided  into  two  stages : 
(i)  External  respiration,  an  interchange  between  the  air  or  water 
and  a  circulating  medium  or  blood  as  it  passes  through  richly 
vascular  skin,  gills,  tracheae,  or  lungs ;  and  (2)  internal  respiration, 
an  interchange  between  the  blood,  or  lymph,  and  the  cells. 

In  the  lower  kinds  of  worms  respiration  goes  on  solely  through  the 
skin,  under  which  plexuses  of  bloodvessels  often  exist,  but  in  some 
higher  worms  there  are  special  vascular  appendages  that  play  the  part 
of  gills.  The  Crustacea  also  possess  gills,  while  in  the  other  arthro- 
poda  respiration  is  carried  on  either  by  the  general  surface  of  the 
body  (in  some  low  forms),  or  more  commonly  by  means  of  tracheae, 
or  branched  tubes  surrounded  by  blood  spaces  and  communicating 
externally  with  the  air  and  internally  by  their  finest  twigs  with  the 
individual  cells.  Most  of  the  mollusca  breathe  by  gills,  but  a  few 
only  by  the  skin. 

Among  vertebrates  the  fishes  and  larval  amphibians  breathe  by 
gills,  but  most  adult  amphibians  have  lungs.  The  skin,  too,  in  such 
animals  as  the  frog  has  a  very  important  respiratory  function,  more 
of  the  gaseous  exchange  taking  place  through  it  than  through  the  lungs. 

One   small   group   of  fishes,  the   dipnoi,  has   the   peculiarity  of 


RESPIRATION  195 

possessing  both  gills  and  a  kind  of  lungs,  the  swim-bladder  being 
surrounded  with  a  plexus  of  bloodvessels  and  taking  on  a  respiratory 
function. 

In  all  the  higher  vertebrates  the  respiration  is  carried  on  by  lungs ; 
the  trifling  amount  of  gaseous  interchange  which  can  possibly  take 
place  through  the  skin  is  not  worth  taking  into  account.  The  lungs 
are  to  be  regarded  as  developed  from  outgrowths  of  the  alimentary 
canal,  beginning  near  the  mouth. 

The  object  of  all  special  respiratory  arrangements  being,  in  the 
first  instance,  to  facilitate  the  gaseous  exchange  between  the  sur- 
rounding medium  (air  or  water)  and  the  blood,  a  prime  necessity  of 
a  respiratory  organ,  be  it  skin,  gill,  trachea,  or  lung,  is  a  free  supply 
of  blood,  in  vessels  so  fine  and  thin  that  diffusion  readily  takes  place 
into  them  and  out  of  them.  But  a  free  supply  of  blood  would  be  of 
no  avail  if  the  medium  to  which  the  blood  gave  up  its  carbon  dioxide 
and  from  which  it  drew  its  oxygen  was  not  being  constantly  and 
sufficiently  renewed. 

Sometimes  the  natural  currents  of  the  water  or  the  air  are  of 
themselves  sufficient  to  secure  this  renewal ;  in  other  cases,  artificial 
currents  are  set  up  by  cilia,  or  special  bailing  organs,  like  the  scapho- 
gnathites  of  the  lobster.  In  all  the  higher  animals  active  move- 
ments, by  which  air  or  water  is  brought  into  contact  with  the  respira- 
tory surfaces,  are  necessary ;  and  it  is  possible  that  such  movements 
take  place  even  in  the  tracheae  of  insects  and  other  air-breathing 
arthropoda.  Fishes,  by  rhythmical  swallowing  movements,  take  in 
water  through  the  mouth  and  pass  it  over  the  gills  and  out  by  the 
gill-slits,  while  the  frog  distends  its  lungs  by  swallowing  air. 

Physiological  Anatomy  of  the  Respiratory  Apparatus. — In  man  O 
the  respiratory  apparatus  consists  of  a  tube  (the  trachea)  widened  at 
its  upper  part  into  the  larynx,  which  contains  the  special  mechanism 
of  voice,  and  communicates  through  the  nose  or  mouth  with  the 
external  air.  Below,  the  trachea  divides  dendritically  into  innumer- 
able branches,  the  ultimate  divisions  of  which  are  called  bronchioles. 
Each  bronchiole  breaks  up  into  several  wider  passages,  or  infundibula, 
the  walls  of  which  are  everywhere  pitted  with  recesses  or  alcoves, 
called  alveoli.  The  trachea  and  larger  bronchi  are  strengthened  by 
hyaline  cartilage  in  the  form  of  incomplete  rings,  connected  behind 
by  non-striped  muscular  fibres,  which  also  exist  in  the  intervals 
between  the  rings.  The  middle-sized  bronchi  within  the  lungs  have 
the  cartilage  in  the  form  of  detached  pieces  in  the  outer  portion  of 
the  wall,  while  nearer  the  lumen  lies  a  complete  ring  of  non-striped 
muscle. 

In  the  bronchioles,  no  cartilage  is  present,  but  the  circularly- 
arranged  muscular  fibres  still  persist,  and  also  form  a  thin  layer  in 
the  infundibula.  In  the  air-cells,  or  alveoli,  however,  there  are  no 
muscular  fibres.  Their  walls  consist  essentially  of  a  network  of 
elastic  fibres,  continuous  with  a  similar  layer  in  the  infundibula  and 
bronchioles,  and  covered  on  the  side  next  the  lumen  by  a  single 
layer  of  large,  clear  epithelial  scales,  with  here  and  there  a  few 
smaller  and  more  granular  polyhedral  cells. 

13—2 


196  A  MANUAL  OF  PHYSIOLOGY 

From  the  larynx  to  the  bronchioles  the  mucous  membrane  is 
ciliated  on  its  free  surface,  the  cilia  lashing  upwards  so  as  to  move 
the  secretion  towards  the  larynx  and  mouth.  In  the  infundibula  the 
ciliated  epithelium  begins  to  disappear,  and  is  absent  from  the  alveoli. 
Part  of  the  nasal  cavity  and  the  upper  part  of  the  pharynx  are  also 
lined  with  ciliated  epithelium.  Mucous  glands  are  present  in 
abundance  in  the  upper  portions  of  the  respiratory  passages,  but 
disappear  in  the  smaller  bronchi. 

C  ,  Blood-supply  of  the  Lungs. — The  quantity  of  blood  traversing  the 
lungs  bears  no  proportion  to  the  amount  required  for  their  actual 
nourishment.  Small,  however,  as  this  latter  quantity  is.  it  cannot 
apparently  be  derived  from  the  vitiated  blood  of  the  right  ventricle, 
but  is  obtained  directly  from  the  aortic  system  by  the  bronchial 
arteries.  These  are  distributed  with  the  bronchi,  which  they  supply 
as  well  as  the  connective-tissue  of  the  interlobular  septa  running 
through  the  substance  of  the  lung,  the  pleura  lining  it  and  the  walls 
of  the  large  bloodvessels.  Most  of  the  blood  from  the  bronchial 
arteries  is  returned  by  the  bronchial  veins  into  the  systemic  venous 
system,  but  some  of  it  finds  its  way  by  anastomoses  into  the  pul- 
monary veins. 

The  branches  of  the  pulmonary  artery  are  also  distributed  with 
the  bronchi,  and  break  up  into  a  dense  capillary  network  around  the 
alveoli.  From  the  capillaries  veins  arise  which,  gradually  uniting, 
form  the  large  pulmonary  veins  that  pour  their  blood  into  the  left 
auricle. 

The  same  quantity  of  blood  must,  on  the  whole,  pass  per  unit  of 
time  through  the  lesser  as  through  the  greater  circulation,  otherwise 
equilibrium  could  not  exist,  and  blood  would  accumulate  either  in 
the  lungs  or  in  the  systemic  vessels.  But  it  does  not  follow  that  at 
each  heart-beat  the  output  of  the  two  ventricles  is  exactly  equal.  If, 
indeed,  the  capacity  of  the  lesser  circulation  were  constant,  the 
quantity  driven  out  at  one  systole  by  the  right  ventricle  would  be 
the  same  as  that  ejected  at  the  next  by  the  left  ventricle.  But  it  is 
known  that  the  capacity  of  the  pulmonary  vessels  is  altered  by  the 
movements  of  respiration  and  probably  in  other  ways,  so  that  it  is 
only  on  the  average  of  a  number  of  beats  that  the  output  of  the  two 
ventricles  can  be  supposed  equal. 

The  time  required  by  a  given  small  portion  of  blood,  e.g.,  by  a 
single  corpuscle,  to  complete  the  round  of  the  lesser  circulation,  is, 
as  we  have  seen  (p.  124),  much  less  than  the  average  time  needed  to 
complete  the  systemic  circulation.  In  the  rabbit  the  ratio  is  probably 
about  1:5.  Since  all  the  blood  in  a  vascular  tract  must  pass  out  of  it 
in  a  period  equal  to  the  circulation  time,  the  average  quantity  of 
blood  in  the  lungs  and  right  heart  of  a  rabbit  must  be  about  one- 
fifth  of  that  in  the  systemic  vessels.  On  the  assumption  that  the 
same  proportion  holds  for  a  man,  not  less  than  900  grm.  out  of  the 
5^  kilos  of  blood  in  a  seventy  kilo  man  must  be  contained  in  the  lesser 
circulation,  and  rather  more  than  4^  kilos  in  the  greater.  This 
corresponds  sufficiently  well  with  calculations  from  other  data. 

For  example,  the  average  weight  of  the  lungs  in  three  persons, 


RESPIRATION  197 

executed  by  beheading,  was  457  grm.  (Gluge).  The  average  weight  of 
the  lungs  in  a  great  number  of  persons  who  had  died  a  natural  death 
was  1024  grm.  (Juncker).  The  weight  of  the  pulmonary  tissue  alone 
in  the  first  set  of  cases  must  be  less  than  457  grm.,  for  the  lungs  of 
a  person  who  has  bled  to  death  are  never  bloodless.  In  a  dog  killed 
by  bleeding  from  the  carotid,  one-quarter  of  the  weight  of  the  lungs  Q 
consisted  of  blood.  Assuming  the  same  proportion  for  the  de- 
capitated individuals,  we  get  343  grm.  as  the  net  weight  of  the  blood- 
free  lungs.  Deducting  this  from  1024  grm.,  we  arrive  at  68 1  grm. 
as  the  average  quantity  of  blood  in  the  lungs.  Adding  to  this  the 
quantity  in  the  right  side  of  the  heart  (p.  127),  we  get,  in  round 
numbers,  750  grm.  as  the  amount  in  the  lesser  circulation.  It  is 
true  that  in  the  living  body  the  conditions  are  not  the  same  as  after 
death  ;  but  it  is  probable  that  in  a  large  number  of  cases  taken  at 
random  the  differences  would  be  approximately  equalized. 

It  has  been  further  calculated — but  here  the  data  are  less  certain — 
that  the  total  area  of  the  alveolar  surface  of  the  lungs  of  a  man  is 
about  100  square  metres  (sixty  times  greater  than  the  area  of  skin), 
of  which,  perhaps,  75  square  metres  are  occupied  by  capillaries. 
The  average  thickness  of  this  immense  sheet  of  blood  has  been 
reckoned  to  be  equal  to  the  diameter  of  a  red  blood-corpuscle,  or, 
say,  S/*.  This  would  give  600  c.c.  (630  grm.)  as  the  quantity  of  Q 
blood  in  the  lungs,  which  is  probably  somewhat  too  low  an  estimate. 

If  we  take  the  pulmonary  circulation-time  as  13  seconds  (p.  124), 

and  the  quantity  of  blood  in  the  lungs  as  800  grm.,  then  - 

=  221  kilos  of  blood  will  pass  through  the  lungs  in  an  hour,  or 
5,304  kilos  (say,  5,000  litres)  in  twenty-four  hours.  This  would  fill 
a  cubical  tank  in  which  the  man  could  just  stand  upright  with  the 
lid  closed. 

Mechanical  Phenomena  of  Respiration. 

The  lungs  are  enclosed  in  an  air-tight  box,  the  thorax ; 
or  it  may  be  said  with  equal  truth  that  they  form  part  of 
the  wall  of  the  thoracic  cavity,  and  the  part  which  has 
by  far  the  greatest  capacity  of  adjustment.  The  alveolar 
surface  of  the  lungs  is  in  contact  with  the  air.  The  pleura, 
which  covers  their  internal  surface,  is  reflected  over  the 
chest-walls  and  diaphragm,  so  as  to  form  two  lateral  sacs, 
the  pleural  cavities.  In  health  these  are  almost  obliterated, 
and  the  visceral  and  parietal  pleurae,  separated  and 
lubricated  by  a  few  drops  of  lymph,  glide  on  each  other 
with  every  movement  of  respiration.  But  in  disease  the 
pleural  cavities  may  be  rilled  and  their  walls  widely  separated 
by  exudation  as  in  pleurisy,  or  by  blood  as  in  rupture  of  an 


A  MANUAL  OF  PHYSIOLOGY 


aneurism,  or  by  air  in  the  condition  known  as  pneumo- 
thorax.  Between  the  two  pleural  sacs  lies  a  mesial  space, 
the  mediastinum,  commonly  divided  into  an  anterior  medias- 
tinum in  front  of  the  heart,  and  a  posterior  mediastinum 
behind  it.  The  pleural  and  pericardial  sacs  and  the  medias- 
tinum constitute  together  the  thoracic  cavity.  The  external 
surface  of  the  chest-wall  and  the  alveolar  surface  of  the  lungs 
are  subjected  to  the  pressure  of  the  atmosphere,  to  which 

the  pressure  in  the  thoracic 
cavity  (intra  -  thoracic  pres- 
sure) would  be  exactly  equal  if 
its  boundaries  were  perfectly 
yielding.  But  in  reality  the 
intra  -  thoracic  pressure  is 
always  normally  something 
less  than  this.  For  even  the 
lungs,  the  least  rigid  part  of  the 
boundary,  oppose  a  certain 
resistance  to  distension,  and 
so  hold  off,  as  it  were,  from 

MOVEMENTS  OF  THE^LUNGS    the  thoracic  cavity  a  portion 

of  the  alveolar  pressure  ;  and 
in  any  given  position  of  the 
chest  the  intra-thoracic  pres- 
sure is  equal  to  the  atmo- 
spheric pressure  minus  this 
elastic  tension  of  the  lungs. 

The  object  of  the  respira- 
tory movements  is  the  renewal 
of  the  air  in  contact  with  the 
alveolar  membrane — in  other 

words,  the  ventilation  of  the  lungs.  Two  main  methods  are 
followed  by  sanitary  engineers  in  the  ventilation  of  buildings: 
they  force  air  in,  or  they  draw  it  in.  In  both  cases  the 
movement  of  the  air  depends  on  the  establishment  of  a 
slope  of  pressure  from  the  inlet  to  the  interior.  In  the  first 
method,  this  is  done  by  increasing  the  pressure  at  the  inlet  ; 
in  the  second,  by  diminishing  the  pressure  at  the  outlet.  In 
certain  animals  Nature,  in  solving  its  problem  of  ventilation, 


FIG.  76. — SCHEME  TO 
THE 
IN  THE  CHEST. 

T  is  a  bottle  from  which  the  bottom 
has  been  removed ;  D  a  flexible  and 
elastic  membrane  tied  on  the  bottle,  and 
capable  of  being  pulled  out  by  the  string 
S  so  as  to  increase  the  capacity  of  the 
bottle.  L  is  a  thin  elastic  bag  represent- 
ing the  lungs.  It  communicates  with  the 
external  air  by  a  glass  tube  fitted  airtight 
through  a  cork  in  the  neck  of  the  bottle. 
When  D  is  drawn  down,  the  pressure  of 
the  external  air  causes  L  to  expand. 
When  the  string  is  let  go,  L  contracts 
again,  in  virtue  of  its  elasticity. 


RESPIRATION  199 

has  made  use  of  the  first  principle.  Thus,  the  frog  forces 
air  into  its  lungs  by  a  swallowing  movement.  In  artificial 
respiration,  as  practised  in  physiological  experiments,  the 
same  method  is  usually  employed  :  air  is  driven  into  the 
lungs  under  pressure.  But  in  the  vast  majority  of  animals, 
including  man,  the  opposite  principle  ha ;  been  adopted  ; 
and  the  '  indraught '  of  air  from  nose  and  pharynx  to  alveoli 
is  not  set  up  by  increasing  the  pressure  in  the  former,  but  by 
diminishing  it  in  the  latter.  This  '  indraught,'  or  inspiration, 
is  brought  about  by  certain  movements  of  the  chest-wall, 
which  increase  the  capacity  of  the  thoracic  cage  and  lower 
the  pressure  in  the  thoracic  cavity.  The  expansion  of  the 
highly-distensible  lungs  keeps  pace  with  the  diminution  of 
pressure  in  the  pleural  sacs,  and  they  follow  at  every  point 
the  retreating  chest-wall  and  diaphragm.  The  pressure  of 
the  air  in  the  alveoli  during  the  rapid  expansion  of  the 
lungs  necessarily  sinks  below  that  of  the  atmosphere,  and 
air  rushes  in  through  the  trachea  and  bronchi  till  the 
difference  is  equalized.  Then  commences  the  movement  of 
expiration,  The  expanded  chest  falls  back  to  its  original 
limits  ;  the  pressure  in  the  thoracic  cavity  increases ;  the 
distended  lungs,  in  virtue  of  their  elasticity,  shrink  to  their 
former  volume ;  the  pressure  of  the  air  in  the  alveoli  rises 
above  that  of  the  atmosphere,  and  with  this  reversal  of 
the  slope  of  pressure  air  streams  out  of  the  bronchi  and 
trachea. 

In  inspiration  the  chest  dilates  in  all  its  diameters.  Its 
vertical  diameter  is  increased  by  the  contraction  of  the 
diaphragm,  which,  composed  of  a  central  tendon  and  a 
peripheral  ring  of  muscular  tissue,  bulges  up  into  the  thorax 
in  the  form  of  a  flattened  dome,  and  closes  its  lower 
aperture.  When  the  diaphragm  contracts,  the  central 
tendon  descends  ;  the  acute  angle  which  the  muscular  ring 
makes  during  relaxation  with  the  thoracic  wall  opens  out 
around  its  whole  circumference,  so  as  to  form  a  deep  groove 
of  triangular  section.  The  lungs  follow  the  descending 
diaphragm,  their  lower  borders  keeping  accurately  in  contact 
with  it,  while  their  apices  move  very  slightly  or  not  at  all. 
Since  the  diaphragm  is  attached  to  the  lower  ribs,  there  is  a 


200  A  MANUAL  OF  PHYSIOLOGY 

tendency  during  its  contraction  for  these  to  be  drawn  in- 
wards and  upwards  ;  but  this  is  opposed  by  the  pressure  of 
the  abdominal  viscera,  and  by  the  action  of  the  quadratics 
lumborum,  which  fixes  the  twelfth  rib,  and  of  the  serratus 
posticus  inferior,  which  draws  the  lower  four  ribs  backward. 
When  these  and  the  other  inspiratory  muscles  that  act 
especially  upon  the  ribs  are  paralyzed  by  injury  to  the  spinal 
cord,  and  respiration  is  carried  on  by  the  diaphragm  alone, 
the  line  of  its  attachment  to  the  ribs  is  distinctly  marked 
during  inspiration  by  a  shallow  circular  groove. 

The  antero-posterior  and  transverse  diameters  of  the 
thorax  are  enlarged  by  the  action  of  certain  muscles  that 
elevate  the  ribs.  Of  these,  the  most  important  are  the 
levatores  costarum — twelve  in  number  on  each  side.  They 
arise  from  the  transverse  processes  of  the  last  cervical  and 
first  eleven  dorsal  vertebrae,  and,  passing  obliquely  down- 
wards and  outwards,  are  inserted  between  the  tubercle  and 
the  angle  into  the  first  or  second  rib  below  their  origin. 
The  scalene  muscles,  which  may  in  a  lean  person  be  felt  to  be 
tense  during  inspiration,  fix  the  first  and  second  ribs  (scalenus 
anticus  and  medius,  the  first  ;  scalenus  posticus,  the  second 
rib),  and  so  afford  a  fixed  line  for  the  intercostal  muscles  to 
work  from  on  the  lower  ribs. 

The  action  of  the  intercostals  has  been  much  debated  ;  but  it 
seems  to  be  certain  that  the  external  intercostals  do  aid  to  a 
slight  extent  in  raising  the  ribs  when  the  upper  two  have 
been  fixed  by  the  contraction  of  the  scaleni.  The  inter- 
cartilaginous  portion  of  the  internal  intercostals  also  con- 
tracts simultaneously  with  the  diaphragm,  and  may  there- 
fore be  reckoned  in  the  list  of  inspiratory  muscles  ;  but  the 
function  of  the  interosseous  portion  is  still  in  doubt.  It  is 
probable  that  the  chief  importance  of  the  intercostal  muscles 
(both  external  and  internal)  is  not  so  much  to  act  upon  the 
ribs,  as  to  increase  by  their  contraction  the  rigidity  of  the 
intercostal  spaces,  and  so  prevent  them  from  being  drawn  in 
when  the  chest  is  expanded  by  the  action  of  the  diaphragm, 
the  levatores,  and  the  scaleni.  Since  the  ribs  slant  down- 
wards and  forwards  to  their  sternal  attachments,  the  sternum 
is  raised  when  they  are  elevated  ;  or,  rather,  since  the  upper 


RESPIRATION  201 

end  of  that  bone  is  practically  immovable  in  ordinary  breath- 
ing, its  lower  extremity  is  tilted  forwards.  This  causes  an 
increase  in  the  antero-posterior  diameter  of  the  thorax. 
Further,  since  the  arches  formed  by  the  ribs  widen  in  regular 
progression  from  above  downwards,  at  least  in  the  upper 
portion  of  the  thoracic  cage,  so  that  the  second  rib  is  a 
segment  of  a  larger  circle  than  the  first,  and  the  third  than 
the  second,  it  is  clear  that  a  general  elevation  of  the  chest 
will  tend  also  to  increase  the  transverse  diameter  at  any 
given  level.  Such  an  increase  is  also  favoured  by  the  open- 
ing out  of  the  angles  between  the  bony  ribs  and  the  costal 
cartilages  under  the  influence  of  the  couple  (or  pair  of 
oppositely  directed  forces)  that  acts  on  them — viz.,  the 
upward  pull  of  the  levatores  costarum  and  the  other  elevators 
exerted  on  the  ribs,  and  the  resistance  of  the  sternum  to 
further  displacement  exerted  on  the  cartilages.  The  widening 
of  the  thorax  from  side  to  side  may  also  be  in  a  slight  degree 
ascribed  to  a  twisting  movement  of  the  ribs,  which  tends  to 
evert  their  lower  borders. 

Expiration  in  perfectly  tranquil  breathing  is  brought  about 
with  very  little  aid  from  active  muscular  contraction.  The 
sense  of  effort  disappears  as  soon  as  the  chest  ceases  to 
expand.  The  diaphragm  and  the  elevators  of  the  ribs  relax. 
The  structures  that  have  been  stretched  or  twisted  recoil 
into  their  original  positions ;  the  structures  that  have  been 
raised  against  the  force  of  gravity  fall  back  by  their  weight, 
and  in  the  measure  in  which  the  pressure  increases  in  the 
thoracic  cavity  the  elasticity  of  the  lungs  causes  them  to 
shrink.  The  pressure  in  the  alveoli,  which  at  the  end  of 
inspiration  was  just  equal  to  that  of  the  atmosphere,  is  thus 
increased,  and  the  air  expelled.  It  is  possible  that,  even 
in  man  and  in  quiet  respiration,  a  slight  contraction  of  the 
abdominal  muscles  hastens  the  return  of  the  diaphragm  to  its 
position  of  rest,  and  that  the  triangularis  sterni  helps  in 
depressing  the  costal  cartilages.  In  reptiles  and  birds, 
expiration  is  normally  effected  by  an  active  muscular  con- 
traction. This  is  also  true  in  some  mammals — the  rabbit, 
for  instance,  in  which  the  external  oblique  muscle  of  the 
abdominal  wall  takes  an  important  share  in  the  expiratory  act. 


202  A  MANUAL  OF  PHYSIOLOGY 

0,  Types  of  Respiration.  —  Differences  exist  also,  not  only 
between  different  groups  of  animals,  but  even  between 
women  and  men,  in  the  relative  importance  in  inspiration 
of  the  diaphragm  on  the  one  hand,  and  the  muscles  that 
elevate  the  ribs  on  the  other.  When  the  movements  of  the 
diaphragm  predominate,  the  respiration  is  said  to  be  of  the 
abdominal  or  diaphragmatic  type ;  when  the  movements  of 
the  ribs  and  sternum  are  most  conspicuous,  of  the  costal  or 
thoracic  type.  In  abdominal  respiration,  the  inspiratory 
movement  commences  at  the  diaphragm,  and  then  involves 
the  lower  ribs  and  the  tip  of  the  sternum.  In  costal 
respiration,  the  upper  ribs  initiate  the  movement,  and  are 
followed  by  the  abdomen.  In  the  rabbit,  during  quiet 
breathing,  the  respiration  is  purely  diaphragmatic,  the  ribs 
remain  motionless;  and  herbivorous  animals  in  general 
conform  more  or  less  closely  to  this  type.  In  the  carnivora, 
on  the  contrary,  the  costal  type  prevails.  Man  allies  him- 
self as  regards  his  respiration  with  the  rabbit  and  the  sheep ; 
he  uses  his  diaphragm  more  than  his  ribs.  Civilized  woman 
falls  into  the  class  of  the  wolf  and  the  tiger ;  she  uses  her 
ribs  more  than  her  diaphragm.  The  cause  of  the  difference 
between  men  and  women  has  been  much  discussed.  It  is 
not  a  primitive  sexual  difference,  for  it  is  far  from  being 
universal  ;  in  the  uncivilized  and  semi-civilized  races  that 
have  been  investigated,  the  women  breathe  like  the  men. 
It  is  therefore  probable  that  the  predominance  of  the  costal 
*  type  among  women  of  European  race  is  a  peculiarity 
developed  by  a  mode  of  dressing  which  hampers  the  move- 
ments of  the  diaphragm  while  permitting  the  elevation  of 
the  ribs.  This  conclusion  is  strengthened  by  the  fact  that 
in  children  no  difference  exists  ;  both  boys  and  girls  show 
the  abdominal  type  of  respiration. 

All  this  refers  to  ordinary  breathing.  In  forced  respira- 
tion, when  the  need  for  air  becomes  urgent,  costal  breathing 
always  becomes  prominent  alike  in  men,  in  women,  and  in 
animals,  for  by  elevation  of  the  ribs  the  capacity  of  the 
chest  can  be  increased  to  a  greater  degree  than  by  any 
contraction  of  the  diaphragm. 

In   forced   inspiration,   indeed,  all   the   muscles   that   can 


RESPIRATION  203 

elevate  the  ribs  may  be  thrown  into  contraction,  as  well  as 
other  muscles  which  give  these  fixed  points  to  act  from. 
During  a  paroxysm  of  asthma,  for  example,  the  patient  may 
grasp  the  back  of  a  chair  with  his  hands,  so  as  to  fix  the 
arms  and  shoulders  and  allow  the  pectoral  and  serratus 
magnus  to  raise  the  ribs.  Similarly  in  forced  expiration 
all  the  muscles  are  used  which  can  depress  the  ribs,  or 
increase  the  intra-abdominal  pressure  and  push  up  the 
diaphragm. 

Certain  accessory  phenomena  (movements  and  sounds)  are 
associated  with  the  proper  movements  of  respiration.  The 
larynx  rises  in  expiration,  and  sinks  in  inspiration.  The 
glottis  (and  particularly  its  posterior  portion,  the  glottis 
respiratoria)  is  widened  during  deep  inspiration  and 
narrowed  during  deep  expiration.  The  same  is  the  case 
with  the  nostrils,  and,  indeed,  in  some  persons  the  alse  nasi 
move  even  in  ordinary  breathing. 

As  regards  the  respiratory  sounds,  all  that  is  necessary  to 
be  said  here  is  that  when  we  listen  over  the  greater  portion 
of  the  lungs  with  the  ear,  or,  much  better,  with  a  stetho- 
scope, a  soft  breezy  murmur,  that  has  been  compared  to  the 
rustling  of  the  wind  through  distant  trees,  is  heard.  This 
has  been  called  the  vesicular  murmur.  It  is  only  heard  in 
health  during  inspiration  and  the  very  beginning  of  expira- 
tion, and  is  louder  in  children  than  in  adults.  It  is  not 
definitely  settled  whether  this  sound  arises  at  the  glottis 
and  is  modified  by  transmission  through  the  pulmonary 
tissue,  or  whether  it  arises  somewhere  in  the  terminal 
bronchi,  the  infundibula  or  the  alveoli.  Both  views  may  be 
supported  by  certain  arguments,  and  to  both  some  objec- 
tions may  be  raised.  But  it  is  generally  admitted,  and  this 
is  of  great  importance  in  practical  medicine,  that  when 
the  normal  sound  is  heard  over  any  portion  of  the  lung 
tissue,  it  may  be  inferred  that  this  portion  is  being  properly 
distended,  and  that  air  is  freely  entering  its  alveoli.  Around 
the  larger  bronchi  and  the  trachea  a  blowing  sound  is  heard. 
In  health  this  is  not  recognised  over  the  greater  portion  of 
the  lung,  but  in  certain  diseases  in  which  the  alveoli  are 
filled  up  with  exudation,  this  bronchial  or  tubular  breathing 


204 


A  MANUAL  OF  PHYSIOLOGY 


may  be  heard  over  a  large  area,  the  vesicular  sound  being 
now  suppressed,  and  the  bronchial  sound  being  better  con- 
ducted by  the  consolidated  tissue  than  by  the  portions  of 
the  lung  that  still  contain  air. 

Up  to  this  point  we  have  contented  ourselves  with  a 
purely  qualitative  description  of  the  mechanical  pheno- 
mena of  respiration.  We  have  now  to  consider  their 
quantitative  relations,  and  the  methods  by  which  these 
have  been  studied. 

The  expansion  of  the  lungs  in  inspiration  may  be  easily  demon- 
strated in  man,  and  even  a  rough  estimate  of  its  amount  obtained, 

by  the  clinical  method  of  percus- 
sion. For  example,  the  resonant 
note  that  is  elicited  when  a  finger 
laid  on  the  chest  at  a  part  where 
it  overlies  the  right  lung  is  smartly 
struck  can  be  followed  down  until 
it  is  lost  in  the  'liver  dulness.' 
If  the  lower  limit  of  the  resonant 
area  be  marked  on  the  chest-wall 
first  in  full  inspiration  and  then 
in  full  expiration,  the  mark  will 
be  lower  in  the  former  than  in 
the  latter,  and  the  difference  will 
represent  the  difference  in  the 
vertical  length  of  the  shrunken 
and  distended  lung.  A  similar 
enlargement  in  the  transverse 
direction  may  be  demonstrated 
in  the  same  way,  the  inner 
borders  of  the  lungs  coming 
nearer  to  the  middle  line  in  in- 
spiration, and  receding  from  it  in 
expiration. 

For    most   physiological    pur- 
poses,    however,     we     require 

methods  more  delicate  and  more  exact,  and  in  many  investigations  a 
faithful  graphic  record  of  the  respiratory  movements  is  indispensable. 
This  may  be  obtained  : 

(i)  By  registering  the  movements  of  a  single  point,  or  the  varia- 
tions in  a  single  circumference,  of  the  boundary  of  the  thoracic 
cavity.  In  animals  the  end  of  a  lever,  or  a  small  compressible  bag 
containing  air  and  connected  with  a  recording  tambour,  may  be 
placed  between  the  lower  surface  of  the  diaphragm  and  the  liver, 
through  an  incision  in  the  abdominal  wall.  In  man  changes  in  the 
circumference  of  the  chest  at  any  level  can  be  recorded  by  means  of 
a  tambour  so  adjusted  that  in  inspiration  the  pressure  of  the  air  in 


FIG.  77.  —  SCHEME  OF  TAMBOUR 
(BRONDGEEST'S)  FOR  RECORDING 
RESPIRATORY  MOVEMENTS. 

C,  a  metal  capsule  connected  airtight 
with  B,  A,  two  caoutchouc  membranes,  the 
chamber  formed  by  which  can  be  inflated 
by  means  of  the  tube  and  stopcock  E. 
The  tube  D  connects  the  space  H  with  a 
registering  tambour  provided  with  a  lever. 
The  membrane  A  is  applied  to  the  chest, 
round  which  the  inextensible  strings  F  are 
tied.  At  every  expansion  of  the  chest  the 
pressure  in  H  is  increased,  and  the  increase 
of  pressure  is  transmitted  to  the  registering 
tambour. 


RESPIRATJON  205 

it  is  increased  and  in  expiration  diminished-  This  tambour  is  in 
communication  with  another,  which  is  provided  with  a  writing  lever 
(Marey's  pneumograph,  Sanderson's  stethomef;er>  Brondgeest's  pan- 
sphygmograph).  (Fig.  77.)  Or  an  elastic  tube,  witn  a  sPiral  spring 
in  its  lumen,  may  be  fastened  around  the  thorax  or  abdomen  and 
connected  with  a  piston-recorder  (a  small  cylinder  ir>  which  works  a 
piston  carrying  a  writing-point)  (Fitz). 

(2)  By  recording  the  changes  of  pressure  produced  in  the  air- 
passages  by  the  respiratory  movements.     This  can  be  done  by  con- 
necting a  cannula  in   the  trachea  of  an  animal  with  a  reccrding 
tambour  in  the  manner  described  in  the  Practical  Exerciser,,  p.  II2- 
The  changes  of  pressure  may  be  measured  by  connecting  a  mane" 
meter  with  the  trachea,  or  in  man  with  the  nostril. 

(3)  By  writing  off  the  changes  of  pressure  which  occur  in  the 
thoracic  cavity  during  respiration.     For    this    purpose  a   trocar   is 


FIG.  78. 

The  upper  tracing  is  a  record  of  the  respiratory  movements  in  a  rabbit,  taken  with 
Kronecker's  lever  between  the  diaphragm  and  liver.  The  lower  curve  is  a  blood- 
pressure  tracing  showing  large  oscillations  (like  Traube-Hering  waves).  E,  expiration ; 
I,  inspiration.  Time  trace,  seconds.  The  animal  was  under  the  influence  of  gelsemin. 

introduced  through  an  intercostal  space  into  one  of  the  pleural  sacs, 
without  the  admission  of  air,  or  into  the  pericardium,  and  then  con- 
nected with  a  manometer  or  other  recording  apparatus.  Or  a  tube, 
similar  in  construction*  to  a  cardiac  sound  (p.  86),  and,  like  it, 
terminating  in  an  elastic  bag,  may  be  pushed  down  the  oesophagus. 
The  variations  in  the  intra-thoracic  pressure  are  transmitted  to  the 
air  in  the  bag,  and  thence  to  a  tambour  connected  with  the  sound. 

When  the  respiratory  movements  are  studied  in  any  of 
these  ways,  it  is  found  that  there  is  practically  no  pause 
between  the  end  of  inspiration  and  the  beginning  of  expira- 
tion. Nor,  although  the  chest  collapses  more  gradually 
than  it  expands,  is  there  any  distinct  interval  in  ordinary 


206  A  MANUAL  0jF  PHYSIOLOGY 

breathing  between  the  e^nd  of  expiration  and  the  beginning 
of  the  succeeding  insr^iration-  When,  however,  the  respira- 
tion is  unusually  slov^i  an  actual  pause  (expiratory  pause)  may 
occur  at  this  prSint.  Expiration  takes  somewhat  longer 
time  than  in$FPiration»  tne  ratio  varying  from  7  :  6  to  3  : 2, 
according  t<*'^  a£e>  sex>  anc^  otner  circumstances. 

The  fre"4uency  °^  respiration  is  by  no  means  constant  even 
in  heaK^h-  ^  kinds  of  influences  affect  it.  It  is  difficult 
even/  *°  direct  the  attention  to  the  respiratory  act  without 
banging  about  a  modification  in  its  rhythm.  In  the  adult 
15  to  20  respirations  per  minute  may  be  taken  as  about  the 
normal.  In  young  children  the  frequency  may  be  twice  as 
great  (new-born  child,  50  to  70 ;  child  from  i  to  5  years  old, 
20  to  30  per  minute).  It  is  greater  in  a  female  than  in  a 
male  of  the  same  age.  A  rise  of  temperature  increases  it, 
and  this  is  probably  one  of  the  causes  of  the  increased  rate 
of  respiration  in  fever;  150  respirations  per  minute  have 
been  seen  in  a  dog  with  a  high  temperature.  Sudden 
cooling  of  the  skin,  exercise,  and  various  emotional  states, 
increase  the  rate,  and  sleep  diminishes  it.  The  will  can 
alter  the  frequency  and  depth  of  respiration  for  a  time,  and 
even  stop  it  altogether,  but  in  about  a  minute,  in  ordinary 
individuals,  the  desire  to  breathe  becomes  imperative,  nor 
can  any  training  extend  this  interval  of  voluntary  inhibition 
beyond  three  minutes.  Cato's  assertion  that  he  could  kill 
himself  at  any  time  '  merely  by  holding  his  breath  '  is  only 
a  proof  that  he  was  a  better  philosopher  than  physiologist. 
In  animals  the  rate  can  be  greatly  affected  by  drugs  and  by 
the  section  and  stimulation  of  certain  nerves  ;  but  to  this 
we  shall  return  when  we  come  to  consider  the  nervous 
mechanism  of  respiration. 

It  cannot  fail  to  be  observed  that  to  a  great  extent  the 
rate  of  respiration  is  affected  by  the  same  circumstances  as 
the  frequency  of  the  heart  (p.  95),  and  in  the  same  direc- 
tion. And,  indeed,  in  health,  these  two  physiological 
quantities,  amid  all  their  absolute  variations,  maintain  to 
each  other  a  fairly  constant  ratio  (i  to  4  or  i  to  5  in  man). 
Even  in  many  diseases  this  proportion  remains  tolerably 
stable,  although  in  others  it  is  disturbed. 


RESPIRATION  207 

The  total  quantity  of  air  expired,  or,  what  comes  to  the 
same  thing,  the  alteration  in  the  capacity  of  the  chest  during 
expiration,  can  be  measured  by  means  of  a  spirometer,  which 
consists  of  an  inverted  graduated  glass  bell  dipping  by  its 
open  mouth  into  water  and  balanced  by  weights.  The 
vessel  is  sunk  till  it  is  full  of  water,  the  air  being  allowed 
to  escape  by  a  cock.  The  expired  air  is  now  permitted  to 
enter  it  through  a  tube,  and  displaces  some  of  the  water. 
The  spirometer  is  adjusted  so  that  the  level  of  the  water 
inside  and  outside  is  the 
same,  and  then  the  volume 
of  air  contained  in  it  is  read 
off.  This  gives  the  volume 
of  the  expired  air  at  atmo- 
spheric pressure.  Similarly, 
by  breathing  air  from  the 
spirometer  the  amount  in- 
spired can  be  measured. 

From  400  to  500  c.c.  of 
air*  are  taken  in  and  given 
out  at  each  respiration  in 
quiet  breathing.  This  is 
called  tidal  air.  It  amounts 

to  35   pounds  by  weight   in 

r         ,  ,      FIG.  79. — DIAGRAM  OF  SPIROMETER. 

twenty-four  hours,  or  enough      A_  ^  fil]ed  wi(h  Kater    B    g]ass 

to    fill,    at    atmospheric    preS-    cylinder  with   scale  C,  swung   on   pulleys 
,.      ,.  .  ,  ..       and  counterpoised  by  weights  W.     D,  tube 

sure,  a  cubical  box  with  a  side  for  breathing  through, 
of  8  feet.     With  the  deepest 

possible  inspiration  room  can  be  made  for  2,000  c.c.  more  ; 
this  is  called  complemental  air.  By  a  forced  expiration 
1,500  c.c.  can  be  expelled  besides  the  tidal  air ;  and  to  this 
quantity  the  name  of  supplemental  or  reserve  air  has  been 
given.  After  the  deepest  expiration  there  always  remain 
about  700  or  800  c.c.  of  air  in  the  lungs,  and  this  is  called 

*  The  average  for  56  healthy  students,  with  an  average  body-weight  of 
66  kilos,  was  457  c.c.,  or  6*9  c.c.  per  kilo.  In  4  newborn  children  the  tidal 
air  varied  from  20  to  30  c.c.,  and  from  7*6  to  7'3  c.c.  per  kilo,  which  is  not 
very  different  from  the  amount  in  the  adult.  The  pulmonary  ventilation 
must  therefore  be  far  more  rapid  in  the  child,  since  its  respiratory 
frequency  is  so  much  greater. 


208  A  MANUAL  OF  PHYSIOLOGY 

the  residual  air.  After  a  normal  expiration  following  a 
normal  inspiration  the  lungs  still  contain  stationary  air  to 
the  amount  of  about  2,500  c.c. 

The  residual  air  may  be  measured  by  causing  a  person,  starting 
immediately  after  the  deepest  possible  expiration,  to  breathe  out  and 
in  several  times  into  a  vessel  (a  spirometer)  filled  with  hydrogen,  till 
it  can  be  assumed  that  the  hydrogen  and  the  residue  of  air  in  the 
lungs  have  been  completely  mixed.  Knowing  the  quantity  of 
hydrogen  originally  contained  in  the  vessel,  we  can  calculate  from 
the  percentage  at  the  end  of  the  experiment  the  quantity  of  air  with 
which  it  has  been  mixed — that  is,  the  residual  air  (Davy). 

Let  V  be  the  quantity  of  hydrogen  in  the  spirometer  at  first,  and 
p  the  percentage  amount  in  it  at  the  end  of  the  experiment.  Let  x 
be  the  volume  of  residual  air  in  the  lungs  at  the  beginning. 

Then,  since  the  quantity  of  hydrogen  remains  unchanged  after  the 

mixture,  -£-  ( 

100 


P 

Suppose         V  =  4,000  c.c., 
and  ^  =  85  per  cent., 

12,000       i 
we  get  x= — - =  about  705  c.c. 

i7 


Vital  ||[|llllllllllllllllllllllllillllllllllllllll|  C^mjile mental  air 


Residual  air 


FIG.  80. — DIAGRAM  TO  ILLUSTRATE  THE  RELATIVE  AMOUNT  OF  COMPLE- 
MENTAL,  TIDAL,  SUPPLEMENTAL,  AND  RESIDUAL  AIR. 

But  some  carbon  dioxide  would  be  given  off  by  the  lungs,  and  some 
oxygen,  and  perhaps  hydrogen,  absorbed,  during  the  experiment,  and 
therefore  slight  corrections  might  have  to  be  made.  Sir  Humphry 
Davy  actually  calculated  the  residual  air  in  his  own  lungs,  as  deter- 
mined by  this  method,  at  672  c.c. 

The  coefficient  of  ventilation,  that  is,  the  ratio  of  the  quantity  of  air 
taken  in  at  each  inspiration  to  the  quantity  already  in  the  lungs,  has 
E>een  estimated  at  about  \  or  £. 

The  term  vital  or  respiratory  capacity  is  applied  to  the 
quantity  of  air  which  can  be  expelled  by  the  deepest  expira- 
tion following  the  deepest  inspiration,  and  amounts  in  an 
adult  of  average  height  to  3,500  or  4,000  c.c.  The  maximum 


RESPIRATION  209 

quantity  of  air  which  the  lungs  can  contain  is  evidently 
equal  to  vital  capacity  plus  residual  air.  At  one  time  the 
vital  capacity  was  thought  to  be  capable  of  affording  valuable 
information  in  the  diagnosis  of  chest  diseases;  but  little 
stress  is  now  laid  upon  it,  as  it  varies  from  so  many  causes. 
It  is  greater  in  mountaineers  than  in  the  inhabitants  of 
lowland  plains. 

It  is  clear  from  the  figures  we  have  given  that  in  ordinary 
breathing  only  a  small  proportion  of  the  air  in  the  lungs 
comes  in  direct  at  each  inspiration  from  the  atmosphere, 
and  only  a  small  proportion  escapes  into  the  atmosphere 
at  each  expiration.  The  greater  part  of  the  air  in  the 
lungs  is  simply  moved  a  little  farther  from  the  upper 
respiratory  passages,  or  a  little  nearer  them ;  and  fresh 
oxygen  reaches  the  alveoli,  as  carbon  dioxide  leaves  them, 
mainly  by  diffusion,  aided  by  convection  currents  due  to 
inequalities  of  temperature,  and  to  the  churning  which  the 
alternate  expansion  and  shrinking  of  the  lungs,  and  the 
pulsations  of  their  arteries,  must  produce.  But  that  some 
of  the  tidal  air  strikes  right  down  to  the  alveoli  is  evident 
enough.  For  the  respiratory  '  dead  space ' — that  is,  the 
capacity  of  the  upper  air  passages  and  the  bronchial  tree 
down  to  the  infundibula — is  only  140  c.c.,  or  one-third  of  the 
amount  of  the  tidal  air  (Zuntz,  Loewy).  The  immense 
extent  of  the  pulmonary  surface,  and  the  extreme  thinness 
of  the  layer  of  blood  in  the  capillaries  of  the  lungs,  facilitate 
the  interchange  between  the  gases  of  the  blood  and  the  gases 
of  the  alveoli. 

The  Amount  and  Variations  of  the  Intra-thoracic  Pressure. — In 
the  deepest  expiration  the  lungs  are  never  completely 
collapsed  ;  their  elastic  fibres  are  still  stretched  ;  and  the 
tension  of  these  acts  in  the  opposite  direction  to  the  external 
atmospheric  pressure,  and  diminishes  by  its  amount  the 
pressure  inside  the  thoracic  cavity.  In  the  dead  body 
Bonders  measured  the  value  of  this  tension,  and  therefore 
of  the  negative  pressure  of  the  thorax,  by  tying  a  mano- 
meter into  the  trachea,  and  then  causing  the  lungs  to 
collapse  by  opening  the  chest.  It  varied  from  7*5  mm.  of 

14 


210  A  MANUAL  OF  PHYSIOLOGY 

mercury  in  the  expiratory  position  to  g  mm.  in  the  in- 
spiratory.  So  far  as  can  be  judged  from  observations  made 
on  persons  suffering  from  various  diseases  of  the  respiratory 
organs,  the  alterations  during  ordinary  breathing  do  not 
amount  to  more  than  3  or  4  mm.  of  mercury.  But  when  an 
attempt  is  made  in  the  dead  body  to  imitate  a  deep  in- 
spiration by  making  traction  on  the  chest-walls  so  as  to 
expand  the  lungs,  the  intra-thoracic  pressure  may  fall  to 
—  30  mm.  of  mercury;  and  in  a  living  rabbit  during  a 
deep  natural  inspiration,  a  pressure  of  —20  mm.  has  been 
seen. 

The  reason  why  the  lungs  collapse  when  the  chest  is 
opened  is  that  the  pressure  is  now  equal  on  the  pleural  and 
alveolar  surfaces,  being  in  both  cases  that  of  the  atmosphere. 
There  is  therefore  nothing  to  oppose  the  elasticity  of  the 
lungs,  which  tends  to  contract  them.  So  long  as  the  chest 
is  unopened,  the  pressure  on  the  pleural  surface  of  the  lungs 
is  less  than  that  on  the  alveolar  surface,  and  the  elastic 
tension  can  only  cause  them  to  shrink  until  it  just  balances 
this  difference. 

In  intra-uterine  life,  and  in  stillborn  children  who  have 
never  breathed,  the  lungs  are  completely  collapsed  (atelec- 
tatic),  and  there  is  no  negative  intra-thoracic  pressure. 
They  are  kept  in  this  condition  by  adhesion  of  the  walls  of 
the  bronchioles  and  alveoli.  If  the  lungs  have  been  once 
inflated,  this  adhesion  ceases  to  act,  and  they  never  com- 
pletely collapse  again. 

Amount  and  Variations  of  the  Respiratory  Pressure. — As  we 
have  already  remarked,  the  pressure  in  the  alveoli  and  air- 
passages  is  less  than  that  of  the  atmosphere  while  the 
inspiratory  movement  is  going  on,  greater  than  that  of  the 
atmosphere  during  the  expiratory  movement,  and  equal  to 
that  of  the  atmosphere  when  the  chest-walls  are  at  rest. 
When  the  external  air-passages  are  closed,  e.g.,  by  connecting 
a  manometer  with  the  mouth  and  pinching  the  nostrils,  the 
greatest  possible  variations  of  pressure  are  produced.  In 
the  deepest  inspiration  under  these  conditions  a  negative 
pressure  of  about  75  mm.  of  mercury  (i.e.,  a  pressure  less 
than  that  of  the  atmosphere  by  this  amount)  has  been  found, 


RESPIRATION  211 

and  in  deep  expiration  a  somewhat  greater  positive  pressure* 
(Practical  Exercises,  p.  274). 

But  with  ordinary  breathing,  the  variations  of  pressure  as 
measured  by  this  method  do  not  exceed  5  to  10  mm.  of 
mercury  above  or  below  the  pressure  of  the  atmosphere. 

When  the  external  openings  are  not  obstructed,  as,  for  c- 
example,  when  the  lateral  pressure  is  taken  in  the  trachea 
of  an  animal  by  means  of  a  cannula  with  a  side-tube  con- 
nected with  a  manometer,  still  smaller,  and  doubtless  truer, 
values  have  been  found  (2-3  mm.  of  mercury  as  the  positive 
expiratory  pressure,  and  I  mm.  as  the  negative  inspiratory  (J 
pressure  in  dogs).  But  since  the  respiratory  passages  are 
abruptly  narrowed  at  the  glottis,  the  variations  of  pressure 
must  be  greater  below  than  above  it,  and  in  general  they 
must  increase  with  the  distance  from  that  orifice,  being 
greater,  for  instance,  in  the  alveoli  than  in  the  bronchi. 

Relation  of  Respiration  to  the  Nervous  System. — Unlike  the  "7 
beat  of  the  heart,  the  respiratory  movements  are  entirely 
dependent  on  the  nervous  system  ;  and  the  '  centre  '  which 
presides  over  them  is  situated  in  the  spinal  bulb.  It  is  a 
bilateral  centre — that  is,  it  has  two  functionally  symmetrical 
halves,  one  on  each  side  of  the  middle  line ;  and  each  of 
these  halves  seems  to  have  to  do  more  particularly  with  the 
respiratory  muscles  of  its  own  side,  for  destruction  of  one- 
half  of  the  spinal  bulb  causes  paralysis  of  respiration  only 
on  that  side.  Anatomically  the  respiratory  centre  has  not 
been  sharply  localized  ;  but  it  lies  higher  than  the  vaso- 
motor  centre.  It  is  brought  into  relation  with  the  muscles 
of  respiration  by  efferent  nerves.  The  phrenic  nerves  to 
the  diaphragm,  and  the  intercostal  nerves  to  the  muscles 
which  elevate  the  ribs,  are  the  most  important  of  those 
concerned  in  ordinary  breathing.  The  circular  muscles  of 
the  bronchi  are  also  supplied  with  motor  fibres  that  run  in 
the  pneumogastric.  The  bronchial  tubes  are  narrowed  by 
their  artificial  excitation,  but  their  function  in  respiration 
is  unknown.  The  respiratory  centre  is  further  related  to 

*  The  maximum  negative  pressure  in  deepest  inspiration  averaged  for 
49  students,  -  73  mm.  (highest  observation  -  137  mm.)  of  mercury  ;  the 
maximum  positive  pressure  in  deepest  expiration,  +80  mm.  (highest 
observation  + 140  mm.). 

14—2 


212  A  MANUAL  OF  PHYSIOLOGY 

afferent  nerves,  of  which  the  most  influential  is  the  vagus, 
particularly  its  pulmonary  fibres,  and  its  superior  laryngeal 
branch.  But  almost  any  afferent  nerve  may  powerfully 
affect  the  centre ;  and  it  is  also  influenced  by  fibres 
passing  to  it  from  the  higher  parts  of  the  central  nervous 
system. 

Section  of  the  spinal  cord  in  animals  above  the  origin  of 
the  phrenic  nerves  causes  complete  paralysis  of  respiration, 
and  consequent  death.  The  phrenics  arise  from  the  third 
and  fourth  cervical  nerves,  and  are  joined  by  a  branch  from 
the  fifth  ;  and  in  man  fracture  of  any  of  the  four  upper 
cervical  vertebrae  is,  as  a  rule,  instantly  fatal.  But  in  one 
case  respiration  was  carried  on,  and  life  maintained  for 
thirty  minutes,  merely  by  the  contraction  of  the  muscles  of 
the  neck  and  shoulders  in  a  man  entirely  paralyzed  below 
this  level  (Bell).  Section  of  the  cord  just  below  the  origin 
of  the  phrenics  leaves  the  diaphragm  working,  although  the 
other  respiratory  muscles  are  paralyzed.  A  case  has  been 
recorded  of  a  man  in  whom,  from  disease  of  the  spine  in 
the  lower  cervical  region,  all  the  ribs  became  completely 
immovable.  He  was  able  to  lead  an  active  life,  and  to 
carry  on  his  business,  although  he  breathed  entirely  by  his 
diaphragm  and  abdominal  muscles  (Hilton). 

Section  of  one  phrenic  is  followed  by  paralysis  of  the 
corresponding  half  of  the  diaphragm,  section  of  both 
phrenics  by  complete  paralysis  of  that  muscle,  and  although 
respiration  still  goes  on  by  means  of  the  muscles  which  act 
upon  the  ribs,  it  is  usually  inadequate  to  the  prolonged 
maintenance  of  life.  In  the  horse,  however,  not  only  has 
survival  been  seen  after  this  severe  operation,  but  the 
animal,  after  the  first  temporary  increase  in  the  frequency 
of  the  breathing  had  disappeared,  could  be  driven  in  a  light 
vehicle  without  any  marked  dyspnoea.  The  phrenic  nuclei 
in  the  two  halves  of  the  cord  are  connected  across  the 
middle  line.  For  when  a  hemisection  of  the  cord  is  made 
between  this  level  and  the  respiratory  centre  in  the  medulla, 
respiratory  impulses  are  still  able  to  reach  both  phrenic 
nerves.  In  some  animals  both  halves  of  the  diaphragm  go 
on  contracting.  But  when,  as  usually  happens,  this  is  not 


RESPIRA  TION  2 1 3 

the  case,  and  the  diaphragm  on  the  side  of  the  hemisection 
has  ceased  to  act,  it  at  once  begins  to  contract  again  when 
the  opposite  phrenic  nerve  is  cut,  and  the  respiratory 
impulse,  descending  from  the  bulb,  is  blocked  out  from  the 
direct,  and  forced  to  follow  the  crossed  path.  It  has  been 
shown  that  the  crossing  takes  place  at  the  level  of  the 
phrenic  nuclei,  and  nowhere  else  (Porter). 

When  one  vagus  is  divided,  there  is  little  or  no  change 
in  the  respiratory  movements.  Half  an  inch  of  one  vagus 
nerve  has  been  excised  in  removing  a  tumour,  and  the 
patient  showed  no  symptoms  whatever  (Billroth).  But 
section  of  both  vagi  generally  (though  not  always)  causes  re- 
spiration to  become  for  a  time  much  deeper  and  slower,  the 
one  change  just  compensating  the  other,  so  that  the  total 
amount  of  air  taken  in  and  given  out,  and  the  amount  of 
carbon  dioxide  eliminated,  are  not  altered.  Gad  has  shown 
that  the  effect  is  really  due  to  the  loss  of  impulses  that 
normally  ascend  the  vagi,  not  to  any  irritation  of  the  cut 
ends.  For  a  nerve  can  be  frozen  without  exciting  it ;  and 
when  a  portion  of  each  vagus  is  frozen,  the  respiration  is 
affected  in  precisely  the  same  way  as  when  the  nerves  are 
divided. 

A  similar  change  follows  the  blocking  of  the  paths  connect- 
ing the  respiratory  centre  with  the  brain  above,  by  injection 
of  paraffin  wax  into  the  common  or  internal  carotid.  The 
bloodvessels  supplying  the  nerve-fibres  which  connect  the 
respiratory  centre  with  the  brain  may  in  this  way  be  closed 
by  artificial  emboli.  The  nerves  lose  their  function,  as  if 
they  had  been  cut ;  no  impulses  now  reach  the  respiratory 
centre  from  above ;  and  the  respiration  becomes  markedly 
slowed  and  deepened,  just  as  happens  when  the  vagi  are 
divided.  Where  only  the  vagus  or  these  'higher  paths,' 
but  not  both,  are  cut  off,  the  respiration  remains  regular, 
although  deep,  and  perhaps  in  course  of  time  tends  to 
resume  its  original  type.  But  when  both  paths  are  cut,  the 
character  of  the  respiration  is  entirely  changed  ;  periods  of 
rapid  and  spasmodic  breathing  alternate  with  periods  of 
complete  cessation,  till  the  animal  dies  (Marckwald). 

From  these  facts  it  appears  that  the  periodic  automatic 


214  A  MANUAL  OF  PHYSIOLOGY 

discharges  of  the  respiratory  centre  are  being  continually 
controlled  and  modified  by  impulses  passing  up  the  vagus  or 
down  from  the  brain,  but  especially  up  the  vagus.  When 
the  vagus  is  severed,  the  control  of  the  higher  paths  becomes 
more  complete,  and  is  sufficient  still  to  keep  the  breathing 
regular.  When  the  higher  paths  are  cut  off,  the  vagus  of 
itself  is  able  to  regulate  the  discharge.  But  when  both  are 
gone,  the  respiratory  centre,  freed  from  control,  passes  into 
a  condition  of  alternate  spasm  and  exhaustion. 

The  continuous  excitation  of  the  regulating  vagus  fibres 
must  be  brought  about  either  by  mechanical  stimulation  of 
the  nerve-endings  in  the  lungs,  due  to  the  alternate  stretching 


FIG.  81. — RESPIRATORY  TRACINGS  (Doc). 

A,  normal ;  B,  effect  of  stimulation  of  the  central  end  of  the  vagus  ;  C,  effect  of 
section  of  both  vagi.  (Tracing  taken  with  arrangement  shown  in  Fig.  100,  p.  273). 
Time-tracing  marks  seconds. 

and  shrinking,  or  by  chemical  stimulation  depending  on  the 
state  of  the  blood.  Both  views  have  found  advocates,  but 
neither  has  been  definitely  proved.  Nor  are  the  results  of 
experimental  stimulation  of  the  nerve-trunk  so  clear  or  so 
constant  that  we  can  confidently  appeal  to  them  in  making 
a  decision.  Excitation,  with  induction  shocks,  of  the  central 
end  of  the  cut  vagus  below  the  origin  of  its  superior  laryn- 
_geal  branch  certainly  causes  quickening  of  respiration,  or, 
if  the  excitation  be  strong,  arrest  in  the  inspiratory  phase. 
A  brief  mechanical  stimulus,  or  a  series  of  such,  has  a 
similar  effect.  But  chemical  stimulation  (e.g.,  with  a  strong 


RESPIRATION  215 

solution  of  potassium  chloride)  or  long-continued  mechanical 
excitation  like  that  produced  by  stretching  or  compression 
of  the  nerve,  or  certain  kinds  of  electrical  stimulation — for 
instance,  the  closure  of  an  ascending  voltaic  current* — 
cause  slowing  of  the  respiratory  movements  or  expiratory 
standstill.  This  is  also  the  usual,  though  not  the  invariable, 
result  of  stimulating  the  superior  laryngeal,  even  when  in- 
duction shocks  are  employed.  These  facts  undoubtedly 
suggest  the  existence  in  the  vagus  of  two  kinds  of  afferent 
nerve-fibres  that  affect  the  respiratory  centre  in  opposite 
ways — inspiratory  fibres,  which  stimulate  it  to  greater 
activity  of  discharge,  and  expiratory  fibres,  which  inhibit 
its  action.  The  latter  variety  we  may  suppose  to  be  more 
numerous  in  the  superior  laryngeal,  the  former  in  the  pul- 
monary branches  of  the  vagus.  And  there  is  nothing  forced 
in  the  hypothesis  that  certain  kinds  of  stimuli  act  par- 
ticularly on  the  one  set  of  fibres,  and  certain  kinds  on  the 
other,  for  we  have  already  seen  an  instance  of  this  in 
studying  the  differences  between  the  vaso-constrictor  and 
the  vaso-dilator  nerves  (p.  150).  It  is  possible,  however 
(although  this  view  has  less  inherent  probability,  in  spite 
of  the  fact  that  it  has  been  maintained  by  some  of  the  most 
recent  writers  on  the  subject),  that,  at  any  rate  in  the  vagus 
trunk,  only  one  set  of  fibres  exists,  and  that  these  are 
affected  differently  by  different  kinds  of  stimulation — 
momentary  stimuli,  for  example,  setting  up  in  them  im- 
pulses which  we  may  call  inspiratory,  and  long-lasting 
stimuli  impulses  which  we  may  call  expiratory  (Boruttau, 
Lewandowsky). 

However  this  may  be,  the  facts  we  have  been  discussing 
have  an  importance  of  their  own,  apart  from  any  hypo- 
thetical explanations  of  them ;  and  they  may  be  readily 
demonstrated  by  means  of  such  a  graphic  method  as  is 
described  in  the  Practical  Exercises  (p.  273),  or  by  merely 
opening  the  abdomen  in  a  rabbit,  and  observing  the  lungs 
through  the  thin  diaphragm  (Gad).  Some  of  them  have 
been  more  than  once  unintentionally  illustrated  on  man.  In 
one  case  the  left  vagus  trunk  was  included  in  a  ligature 
*  I.e.,  a  current  passing  towards  the  head  in  the  nerve. 


216  A  MANUAL  OF  PHYSIOLOGY 

with  the  common  carotid.  The  respiratory  movements  imme- 
diately stopped,  the  pulse  was  slowed,  and  death  occurred 
in  thirty  minutes  (Rouse).  The  superior  laryngeal  fibres, 
unlike  those  of  the  vagus  proper,  do  not  appear  to  be  con- 
stantly in  action,  as  section  of  both  nerves  has  no  effect  on 
respiration.  Any  source  of  irritation  in  the  larynx  may 
stimulate  these  fibres  and  produce  a  cough,  which  may 
also  be  caused  by  irritation  of  the  pulmonary  fibres  of  the 
vagus. 

The  cutaneous  nerves,  and  especially  those  of  the  face 
(fifth  nerve),  abdomen  and  chest,  have  a  marked  influence 
on  respiration.  They  can  be  easily  excited  in  the  intact 
body  by  thermal  and  mechanical  stimulation.  A  cold 
bath,  for  instance,  usually  causes  acceleration  and  deepen- 
ing of  the  respiratory  movements ;  and  the  efficacy  of 
mechanical  stimulation  of  sensory  nerves  in  stirring  up 
a  sluggish  respiratory  centre  is  well  known  to  midwives, 
who  sometimes  slap  the  buttocks  of  a  newborn  child  to 
start  its  breathing. 

Another  set  of  afferent  nerves  that  seem  to  have  an 
important  relation  to  the  respiratory  centre  are  those  which 
supply  the  muscles.  We  have  already  noticed  that  the 
frequency  of  respiration  is  greatly  augmented  by  muscular 
exercise.  This  seems  to  be  brought  about  in  part  through 
the  stimulation  of  those  afferent  muscular  nerves  either  by 
mechanical  compression  of  their  terminal  '  spindles,'  or  by 
the  chemical  action  on  them  of  certain  waste  products 
produced  in  contraction.  But  this  cannot  be  the  only  way 
in  which  the  respiratory  centre  is  affected  by  muscular 
activity.  For  everybody  is  agreed  that  an  increase  in  the 
respiratory  movements  is  caused  by  tetanizing  the  muscles 
of  a  limb  whose  nerves  have  been  completely  severed,  and 
which  is  indeed  connected  with  the  rest  of  the  body  by  no 
other  structures  than  its  bloodvessels.  This  can  only  be 
due  to  two  things :  a  direct  action  on  the  respiratory  centre 
by  the  blood  that  has  passed  through,  and  been  altered 
in,  the  contracting  muscles,  or  an  action  exerted  by  the  blood 
indirectly  on  the  centre  through  the  excitation  of  afferent 
respiratory  nerves  whose  connection  with  it  is  still  intact — 


RESPIRATION  217 

for  example,  the  other  muscular  nerves  or  the  pulmonary 
branches  of  the  vagus. 

That  the  respiratory  centre  is  greatly  affected  by  the 
quality  of  the  blood  which  circulates  through  it  is  well 
known.  And  it  is  generally  acknowledged  that  it  may  be 
excited  both  by  blood  that  is  rich  in  carbon  dioxide  and  by 
blood  that  is  poor  in  oxygen,  the  actual  stimulating  sub- 
stance in  the  latter  case  being,  perhaps,  an  easily  oxidizable 
body  which  rapidly  disappears  from  properly  oxygenated 
blood  (Pfliiger). 

But  it  has  been  the  subject  of  long-continued  discussion 
whether  excess  of  carbon  dioxide  or  deficiency  of  oxygen  is 
the  more  potent  stimulus.  The  truth  appears  to  be  that 
much  depends  upon  the  conditions  of  the  experiment,  upon 
the  size  of  the  chamber,  for  instance,  in  which  an  animal 
or  a  man  is  made  to  breathe.  The  best  evidence  points 
to  the  conclusion  that  comparatively  small  alterations  in 
the  amount  of  carbon  dioxide  in  the  inspired  air  cause  a 
relatively  great  increase  in  the  respiration,  while  in  the  case 
of  the  oxygen  the  departure  from  the  normal  proportion 
must  be  much  more  decided  to  bring  about  any  notable 
effect  (Zuntz  and  Loewy).  Nor  is  it  at  all  out  of  harmony 
with  this  that,  when  very  large  quantities  of  carbon  dioxide 
(30  per  cent,  and  upwards  in  rabbits)  are  inhaled,  a  condi- 
tion of  narcosis  comes  on  without  any  previous  respiratory 
distress  (Benedicenti).  For  many  substances  act  differently 
in  large  and  in  small  doses. 

Be  this  as  it  may,  when  the  gaseous  interchange  from  any 
cause  becomes  insufficient,  the  respiratory  movements  are 
exaggerated,  and  ultimately  every  muscle  which  can  directly 
or  indirectly  act  upon  the  chest-walls  is  called  into  play  in 
the  struggle  to  pass  more  air  into  and  out  of  the  lungs.  To 
a  lesser  and  greater  degree  of  this  exaggeration  of  breathing^ 
the  terms  Hyperpncea  and  Dyspnoea  have  been  respectively!  ^i- 
applied.  If  the  gaseous  interchange  remains  insufficient, 
or  is  altogether  prevented,  asphyxia  or  suffocation  sets  in. 
Sometimes  in  man  impending  asphyxia  from  loss  of  function 
by  a  part  of  the  lungs,  as  in  pneumonia,  may  be  warded  off 
by  inhalations  of  oxygen.  Increase  in  the  temperature  of 


2i8  A  MANUAL  OF  PHYSIOLOGY 

the  blood  circulating  through  the  spinal  bulb,  as  when  the 
carotid  arteries  of  a  dog  are  laid  on  metal  boxes  through 
which  hot  water  is  kept  flowing,  also  causes  dyspnoea  (heat- 
dyspnaa),  (p.  272).  But  if  the  temperature  be  too  high,  the 
respiratory  movements  may  be  slowed,  perhaps  by  a  partial 
paralysis  or  inhibition  of  the  respiratory  centre.  When  the 
blood  is  cooled  the  respiration  becomes  deeper  and  slower, 
but  if  the  temperature  is  greatly  and  suddenly  lowered,  the 
centre  may  be  stimulated  and  the  breathing  quickened.  In 
man  the  increased  temperature  of  the  blood  in  fever  is  prob- 
ably connected  with  the  increase  in  the  rate  of  respiration. 

The  physiological  opposite  of  dyspnoea  is  apnoea.  This 
condition  may  be  produced  in  an  animal  by  rapid  artificial 
respiration.  For  some  seconds,  in  a  successful  experiment, 
after  the  artificial  respiration  is  stopped,  the  animal  remains 
without  breathing.  The  apnoeic  state  seems  to  be  due 
partly  to  an  excess  of  oxygen  in  the  arterial  blood  or  in  the 
lungs,  partly  to  some  nervous  effect  produced  through  the 
vagi  on  the  respiratory  centre.  Possibly  the  pulmonary 
nerve-endings  of  the  vagi  are  affected  mechanically  by  the 
inflation  ;  for  rapid  and  repeated  inflation  of  the  lungs  with 
hydrogen  may  cause  apnoea  (Traube).  The  venous  blood  in 
apnoea  is,  if  anything,  poorer  in  oxygen  than  normal  venous 
blood. 

That  poorly  oxygenated  blood  produces  dyspnoea  by  acting 
on  some  portion  of  the  brain  may  be  shown  in  an  interesting 
manner  by  establishing  what  is  called  a  cross-circulation  in 
two  rabbits  or  dogs.  The  vertebral  arteries  and  one  carotid 
are  tied  in  both  animals  ;  the  remaining  carotids  are  divided 
and  connected  crosswise  by  glass  tubes,  so  that  the  brain  of 
each  is  supplied  by  blood  from  the  other  (Bienfait  and 
Hogge).  When  the  respiration  is  artificially  hindered  or 
stopped  in  one  of  the  animals,  it  shows  no  dyspnoea  ;  it 
is  in  the  other,  whose  brain  is  being  fed  with  improperly 
oxygenated  blood,  that  the  respiratory  movements  become 
exaggerated.  The  point  of  attack  of  the  '  venous '  blood 
has  been  further  localized  in  the  spinal  bulb  by  the  observa- 
tion that  when  the  brain  has  been  cut  away  above  it,  the 
cord  severed  below  the  origin  of  the  phrenics,  and  all  other 


RESPIRATION  219 

nerves  connected  with  the  region  between  the  two  planes  of 
section  divided,  any  interference  with  the  gaseous  exchange 
in  the  lungs  is  at  once  followed  by  dyspnoea.* 

The  question  has  been  raised  whether,  in  the  absence  of 
this  '  natural '  stimulation  by  the  blood,  and  of  the  impulses 
that  constantly  reach  the  centre  along  its  afferent  nerves,  it 
would  continue  to  discharge  itself,  or  whether  it  would  sink 
into  inaction.  We  have  already  discussed  a  similar  question 
in  regard  to  the  cardiac  and  vaso-motor  centres,  and  the 
subject  must  again  present  itself  when  we  come  to  examine 
the  functions  of  the  central  nervous  system.  In  the  mean- 
time it  is  only  necessary  to  say  that  the  apparent  auto- 
matism of  the  respiratory  centre,  although  modified  by 
the  quality  of  the  blood  which  circulates  in  it,  is  not  essen- 
tially dependent  on  it ;  for  in  animals  whose  blood  has  been 
replaced  by  normal  saline  solution  or  serum,  and  in  frogs 
after  excision  of  the  heart,  quiet,  regular  breathing  has  been 
seen  to  go  on. 

Action  of  Drugs  on  the  Respiratory  Centre. — The  respiratory  o 
centre  is  directly  affected  by  numerous  drugs,  j'ituri  and  nicotin, 
for  instance,  cause  in  various  animals  a  quickening  and  deepening 
of  the  respiration,  followed,  if  the  dose  has  been  large,  by  slowing 
and  ultimate  cessation.  The  action  of  the  great  majority  of  such 
substances,  however,  possesses  only  a  pharmacological  interest,  and 
it  would  be  out  of  place  even  to  enumerate  them  in  a  text-book  of 
physiology.  But  there  are  one  or  two  points  in  the  action  on  the 
respiratory  centre  of  chloroform  and  alcohol — substances  so  greatly 
employed  in  practical  medicine  and  in  physiological  research — which 
may  properly  be  touched  on  here  : 

Chloroform. — The  cause  of  the  deaths  from  chloroform  which,  at 
rare  intervals,  startle  the  operating  theatre  of  every  great  hospital 
where  this  anaesthetic  is  used,  has  been,  on  account  of  its  extreme 
practical  interest,  the  subject  of  prolonged  discussion  and  experiment. 
Is  it  the  heart  that  fails  ?  Or  is  it  the  respiration  ?  The  answer  of 
what  is  known  as  the  '  Edinburgh  School '  is  that  the  respiration  (in 
physiological  terms,  the  respiratory  centre)  is  always  first  paralyzed. 
Their  golden  rule  of  doctrine  in  chloroform  administration  is, 
'Watch  the  respiration;  the  heart  will  take  care  of  itself — a  rule 
which,  however,  in  '  Edinburgh  '  practice  does  not  exclude  careful 
observation  of  the  pulse.  This  view,  having  the  merit  of  simplicity, 
has  been  widely  adopted.  It  has  been  lately  upheld  by  a  scientific 

*  The  conclusion  is  doubtless  correct,  but  this  experiment  is  not 
decisive.  For  the  phrenic  nerves  themselves  contain  afferent  fibres, 
through  which  the  respiratory  centre  might  have  been  affected. 


220  A  MANUAL  OF  PHYSIOLOGY 

commission  appointed  by  the  Nizam  of  Hyderabad  for  the  special 
purpose  of  investigating  the  question  with  the  aid  of  modern 
physiological  methods.  But  the  conclusions  of  the  Hyderabad 
Commission,  valuable  as  they  are,  seem  to  have  been  too  abso- 
lutely drawn.  For  it  has  been  shown  by  a  number  of  observers 
(Mac William,  Gaskell  and  Shore,  etc.)  that  chloroform  undoubtedly 
may  paralyze  the  heart  without  affecting  the  respiration ;  and,  further, 
that  the  paralysis  of  the  vaso-motor  centre,  and  the  consequent 
withdrawal  of  blood  from  the  heart  and  brain  to  the  dilated 
splanchnic  area,  may  be  an  important  factor  in  bringing  about  a 
fatal  result  (p.  164).  A  second  table  might  therefore  be  added  to  the 
'  Edinburgh  law ' :  '  Watch  the  breathing  ;  watch  the  pulse.  If  the 
heart  threatens  to  fail  for  want  of  blood,  fill  it  by  raising  the  legs  and 
compressing  the  abdomen.' 

Alcohol  in  small  doses,  when  given  by  the  stomach  or  (in  animals) 
injected  into  the  blood,  causes  stimulation  of  the  respiratory  centre 
and  increase  in  the  pulmonary  ventilation.  In  man,  this  increase 
usually  amounts  to  8-15  per  cent.,  but  is  occasionally  much  greater. 
But  the  limit  which  separates  the  favourable  action  of  the  small  dose 
from  the  hurtful  action  of  the  large,  is  easily  overstepped.  When 
this  is  done,  and  the  dose  is  continually  increased,  the  activity  of  the 
respiratory  centre  is  first  diminished  and  finally  abolished.  In  dogs, 
for  instance,  after  the  injection  of  considerable  quantities  of  alcohol 
into  the  stomach,  death  takes  place  from  respiratory  failure,  and  the 
breathing  stops  while  the  heart  is  still  unweakened  (Fig.  57,  p.  165). 
This  is  the  final  outcome  of  a  progressive  impairment  in  the  activity 
of  the  centre,  of  which  the  slow  and  heavy  breathing  of  the  drunken 
man  represents  an  earlier  stage. 

0  Although  the  chief  respiratory  centre  undoubtedly  lies  in 
the  medulla  oblongata,  it  appears  that  under  certain  condi- 
tions impulses  to  the  respiratory  muscles  may  originate  in 
the  spinal  cord.  Thus,  in  young  mammals  (kittens,  puppies), 
especially  when  the  excitability  of  the  cord  has  been  in- 
creased by  strychnia,  in  birds  and  in  alligators,  movements, 
apparently  respiratory,  have  been  seen  after  destruction  of 
the  brain  and  spinal  bulb.  But  no  proof  has  ever  been 
given  that  in  the  intact  organism  the  spinal  cord  below 
the  level  of  the  bulb  takes  any  other  part  in  respiration  than 
that  of  a  mere  conductor  of  nerve  impulses  ;  and  it  is  not 
justifiable  to  assume  the  existence  of  spinal  respiratory 
centres  on  the  strength  of  such  experiments  as  these. 
0  Death  after  Double  Vagotomy. — Alterations  in  the  rhythm 
of  respiration  are  not  the  only  effects  that  follow  division  of 
both  vagi.  In  certain  animals,  at  least,  this  operation  is 


RESPIRATION  221 

incompatible  with  life.  In  the  rabbit,  as  a  rule,  death  takes 
place  in  twenty-four  hours.  A  sheep  may  live  three  days, 
and  a  horse  five  or  six.  Dogs  often  live  a  week,  occasionally 
a  month  or  even  two,  and  in  rare  instances  they  may  survive 
indefinitely.  The  most  prominent  symptoms  (in  the  dog), 
in  addition  to  the  marked  and  permanent  slowing  of 
respiration,  quickening  of  the  pulse  and  contraction  of  the 
pupils,  are  the  frequent  vomiting  and  progressive  emacia- 
tion. The  appetite  is  sometimes  ravenous,  but  no  sooner  is 
the  food  swallowed  than  it  is  rejected ;  and  this  is  par- 
ticularly true  of  water  or  liquid  food.  The  fatal  result  is 
usually  caused,  or  at  least  preceded,  by  changes  of  a 
pneumonic  nature  in  the  lungs.  The  precise  significance  of 
the  pulmonary  lesion  is  obscure.  But  it  would  seem  that 
paralysis  of  the  laryngeal  and  cesophageal  muscles,  with  the 
consequent  entrance  of  food,  foreign  bodies,  and  perhaps 
bacteria,  into  the  lungs,  is  responsible  to  a  great  extent. 
And  when  only  a  partial  palsy  of  the  glottis  is  produced,  by 
dividing  the  right  vagus  below  the  origin  of  the  recurrent 
laryngeal,  and  the  left,  as  usual  in  the  neck,  pneumonia  either 
does  not  occur  or  is  long  delayed.  It  may  be  that  the 
tissue  of  the  lungs  is  rendered  particularly  susceptible  to 
such  insults  in  consequence  of  a  hypersemic  condition  in- 
duced by  the  section  of  pulmonary  vaso-motor  fibres  in  the 
vagi.  The  vomiting  is  certainly  connected  with  the  paralysis 
and  consequent  dilatation  of  the  oesophagus ;  and  by  pre- 
viously making  an  artificial  opening  into  the  stomach,  or  by 
a  surgical  prophylaxis  still  more  heroic,  the  establishment 
of  a  double  gastric  and  ossophageal  fistula,  certain  observers 
have  been  able  to  prevent  death  for  many  months. 

Special  Modifications  of  the  Respiratory  Movements. — Cheyne- 
Stokes  Respiration  is  the  name  given  to  a  peculiar  type  of 
breathing,  marked  by  pauses  of  many  seconds  alternating 
with  groups  of  respirations.  In  each  group  the  movements 
gradually  increase  to  a  maximum  amplitude,  and  then 
become  gradually  shallower  again,  till  they  cease  for  the 
next  pause.  The  cause  is  unknown.  The  phenomenon  is 
not  peculiar  to  pathological  conditions,  although  it  often 
occurs  in  certain  diseases  of  the  brain,  and  although  pressure 


222  A  MANUAL  OF  PHYSIOLOGY 

on  the  spinal  bulb  may  produce  it.  But  it  is  also  seen,  more 
or  less  perfectly,  in  normal  sleep,  especially  in  children,  and 
in  morphia  and  chloral  poisoning.  A  periodic  change  in  the 
activity  of  the  respiratory  centre,  corresponding  to  the 
change  in  the  vaso-motor  centre  which  is  credited  with  the 
production  of  Traube-Hering  oscillations  in  the  blood- 
pressure  (p.  250),  has  been  suggested  as  the  cause,  but  there 
is  no  certainty  as  to  this. 

In  frogs,  Cheyne-Stokes'  breathing  has  been  observed  as 
the  result  of  interference  with  the  circulation  in  the  spinal 
bulb,  '  drowning,'  or  ligature  of  the  aorta,  and  also  as  a  con- 
sequence of  removal  of  the  brain,  or  parts  of  it  (hemispheres 
and  optic  thalami)  (Langendorff,  Sherrington,  etc.). 

Peculiarly  modified,  but  more  or  less  normal  respiratory 
acts  are  coughing,  sneezing,  yawning,  sighing  and  hiccup. 

A  cough  is  an  abrupt  expiration  with  open  mouth,  which 
forces  open  the  previously  closed  glottis.  It  may  be  excited 
reflexly  from  the  mucous  membrane  of  the  respiratory  tract 
or  stomach  through  the  afferent  fibres  of  the  vagus,  from  the 
back  of  the  tongue  or  mouth,  and  (by  cold)  from  the  skin. 

Sneezing  is  a  violent  expiration  in  which  the  air  is  chiefly 
expelled  through  the  nose.  It  is  usually  excited  reflexly 
from  the  nasal  mucous  membrane  through  the  branch  of 
the  fifth  nerve  which  supplies  it.  Pressure  on  the  course  of 
the  nasal  nerve  will  often  stop  a  sneeze.  A  bright  light 
sometimes  causes  a  sneeze,  and  so  in  some  individuals  does 
pressure  on  the  supra-orbital  nerve,  when  the  skin  over  it  is 
slightly  inflamed. 

Yawning  is  a  prolonged  and  very  deep  inspiration,  some- 
times accompanied  with  stretching  of  the  arms  and  the 
whole  body.  It  is  a  sign  of  mental  or  physical  weariness. 

A  sigh  is  a  long-drawn  inspiration,  followed  by  a  deep 
expiration. 

Hiccup  is  due  to  a  spasmodic  contraction  of  the  diaphragm, 
which  causes  a  sudden  inspiration.  The  abrupt  closure  of 
the  glottis  cuts  this  short  and  gives  rise  to  the  characteristic 
sound.  The  following  readings  of  the  intervals  between 
successive  spasms  were  obtained  in  one  attack :  13  sees., 
12  sees.,  15  sees.,  9  sees.,  14  sees.,  etc. — i.e.,  one-fourth  or 


RESPIRATION  223 

one-fifth  of  the  frequency  of  the  ordinary  respiratory  move- 
ments. The  mere  fixing  of  the  attention  on  the  observations 
soon  stopped  the  hiccup. 

Chemistry  of  Respiration. 

Our  knowledge  of  this  subject  has  been  entirely  acquired 
in  the  last  200  years,  and  chiefly  in  the  last  century. 

Boyle  showed  by  means  of  the  air-pump  that  animals  die 
in  a  vacuum,  and  Bernoulli  that  fish  cannot  live  in  water 
from  which  the  air  has  been  driven  out  by  boiling. 

Mayow,  of  Oxford,  seems  to  a  considerable  extent  to  have 
anticipated  Black,  who  in  1757  demonstrated  the  presence 
of  carbonic  acid  (carbon  dioxide)  in  expired  air  by  the 
turbidity  which  it  causes  in  lime-water. 

A  most  fundamental  step  was  the  discovery  of  oxygen  by 
Priestley  in  1771,  and  his  proof  that  the  venous  blood  could 
be  made  crimson,  like  arterial,  by  being  shaken  up  with 
oxygen. 

Lavoisier  discovered  the  composition  of  carbonic  acid, 
and  applied  his  discovery  to  the  explanation  of  the  respira- 
tory processes  in  animals,  the  heat  of  which  he  showed  to  be 
generated  like  that  of  a  candle  by  the  union  of  carbon  and 
oxygen.  He  made  many  further  important  experiments  on 
respiration,  publishing  some  of  his  results  in  1789,  when  the 
French  Revolution,  in  which  he  was  to  be  one  of  the  most 
distinguished  victims,  was  breaking  out.  He  made  the 
mistake,  however,  of  supposing  that  the  oxidation  of  the 
carbon  takes  place  in  the  blood  as  it  passes  through  the 
lesser  circulation. 

That  some  carbon  dioxide  is  formed  in  the  lungs  there  is 
no  reason  to  doubt,  and  the  quantity  may  even  be  consider- 
able (Bohr  and  Henriques).  But  that  they  are  not  the  chief 
seat  of  oxidation  was  sufficiently  proved  as  soon  as  it  was 
known  that  the  blood  which  comes  to  them  from  the  right 
heart  is  rich  in  carbon  dioxide,  while  the  blood  which  leaves 
them  through  the  pulmonary  artery  is  comparatively  poor. 

There  are  two  main  lines  on  which  research  has  gone  in 
trying  to  solve  the  chemical  problems  of  respiration  :  (i) 
The  analysis  and  comparison  of  the  inspired  and  expired 


224  A  MANUAL  OF  PHYSIOLOGY 

air,  or,  in  general,  the  investigation  of  the  gaseous  inter- 
change between  the  blood  and  the  air  in  the  lungs.  (2)  The 
analysis  and  comparison  of  the  gases  of  arterial  and  venous 
blood,  of  the  other  liquids,  and  of  the  solid  tissues  of  the 
body,  with  a  view  to  the  determination  of  the  gaseous  inter- 
change between  the  tissues  and  the  blood.  We  shall  take 
these  up  as  far  as  possible  in  their  order. 

The   methods  which  have  been  used  for  comparing  the 
composition  of  inspired  and  expired  air  are  very  various. 

/  (i)  Breathing  into  one  spirometer  and  out  of  another,  the  inspired 
and  expired  air  being  directed  by  valves.  The  contents  of  the  spiro- 
meters  are  analyzed  at  the  end  of  the  experiment  (Speck). 

(2)  A  small  apparatus,  much  on  the  same  principle,  was  used  for 
rabbits  by  Pfliiger  and  his  pupils.     A  cannula  in  the  trachea  was 
connected  with  a  balanced  and  self-adjusting  spirometer  containing 
oxygen,  and  the  inspired  and  expired  air  separated  by  caustic  potash 
valves,  which  absorbed  the  carbon  dioxide.     The  amount  of  oxygen 
used  could  be  read  off  on  the  spirometer,  and  the  amount  of  carbon 
dioxide  produced  estimated  in  the  liquid  of  the  valves. 

(3)  Larger  and  more  elaborate  arrangements,  such  as  Pettenkofer's 
great  respiration  apparatus,  in  which  a  man  can  remain  for  an  in- 
definite period,  working,  resting,  or  sleeping.     Smaller  chambers  of 
the  same  kind  have  also  been  used  for  animals.     In  Pettenkofer's 
apparatus  air  is   drawn   through   by  an   engine,  its   volume  being 
measured  by  a  gasometer.     But  as  it  would  be  far  too  troublesome 
to  analyze  the  whole  of  the  air  coming  from  the  chamber,  a  sample 
stream  of  it  is  constantly  drawn  off,  which  also  passes  through  a 
gasometer,    through    drying    tubes    containing   sulphuric   acid,   and 
through   tubes    filled    with   baryta-water.      The  baryta   solution    is 
titrated  to  determine  the  quantity  of  carbon  dioxide ;  the  increase  in 
weight  of  the  drying  tubes  gives  the  quantity  of  aqueous  vapour.     A 
similar  sample  stream  of  the  air  before  it  passes  into  the  chamber  is 
treated  exactly  in  the  same  way,  and  from  the  data  thus  got  the 
quantity  of  carbon  dioxide  and  aqueous  vapour  given  off  can  readily 
be  ascertained.     But  the  oxygen  has  to  be  calculated  by  difference, 
and  all  the  errors  fall  upon  it. 

(4)  Haldane  and  Pembrey  have  elaborated  a  gravimetric  method, 
which  is  the  most  suitable  of  any — at  least,  for  small  animals.     It 
depends  upon  the  absorption  of  carbon  dioxide  by  soda  lime.     See 
Practical  Exercises,  p.  276. 

The  expired  air  is  at  or  near  the  body  temperature,  is 
saturated  with  watery  vapour,  and  contains  about  4  per  cent. 
more  carbon  dioxide  and  4  to  5  per  cent,  less  oxygen  than 
the  inspired.  There  may  be  in  addition  in  expired  air  small 
quantities  of  hydrogen  or  ammonia,  but  these  are  probably 


RESPIRATION  225 

derived  from  the  alimentary  canal,  either  directly  or  after 
absorption  into  the  blood.  It  is  entirely  free  from  floating 
matter  (dust),  which  is  always  present  in  the  inspired  air. 
The  volume  of  the  expired  air,  owing  to  its  higher  tempera- 
ture and  excess  of  watery  vapour,  is  somewhat  greater  than 
that  of  the  inspired  air,  but  if  it  be  measured  at  the  tem- 
perature and  degree  of  saturation  of  the  latter,  the  volume 
is  somewhat  less.  Since  the  oxygen  of  a  given  quantity  of 
carbon  dioxide  would  have  exactly  the  same  volume  as  the 
carbon  dioxide  itself  at  a  given  temperature  and  pressure,  it 
is  clear  that  the  deficiency  is  due  to  the  fact  that  all  the 
oxygen  which  is  taken  up  in  the  lungs  is  not  given  off  as 
carbon  dioxide ;  some  of  it,  going  to  oxidize  hydrogen, 
reappears  as  water — a  small  amount  of  it  unites  with  the 
sulphur  of  the  proteids  (p.  390).  The  quotient  of  the  volume 
of  oxygen  given  out  as  carbon  dioxide  by  the  volume  of 
oxygen  taken  in  is  the  respiratory  quotient.  It  shows  what 
proportion  of  the  oxygen  is  used  to  oxidize  carbon.  It  may 
approach  unity  on  a  carbo-hydrate  diet,  which  contains 
enough  oxygen  to  oxidize  all  its  own  hydrogen  to  water. 
With  a  diet  rich  in  fat  it  is  least  of  all ;  with  a  diet  of  lean 
meat  it  is  intermediate  in  amount.  For  ordinary  fat  con- 
tains no  more  than  one-sixth,  and  proteids  not  one-half, 
of  the  oxygen  needed  to  oxidize  their  hydrogen.  In  man 
on  a  mixed  diet  the  respiratory  quotient  may  be  taken 
as  *8  or  *g.  So  long  as  the  type  of  respiration  is  not 
changed,  the  respiratory  quotient  may  remain  constant  for 
a  wide  range  of  metabolism.  In  hibernating  animals,  how- 
ever, the  respiratory  quotient  becomes  very  small  during 
winter  sleep  (as  low  as  "4),  the  output  of  carbon  dioxide  falling 
far  more  than  the  consumption  of  oxygen.  On  the  other 
hand,  in  excised  mammalian  muscles  at  a  low  temperature 
the  consumption  of  oxygen  is  lessened  to  a  greater  extent 
than  the  production  of  carbon  dioxide,  and  the  respiratory 
quotient  may  be  as  high  as  3*2  (Rubner).  Muscular  work 
increases  the  respiratory  quotient,  because  carbo-hydrates 
are  chiefly  used  up.  In  starvation  the  respiratory  quotient 
diminishes,  the  production  of  carbon  dioxide  falling  off  at 
a  greater  rate  than  the  consumption  of  oxygen,  for  the 


CO, 

••          ••  • 

0, 


226  A  MANUAL  OF  PHYSIOLOGY 

starving  organism  lives  on  its  own  fat  and  proteids,  and 
has  only  a  trifling  carbo-hydrate  stock  to  draw  upon.  In  a 
diabetic  patient,  fed  on  a  diet  of  fat  and  proteid  alone,  the 
respiratory  quotient  was  only  *6  to  '7,  just  as  in  a  starving 
man. 

In  an  average  man  weighing  70  kilos  the  mean  produc- 
tion of  carbon  dioxide  is  about  800  grammes  (400  litres)  in 
twenty-four  hours,  and  the  mean  consumption  of  oxygen  about 
700  grammes  (490  litres)  (Pettenkofer  and  Voit).  But  there 
are  very  great  variations  depending  upon  the  state  of  the 
body  as  regards  rest  or  muscular  activity,  and  on  other 
circumstances.  In  hard  work  the  production  of  carbon 
dioxide  was  found  to  rise  to  nearly  1,300  grammes,  and  in  rest 
to  sink  to  less  than  700  grammes,  the  consumption  of 
oxygen  in  the  same  circumstances  increasing  to  nearly  1,100 
grammes  and  diminishing  to  600  grammes.  In  rest,  in 
moderate  exertion,  and  in  hard  work,  the  production  of 
carbon  dioxide  was  found  to  be  nearly  proportionate  to  the 
numbers  2,  3  and  6,  respectively.  In  a  case  of  diabetes  the 
consumption  of  oxygen  was  50  per  cent,  greater  than  in  a 
healthy  man,  corresponding  to  the  higher  heat-equivalent 
of  the  food  of  the  diabetic  patient  (Weintraud  and  Laves). 

Taking  400  litres  per  twenty-four  hours,  or  1 7  litres  per  hour,  as 
the  mean  production  of  carbon  dioxide  by  an  average  male  adult  at 
rest  or  doing  only  light  work,  we  can  calculate  the  quantity  of  fresh 
air  which  must  be  supplied  to  a  room  in  order  to  keep  it  properly 
ventilated. 

It  has  been  found  that  when  the  carbon  dioxide  given  off  in 
respiration  amounts  to  no  more  than  2  parts  in  10,000  in  the  air  of 
an  ordinary  room,  the  air  remains  sweet.  When  the  carbon  dioxide 
given  off  reaches  4  parts  in  10,000,  the  room  feels  distinctly,  and  at 
6  in  10,000  disagreeably,  close,  while  at  9  parts  in  10,000  it  is 
oppressive  and  almost  intolerable.  This  has  been  supposed  by  some 
to  be  due  to  a  volatile  poison  exhaled  from  the  lungs,  for  pure  carbon 
dioxide  added  alone  in  similar  proportions  to  the  air  of  a  room  has 
not  the  same  bad  effect.  Certain  observers,  indeed,  alleged  that  the 
condensed  vapour  of  the  breath,  when  injected  into  rabbits,  produced 
fatal  symptoms.  But  this  has  been  shown  to  be  erroneous  ;  and  the 
most  careful  experiments  have  failed  to  detect  in  the  air  expired  by 
healthy  persons  any  trace  of  such  a  poison.  It  has  therefore  been 
suggested  that  the  odour  and  other  ill  effects  of  a  close  room  are  due 
to  substances  given  off  in  the  sweat  and  the  sebum,  and  allowed  by 
persons  of  uncleanly  habits  to  accumulate  on  the  skin,  and  also  to 


I 


RESPIRATION  227 

the  products  of  slow  putrefactive  processes  constantly  going  on,  under  o 
favourable  conditions,  on  the  walls,  floors  or  furniture,  but  only 
becoming  perceptible  to  the  sense  of  smell  when  ventilation  is  in- 
sufficient. In  a  small,  newly-painted  chamber,  presumably  free 
from  such  impurities,  it  was  not  until  the  carbon  dioxide  reached 
3  to  4  per  cent,  that  discomfort  began  to  be  felt  and  the  respiration 
to  be  quickened.*  No  close  odour  could  be  detected  (Haldane  and 
Lorrain  Smith). 

Nevertheless,  experience  has  shown  that  it  is  a  good  working  rule 
for  ventilation  to  take  the  limit  of  permissible  respiratory  impurity 
at  2  parts  of  carbon  dioxide  per  10,000;  and  the  17  litres  of  carbon 
dioxide  given  off  in  the  hour  will  require  85,000  litres  (or  3,000  cubic 
feet)  of  air  to  dilute  it  to  this  extent.  This  is  the  average  quantity 
required  for  the  male  adult  per  hour.  For  men  engaged  in  active 
labour,  as  in  factories  or  mines,  twice  this  amount  may  not  be  too 
much.  For  women  and  children  less  is  required  than  for  men.  If  a 
room  smells  close,  it  needs  ventilation,  whatever  be  the  proportion  of 
carbon  dioxide  in  the  air. 

It  must  be  remembered  that  in  permanently-occupied  rooms  mere 
increase  in  the  size  will  not  compensate  for  incomplete  renewal  of  the 
air,  although  it  may  be  easier  to  ventilate  a  large  room  than  a  small 
one  without  causing  draughts  and  other  inconveniences.  But  as  few 
apartments  are  occupied  during  the  whole  twenty-four  hours,  a  large 
room  which  can  be  thoroughly  ventilated  in  the  absence  of  its 
inmates  has  a  distinct  advantage  over  a  small  one  in  its  great  initial 
stock  of  fresh  air. 

The  cubic  space  per  head  in  an  ordinary  dwelling-house  should  be 
not  less  than  28  cubic  metres  or  1,000  cubic  feet. 

The  quantity  of  carbon  dioxide  given  off  (and  of  oxygen 
consumed)  is  not  only  affected  by  muscular  work,  but  also  by 
everything  which  influences  the  general  metabolism.  In 
males  it  is  greater  than  in  females  (in  the  latter  there  is  a 
temporary  increase  during  pregnancy),  and  greater  in  pro- 
portion to  the  body-weight  in  the  young  than  the  old.  This 
depends,  partly  at  least,  on  the  fact  that  the  metabolism  is 
relatively  more  active  in  a  small  than  in  a  large  organism. 
The  taking  of  food  increases  it,  chiefly  in  consequence 
of  the  increased  mechanical  and  chemical  work  per- 
formed by  the  alimentary  canal  and  the  digestive  glands. 
Sleep  diminishes  the  production  of  carbon  dioxide  partly 

*  Hyperpnoea  from  defect  of  oxygen  also  appears  when  the  amount  of 
it  in  the  air  has  fallen  to  a  point  which  varies  in  different  individuals  (in 
one  case  12  per  cent.).  Warm-blooded  animals  confined  in  a  small  air- 
space die  from  want  of  oxygen,  and  not  from  the  accumulation  of  carbon 
dioxide  ;  but  the  opposite  appears  to  be  the  case  with  cold-blooded 
animals. 

15—2 


228 


A  MANUAL  OF  PHYSIOLOGY 


because  the  muscles  are  at  rest,  but  also  to  some  extent 
because  the  external  stimuli  that  in  waking  life  excite  the 
nerves  of  special  sense  are  absent  or  ineffective.  Even  a 
bright  light  is  said  to  cause  an  increase  in  the  amount  of 
carbon  dioxide  produced  and  of  oxygen  consumed ;  but 
recent  experiments  have  cast  doubt  on  the  statement 
(C.  Ewald).  The  external  temperature  also  has  an  influence. 
In  poikil oilier mal  animals  (such  as  the  frog),  the  temperature 
of  which  varies  with  that  of  the  surrounding  medium,  the 
production  of  carbon  dioxide,  on  the  whole,  diminishes  as 
the  external  temperature  falls,  and  increases  as  it  rises.  In 
homoiothermal  animals,  that  is,  animals  with  constant  blood 
temperature,  external  cold  increases  the  production  of 
carbon  dioxide  and  the  consumption  of  oxygen.  But  if  the 
connection  of  the  nervous  system  with  the  striated  muscles 
has  been  cut  out  by  curara,  the  warm-blooded  animal  behaves 
like  the  cold-blooded  (Pfliiger  and  his  pupils  in  guinea-pig 
and  rabbit).  These  interesting  tacts  will  be  returned  to 
under  Animal  Heat. 

Cold-blooded  animals  produce  far  less  carbon  dioxide, 
and  consume  far  less  oxygen,  per  kilo  of  body-weight  than 
warm-blooded. 

The  following  table  shows  the  relation  between  the  body- 
weight  and  the  excretion  of  carbon  dioxide  in  man : 


Age. 

Weight  in  kilos. 

COa  excreted  per 
kilo  per  hour. 

T35 

65 

•51  gramme 

Male  1  ^ 

82 

577 

'49 
'59 

(  9-6 

22 

•92 

I19 

557 

'45 

emae|lo 

23 

•83         , 

The  next  table  illustrates  the  difference  in  the  intensity  of 
metabolism  in  different  kinds  of  animals,  a  difference,  how- 
ever, largely  dependent  upon  relative  size : 


RESPIRATION 


229 


Animal. 

Oxygen  absorbed  per 
kilo  per  hour 

Carbon  dioxide  given 
off  per  kilo  per  hour 

Respiratory  quotient 
C02  np  02  (in  COo). 

Oa                  O2 

in  grms.        in  c.c, 

in  grms.         in  c.c. 

Greenfinch 

13-000 

9091 

I3'59Q 

6909 

76 

Hen     -     - 

1-058 

740 

1-327 

675 

•91 

Dog      -     - 

I'303 

911 

1-325 

674 

74 

Rabbit  -     - 

0-987 

690 

1-244 

632 

•91 

Sheep  -     - 

0-490 

343 

0-671 

341 

'99 

Boar     -     - 

0-391 

273 

0-443 

225 

•82 

Frog    -     - 

OT05 

73'4 

0-113 

577 

78 

Crayfish    - 

0-054 

38 

0*064 

327 

•86 

Forced  respiration,  although  it  will  temporarily  increase 
the  quantity  of  carbon  dioxide  given  off  by  the  lungs,  does 
not  sensibly  affect  the  production ;  it  is  only  the  store  of 
already  formed  carbon  dioxide  in  the  body  which  is  drawn 
upon.  The  amount  of  oxygen  taken  up  is  little  altered  by 
changes  in  the  movements  of  respiration  except  for  a  very 
short  time. 

How  it  is  that  the  depth  of  the  respiration  may  affect  the 
rate  at  which  carbon  dioxide  is  eliminated,  we  can  only 
understand  when  we  have  examined  the  process  by  which 
the  gaseous  interchange  between  the  blood  and  the  air  of 
the  alveoli  is  accomplished;  and  before  doing  this  it  is 
necessary  to  consider  the  condition  of  the  oxygen  and  carbon 
dioxide  in  the  blood. 


The  Gases  of  the  Blood. 

Physical  Introduction. — Matter  may  be  assumed  to  be  made  up 
of  molecules  beyond  which  it  cannot  be  divided  without  altering  its 
essential  character.  A  molecule  may  consist  of  two  or  more  particles 
of  matter  (atoms)  bound  to  each  other  by  chemical  links.  The  kinetic 
theory  of  matter  supposes  the  molecules  of  a  substance  to  be  in 
constant  motion,  frequently  colliding  with  each  other,  and  thus  having 
the  direction  of  their  motion  changed. 

In  a  gas  the  mean  free  path,  that  is,  the  average  distance  which  a 
molecule  travels  without  striking  another,  is  comparatively  long,  and 
far  more  time  is  passed  by  any  molecule  without  an  encounter  than 
is  taken  up  with  collisions.  Although  the  average  velocity  of  the 
molecules  is  very  great,  these  collisions  will  produce  all  sorts  of 
differences  in  the  actual  velocity  of  different  molecules  at  any  given 
time.  Some  will  be  moving  at  a  greater,  some  at  a  slower  rate, 
than  the  average ;  while  some  may  be  for  a  moment  at  rest.  If  the 


230  A  MANUAL  OF  PHYSIOLOGY 

gas  is  in  a  closed  vessel,  the  molecules  will  be  constantly  striking  its 
sides  and  rebounding  from  them.  If  a  very  small  opening  is  made 
in  the  vessel,  some  molecules  will  occasionally  hit  on  the  opening 
and  escape  altogether.  If  the  opening  is  made  larger,  or  the  experi- 
ment continued  for  a  longer  time  with  the  small  opening,  all  the 
molecules  will  in  course  of  time  have  passed  out  of  the  vessel  into 
the  air,  while  molecules  of  the  oxygen,  nitrogen,  and  argon  of  the  air 
will  have  passed  in.  In  a  gas,  then,  not  enclosed  by  impenetrable 
boundaries,  there  is  no  restriction  on  the  path  which  a  molecule  may 
take,  no  tendency  for  it  to  keep  within  any  limits. 

When  two  chemically  indifferent  gases  are  placed  in  contact  with 
each  other,  diffusion  will  go  on  till  they  are  uniformly  mixed.  The 
diffusion  of  gases  may  be  illustrated  thus .  Suppose  we  have  a 
perfectly  level  and  in  every  way  uniform  field  divided  into  two 
equal  parts  by  a  visible  but  intangible  line,  the  well-known  whitewash 
line,  for  instance.  On  one  side  of  the  line  place  500  blind  men  in 
green,  and  on  the  other  500  blind  men  in  red.  At  a  given  signal  let 
them  begin  to  move  about  in  the  field.  Some  of  the  men  in  green 
will  pass  over  the  line  to  the  '  red '  side ;  some  of  the  men  in  red 
will  wander  to  the  '  green  '  side.  Some  of  the  men  may  pass  over 
the  line  and  again  come  back  to  the  side  they  started  from.  But, 
upon  the  whole,  after  a  given  interval  has  elapsed,  as  many  green 
coats  will  be  seen  on  the  red  side  as  red  coats  on  the  green.  And  if 
the  interval  is  long  enough  there  will  be  at  length  about  250  men  in 
red  and  250  in  green  on  each  side  of  the  boundary-line.  When  this 
state  of  equilibrium  has  once  been  reached,  it  will  henceforth  be 
maintained,  for,  upon  the  whole,  as  many  red  uniforms  will  pass 
across  the  line  in  one  direction,  as  will  recross  it  in  the  other. 

In  a  liquid  it  is  very  different ;  the  molecule  has  no  free  path.  In 
the  depth  of  the  liquid  no  molecule  ever  gets  out  of  the  reach  of 
other  molecules,  although  after  an  encounter  there  is  no  tendency  to 
return  on  the  old  path  rather  than  to  choose  any  other ;  so  that  any 
molecule  may  wander  through  the  whole  liquid.  Although  the 
average  velocity  of  the  molecules  is  much  less  in  the  liquid  state 
than  it  would  be  for  the  same  substance  in  the  state  of  gas  or  vapour 
(gas  in  presence  of  its  liquid),  some  of  them  may  have  velocities 
much  above  the  average.  If  any  of  these  happen  to  be  moving  near 
the  surface  and  towards  it,  they  may  overcome  the  attraction  of  the 
neighbouring  molecules  and  escape  as  vapour,  But  if  in  their 
further  wanderings  they  strike  the  liquid  again,  they  may  again 
become  bound  down  as  liquid  molecules.  And  so  a  constant  inter- 
change may  take  place  between  a  liquid  and  its  vapour,  or  between 
a  liquid  and  any  other  gas,  until  the  state  of  equilibrium  is  reached, 
in  which  on  the  average  as  many  molecules  leave  the  liquid  to 
become  vapour  as  are  restored  by  the  vapour  to  the  liquid,  or  as 
many  molecules  of  the  dissolved  gas  escape  from  solution  as  enter 
into  it. 

For  the  sake  of  a  simple  illustration,  let  us  take  the  case  of  a 
shallow  vessel  of  water  originally  gas-free,  standing  exposed  to  the 
air.  It  will  be  found  after  a  time  that  the  water  contains  the  atmo- 


RESPIRATION  231 

spheric  gases  in  certain  proportions — in  round  numbers,  about  TJB  of 
its  volume  of  oxygen  and  ^  of  its  volume  of  nitrogen  (measured  at 
760  mm.  mercury  and  o°  C.). 

Now,  let  a  similar  vessel  of  gas-free  water  be  placed  in  a  large  air- 
tight box  filled  with  air  at  atmospheric  pressure,  and  let  the  oxygen 
be  all  absorbed  before  the  water  is  exposed  to  the  atmosphere  of  the 
box.  The  latter  now  consists  practically  only  of  the  nitrogen  of  the 
air,  and  its  pressure  will  be  only  about  four-fifths  that  of  the  external 
atmosphere.  Nevertheless,  the  quantity  of  nitrogen  absorbed  by  the 
water  will  be  exactly  the  same  as  was  absorbed  from  the  air.  If 
the  box  was  completely  exhausted,  and  then  a  quantity  of  oxygen, 
equal  to  that  in  it  at  first,  introduced  before  the  water  was  exposed 
to  it,  the  pressure  would  be  found  to  be  only  about  one-fifth  that  of 
the  external  atmosphere ;  but  the  quantity  of  oxygen  taken  up  by 
the  water  would  be  exactly  equal  to  that  taken  up  in  the  first 
experiment. 

Two  well-known  physical  laws  are  illustrated  by  our  supposed 
experiments:  (i)  In  a  mixture  of  gases  which  do  not  act  chemically 
on  each  other  the  pressure  exerted  by  each  gas  (called  the  partial  pres- 
sure of  the  gas)  is  the  same  as  it  would  exert  if  the  others  were  absent. 
(2)  The  quantity  (mass)  of  a  gas  absorbed  by  a  liquid  which  does  not 
act  chemically  upon  it  is  proportional  to  the  partial  pressure  of  the  gas. 
It  also  depends  upon  the  nature  of  the  gas  and  of  the  liquid,  and  on 
the  temperature,  increase  of  temperature  in  general  diminishing  the 
quantity  of  gas  absorbed.  It  is  to  be  noted  that  when  the  volume 
of  the  absorbed  gas  is  measured  at  a  pressure  equal  to  the  partial 
pressure  under  which  it  was  absorbed,  the  same  volume  of  gas  is 
taken  up  at  every  pressure. 

Suppose,  now,  that  a  vessel  of  water,  saturated  with  oxygen  and 
nitrogen  for  the  partial  pressures  under  which  these  gases  exist  in  the 
air,  is  placed  in  a  box  filled  with  pure  nitrogen  at  full  atmospheric 
pressure.  As  we  have  seen,  there  is  a  constant  interchange  going  on 
between  a  liquid  which  contains  gas  in  solution  and  the  atmosphere 
to  which  it  is  exposed.  Oxygen  and  nitrogen  molecules  will  there- 
fore continue  to  leave  the  water  ;  but  if  the  box  is  large,  few  oxygen 
molecules  will  find  their  way  back  to  the  water,  and  ultimately  little 
oxygen  will  remain  in  it.  In  other  words,  the  quantity  of  oxygen 
absorbed  by  the  water  will  become  again  proportional  to  the  partial 
pressure  of  oxygen,  which  is  now  not  much  above  zero.  On  the 
other  hand,  molecules  of  nitrogen  will  at  first  enter  the  water  in 
larger  number  than  they  escape  from  it,  ,for  the  pressure  of  the 
nitrogen  is  now  that  of  the  external  atmosphere,  of  which  its  partial 
pressure  was  formerly  only  four-fifths.  In  unit  volume  of  the  gas 
above  the  water  there  will  be  5  molecules  of  nitrogen  for  every  4 
molecules  in  the  same  volume  of  atmospheric  air.  Therefore,  on  the 
average  5  nitrogen  molecules  will  in  a  given  time  get  entangled  by 
liquid  molecules  for  every  4  which  came  within  their  sphere  of  attrac- 
tion before.  On  the  whole,  then,  the  water  will  lose  oxygen  and  gain 
nitrogen,  while  the  atmosphere  of  the  air-tight  box  will  gain  oxygen 
and  lose  nitrogen. 


232  A  MANUAL  OF  PHYSIOLOGY 

If,  now,  the  partial  pressures  of  oxygen  and  nitrogen  under  which 
the  water  had  been  originally  saturated  were  unknown,  it  is  evident 
that  by  exposing  it  to  an  atmosphere  of  known  composition,  and 
afterwards  determining  the  changes  produced  in  the  composition  of 
that  atmosphere  by  loss  to,  or  gain  from,  the  gases  of  the  water,  we 
could  find  out  something  about  the  original  partial  pressures.  If, 
for  example,  the  quantity  of  oxygen  in  the  atmosphere  of  the  chamber 
was  increased,  we  could  conclude  that  the  partial  pressure  of  oxygen 
under  which  the  water  had  been  saturated  was  greater  than  that  in 
the  chamber  at  the  beginning  of  the  experiment.  And  if  we  found 
that  with  a  certain  partial  pressure  of  oxygen  in  the  atmosphere  of 
the  chamber  there  was  neither  gain  nor  loss  of  this  gas,  we  might  be 
sure  that  the  partial  pressure  (the  temperature  being  supposed  not 
to  vary)  was  the  same  when  the  water  was  saturated.  We  shall  see 

P,  frictionless  piston  ;  L,  liquid  in 
cylinder;  G,  gas  beginning  to  es- 
cape from  liquid.  P  is  exactly 
counterpoised.  In  addition  to  the 
manner  described  in  the  text,  the  ex- 
periment may  be  supposed  to  be  per- 
formed thus.  Let  the  weight,  W,  be 
determined  which,  when  the  receiver 
is  completely  exhausted,  suffices  just 
to  keep  the  piston  in  contact  with  the 
liquid.  The  pressure  of  the  gas  is 
then  just  counterbalanced  by  W; 
and  if  S  is  the  area  of  the  cross- 
section  of  the  piston  the  pressure  of 

the  gas  per  unit  of  area  is  — .    Or  if 

the  piston  is  hollow,  and  mercury  is 
poured  into  it  so  as  just  to  keep  it  in 
contact  with  the  liquid,  the  height  of 
the  column  of  mercury  required  is 
also  equal  to  the  pressure  or  tension 
of  the  gas. 

FIG.  82. — IMAGINARY  EXPERIMENT  TO  ILLUSTRATE  'TENSION'  OF  A  GAS  IN 

A  LIQUID. 

later  on  how  this  principle  has  been  applied  to  determine  the  partial 
pressure  of  oxygen  or  carbon  dioxide  which  just  suffices  to  prevent 
blood,  or  any  other  of  the  liquids  of  the  body,  from  losing  or  gaining 
these  gases.  This  pressure  is  evidently  equal  to  that  exerted  by  the 
gases  of  the  liquid  at  its  surface,  which  is  sometimes  called  their 
'  tension  ' ;  for  if  it  were  greater,  gas  would,  upon  the  whole,  pass 
into  the  blood  ;  and  if  it  were  less,  gas  would  escape  from  the  blood. 
Thus,  the  tension  of  a  gas  in  solution  in  a  liquid  is  equal  to  the  partial 
pressure  of  that  gas  in  an  atmosphere  to  which  the  liquid  is  exposed, 
which  is  just  sufficient  to  prevent  gain  or  loss  of  the  gas  by  the  liquid 
(p.  .240). 

The  following  imaginary  experiment  may  further  illustrate  the 
meaning  of  the  term  *  tension  '  of  a  gas  in  a  liquid  in  this  connection: 

Suppose  a  cylinder  filled  with  a  liquid  containing  a  gas  in  solution, 
and  closed  above  by  a  piston  moving  air-tight  and  without  friction, 
in  contact  with  the  surface  of  the  liquid  (Fig.  82).  Let  the  weight 


RESPIRATION 


233 


of  the  piston  be  balanced  by  a  counterpoise.  The  pressure  at  the 
surface  of  the  liquid  is  evidently  that  of  the  atmosphere.  Now,  let 
the  whole  be  put  into  the  receiver  of  an  air-pump,  and  the  air  gradu- 
ally exhausted.  Let  exhaustion  proceed  until  gas  begins  to  escape 
from  the  liquid  and  lies  in  a  thin  layer  between  its  surface  and  the 
piston,  the  quantity  of  gas  which  has  become  free  being  very  small 
in  proportion  to  that  still  in  solution.  At  this  point  the  piston  is 

A,  the  blood  bulb;  B,  the  froth 
chamber  ;  C,  the  drying  tube  ;  D,  fixed 
mercury  tube ;  E,  movable  mercury  bulb 
connected  by  a  flexible  tube  with  D  ;  F, 
eudiometer  ;  G,  a  narrow  delivery  tube  ; 
i,  2,  3,  4,  taps,  4  being  a  three-way  tap. 
A  is  filled  with  blood  by  connecting  the 
tap  i  by  means  of  a  tube  with  a  blood- 
vessel. Taps  i  and  2  are  then  closed. 
The  rest  of  the  apparatus  from  B  to  D 
is  now  exhausted  by  raising  E,  with  tap 
4  turned  so  as  to  place  E  only  in  com- 
munication with  G,  till  the  mercury  fills 
D.  Tap  4  is  -now  turned  so  as  to  con- 
nect C  with  D,  and  cut  off  G  from  D, 
and  E  is  lowered.  The  mercury  passes 
out  of  D,  and  air  passes  into  it  from  B 
and  C.  Tap  4  is  again  turned  so  as  to 
cut  off  C  from  D  and  connect  G  and  D. 
E  is  raised,  and  the  mercury  passes  into 
D  and  forces  the  air  out  through  G,  the 
end  of  which  has  not  hitherto  been 
placed  under  F.  This  alternate  raising 
and  lowering  of  E  is  continued  till  a 
manometer  connected  between  C  and  4 
indicates  that  the  pressure  has  been 
sufficiently  reduced.  The  tap  2  is  now 
opened ;  the  gases  of  the  blood  bubble 
up  into  the  froth  chamber,  pass  through 
the  drying-tube  C,  which  is  filled  with 
pumice-stone  and  sulphuric  acid,  and 
enter  D.  The  end  of  G  is  placed  under 
the  eudiometer  F,  and  by  raising  E, 
with  tap  4  turned  so  as  to  cut  off  C, 
the  gases  are  forced  out  through  G  and 
collected  in  F.  The  movements  re- 
quired for  exhaustion  can  be  repeated 
several  times  till  no  more  gas  comes  off. 
The  escape  of  gas  from  the  blood  is 
facilitated  by  immersing  the  bulb  A  in 
water  at  4o°-5o°  C. 

FIG.  83.— SCHEME  OF  GAS-PUMP. 

acted  upon  by  two  forces  which  balance  each  other,  the  pressure  of  the 
air  in  the  receiver  acting  downwards,  and  the  pressure  of  the  gas  escap- 
ing from  the  liquid  acting  upwards.  If  the  pressure  in  the  receiver 
is  now  slightly  increased,  the  gas  is  again  absorbed.  The  pressure  at 
which  this  just  happens,  and  against  which  the  piston  is  still  sup- 
ported by  the  impacts  of  gaseous  molecules  flying  out  of  the  liquid, 
while  no  pressure  is  as  yet  exerted  directly  between  the  liquid  and 
the  piston,  is  obviously  equal  to  the  pressure  or  tension  of  the  gas  in 
the  liquid. 

From  the  above  principles  it  follows  that  a  gas  held  in  solution 


234  A  MANUAL  OF  PHYSIOLOGY 

may  be  extracted  by  exposure  to  an  atmosphere  in  which  the  partial 
pressure  of  the  gas  is  made  as  small  as  possible.  Thus,  oxygen  can 
be  obtained  from  liquids  in  which  it  is  simply  dissolved  by  putting 
them  in  an  atmosphere  of  hydrogen  or  nitrogen,  in  which  the  partial 
pressure  of  oxygen  is  zero,  or  in  the  vacuum  of  an  air-pump,  in 
which  it  is  extremely  small.  Heat  also  aids  the  expulsion  of  dis- 
solved gases.  Some  gases  held  in  weak  chemical  union,  like  the 
loosely-combined  oxygen  of  oxyhaemoglobin,  can  be  obtained  by  dis- 
sociation of  their  compounds  when  the  partial  pressure  is  reduced. 
More  stable  combinations  may  require  to  be  broken  up  by  chemical 
agents — carbonates,  for  instance,  by  acids. 

Extraction  of  the  Blood-gases. — This  is  best  accomplished  by 
exposing  blood  to  a  nearly  perfect  vacuum.  The  gas-pumps  which 
have  been  most  largely  used  in  blood  analysis  are  constructed  on  the 
principle  of  the  Torricellian  vacuum.  A  diagram  of  a  simple  form  of 
Pfliiger's  gas-pump  is  given  in  Fig.  83.  The  gases  obtained  are 
ultimately  dried  and  collected  in  a  eudiometer,  which  is  a  graduated 
glass  tube  with  its  mouth  dipping  into  mercury.  The  carbon  dioxide 
is  estimated  by  introducing  a  little  caustic  potash  to  absorb  it.  The 
diminution  in  the  volume  of  the  gas  contained  in  the  eudiometer 
gives  the  volume  of  the  carbon  dioxide.  The  oxygen  may  be 
estimated  by  putting  into  the  eudiometer  more  than  enough  hydrogen 
to  unite  with  all  the  oxygen  so  as  to  form  water,  and  then,  after 
reading  off  the  volume,  exploding  the  mixture  by  means  of  an 
electric  spark  passed  through  two  platinum  wires  fused  into  the  glass. 
One-third  of  the  diminution  of  volume  represents  the  quantity  of 
oxygen  present.  It  can  also  be  estimated  by  absorption  with  a 
solution  of  pyrogallic  acid  and  potassium  hydrate.  The  remainder 
of  the  original  mixture  of  blood-gases,  after  deduction  of  the  carbon 
dioxide  and  oxygen,  is  put  down  as  nitrogen  (with,  no  doubt,  a  small 
proportion  of  argon).  For  the  sake  of  easy  comparison,  the  observed 
volume  of  gas  is  always  stated  in  terms  of  its  equivalent  at  a  standard 
pressure  and  temperature  (760  mm.,  or  sometimes  on  the  Continent 
i  metre  of  mercury,  and  o°  C.). 

It  is  also  possible  in  various  ways,  to  estimate  the  amount  of 
oxygen  in  blood  without  the  use  of  the  pump.  Thus,  since  a  definite 
volume  of  oxygen  ( 1*338  c.c.  at  o°  C.  and  760  mm.  pressure) 
combines  with  a  gramme  of  haemoglobin,  we  can  calculate  the  total 
volume  of  oxygen  present  if  we  know  how  much  of  the  blood-pigment 
is  in  the  form  of  oxyhaemoglobin ;  and  this  can  be  determined  by 
means  of  the  spectrophotometer  (Hiifner).  Or  the  blood  may  be 
shaken  with  carbon  monoxide  (carbonic  oxide),  which  expels  the 
oxygen  from  its  combination  with  the  haemoglobin.  The  oxygen  can 
then  be  estimated  in  the  gas  collected  (Bernard). 

In  dog's  blood,  which  has  been  up  to  this  time  chiefly  in- 
vestigated, there  are  considerable  variations  in  the  quantity 
of  oxygen  and  carbon  dioxide  which  can  be  extracted  ;  and 
this  is  particularly  true  of  the  venous  blood,  as  might 


RESPIRATION  235 

naturally  be  expected,  since  even  to  the  eye  it  varies  greatly 
according  to  the  vein  it  is  obtained  from,  the  rapidity  of  the 
circulation,  and  the  activity  of  the  tissues  which  it  has  just 
left.  On  the  average, 

Volumes  of 


02         C02          N2 
ioo  volumes  of  arterial  blood  yield  -         -        -  20        40         1-2 

„  mixed  venous  blood  (from  right 

heart)  yield  -  -      10-12      45-5°      1-2 

(reduced  to  o°  C.  and  760  mm.  of  mercury). 

Average  venous  blood  contains  7  or  8  per  cent,  by  volume 
less  oxygen,  and  7  or  8  per  cent,  more  carbon  dioxide,  than 
arterial  blood.  Thus,  in  the  lungs  the  blood  gains  about 
twice  as  many  volumes  of  oxygen  per  cent,  as  the  air  loses, 
and  the  air  gains  about  half  as  many  volumes  of  carbon 
dioxide  per  cent,  as  the  blood  loses.  And  it  is  easy  to  see 
that  this  must  be  so,  for  the  volume  of  the  air  inspired  in  a 
given  time  is  about  twice  as  great  as  that  of  the  blood  which 
passes  through  the  pulmonary  circulation  (pp.  197,  207,  224). 
Even  arterial  blood  is  not  quite  saturated  with  oxygen ;  it 
can  generally  still  take  up  one-tenth  to  one-fifteenth  of  the 
quantity  contained  in  it.  Nor  is  venous  blood  nearly 
saturated  with  carbon  dioxide ;  when  shaken  with  the  gas  it 
can  take  up  about  150  volumes  per  cent 

When  the  gases  are  not  removed  from  blood  immediately 
after  it  is  drawn,  its  colour  becomes  darker,  and  it  yields 
more  carbon  dioxide  and  less  oxygen  than  if  it  is  evacuated 
at  once  (Pfluger).  From  this  it  is  concluded  that  oxidation 
goes  on  in  the  blood  for  some  time  after  it  is  shed.  The 
oxidizable  substances  appear,  however,  to  be  confined  to  the 
corpuscles,  which  suggests  that  ordinary  metabolism  simply 
continues  for  some  time  in  the  formed  elements  of  the  shed 
blood,  and  that  the  disappearance  of  oxygen  is  not  due  to 
the  oxidation  of  substances  which  have  reached  the  blood 
from  the  tissues. 

The  Distribution  of  the  Gases  in  the  Blood. — The  oxygen  is 
nearly  all  contained  in  the  corpuscles.  A  little  oxygen  can 
be  pumped  out  of  serum  ('I  to  *2  per  cent,  by  volume),  but 
this  follows  the  Henry-Dalton  law  of  pressures;  that  is,  it 


236  A  MANUAL  OF  PHYSIOLOGY 

comes  off  in  proportion  to  the  reduction  of  the  partial 
pressure  of  the  oxygen  in  the  pump,  and  is  simply  in  solution. 
When  blood  is  being  pumped  out,  very  little  oxygen 
comes  off  till  the  pressure  has  been  reduced  to  about  half  an 
atmosphere.  At  about  a  third  of  an  atmosphere,  if  the 
blood  is  nearly  at  body  temperature,  the  oxygen  begins  to 
escape  a  little  more  freely ;  and  when  the  pressure  has  fallen 


FIG.  84. — CURVE  OF  DISSOCIATION  OF  OXYH^EMOGLOBIN  AT  35°  C. 

HtJFNER'S   RESULTS.) 


(AFTER 


Along  the  horizontal  axis  are  plotted  the  partial  pressures  (numbers  below  the 
curve)  of  oxygen  in  air,  to  which  a  solution  of  haemoglobin  was  exposed.  The  corre- 
sponding percentages  of  oxygen  are  given  above  the  curve.  Along  the  vertical  axis  is 
plotted  the  percentage  saturation  of  the  haemoglobin  with  oxygen.  Thus,  on  exposure 
to  an  atmosphere  in  which  oxygen  existed  to  the  extent  of  i  per  cent.,  corresponding 
to  a  partial  pressure  of  7*6  millimetres  of  mercury,  the  haemoglobin  took  up  about 
75  per  cent,  of  the  amount  of  oxygen  required  to  saturate  it.  When  the  oxygen  was 
present  in  the  atmosphere  to  the  amount  of  about  10  per  cent. ,  corresponding  to  a 
partial  pressure  of  76  millimetres  of  mercury,  the  quantity  taken  up  by  the  haemo- 
globin was  about  96  per  cent,  of  that  required  for  saturation. 


to  about  one-sixth  of  an  atmosphere  (corresponding  to  a 
partial  pressure  of  oxygen  of  25-30  mm.  of  mercury),  it  is 
disengaged  with  a  burst.  This  shows  that  it  is  not  simply 
absorbed,  but  is  united  by  chemical  bonds  to  some  con- 
stituent of  the  blood.  The  same  thing  is  seen  when  de- 
fibrinated  blood  is  saturated  at  body  temperature  with 
oxygen  at  different  pressures.  The  quantity  taken  up 


RESPIRATION  237 

lessens  but  slowly  as  the  pressure  is  reduced,  till  at  about 
25  to  30  mm.  of  mercury  an  abrupt  diminution  takes  place. 
It  is  found  that  a  solution  of  pure  haemoglobin  crystals 
behaves  towards  oxygen  just  like  blood ;  and  there  is  no 
doubt  that  the  body  in  blood  with  which  the  oxygen  is 
loosely  united  is  haemoglobin. 

We  may  suppose  that  at  the  ordinary  temperature  and  pressure* 
some  oxygen  is  continually  escaping  from  the  bonds  by  which  it  is 
tied  to  the  haemoglobin  :  but,  on  the  whole,  an  equal  number  of 
free  molecules  of  oxygen,  coming  within  the  range  of  the  haemoglobin 
molecules,  are  entangled  by  them,  and  thus  equilibrium  is  kept  up.' 
If  now  the  atmospheric  pressure,  and  therefore  the  partial  pressure  of 
oxygen,  is  reduced,  the  tendency  of  the  oxygen  molecules  to  break  off 
from  the  haemoglobin  will  be  unchanged,  and  as  many  molecules  on 
the  whole  will  escape  as  before ;  but  even  after  a  considerable 
reduction  of  pressure  the  haemoglobin,  such  is  its  avidity  for  oxygen, 
will  still  be  able  to  seize  as  many  atoms  as  it  loses.  The  more,  how- 
ever, the  partial  pressure  of  the  oxygen  is  diminished — that  is  to  say, 
the  fewer  oxygen  molecules  there  are  in  a  given  space  above  the 
haemoglobin — the  smaller  will  be  the  chance  of  the  loss  being  made 
up  by  accidental  captures.  At  a  certain  pressure  the  escapes  will 
become  conspicuously  more  numerous  than  the  captures ;  and  the 
gas-pump  will  give  evidence  of  this,  although  it  could  give  us  no 
information  as  to  mere  molecular  interchange,  so  long  as  equilibrium 
was  maintained. 

The  higher  the  temperature  of  the  haemoglobin  is,  the  greater  will 
be  the  average  velocity  of  the  molecules,  and  the  greater  the  chance 
of  escape  of  molecules  of  oxygen.  The  '  dissociation  tension  '  of  oxy- 
haemoglobin,  or  the  partial  pressure  of  oxygen  at  which  the  oxyhaemo- 
globin  begins  to  lose  more  oxygen  than  it  gains,  is  increased  by  raising 
the  temperature.  The  curve  of  dissociation  of  oxyhaemoglobin  at  a 
temperature  of  35°  C.  is  shown  in  Fig.  84. 

The  Carbon  Dioxide  of  the  Blood. — Blood  freed  from  gas 
absorbs  carbon  dioxide  partly  in  proportion  to  the  pressure, 
and  in  part  independently  of  it.  Some  of  the  carbon  dioxide 
must  therefore  be  simply  dissolved ;  some,  and  this  the 
greater  portion,  is  chemically  combined.  The  serum  con- 
tains a  larger  percentage  of  carbon  dioxide  than  the  clot,  but 
this  percentage  is  not  great  enough  to  allow  us  to  assume 
that  the  whole  of  the  carbon  dioxide  is  confined  to  the 
serum.  Some  of  it  must  belong  to  the  corpuscles. 

*  The  partial  pressure  of  oxygen  in  air  at 760  mm.  atmospheric  pressure 
*s  —  x  760,  or  159*6  mm. 


238  A  MANUAL  OF  PHYSIOLOGY 

Since  the  serum  contains  alkalies  (especially  soda),  it  is 
natural  to  suppose  that  the  combined  carbon  dioxide  must 
exist  chiefly  as  carbonate  or  bicarbonate  of  sodium.  That 
there  is  something  more,  however,  is  shown  by  the  fact  that 
from  defibrinated  blood  the  whole  of  the  carbon  dioxide  can 
in  time  be  pumped  out  without  the  addition  of  an  acid  to 
displace  it  from  the  bases  with  which  it  is  combined.  It  is 
hardly  necessary  to  say  that  this  could  not  be  done  with  a 
solution  of  sodium  carbonate.  Yet  when  sodium  carbonate 
is  added  to  blood,  even  in  considerable  amount,  all  the 
carbon  dioxide  in  it  can  be  obtained  by  the  pump.  From 
serum  a  great  deal,  but  not  the  whole,  of  the  carbon 
dioxide  can  be  likewise  pumped  out.  The  residue  is  set 
free  on  the  addition  of  an  acid,  phosphoric  acid,  for 
example. 

The  most  satisfactory  explanation  seems  to  be  that  in  the 
serum  there  exist  substances  which  can  act  as  weak  acids 
in  gradually  driving  out  the  carbon  dioxide,  when  its  escape 
is  rendered  easier  by  the  vacuum,  but  which,  nevertheless, 
do  not  affect  litmus  paper  (since  the  reaction  of  serum  is 
alkaline).  The  quantity  of  these,  however,  is  so  small  that 
a  portion  of  the  carbon  dioxide  remains  in  the  serum.  The 
proteids  of  the  serum,  such  as  serum-globulin,  behave  in 
certain  respects  like  weak  acids,  and  may  contribute  to  the 
driving  out  of  the  carbon  dioxide. 

When  defibrinated  blood  is  pumped  out,  the  whole  of  the 
carbon  dioxide  can  be  removed,  apparently  because  sub- 
stances of  an  acid  nature  pass  from  the  corpuscles  into 
the  liquid  part  of  the  blood  and  help  to  break  up  the 
carbonates. 

In  the  red  corpuscles  a  portion  of  the  carbon  dioxide  may 
be  in  combination  with  alkalies.  We  know  that  the  cor- 
puscles contain  alkalies,  for  the  alkalinity  of  '  laked  '  blood 
(pp.  34,  35),  in  which  the  red  corpuscles  have  been  broken 
up,  is  found  to  be  greater  than  that  of  unlaked  blood,  unless 
a  long  time  is  allowed  in  the  case  of  the  latter  for  the 
alkalies  of  the  corpuscles  to  reach  the  acid  used  in  titration 
(Loewy).  Some  observers  believe  that  a  weak  compound 
of  carbon  dioxide  can  be  formed  with  haemoglobin ;  for 


RESPIRATION  239 

a  solution  of  haemoglobin  absorbs  more  of  this  gas  than 
water,  and  the  quantity  absorbed  is  not  proportional  to  the 
pressure.  The  haemoglobin  of  the  corpuscles  may  therefore 
hold  a  portion  of  the  carbon  dioxide  in  combination  (Bohr). 
This  cannot,  however,  be  considered  as  settled. 

When  blood  is  saturated  with  carbon  dioxide  and  then 
separated  into  serum  and  clot,  the  serum  is  found  to  yield 
more  gas  than  the  clot ;  but  if  the  serum  and  clot  are 
separately  saturated,  the  latter  takes  up  more  carbon  dioxide 
than  the  former.  From  this  it  is  argued  that  a  substance 
combined  with  carbon  dioxide  must  in  blood  saturated  with 
the  gas  pass  out  of  the  corpuscles  into  the  serum.  This 
cannot  be  haemoglobin,  for  it  remains  in  the  corpuscles,  but 
it  may  very  well  be  an  alkali,  combined  with  the  carbon 
dioxide,  and  thus  set  free  from  its  connection  with  the 
haemoglobin.  And,  as  a  matter  of  fact,  under  the  circum- 
stances described,  it  has  been  found  that  alkalies,  and, 
perhaps,  certain  food-substances  (proteid,  fat,  and  sugar) 
do  pass  from  the  clot  into  the  serum  (Zuntz,  Hamburger), 
and  chlorine  from  the  serum  into  the  corpuscles  (Lehmann), 
which  at  the  same  time  gain  water  and  become  larger.  On 
the  other  hand,  when  blood  is  saturated  with  oxygen, 
alkalies  and  possibly  the  food-substances  mentioned  pass 
out  of  the  serum  into  the  corpuscles,  which  at  the  same 
time  lose  water  and  shrink  in  volume.  Hamburger  has 
extended  these  observations  to  living  blood,  and  has  shown 
that  the  plasma  of  venous  blood  has  more  alkali,  proteid, 
sugar  and  fat  than  the  plasma  of  arterial  blood,  and  that 
the  corpuscles  have  a  greater  volume,  though  not  a  greater 
diameter.  In  the  pulmonary  capillaries,  according  to  him, 
food-substances  go  over,  under  the  influence  of  oxygen, 
from  the  plasma  to  the  corpuscles.  In  the  systemic 
capillaries  the  blood  becomes  loaded  with  carbon  dioxide, 
and  therefore  the  corpuscles  give  up  proteids,  etc.,  to  the 
plasma,  which  accordingly  has  a  greater  supply  of  food- 
substances  to  offer  to  the  tissues  than  the  plasma  of  arterial 
blood  itself.  In  both  cases  he  sees  in  this  interchange  an 
arrangement  by  which  oxidation  is  favoured.  Whatever 
may  be  thought  of  this  view — and  it  is  a  serious  objection 


240  A  MANUAL  OF  PHYSIOLOGY 

to  it  that  the  amount  of  oxidation  which  can  be  supposed  to 
take  place  in  the  red  corpuscles  is  small — the  current  theory, 
that  the  corpuscles  are  simply  passive  carriers  of  oxygen, 
and  exercise  no  further  influence  on  the  plasma,  breaks 
down  in  face  of  the  facts.  We  must  admit  that  an  active 
and  many-sided  commerce  exists  between  them  and  the 
liquid  in  which  they  float. 

The  nitrogen  of  the  blood  is  simply  absorbed. 

The  Tension  of  the  Blood-gases. — If  the  gases  of  the  blood  existed 
in  simple  solution,  their  tension  or  partial  pressure  could  be  deduced 
from  the  amount  dissolved  and  the  co-efficient  of  absorption.  Since 
they  are  chemically  combined,  it  is  necessary  to  determine  it  directly. 
This  has  been  done  by  means  of  an  apparatus  called  the  aerotono- 
meter  (Pfliiger,  Strassburg).  The  blood  is  made  to  pass  directly  from 
the  vessel  to  two  tubes,  which  it  traverses  at  the  same  time,  the 
stream  being  divided  between  them ;  it  then  passes  out  again.  The 
tubes  are  warmed  by  means  of  a  water-jacket  to  the  body-temperature. 
One  of  them  is  filled  with  a  gaseous  mixture  having  a  greater,  and 
the  other  with  a  mixture  having  a  smaller,  partial  pressure,  say  of 
carbon  dioxide,  than  is  expected  to  be  found  in  the  blood.  As  the 
latter  runs  in  a  thin  sheet  over  the  walls  of  the  tubes,  it  loses  carbon 
dioxide  to  the  one  and  takes  up  carbon  dioxide  from  the  other. 
From  the  alteration  in  the  proportion  of  the  carbon  dioxide  in  the 
two  tubes,  it  is  easy  to  calculate  the  partial  pressure  of  that  gas  in 
the  blood  ;  that  is,  the  partial  pressure  which  it  would  be  necessary 
to  have  in  the  tubes  in  order  that  the  blood  might  pass  through  them 
without  losing  or  gaining  carbon  dioxide  (p.  232). 

The  pressure  of  oxygen  in  arterial  blood  was  given  by 
Strassburg  as  about  30  mm.  of  mercury  in  the  dog,  and  in 
venous  blood  as  something  like  20  mm.  If  we  were  to 
accept  the  recent  experiments  of  Bohr,  made  by  means  of  a 
special  form  of  aerotonometer  constructed  and  worked  much 
in  the  same  way  as  Ludwig's  stromuhr  (p.  no),  and  inserted 
into  the  course  of  a  bloodvessel,  it  would  be  necessary  to 
treble  or  quadruple  these  numbers. 

The  pressure  of  carbon  dioxide  in  arterial  blood  we  may 
take  at  10  to  40  mm.,  in  venous  blood  at  30  to  50  mm., 
according  to  the  results  of  different  observers. 

Whenever  the  venous  blood  has  to  pass  through  a  region 
in  which  the  pressure  of  carbon  dioxide  is  kept  lower  than 
in  itself,  it  will  begin  to  lose  carbon  dioxide  by  diffusion. 
If  the  pressure  of  oxygen  in  this  region  is  at  the  same  time 


RESPIRATION  2*1 

higher  than  in  the  venous  blood,  some  of  it  will  be  taken  up. 
And  to  bring  about  these  results  no  peculiar  '  vital '  force 
need  be  invoked  ;  ordinary  physical  processes  will,  under  the 
assumed  conditions,  be  alone  required. 

Now,  we  know  that  in  the  lungs  carbon  dioxide  is  given 
off  from  the  blood,  and  oxygen  taken  up  by  it.  We  have, 
therefore,  to  inquire  what  the  partial  pressures  of  these 
gases  are  in  the  alveoli,  and  whether  they  are  so  related  to 
the  corresponding  partial  pressures  in  the  blood  that  a 
simple  process  of  dissociation  and  diffusion  will  be  sufficient 
to  explain  pulmonary  respiration. 

The  percentage  of  carbon  dioxide  in  expired  air  cannot 
tell  us  the  pressure  of  that  gas  in  the  alveoli,  for  the  air  in 
the  upper  part  of  the  respiratory  tract  is  necessarily  expelled 
along  with  the  alveolar  air.  But  it  gives  us  a  minimum  value, 
below  which  it  is  not  conceivable  that  the  alveolar  partial 
pressure  can  lie,  for  we  cannot  imagine  that  any  air  in  the 
respiratory  tract  can  be  richer  ki  carbon  dioxide  than  that  of 
the  alveoli.  Now,  Vierordt  found  with  the  deepest  possible 
expiration  a  little  over  5  per  cent,  of  carbon  dioxide  in  the 
expired  air.  From  this  it  seems  justifiable  to  conclude  that 
in  man  the  partial  pressure  of  carbon  dioxide  in  the  alveoli 
may  be  at  least  one-twentieth  of  an  atmosphere,  or  38  mm. 
of  mercury. 

In  animals,  samples  of  the  alveolar  air  have  been  drawn 
off  directly  (Wolffberg)  by  means  of  Pfltiger's  pulmonary 
catheter.  This  consists  of  two  tubes,  one  within  the  other. 
The  inner  tube,  which  is  a  fine  elastic  catheter,  projects 
free  from  the  other  for  a  little  distance  at  its  lower  end. 
The  outer  tube  terminates  in  an  indiarubber  ball,  which  can 
be  inflated  so  as  to  block  the  bronchus  into  which  it  is 
passed,  and  cut  off  the  corresponding  portion  of  the  lung 
from  communication  with  the  outer  air.  A  sample  of  the 
air  below  the  block  can  be  drawn  off  through  the  inner  tube. 
In  this  way  the  proportion  of  carbon  dioxide  in  the  alveoli  of 
the  dog  was  found  to  be  only  about  3*8  per  cent.,  corre- 
sponding to  a  partial  pressure  of  about  29  mm.  of  mercury. 
But  this  would  be  undoubtedly  too  high,  owing  to  the  im- 
possibility of  interchange  with  the  external  atmosphere,  and 

16 


242  A  MANUAL  OF  PHYSIOLOGY 

would  represent  the  partial  pressure  of  the  carbon  dioxide 
in  the  blood  rather  than  in  the  alveolar  air  under  normal 
conditions.  For  gaseous  equilibrium  is  soon  established 
between  blood  and  air  separated  only  by  a  thin  membrane 
like  the  alveolar  wall. 

In  Bohr's  experiments,  in  some  of  which  the  animals 
were  made  to  breathe  air  containing  carbon  dioxide  in 
various  proportions,  the  tension  of  that  gas  in  the  air  of 
the  lungs  varied  from  5'8  to  34*6  mm.  of  mercury,  while  in 
arterial  blood,  taken  at  the  same  time,  it  usually  ranged 
from  10  to  38  mm.,  and  was  often  less  than  in  the  alveolar  air. 

If  we  accept  these  results,  we  seem  shut  up  to  the  con- 
clusion that  carbon  dioxide  does  not  pass  through  the  walls 
of  the  alveoli  solely  by  diffusion.  And  although  Bohr's 
experiments  have  been  severely  criticised,  it  does  not  seem 
improbable  in  itself  that  the  physical  process  of  diffusion  is 
aided  by  some  other  process,  which  may  provisionally  be 
termed  secretion.  It  is  possible,  too,  that  when  the  con- 
ditions are  especially  unfavourable  to  diffusion — when,  for 
instance,  the  partial  pressure  of  carbon  dioxide  is  artificially 
increased  in  the  alveoli — the  cells  which  line  them  are 
stimulated  to  increased  activity. 

As  to  the  oxygen,  we  are  in  the  same  position.  Its  partial 
pressure  does  not  appear  to  be  always  higher,  even  under 
normal  conditions,  in  the  alveoli  than  in  the  arterial  blood 
as  it  leaves  the  lungs.  Indeed,  Bohr  found  that,  in  the 
majority  of  his  observations  on  dogs,  the  oxygen  tension 
was  distinctly  greater  in  the  blood  than  in  the  pulmonary 
air.  And  Haldane  and  Smith,  using  a  new  method,  have 
obtained  a  value  for  the  oxygen  tension  in  human  blood 
(26*2  per  cent.,  equal  to  200  mm.  of  mercury)  that  even 
exceeds  the  partial  pressure  of  oxygen  in  the  external  air, 
and  is  about  twice  as  great  as  that  of  the  air  of  the  alveoli. 
This  extraordinary  result  cannot  be  reconciled  with  any 
purely  physical  explanation  of  the  absorption  of  oxygen,  and 
would  settle  the  question,  if  the  accuracy  of  the  method 
could  be  relied  on. 

Additional  evidence  in  favour  of  the  view  that  there  is, 
besides  diffusion,  an  element  of  selective  secretion  in  the 


RESPIRATION 


243 


interchange  of  gases  through  the  pulmonary  membrane  is 
afforded  by  a  study  of  the  gases  of  the  swim-bladder  in 
fishes.  These  consist  of  oxygen,  nitrogen,  and  usually  a 
small  quantity  of  carbon  dioxide,  but  in  very  different  pro- 
portions from  those  in  which  they  exist  in  the  air  or  the 
water.  Thus,  Biot  found  as  much  as  87  per  cent,  of  oxygen 
in  the  bladder  of  fishes  taken  at  a  considerable  depth,  but  a 
smaller  amount  in  those  captured  near  the  surface.  Moreau 
observed  that  when  the  gas  is  withdrawn  by  puncturing 
the  bladder  with  a  trocar,  the  organ  rapidly  refills,  and  the 
percentage  of  oxygen  increases.  Further,  this  process  of 
gaseous  secretion  is  under  the  influence  of  nerves,  for  gas 
ceases  to  accumulate  in  the  organ  when  the  branches  of  the 
vagi  that  supply  it  are  cut  (Bohr\ 

We  have  now  completed  the  description  of  the  pheno- 
mena of  external  respiration,  with  the  discussion  of  its 
central  fact,  the  exchange  of  gases  between  the  blood  and 
the  air  at  the  surface  of  the  lungs.  It  remains  to  trace  the 
fate  of  the  absorbed  oxygen,  and  to  determine  how  and 
where  the  carbon  dioxide  arises. 

Internal  Respiration — Seats  of  Oxidation. — The  suggestion 
which  lies  nearest  at  hand,  and  which,  as  a  matter  of  fact, 
was  first  put  forward,  is  that  the  oxygen  does  not  leave  the 
blood  at  all,  but  that  it  meets  with  oxidizable  substances  in 
it,  and  unites  with  their  carbon  to  form  carbon  dioxide. 
While  there  is  a  certain  amount  of  truth  in  this  view, 
oxygen,  as  already  mentioned,  being  to  some  extent  taken 
up  by  freshly-shed  blood,  and  also  by  blood  under  other 
conditions,  to  oxidize  bodies,  other  than  haemoglobin,  either 
naturally  contained  in  it  or  artificially  added,  there  is  no 
doubt  that  the  cells  of  the  body  are  the  busiest  seats  of 
oxidation.  This  is  shown  by  the  presence  of  carbon  dioxide 
in  large  amount  in  lymph  and  other  liquids  which  are,  or 
have  been,  in  intimate  relation  with  tissue  elements  ;  by  its 
presence,  also  in  considerable  amount,  in  the  tissues  them- 
selves—  in  muscle,  for  instance;  by  its  continued  and 
scarcely  lessened  production  not  only  in  a  frog  whose  blood 
has  been  replaced  by  normal  saline  solution,  and  which 
continues  to  live  in  an  atmosphere  of  pure  oxygen,  but  in 

1 6 — 2 


244  A  MANUAL  OF  PHYSIOLOGY 

excised  muscles ;  and  by  the  remarkable  connection  between 
the  amount  of  this  production  and  the  functional  state  of 
those  tissues.  In  insects  the  finest  twigs  of  the  tracheae, 
through  which  oxygen  passes  to  the  tissues,  actually  end  in 
the  cells  ;  and  in  luminous  insects,  like  the  glowworm,  it  has 
been  noticed  that  the  phosphorescence,  which  is  certainly 
dependent  on  oxidation,  begins  and  is  most  brilliant  in  those 
parts  of  the  cells  of  the  light-producing  organ  that  surround 
the  ends  of  the  tracheae. 

Lymph,  bile,  urine,  and  the  serous  fluids  contain  very 
little  oxygen,  but  so  much  carbon  dioxide  that  the  pressure 
of  that  gas  in  all  of  them  is  greater  than  in  arterial  blood, 
while  in  lymph  alone  (taken  from  the  large  thoracic  duct) 
has  it  been  found  less  than  that  of  venous  blood.  And  it  is 
extremely  probable  that  lymph  gathered  nearer  the  primary 
seats  of  its  production  (the  spaces  of  areolar  tissue)  would 
show  a  higher  proportion  of  carbon  dioxide. 

Strassburg  found  that  with  a  pressure  of  carbon  dioxide  in 
the  arterial  blood  of  21  mm.  of  mercury,  the  pressure  in  bile 
was  50  mm.,  in  peritoneal  fluid  58  mm.,  in  urine  68  mm.,  in 
the  surface  of  the  empty  intestine  58  mm.  Saliva,  pan- 
creatic juice,  and  milk,  also  contain  much  carbon  dioxide, 
and  only  a  little,  if  any,  oxygen. 

From  muscle  (to  facilitate  pumping,  the  muscle  is  minced, 
and  often  warmed)  no  free  oxygen  at  all  can  be  pumped  out, 
but  as  much  as  15  volumes  per  100  of  carbon  dioxide,  some 
of  which  is  free,  that  is,  is  given  up  to  the  vacuum  alone, 
while  some  of  it  is  fixed,  and  only  comes  off  after  the  addi- 
tion of  an  acid,  such  as  phosphoric  acid.  If  the  muscle  be 
left  long  in  the  pump,  putrefaction  begins  to  appear,  and 
this  causes  a  discharge  of  carbon  dioxide,  which  may  last 
indefinitely. 

Muscle  may  be  safely  taken  as  a  type  of  the  other  tissues 
in  regard  to  the  problems  of  internal  respiration.  It  is 
instructive,  therefore,  to  observe  that  the  great  scarcity  of 
oxygen  in  the  parenchymatous  liquids  which  bathe  the  tissues, 
here  in  the  tissues  themselves  deepens  into  actual  famine. 
The  inference  is  plain.  The  active  tissues  are  greedy  of 
oxygen ;  as  soon  as  it  enters  the  muscle  it  is  seized  and 


RESPIRATION  245 

*  fixed  '  in  some  way  or  other.  The  traces  of  oxygen  in  the 
lymph  cannot  therefore  be  journeying  away  from  the  tissue 
elements ;  they  must  have  come  from  another  source,  and 
this  can  only  be  the  blood.  Could  we  gather  lymph  for 
analysis  directly  from  the  thin  sheets  that  lie  between  the 
blood  capillaries  and  the  tissues,  we  might  find  more  oxygen 
present  as  well  as  more  carbon  dioxide.  But  if  we  did  find 
more  oxygen,  it  would  still  be  oxygen  in  transit  from  the 
capillaries  towards  places  where  the  partial  pressure  of 
oxygen  is  less.  In  the  lymph,  the  pressure  is  kept  low  by 
the  avidity  of  the  tissues  with  which  it  is  in  contact,  and 
possibly  by  the  existence  in  it  of  oxidizable  substances  which 
have  come  from  the  tissues.  In  the  tissues  there  is  no 
partial  pressure  at  all,  because  the  oxygen  that  reaches 
them  is  at  once  stowed  away  in  some  compound,  in  which 
it  has  lost  the  properties  of  free  oxygen. 

Assuming,  then,  that  at  least  a  great  part  of  the  oxidation 
and  consequent  production  of  carbon  dioxide  goes  on  in  the 
tissues,  we  have  yet  to  follow  the  steps  of  the  process,  as  far 
as  we  can,  in  the  light  of  our  knowledge  of  the  respiration  of 
muscle. 

Respiration  of  Muscle. — Three  methods  have  been  used  to 
determine  the  respiratory  changes  going  on  in  resting  muscle, 
or  to  compare  them  with  those  in  the  excited  state : 

(1)  The  excised  muscles  of  cold-blooded  animals  are  exposed  for 
a  considerable  time  to  an  atmosphere  of  known  composition  in  a 
small  chamber ;  and  the  changes  in  this  atmosphere  are  then  deter- 
mined (G.  Liebig,  Matteucci,  Hermann). 

(2)  Samples  of  the  blood  coming  to  and  leaving  a  muscle  of  a 
warm-blooded  animal  may  be  taken  in  its  natural  position,  and  the 
gases  analyzed  and  compared  (Ludwig,  Chauveau  and  Kaufmann). 

(3)  Artificial  circulation  may  be  kept  up  through  a  muscle  or 
group  of  muscles  ;  for  example,  through  one  or  both  hind-limbs  of  a 
dog.     In  the  newest  forms  of  apparatus  for  artificial  circulation  the 
blood  is  oxygenated  in  a  special  chamber  from  a  graduated  cylinder 
containing  oxygen,  and  the  carbon  dioxide  collected  in  baryta  or 
caustic   potash  valves.     The  oxygen  consumption  can  be  read  off 
from  the  cylinder,  and  the  production  of  carbon  dioxide  estimated 
by  titrating  from  time  to  time  samples  of  the  baryta  water  or  potash 
(v.  Frey  and  Gruber,  and  Jacobi).     (Fig.  85.) 

By  the  first  of  these  methods  a  very  remarkable  fact, 
among  others,  has  been  brought  to  light.  It  has  been 


246 


A  MANUAL  OF  PHYSIOLOGY 


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RESPIRATION  247 

found  that  a  frog's  muscle  is  capable  of  going  on  producing 
carbon  dioxide,  and  that  at  an  undiminished  rate,  in  the 
entire  absence  of  oxygen,  when  the  chamber,  for  instance, 
is  filled  with  nitrogen  or  other  indifferent  gas.  Not  only  so, 
but  it  can  be  made  to  contract  many  times  and  to  perform 
a  comparatively  large  amount  of  work  in  this  oxygen-free 
atmosphere,  and  to  produce  a  correspondingly  large  quantity 
of  carbon  dioxide.  In  mammals  the  muscles  can  also  be( 
made  to  contract  repeatedly  when  the  dissociable  oxygen 
has,  as  far  as  possible,  been  got  rid  of  from  the  blood  by 
asphyxiating  the  animal,  although  they  lose  their  con- 
tractility much  more  rapidly  than  the  muscles  of  the  frog. 
This  leads  us  to  the  very  important  conclusion  that  the 
carbon  dioxide  does  not  arise,  so  to  speak,  on  the  spot,  from 
the  immediate  union  of  carbon  and  oxygen.  Oxygen  is 
essential  to  muscular  life  and  action.  But  a  stock  of  it  is 
apparently  taken  up  by  the  muscle,  and  stored  in  some 
compound  or  compounds  which  are  broken  down  during 
muscular  contraction,  and  more  slowly  during  rest,  carbon 
dioxide  in  both  cases  being  one  of  the  end  products.  It  is 
very  possible  that  there  may  be  an  ascending  series  of 
bodies  through  which  oxygen  passes  up,  and  a  descending 
series  through  which  it  passes  down,  before  the  final  stage  is 
reached. 

When  muscle  goes  into  rigor  (p.  565) — and  this  is  most 
strikingly  seen  when  the  rigor  is  caused  by  raising  the 
temperature  of  frog's  muscle  to  about  40°  or  41°  C. — there 
is  a  sudden  increase  in  the  quantity  of  carbon  dioxide  given 
off.  Moreover,  in  an  isolated  muscle  the  total  quantity  of 
carbon  dioxide  obtainable  during  rigor  is  less  if  the  muscle 
has  been  previously  tetanized,  and  less,  it  is  said,  by  just 
the  amount  given  out  during  the  contractions  (Hermann). 
From  this  it  has  been  argued  that  the  hypothetical  substance 
(inogen),  the  decomposition  of  which  yields  carbon  dioxide 
in  contraction,  is  also  the  substance  which  decomposes  so 
rapidly  in  rigor  ;  that  a  given  amount  of  it  exists  in  the 
muscle  at  the  time  it  is  removed  from  the  influence  of  the 
blood ;  and  that  this  can  all  explode  either  in  contraction 
or  in  rigor,  or  partly  in  the  one  and  partly  in  the  other. 


o. 


243  A  MANUAL  OF  PHYSIOLOGY 

Many  of  the  older  experiments  made  by  method  (2)  are 
too  inexact  to  yield  more  than  qualitative  results,  and  the 
same  is  true  of  some  of  the  researches  with  the  more  primi- 
tive and  imperfect  methods  of  artificial  circulation.  The 
mere  difference  of  colour  between  the  venous"  and  arterial 
blood  of  a  muscle,  or  other  active  organ,  is  sufficient  to 
show  that  oxygen  is  taken  up  and  carbon  dioxide  given  put 
by  it  to  the  blood.  This  is  the  case  in  muscles  at  rest, 
and  even  in  muscles  with  artificial  circulation  after  they  have 
become  inexcitable. 

In  active  muscles  more  oxygen  is  used  up  and  more 
carbon  dioxide  produced  than  in  the  resting  state.  Chauveau 
and  Kaufmann,  in  their  experiments  on  one  of  the  muscles 
used  by  the  horse  in  feeding,  found  that  the  consumption  of 
oxygen  and  the  production  of  carbon  dioxide  might  be  three 
times  as  great  in  activity  as  in  rest. 

In  the  submaxillary  salivary  gland  there  was  also  an 
increase  of  carbon  dioxide  during  activity,  but  not  propor- 
tionally so  great  as  in  muscle.  In  the  active  brain  it  is  not 
easy  to  demonstrate  any  increase  at  all  (Hill). 

For  excised  mammalian  muscles  (hind-limbs  of  dog),  as 
has  been  said,  the  respiratory  quotient  increases  when  the 
temperature  is  reduced.  As  the  temperature  is  raised,  the 
opposite  effect  is  observed.  Stimulation  of  the  muscle  causes 
a  rise  in  both  oxygen  consumption  and  carbon  dioxide  pro- 
duction, but  proportionally  more  in  the  former,  and  the 
respiratory  quotient  diminishes.  When  the  excised  muscle 
begins  to  deteriorate  in  the  course  of.  some  hours,  the  con- 
sumption of  oxygen  falls  off  more  quickly  than  the  produc- 
tion of  carbon  dioxide. 

All  this  goes  to  show  that  the  two  processes  are  to  a  great 
extent  independent  of  each  other.  At  the  higher  tempera- 
tures, during  muscular  contraction,  and  when  the  vitality  of 
the  muscle  is  still  but  little  impaired,  the  conditions  are 
relatively  favourable  to  the  chemical  changes  in  which 
oxygen  is  combined.  Low  temperature,  rest,  and  diminished 
vitality,  are  relatively  favourable  to  the  splitting  up  of  sub- 
stances that  yield  carbon  dioxide.  But  it  must  be  remem- 


RESPIRATION  249 

bered  that  in  the  intact  organism  the  conditions  are  different 
(p.  225). 

The  Influence  of  Respiration  on  the  Blood-pressure. — We  have 
already  stated,  in  treating  of  arterial  blood-pressure  (p.  103), 
that  a  normal  tracing  shows  a  series  of  waves  corresponding 
with  the  respiratory  movements. 

When  the  respiratory  movements  are  recorded  simul- 
taneously with,  and  immediately  below  the  pressure  curve,  it 
is  seen  that  although  the  mean  blood-pressure  is  falling  for  a 
short  time  at  the  beginning  of  inspiration,  it  soon  reaches 
its  minimum,  then  begins  to  rise,  and  continues  rising  during 
the  rest  of  this  period.  At  the  commencement  of  expiration 
it  is  still  mounting,  but  soon  reaches  its  maximum,  begins 
to  fall,  and  continues  falling 
through  the  remainder  of 
the  expiratory  phase. 

The  explanations  given 
of  this  phenomenon  are 
many,  but  » they  may  all 
be  grouped  into  two  divi- 
sions, in  which  nervous  and  FlG-  86- 

mechanical     influences      are  The  uPPer  tracinS  shows  the  respiratory 

'  movements  in  a  rabbit ;  the  lower  tracing  is 

respectivelv  invoked  as  the  the  blood-pressure  curve ;  I,  inspiration  ;  E, 

.  expiration,  including  the  pause. 

chief  cause. 

Theory  of  Nervous  Influences. — Everybody  admits  that  in 
certain  animals  (the  dog,  for  instance),  and  very  often,  if  not 
constantly,  in  man,  the  rate  of  the  heart  is  greater  during 
inspiration,  especially  towards  its  end,  than  in  expiration. 
This  is  due  to  nervous  influence,  to  a  rhythmical  rise  and 
fall  in  the  activity  of  the  cardio-mhibitory  centre,  synchronous 
with  the  respiratory  movements,  for  the  difference  disappears 
after  division  of  both  vagi.  Now,  it  might  be  said  that  the 
rise  of  blood-pressure  during  the  latter  part  of  inspiration  is 
simply  caused  by  the  increased  rate  of  the  heart,  which,  as 
we  know,  can  raise  the  blood-pressure.  Nevertheless,  this  is 
not  the  explanation,  for  the  respiratory  oscillations  persist 
after  section  of  the  vagi,  and  they  are  seen  in  animals  like 
the  rabbit,  in  which  little  or  no  variation  in  the  rate  of  the 
heart  is  connected  with  the  phases  of  respiration. 


250  A  MANUAL  OF  PHYSIOLOGY 

Quite  a  number  of  observers  have  supposed  that  rhyth- 
mical discharges  from  the  vaso  -  motor  centre,  either 
automatic  or  due  to  stimulation  of  the  centre  by  the  venous 
blood,  and  causing  a  periodic  increase  and  diminution  in  the 
peripheral  resistance,  are  responsible  for  the  respiratory 
oscillations.  Such  rhythmical  variations  in  the  blood- 
pressure  (Traube-Hering  curves)  may,  under  certain  condi- 
tions, appear  in  the  absence  of  respiratory  movements,  e.g., 
when  in  a  curarized  animal  the  artificial  respiration  is 
stopped.  But  this  is  hardly  an  argument  in  favour  of  the 
central  origin  of  the  normal  respiratory  waves,  since  the 
Traube-Hering  curves  have  a  much  longer  period.  This  is 
well  seen  when,  as  sometimes  happens,  Traube-Hering 
oscillations  appear  while  respiration  is  still  going  on.  Their 
long  sweeping  curves  then  show  the  ordinary  respiratory 
waves  superposed  on  them. 

Mechanical  Theory. — A  more  satisfactory  explanation  is 
afforded  by  a  consideration  of  the  mechanical  changes  pro- 
duced in  the  thorax  by  the  respiratory  movements.  Of 
these  two  are  of  special  importance :  (i)  the  changes  of 
intra-thoracic  pressure,  (2)  the  changes  of  vascular  resist- 
ance in  the  lungs. 

The  intra-thoracic  pressure,  which,  as  we  have  seen,  is 
always  less  than  that  of  the  atmosphere,  unless  during  a 
forced  expiration  when  the  free  escape  of  air  from  the  lungs 
is  obstructed,  diminishes  in  inspiration  and  increases  in 
expiration.  The  great  veins  outside  the  chest,  the  jugular 
veins  in  the  neck,  for  example,  are  under  the  atmospheric 
pressure,  which  is  readily  transmitted  through  their  thin 
walls,  while  the  heart  and  thoracic  veins  are  under  a  smaller 
pressure.  The  venous  blood  both  in  inspiration  and  ex- 
piration will,  therefore,  tend  to  be  drawn  into  the  right 
auricle.  In  inspiration  the  venous  flow  will  be  increased, 
since  the  pressure  in  the  thorax  is  diminished  ;  and  upon 
the  whole  more  venous  blood  will  pass  into  the  right  heart 
during  inspiration  than  during  expiration.  But  all  the  blood 
which  reaches  the  right  heart  during  an  inspiration  is  at 
once  sent  into  the  lungs,  although  not  even  the  first  of  it 
can  have  passed  through  to  the  left  side  of  the  heart  at  the 


RESPIRATION  251 

.  /^Y 
end  of  the  inspiration,  since  the  pulmonary  circulation-time 

(four  to  five  seconds  in  a  small  dog,  two  to  three  seconds 
in  a  rabbit)  is  longer  than  the  time  of  a  complete  inspira- 
tion at  any  ordinary  rate.  The  increase  in  the  quantity  of 
blood  pumped  into  the  pulmonary  artery  will,  if  not  counter- 
acted by  other  circumstances,  tend  to  raise  the  blood- 
pressure  in  the  artery  and  its  branches,  and  therefore  at 
once  to  accelerate  the  outflow  through  the  pulmonary  vein. 
This  will  be  greatly  aided  if  at  the  same  time  the  vascular 
resistance  in  the  lungs  is  reduced,  as  there  seems  good  reason 
for  believing  is  the  case. 

The  increased  blood-flow  into  the  left  ventricle  will  of 
course  correspond  to  better  filling  of  the  systemic  arteries ; 
that  is,  to  a  rise  of  arterial  blood-pressure. 

In  expiration  the  contrary  will  happen.  The  return  of 
blood  to  the  thorax  will  be  checked.  This  is  well  shown  by 
the  swelling  of  the  veins  at  the  root  of  the  neck  in  expiration, 
their  shrinking  in  inspiration,  the  so-called  pulsus  venosus. 
Less  blood  being  drawn  into  the  right  heart,  less  will  be 
pumped  into  the  pulmonary  artery,  in  which  the  pressure 
will,  of  course,  fall.  The  outflow  into  the  left  auricle  will 
thus  be  diminished — all  the  more  as  in  the  expiratory  phase 
the  vascular  resistance  in  the  lungs  is  increased — and  the 
systemic  arterial  pressure  will  be  lowered.  Now,  this  is 
just  what  is  seen  on  the  blood-pressure  curve,  except  that 
in  both  cases  the  change  is  somewhat  belated,  and  does  not 
coincide  exactly  with  the  commencement  of  the  inspiration 
or  the  expiration.  But  this  delay  may  be  explained  on 
several  grounds.  First,  we  cannot  expect  the  curve  of 
pressure  to  alter  its  course  quite  suddenly,  at  the  very 
moment  when  the  respiration  changes  its  phase ;  for  the 
change  in  the  blood-flow  through  the  lungs  must  require 
time  to  establish  itself,  in  the  face  of  the  opposite  tendency 
to  which  it  succeeds.  The  same  is  true  of  the  systemic 
arteries,  in  which  at  the  end  of  expiration  the  movements  of 
the  blood  associated  with  the  falling  pressure  are  going  on. 
It  is  impossible  that  these  movements  can  be  checked  at 
once ;  inertia  must  carry  them  on  into  inspiration. 

The   negative  pressure  of  the   thorax   acts   also  on   the 


252  A  MANUAL  OF  PHYSIOLOGY 

aorta,  although,  on  account  of  the  greater  thickness  of  its 
walls,  to  a  much  smaller  extent  than  on  the  thoracic  veins. 
The  diminution  of  pressure  in  inspiration  tends  to  expand 
the  thoracic  aorta,  and  to  draw  blood  back  out  of  the 
systemic  arteries,  while  expiration  has  the  opposite  effect. 
And  although  the  hindrance  caused  in  this  way  to  the 
flow  of  blood  into  the  arteries  during  inspiration,  and  the 
acceleration  of  the  flow  during  expiration,  cannot  be  great, 
the  tendency  will  be  to  diminish  the  pressure  in  the  one 
phase  and  increase  it  in  the  other.  As  soon  as  the  changes 
of  pressure  produced  by  alterations  in  the  flow  of  venous 
blood  into  the  chest  and  through  the  lungs  are  thoroughly 
established,  the  slight  arterial  effect  will  be  overborne ;  but 
before  this  happens,  that  is,  at  the  beginning  of  inspiration 
and  expiration,  it  will  be  in  evidence,  and  will  help  to  delay 
the  main  change. 

Another  factor  in  this  delay  may  be  found  in  the  changes 
of  vascular  resistance  and  capacity  which  take  place  in  the 
lungs  when  they  pass  from  the  expanded  to  the  collapsed 
condition. 

According  to  the  most  careful  of  recent  observations,  the 
expansion  of  the  lungs  in  natural  respiration  causes  a 
widening  of  the  pulmonary  capillaries,  with  a  con-sequent 
increase  of  their  capacity  and  diminution  of  their  resistance 
(De  Jager).  This  is  supported  by  experiments  on  the 
rabbit,  in  which  the  vessels  at  the  base  of  the  heart  were 
ligatured  either  at  the  height  of  inspiration  or  the  end  of 
expiration,  so  as  to  obtain  the  whole  of  the  blood  in  the 
lungs.  It  was  found  that  the  lungs  invariably  contained 
more  blood  in  inspiration  than  in  expiration  (Heger  and 
Spehl). 

During  inspiration,  as  we  have  seen,  the  right  ventricle 
is  sending  an  increased  supply  of  blood  into  the  pulmonary 
artery ;  but  before  any  increase  in  the  outflow  through  the 
pulmonary  veins  can  take  place,  the  vessels  of  the  lung  must 
be  filled  to  their  new  capacity.  The  first  effect,  then,  of  the 
lessened  vascular  resistance  of  the  lungs  m  inspiration  is  a 
temporary  falling  off  in  the  outflow  through  the  aorta,  and 
therefore  a  temporary  fall  of  arterial  pressure.  As  soon  as 


RESPIRATION  253 

a  more  copious  stream  begins  to  flow  through  the  lungs, 
this  is  succeeded  by  a  rise. 

In  like  manner  the  first  effect  of  expiration,  which 
increases  the  resistance  and  diminishes  the  capacity  of  the 
pulmonary  vessels,  is  to  force  out  of  the  lungs  into  the  left 
auricle  the  blood  for  which  there  is  no  room.  This  causes 
a  temporary  rise  of  arterial  blood-pressure,  succeeded  by  a 
fall  as  soon  as  the  lessened  blood-flow  through  the  lungs  is 
established. 

In  artificial  respiration  oscillations  of  blood -pressure, 
synchronous  with  the  movements  of  the  lungs,  are  also 
seen,  even  when  the  thorax  is  opened.  In  the  latter  case 


FIG.  87.— EFFECT  ON  BLOOD-PRESSURE  OF  INFLATION  OF  THE  LUNGS 

(RABBIT). 

Artificial  respiration  stopped  in  inflation  at  i.  Interval  between  2  and  3  (not  repro- 
duced) 51  seconds,  during  which  the  curve  was  almost  a  straight  line.  Time-tracing 
shows  seconds. 

there  are,  of  course,  no  variations  of  intra-thoracic  pressure, 
and  the  oscillations  must  be  connected  with  the  changes  in 
the  pulmonary  circulation.  The  respiratory  waves  differ  in 
certain  respects  from  those  in  natural  breathing,  as  might 
be  expected  from  the  very  different  mechanical  conditions. 
During  inspiration  (inflation)  there  is  first  a  small  rise  and 
then  a  large  fall  of  pressure.  In  expiration  (collapse)  there 
is  first  a  slight  fall  and  then  a  great  rise. 

The  meaning  of  this  is  clearly  seen  when  artificial  respira- 
tion is  stopped  at  the  height  of  inflation  (Fig.  87).  The 
arterial  blood-pressure  then  falls  rapidly,  and  continues  low 
until  the  stock  of  oxygen  is  exhausted  and  the  rise  of 


254  A  MANUAL  OF  PHYSIOLOGY 

asphyxia  begins.  When  the  respiration  is  stopped  in 
collapse,  instead  of  a  fall  a  steady  rise  of  pressure  occurs 
(as  in  Fig.  56,  p.  163).  This  ultimately  merges  in  the 
elevation  due  to  asphyxia,  which  shows  itself  sooner  than 
in  inflation,  since  the  lungs  contain  less  air.  The  difference 
in  the  course  of  the  blood -pressure  curve  in  the  two  cases 
immediately  after  stoppage  of  respiration  cannot,  however, 
depend  on  this  latter  circumstance.  It  is  undoubtedly  due 
to  the  fact  that  in  artificial  inflation  the  vascular  capacity 
*  rCc4°^  *^e  lungs  is  less  and  the  resistance  greater  than  in 
-I collapse.  When  the  tracheal  cannula  is  closed  in  natural 
respiration,  no  initial  fall  of  pressure  takes  place  (Fig.  88). 
To  sum  up  the  causes  of  the  respiratory  oscillations  in  the 


FIG.  88.— BLOOD-PRESSURE  TRACING  (RABBIT,  UNDER  CHLORAL). 

Natural  respiration  stopped  at  I  in  inspiration,  at  E  in  expiration.  The  mean  blood- 
pressure  is  scarcely  altered ;  but  the  respiratory  waves  become  much  larger  owing  to 
the  abortive  efforts  at  breathing.  Time-tracing  shows  seconds. 

arterial  blood-pressure  :  The  changes  of  intra-thoracic  pressure 
and  of  the  vascular  resistance  in  the  lungs  seem  the  most  important 
factors,  but  nervous  influences  may  also  play  a  subordinate  part. 

The  respiratory  oscillations  in  the  veins,  as  might  be 
expected,  run  precisely  in  the  opposite  direction  to  those  in 
the  arteries,  and  so  do  the  Traube-Hering  curves.  The 
increased  flow  from  the  veins  to  the  thorax  during  inspira- 
tion lowers  the  pressure  in  the  jugular  vein,  while  it 
increases  the  pressure  in  the  carotid.  The  constriction  of 
the  small  bloodvessels  to  which  the  Traube-Hering  curves 
are  due  increases  the  blood-pressure  in  the  arteries,  because 
it  increases  the  peripheral  resistance  to  the  blood-flow ;  in 
the  veins  it  lowers  the  pressure,  because  less  blood  gets 
through  to  them.  Accordingly,  when  the  Traube-Hering 


RESPIRATION  255 

curve  is  ascending  in  the  carotid,  it  is  descending  in  the 
jugular. 

The  respiratory  variations  in  the  volume  of  the  brain, 
which  are  so  striking  a  phenomenon  when  a  trephine  hole  is 
made  in  the  skull,  have  by  some  been  attributed  to  inter- 
ference with  the  venous  outflow  from  the  cranial  cavity 
during  expiration,  and  by  others  to  those  changes  in  the 
arterial  pressure  whose  causes  we  have  just  been  discussing. 
The  question  turns  largely  upon  the  time-relations  of  the 
movements.  The  swelling  of  the  brain  is  usually  syn- 
chronous with  expiration,  and  the  shrinking  with  inspiration ; 
and  this  is  in  favour  of  the  first  view.  But  sometimes  the 
dura  mater  bulges  into  the  trephine  hole  in  inspiration  and 
sinks  down  in  expiration.  This  is  in  favour  of  the  second. 
The  truth  appears  to  be  that  both  factors  may  be  involved. 

The  effects  of  breathing  condensed  and  rarefied  air  are — (i) 
mechanical,  shown  chiefly  by  changes  in  the  circulation,  in 
the  blood-pressure,  for  instance  ;  (2)  chemical. 

The  mechanical  effects  differ  according  to  whether  the 
whole  body,  or  only  the  respiratory  tract,  is  exposed  to  the 
altered  pressure.  When  the  trachea  of  an  animal  is  con- 
nected with  a  chamber  in  which  the  pressure  can  be  raised 
or  lowered,  it  is  found  that  at  first  the  arterial  blood-pressure 
rises  as  the  pressure  of  the  air  of  respiration  is  increased 
above  that  of  the  atmosphere.  But  a  maximum  is  soon 
reached  ;  and  when  respiration  begins  to  be  impeded,  the 
pressure  falls  in  the  arteries  and  increases  in  the  veins. 

When  the  pressure  of  the  air  in  the  chamber  is  diminished 
a  little  below  that  of  the  atmosphere,  there  is  a  slight  sinking 
of  the  arterial  blood-pressure,  which  rises  if  the  air-pressure 
is  further  diminished  (Einbrodt). 

It  is  clear  that  any  change  of  the  air-pressure  which  tends 
to  diminish  the  intra-thoracic  pressure  will  favour  the 
venous  return  to  the  heart,  and  therefore,  if  the  exit  of 
blood  from  the  thorax  is  not  proportionally  impeded,  the 
filling  of  the  arteries.  An  increase  in  the  intra-alveolar 
pressure  must  tend  on  the  whole  to  increase,  and  a  diminu- 
tion in  it  to  lessen,  the  pressure  inside  the  thorax,  which 
always  remains  equal  to  the  intra-alveolar  pressure,  minus 


256 


A  MANUAL  OF  PHYSIOLOGY 


the  elastic  tension  of  the  lungs.  Breathing  compressed  air 
should,  therefore,  under  the  conditions  described,  be  upon 
the  whole  unfavourable  to  the  venous  return  to  the  heart 
and  to  the  filling  of  the  arteries,  and  the  arterial  pressure 
should  fall ;  while  breathing  rarefied  air  should  have  the 
opposite  effect.  But  a  very  great  diminution  of  the  intra- 
thoracic  pressure  is  not  necessarily  favourable  to  the  cir- 
culation. 

Certain  chest  diseases  have  been  treated  by  the  use  of  apparatus 
by  which  the  patient  is  made  to  breathe  either  compressed  or  rarefied 
air ;  or  to  inspire  air  at  one  pressure  and  to  expire  into  air  at  another 
pressure.  And  it  has,  upon  the  whole,  been  found,  in  agreement 
with  theory,  that  condensed  air  cannot  help  the  circulation  however 
it  is  applied,  but  always  hinders  it ;  while  rarefied  air  aids  the  cir- 
culation both  in  inspiration  and  in  expiration.  But  the  increased 

work  of  the  inspiratory 
muscles  may  counter- 
balance the  advantage. 

Valsalvas  experiment, 
which  is  performed  by 
closing  the  mouth  and 
nostrils  after  a  previous  in- 

FIG.    89.— PULSE-TRACING    IN   VALSALVA'S    spiration,  and  then  forcibly 
EXPERIMENT  (ROLLETT).  trying  to  expire,  is  an  imi- 

tation   of    breathing    into 

compressed  air.  The  intra-thoracic  pressure  is  raised,  it  may  be,  to 
considerably  more  than  that  of  the  atmosphere ;  the  venous  return 
to  the  heart  is  impeded,  and  may  be  stopped ;  and  the  pulse  curve 
is  altered  in  such  a  way  as  to  indicate  first  an  increase  and  then  a 
decrease  of  the  arterial  blood-pressure  (Fig.  89). 

Miillers  experiment,  which 
should  be  bracketed  with  Val- 
salva's,  consists  in  making,  after  a 
previous  expiration,  a  strong  in- 
spiratory effort  with  mouth  and 

nostrils  closed.     Here  the  intra- 

FIG,  90.— PULSE-TRACING  IN  MULLER'S  thoracic  pressure  is  greatly  dimin- 
EXPERIMENT  (ROLLETT).  ished,  more  blood  is  drawn  into 

the  chest,   and  upon  the  whole 

effects  opposite  to  those  of  Valsalva's  experiment  are  produced 
(Fig.  90).  Neither  experiment  is  quite  free  from  danger.  In  both 
the  dicrotism  of  the  pulse  becomes  more  marked. 

When  the  whole  body  is  subjected  to  the  changed 
pressure,  as  in  a  balloon  or  on  a  mountain,  in  a  diving-bell 
or  a  caisson  used  in  building  the  piers  of  a  bridge,  the 


RESPIRATION  257 

conditions  are  very  different.  For  the  blood-pressure,  the 
intra-thoracic  pressure,  and  the  intra-alveolar  pressure,  all 
fall  together  when  the  pressure  of  the  atmosphere  is 
diminished,  and  all  rise  together  when  it  is  increased.  It  is 
possible  not  only  to  live,  but  to  do  hard  manual  labour,  at 
very  different  atmospheric  pressures.  Loewy  found  that 
the  quantity  of  oxygen  absorbed  by  a  man  breathing  air  in 
the  pneumatic  cabinet  remained  constant  at  all  pressures 
between  about  two  atmospheres  and  half  an  atmosphere. 
At  440  mm.  of  mercury  dyspnoea  became  evident ;  but  if 
the  person  was  now  made  to  work,  the  dyspnoea  passed 
away,  and  did  not  again  manifest  itself  till  the  pressure  was 
reduced  to  410  mm.  There  are  towns  on  the  high  table- 
lands of  the  Andes,  and  in  the  Himalayas,  where  the 
barometric  pressure  is  not  more  than  16  to  20  inches,  yet 
the  inhabitants  feel  no  ill  effects.  And  in  the  caissons  of 
the  Forth  Bridge  the  workmen  were  engaged  in  severe  toil 
under  a  maximum  pressure  of  over  three  atmospheres,  while 
in  the  caissons  of  the  St.  Louis  Bridge  in  America  a  maximum 
pressure  of  more  than  four  atmospheres  was  reached. 

Inside  the  caissons  the  men  sometimes  suffer  from  pain  and  noise 
in  the  ears,  due  to  excessive  pressure  on  the  external  surface  of  the 
tympanic  membrane.  If  the  pressure  in  the  tympanum  is  raised 
by  a  swallowing  movement,  which  opens  the  Eustachian  tube  and 
permits  air  to  enter  it,  the  symptoms  generally  disappear.  The 
suddenness  of  the  change  of  pressure  has  a  great  deal  to  do  with  its 
effects,  and  it  is  found  that  the  men  are  most  liable  to  dangerous 
symptoms  while  passing  through  the  air-lock  from  the  caissons  to 
the  external  air.  It  is  probable,  from  experiments  on  animals,  that 
the  most  serious  and  permanent  of  these— for  instance,  the  localized 
paralysis  and  the  circulatory  disturbances — are  due  to  the  formation 
of  gaseous  emboli,  by  the  liberation  of  nitrogen  in  the  blood  when 
the  pressure  is  abruptly  reduced.  And,  indeed,  it  is  found  that  the 
symptoms  can  often  be  caused  to  disappear,  both  in  animals  and 
men,  by  again  subjecting  them  to  compressed  air. 

But  that  the  action  of  oxygen  under  a  high  pressure  rs  not  merely 
mechanical  seems  to  follow  from  the  experiments  of  Bert.  He 
discovered  the  singular  fact  that  in  pure  oxygen  at  a  pressure  of  three 
atmospheres,  which  corresponds  to  air  at  fifteen  atmospheres,  animals 
die  in  convulsions.  The  consumption  of  oxygen  and  elimination  of 
carbon  dioxide  are  both  much  diminished.  Even  seeds  and  vegetable 
organisms  in  general  are  killed  in  a  short  time ;  and  an  atmosphere 
of  pure  oxygen,  equal  to  five  atmospheres  of  air,  hinders  the  develop- 
ment of  eggs. 

17 


258  A  MANUAL  OF  PHYSIOLOGY 

When  the  air-pressure  is  diminished  below  a  certain 
limit,  death  takes  place  from  asphyxia,  more  or  less  gradual 
according  to  the  rate  at  which  the  pressure  is  reduced.  The 
haemoglobin  cannot  get  or  retain  enough  oxygen  to  enable 
it  to  perform  its  respiratory  function ;  its  dissociation  tension 
is  no  longer  balanced  by  an  equal  or  greater  partial  pressure 
of  oxygen  in  the  air.  The  quantity  of  carbon  dioxide  in  the 
blood  is  also  lessened.  These  belong  to  the  chemical  effects 
of  changes  of  pressure  in  the  air  of  respiration. 

To  such  changes,  as  well  as  to  the  cold,  some  of  the 
deaths  in  high  balloon  ascents  must  be  attributed.  Messrs. 
Glaisher  and  Coxwell  reached  the  height  of  36,000  feet ;  the 
former  became  unconscious  at  29,000  feet  (8,800  metres), 
at  which  height  the  amount  of  oxygen  in  the  arterial  blood 
would  probably  not  exceed  10  volumes  per  cent.,  but 
recovered  during  the  descent.  The  symptoms  of  the 
*  mountain  sickness,'  so  familiar  to  Alpine  climbers,  are  also 
undoubtedly  due  in  part  to  deficiency  of  oxygen  in  the  blood. 
But  evidence  has  been  brought  forward  that  changes  in  the 
mechanics  as  well  as  in  the  chemistry  of  respiration  are 
concerned,  and  that  there  is  something  not  connected  with 
the  want  of  oxygen  which  diminishes  the  capacity  for 
muscular  work.  This  *  something '  is  perhaps  a  peculiar 
excitation  of  the  nervous  system  in  the  fierce  light  of  those 
high  levels,  which  acts  not  only  on  the  retina,  but  on  the 
skin,  and  may  even  affect  the  distribution  of  the  blood 
(Zuntz  and  Schumburg). 

Cutaneous  Respiration. — It  has  already  been  remarked  that  a  frog 
survives  the  loss  of  its  lungs  for  sorrfe  time,  respiration  going  on 
through  the  skin.  Indeed,  it  has  been  calculated  that  in  the  intact 
frog  as  much  as  three-quarters  of  the  total  gaseous  interchange  is 
cutaneous.  In  mammals  the  structure  of  the  skin  is  different,  and 
respiration  can  only  go  on  through  it  to  a  very  slight  extent.  The 
amount  of  carbon  dioxide  excreted  in  man,  although  only  about 
4  grm.  or  2  litres  in  twenty-four  hours,  is  much  greater  than  cor- 
responds to  the  quantity  of  oxygen  absorbed  through  the  skin.  It 
has  been  asserted,  and  no  doubt  with  justice,  that  some  at  least  of 
the  carbon  dioxide  given  off  is  due  to  putrefactive  processes  taking 
place  on  the  surface  of  the  body.  Such  processes,  as  has  already 
been  pointed  out,  seem  also  responsible  in  part  for  the  heavy  odour 
of  a  *  close '  room.  For  no  harmful  products  appear  to  be  exhaled 
from  the  skin  when  it  is  properly  cleansed  In  spite  of  the  romantic 


RESPIRATION  259 

statements  to  the  contrary  in  ancient  and  modern  books  (for  instance, 
the  story  of  the  child  that  was  gilded  to  play  the  part  of  an  angel  at 
the  coronation  of  a  mediaeval  pope,  but  died  before  the  ceremony 
began),  the  whole  of  the  human  skin  may  be  coated  with  an  im- 
permeable varnish  without  any  ill  effects.  The  entire  surface  of  the 
body  of  a  patient  with  cutaneous  disease  was  covered  with  tar,  and 
kept  covered  for  ten  days.  There  was  not  the  least  disturbance  of 
any  normal  function  (Senator).  The  serious  effects  of  varnishing 
the  skin  in  animals  are  due,  not  to  retention  of  poisonous  sub- 
stances, but  to  increased  heat  loss.  Varnishing  is  not  so  rapidly 
harmful  in  large  animals  like  dogs,  as  in  rabbits,  which  have  a 
relatively  great  surface  and  a  delicate  skin.  The  danger  of  wide- 
spread superficial  burns  is  well  known.  But  it  is  not  due  to 
diminished  excretion  by  the  skin,  for  death  occurs  when  large 
cutaneous  areas  remain  uninjured.  The  patient  nearly  always  dies 
when  a  quarter  of  the  whole  skin  is  burnt ;  yet  the  remaining  three- 
quarters  may  surely  be  considered  capable,  from  all  analogy,  of 
making  up  the  loss  by  increased  activity.  One  kidney  is  enough  to 
eliminate  the  products  of  the  nitrogenous  metabolism  of  the  whole 
body.  It  is  difficult  to  see  why  the  excretion  of  the  trifling  amount 
of  solid  matter  in  the  perspiration  should  be  interfered  with  by  the 
loss  of  25  per  cent,  of  the  sweat-glands.  The  real  explanation  of 
the  serious  effects  of  extensive  superficial  burns  is  perhaps  the  ex- 
cessive irritation  of  the  sensory  nerves,  which  may  lead  to  changes 
in  the  nervous  centres,  or  reflexly  in  other  organs.  Some  observers 
have  supposed  that  the  chemical  changes  in  the  damaged  tissue, 
for  example,  in  the  blood-corpuscles,  may  be  the  cause  of  death 
(Hunter),  and  others  that  it  may  be  due  to  the  transudation  of  lymph 
at  the  injured  part,  and  the  consequent  increase  in  the  concentration 
of  the  blood. 


Voice  and  Speech. 

Voice. — Sounds  of  various  kinds  are  frequently  produced 
by  the  movements  of  animals  as  a  whole,  or  of  individual 
organs.  The  muscular  sound,  the  sounds  of  the  heart  and 
of  respiration,  we  have  already  had  to  speak  of.  Such 
sounds  may  be  considered  as  purely  accidental  as  the  foot- 
fall of  a  man  or  the  buzzing  of  a  fly.  The  wings  of  an  insect 
beat  the  air,  not  to  cause  sound,  but  to  produce  motion ; 
the  respiratory  murmur  is  a  mere  indication  that  air  is 
rinding  its  way  into  the  lungs,  it  is  in  no  way  related  to  the 
oxidation  of  the  blood  in  the  pulmonary  capillaries.  But  in 
many  of  the  higher  animals  mechanisms  exist  which  are 
specially  devoted  to  the  utterance  of  sounds  as  their  prime 
and  proper  end.  In  man  the  voice-producing  mechanism 
consists  of  a  triple  series  of  tubes  and  chambers:  (i)  The 

17 — 2 


260  A  MANUAL  OF  PHYSIOLOGY 

trachea,  through  which  a  blast  of  air  is  blown  ;  (2)  the 
larynx,  with  the  vocal  cords,  by  the  vibrations  of  which 
sound  waves  are  set  up ;  and  (3)  the  upper  resonance 
chambers,  the  pharynx,  mouth,  and  nasal  cavities,  in  which 
the  sounds  produced  in  the  larynx  are  modified  and  intensi- 
fied, and  in  which  independent  notes  and  noises  arise. 

The  larynx  is  a  cartilaginous  box,  across  which  are 
stretched,  from  front  to  back,  two  thin  and  sharp-edged 
membranes,  the  (true)  vocal  cords.  In  front  the  cords  are 
attached  to  the  thyroid  cartilage,  one  a  little  to  each  side  of 
the  middle  line ;  behind  they  are  connected  to  the  vocal  or 
anterior  processes  of  the  pyramidal  arytenoid  cartilages. 
The  thyroid  and  the  two  arytenoids  are  mounted  upon  a 
cartilaginous  ring,  the  cricoid,  on  which  the  former  can 
rotate  about  a  transverse  horizontal  axis,  the  latter  around 
a  vertical  axis.  The  thyroid  can  thus  be  depressed  by  the 
contraction  of  the  crico-thyroid  muscle,  and  the  vocal  cords 
stretched.  By  the  pull  of  the  posterior  crico-arytenoid 
muscles,  attached  to  the  external  or  muscular  processes  of 
the  arytenoid  cartilages,  the  vocal  processes  are  rotated  out- 
wards, the  cords  separated  from  each  other  or  abducted,  and 
the  chink  between  them,  the  rima  glottidis,  widened.  When 
the  vocal  processes  are  approximated  by  contraction  of  the 
lateral  crico-arytenoid  muscles  and  the  consequent  forward 
movement  of  the  muscular  processes,  the  vocal  cords  are 
brought  closer  together,  or  adducted,  and  the  rima  is  narrowed. 
The  transverse  or  posterior  arytenoid  muscle,  which  con- 
nects the  two  arytenoid  cartilages  behind,  also  helps  by  its 
contraction  to  narrow  the  glottis  by  shifting  the  cartilages 
on  their  articular  surfaces  somewhat  nearer  the  middle  line. 
Running  in  each  vocal  cord,  and,  in  fact,  incorporated  with 
its  elastic  tissue,  is  a  muscle,  the  thyro-arytenoid,  the  ex- 
ternal portion  of  which  may  to  some  extent  cause  inwarc 
rotation  of  the  vocal  processes  and  adduction  of  the  cords 
but  the  main  function,  at  least  of  its  inner  part,  is  to  alt< 
the  tension  of  the  cords.  The  diagrams  in  Figs.  91  and  9: 
illustrate  the  action  of  the  abductors  and  adductors  of  th; 
vocal  cords. 

The  crico-thyroid  muscle  and  the  deflectors  of  the  epi- 


RESPIRATION 


261 


glottis  are  supplied  by  the  superior  laryngeal  branch  of  the  "A 
vagus,  which  also  contains  the  sensory  fibres  for  the  mucous 
membrane  of  the  larynx  above  the  vocal  cords.  All  the  other  "pv\  a  *  MI 
intrinsic  muscles  are  supplied  by  the  recurrent  laryngeal 
branch  of  the  vagus.  It  receives  these  motor  fibres  from 
the  spinal  accessory,  and  supplies  sensory  fibres  to  the 
mucous  membrane  of  the  larynx  below  the  vocal  cords  and 
to  the  trachea. 

The  voice  is  produced,  like  the  sounds  of  a  reed  instru- 
ment, by  the  rhythmical  interruption  of  an  expiratory  blast 
of  air  by  the  vibrating  vocal  cords.  When  a  bell  is  struck, 


FIG.  92. — DIRECTION  OF 
PULL  OF  THE  LATERAL 
CRICO-ARYTENOIDS, 
WHICH  ADDUCT  THE 
VOCAL  CORDS. 

Dotted  lines  show  position  in 
adduction. 


FIG.  91. — DIAGRAMMATIC 
HORIZONTAL  SECTION  OF 
LARYNX  TO  SHOW  THE 
DIRECTION  OF  PULL  OF 
THE  POSTERIOR  CRICO- 
ARYTENOID  MUSCLES, 
WHICH  ABDUCT  THE 
VOCAL  CORDS. 

Dotted  lines  show  position  in 
abduction. 


vibrations  are  set  up  in  the  metal,  which  are  communicated 
to  the  air.  It  is  not  the  same  with  the  vibrations  of  the 
vocal  cords  ;  if  they  were  plucked  or  struck,  they  would  only 
produce  a  feeble  note.  The  air  in  the  mouth,  pharynx, 
larynx,  trachea,  and  lungs  is  the  real  sounding  body;  a  pulse 
of  alternate  rarefaction  and  condensation  is  set  up  in  it  by 
the  interference,  at  regular  intervals,  of  the  vocal  cords  with 
the  expiratory  blast.  Forced  abruptly  from  their  position 
of  equilibrium  as  the  blast  begins,  they  almost  immediately 
regain  and  pass  below  it,  in  virtue  of  their  elasticity,  and 
continue  to  vibrate  as  long  as  the  stream  of  air  continues  to 
issue  in  sufficient  strength.  The  sound-waves  thus  set  up 


262  A  MANUAL  OF  PHYSIOLOGY 

spread  out  on  every  side,  impinge  on  the  tympanic  mem- 
brane, set  it  quivering  in  response,  and  give  rise  to  the 
sensation  of  sound. 

We  may  say,  in  a  word,  that  the  whole  exquisite 
mechanism  of  cartilages,  ligaments,  and  muscles,  has  for  its 
object  the  production  of  a  sufficient  pressure  in  the  blast  of 
air  driven  through  the  windpipe  by  an  expiratory  act,  and 
of  a  suitable  tension  in  the  vibrating  cords.  An  approxima- 
tion of  the  cords,  a  narrowing  of  the  glottis,  is  essential  to 
the  production  of  voice ;  with  a  widely-opened  glottis  the 
air  escapes  too  easily,  and  the  necessary  pressure  cannot  be 
attained.  The  pressure  in  the  windpipe  was  found  in  a 
woman  with  a  tracheal  fistula  to  be  about  12  mm.  of  mer- 
cury for  a  note  of  medium  height,  about  15  mm.  for  a  high 
note,  and  about  72  mm.  for  the  highest  possible  note.  The 
period  of  vibration  of  structures  like  the  vocal  cords  depends 
on  their  length,  thickness,  and  tension ;  the  shorter,  thinner, 
more  tense  and  tass  dense  a  stretched  string  is,  the  greater 
is  the  vibration  frequency,  the  higher  the  note.  In  the  child 
the  cords  are  short  (6  to  8  mm.),  in  woman  longer  (10  to 
15  mm.  when  slack,  15  to  20  mm.  when  stretched),  in  man 
longest  of  all  (15  to  20  mm.  in  the  relaxed,  and  20  to 
25  mm.  in  the  stretched  position) ;  and  the  lower  limit  of 
the  voice  is  fixed  by  the  maximum  length  of  the  relaxed 
cords.  A  boy  or  a  woman  cannot  utter  a  deep  bass  note, 
because  their  vocal  cords  are  relatively  short,  and  do  not 
vibrate  with  sufficient  slowness.  It  is  true  that  by  the  action 
of  the  crico-thyroid  muscle  the  cords  can  be  lengthened, 
and  that  the  maximum  length  in  a  woman  approaches  or 
exceeds  the  minimum  length  in  a  man.  But  the  lengthening 
of  the  vocal  cords  in  one  and  the  same  individual  is  always 
accompanied  by  other  changes — increase  of  tension,  decrease 
of  breadth  and  thickness — which  tell  upon  the  vibration 
frequency  in  the  opposite  way,  and  more  than  compensate 
the  effect  of  the  increase  of  length.  It  is  probable  that  when 
the  highest  notes  are  uttered,  only  the  anterior  portions  of 
the  cords  are  free  to  vibrate,  their  posterior  portions  being 
damped  by  the  approximation  of  the  vocal  processes  of  the 
arytenoid  cartilages  by  the  contraction  of  the  lateral  crico- 


RESPIRATION  263 

arytenoid  and  transverse  arytenoid  muscles.  The  range  of 
an  ordinary  voice  is  2  octaves ;  by  training  2,\  octaves  can 
be  reached ;  but  in  exceptional  cases  a  range  of  3,  and  even 
3^,  octaves  has  been  known. 

The  development  of  the  voice  in  children  is  of  great  interest.  At 
the  age  of  six  years  the  boy's  voice  has  a  rather  narrower  range  than 
the  girl's  in  both  directions.  The  boy's  voice  reaches  its  full  height 
in  the  twelfth  and  its  full  depth  in  the  thirteenth  year,  when  the 
range  is  almost  3  octaves,  its  upper  limit  being  a  semitone  higher 
than  the  girl's,  but  its  lower  limit  a  whole  tone  deeper.  When  the 
voice  *  breaks  '  in  boys  at  the  age  of  puberty,  the  control  of  the  vocal 
organs  becomes  so  incomplete  that  only  in  one-fourth  of  the  cases 
can  notes  of  sufficient  steadiness  to  be  used  in  music  be  produced. 
The  vocal  cords,  as  may  be  seen  with  the  laryngoscope,  are 
frequently,  though  not  always,  congested  (Paulsen). 

The  pitch  of  a  note,  while  it  depends  chiefly,  as  has  been 
said,  on  the  tension  of  the  vocal  cords,  rises  and  falls  some- 
what with  the  strength  of  the  expiratory  blast ;  the  highest 
notes  are  only  reached  with  a  strong  expiratory  effort.  The 
intensity  of  all  sounds  is  determined  by  the  strength  of  the 
blast,  for  the  amplitude  of  vibration  of  the  vocal  cords  is 
proportional  to  this.  Besides  pitch  and  intensity,  the  ear 
can  still  distinguish  the  quality  or  timbre  of  sounds ;  and  the 
explanation  is  as  follows  :  Two  simple  tones  of  the  same 
pitch  and  intensity,  that  is,  the  sounds  caused  by  two  series 
of  air-waves  of  the  same  period  and  amplitude — of  the  same 
frequency  and  height,  if  these  terms  seem  simpler — would 
appear  absolutely  identical  to  the  sense  of  hearing;  just  as 
the  aerial  disturbances  on  which  they  depend  would  be 
absolutely  alike  to  any  physical  test  that  could  be  applied. 
But  no  musical  instrument  ever  produces  sound-waves  of 
one  definite  period,  and  one  only ;  and  the  same  is  true  of 
the  voice.  When  a  stretched  string  is  displaced  in  any 
way  from  its  position  of  rest,  it  is  set  into  vibration ;  and 
not  only  does  the  string  vibrate  as  a  whole,  but  portions  of 
it  vibrate  independently  and  give  out  separate  tones.  The 
tone  corresponding  to  the  vibration  period  of  the  whole 
string  is  the  lowest  of  all.  It  is  also  the  loudest,  for  it  is 
more  difficult  to  set  up  quick  than  slow  vibrations.  The  ear 
therefore  picks  it  out  from  all  the  rest ;  and  the  pitch  of  the 
compound  note  is  taken  to  be  the  pitch  of  this,  its  funda- 


264  A  MANUAL  OF  PHYSIOLOGY 

mental  tone.  The  others  are  called  partial  or  over-tones, 
or  harmonics  of  the  fundamental  tone,  their  vibration 
frequency  being  twice,  three  times,  four  times,  etc.,  that  of 
the  latter.  Now,  the  fundamental  tone  of  a  compound  note 
or  clang  produced  by  two  musical  instruments  may  be  the 
same,  while  the  number,  period,  and  intensity  of  the  har- 
monics are  different ;  and  this  difference  the  ear  recognises 
as  a  difference  of  timbre  or  quality.  The  timbre  of  the  voice 
depends  for  the  most  part  on  partial  tones  produced  or  in- 
tensified in  the  upper  resonance  chambers. 


FIG.  93. — DIAGRAM  OF  LARYNGOSCOPE. 

A  great  deal  of  our  knowledge  as  to  the  mode  and 
mechanism  of  the  production  of  voice  has  been  acquired  by 
means  of  the  laryngoscope  (Fig.  93).  This  consists  of  a  small 
plane  mirror  mounted  on  a  handle,  which  is  held  at  the 
back  of  the  mouth  in  such  a  position  that  a  beam  of  light, 
reflected  from  a  larger  concave  mirror  fastened  on  the 
forehead  of  the  observer,  is  thrown  into  the  larynx  of  the 
patient.  The  observer  looks  through  a  hole  in  the  centre 
of  the  large  mirror ;  and  a  reversed  image  of  the  interior  of 
the  larynx  is  thus  seen  in  the  small  mirror,  the  arytenoid 
cartilages  appearing  in  front,  the  thyroid  behind,  and  the 
vocal  cords  stretching  between.  The  small  mirror  is 


RESPIRATION 


265 


warmed  to  body  temperature  before  being  introduced,  so 
as  to  prevent  the  condensation  of  moisture  on  it.  And  the 
tendency  to  retch  which  is  caused  by  contact  of  the  instru- 
ment with  the  soft  palate  may  be  removed  or  lessened  by 
the  application  of  a  solution  of  cocaine. 

Examined  with  the  laryngoscope  during  quiet  respiration, 
the  glottis  is  seen  to  be  moderately,  though  not  widely, 
open,  and  the  vocal  cords  almost  motionless.  Although  the 
portion  between  the  arytenoid  cartilages  has  received  the 
name  of  glottis  respiratoria,  in  contradistinction  to  the 
glottis  vocalis  between  the  vocal  cords,  the  rima  in  its  whole 


FIG.    94. — POSITION    OF   THE 
GLOTTIS    PRELIMINARY    TO 

THE  UTTERANCE  OF    SOUND. 

rs,  false  vocal  cord ;  ri,  true 
vocal  cord  ;  ar,  arytenoid  carti- 
lage ;  b,  pad  of  the  epiglottis. 


FIG.    95.  — POSITION     OF    OPEN 
GLOTTIS. 

/,  tongue ;  e,  epiglottis ;  ae,  ary- 
epiglottidean  fold  ;  c,  cartilage  of 
Wrisberg  ;  ar,  arytenoid  cartilage  ;  o, 
glottis  ;  v,  ventricle  of  Morgagni ;  ti, 
true  vocal  cord  ;  ts,  false  vocal  cord. 


extent  from  front  to  back  is  really  concerned  in  the  re- 
spiratory act.  In  deep  expiration  the  vocal  cords  come 
nearer  to  the  middle  line,  and  the  glottis  is  narrowed  ;  in 
deep  inspiration  they  are  widely  separated,  and  the  rings  of 
the  trachea,  and  even  its  bifurcation,  may  be  disclosed  to 
view.  When  a  sound  is  produced,  a  note  sung,  for  example, 
the  cords  are  approximated  (Figs.  94  and  95)  ;  and  with  a 
high  note  more  than  with  a  low. 

The  essential  difference  between  the  production  of  notes  in  the 
lower  register,  or  chest  voice,  and  in  the  higher  register,  or  falsetto, 
has  been  much  debated.  The  lowest  notes  which  can  be  uttered  by 
any  given  voice  are  chest  notes,  the  highest  are  falsetto  notes  ;  but 
there  is  a  debatable  land  common  to  both  registers,  and  medium 
notes  can  be  sung  either  from  the  chest  or  from  the  head.  Chest 
notes  impart  a  vibration  or  fremitus  to  the  thoracic  walls,  from  the 
resonance  of  the  lower  air  chambers,  the  trachea  and  bronchi ;  and 


266  A  MANUAL  OF  PHYSIOLOGY 

this  can  be  distinctly  felt  by  the  hand.  In  head  notes  or  falsetto 
the  resonance  is  chiefly  in  the  upper  cavities,  the  pharynx,  mouth, 
and  nose.  As  to  the  mechanical  conditions  in  the  larynx,  there  is  a 
pretty  general  agreement  that  during  the  production  of  falsetto  notes 
the  vocal  cords  are  less  closely  approximated  than  in  the  sounding  of 
chest  notes.  The  escape  of  air  is  consequently  more  rapid  in  the 
head  voice,  and  a  falsetto  note  cannot  be  maintained  so  long  as  a 
note  sung  from  the  chest  But  it  is  only  the  anterior  part  of  the 
rima  glottidis  that  is  wider  in  the  falsetto  voice ;  the  whole  of  the 
glottis  respiratoria,  and  even  the  posterior  portion  of  the  glottis 
vocalis,  are  closed  during  the  emission  of  falsetto  notes. 

Oertel  has  stated,  and  the  statement  has  been  confirmed  by  others, 
that  the  free  edge  of  the  vocal  cord  alone  vibrates  in  the  falsetto 
voice,  one  or  more  nodes  or  motionless  lines  parallel  to  the  edge 
being  formed  by  the  contraction  of  the  internal  part  of  the  thyro- 
arytenoid  muscle,  which  thus  acts  like  a  stop  upon  the  cord. 

Approximation  of  the  vocal  cords  may  take  place  in 
certain  acts  unconnected  with  the  production  of  voice. 
Thus,  a  cough,  as  has  already  been  mentioned,  is  initiated 
by  closure  of  the  glottis.  During  a  strong  muscular  effort, 
too,  the  chink  of  the  glottis  is  obliterated,  and  respiration 
and  phonation  both  arrested.  The  object  of  this  is  to  fix 
the  thorax,  and  so  afford  points  of  support  for  the  action 
of  the  muscles  of  the  limbs  and  abdomen.  But  consider- 
able efforts  can  be  made  even  by  persons  with  a  tracheal 
fistula. 

Speech.  —  Ordinary  speech  is  articulated  voice  —  voice 
shaped  and  fashioned  by  the  resonance  of  the  upper  air 
cavities,  and  jointed  together  by  the  sounds  or  noises  to 
which  the  varying  form  of  these  cavities  gives  rise.  Here 
we  come  upon  the  fundamental  distinction  between  vowels 
and  consonants.  Vowels  are  musical  sounds ;  consonants 
are  not  musical  sounds,  but  noises — that  is  to  say,  they  are 
due  to  irregular  vibrations,  not  to  regularly  recurring  waves, 
the  frequency  of  which  the  ear  can  appreciate  as  a  definite 
pitch.  This  difference  of  character  corresponds  to  a  differ- 
ence of  origin  :  the  vowels  are  produced  by  the  vibrations  of 
the  vocal  cords;  the  consonants  are  due  to  the  rushing  of  the 
expiratory  blast  through  certain  constricted  portions  of  the 
buccal  chamber,  where  a  kind  of  temporary  glottis  is  estab- 
lished by  the  approximation  of  its  walls.  One  of  these 
'  positions  of  articulation '  is  the  orifice  of  the  lips  ;  the 


RESPIRA  TION  267 

consonants  formed  there,  such  as  p  and  6,  are  called  labials. 
A  second  articulation  position  is  between  the  anterior  part 
of  the  tongue  and  the  teeth  and  hard  palate.  Here  are 
formed  the  dentals,  t,  d,  etc.  The  ordinary  English  r,  and 
the  r  of  the  Berwickshire  and  East  Prussian  'burr,'  also  arise 
in  this  position  through  a  vibratory  motion  of  the  point  of 
the  tongue.  The  third  position  of  articulation  is  the  narrow 
strait  formed  between  the  posterior  portion  of  the  arched 
tongue  and  the  soft  palate.  To  the  consonants  arising  here 
the  name  of  gutturals  has  been  given.  They  include  k,  g, 
the  Scottish  ch,  and  the  uvular  German  r.  The  latter  is 
produced  by  a  vibration  of  the  uvula.  The  aspirated  h  is  a 
noise  set  up  by  the  air  rushing  through  a  moderately  wide 
glottis,  and  some  have  therefore  included  the  glottis  as  a 
fourth  articulation  position  for  consonants.  Certain  sounds 
like  n,  m,  and  ng,  when  final  (as  in  pen,  dam,  ring),  although 
produced  at  the  glottis,  are  intensified  by  the  resonance  of 
the  air  in  the  nose  and  pharynx,  and  are  sometimes  spoken 
of  as  nasal  consonants. 

As  we  have  said,  the  vowels  are  produced  by  vibrations  of 
the  vocal  cords,  but  they  owe  their  special  timbre  to  the 
reinforcement  of  certain  overtones  by  the  resonating  cavities, 
the  shape  and  fundamental  tone  of  which  are  different  for 
each  vowel.  When  a  vowel  is  whispered,  the  mouth  assumes 
a  characteristic  shape,  and  emits  the  fundamental  tone  proper 
to  the  form  and  size  of  the  particular  '  vowel-cavity,'  not  as 
a  reinforcement  of  a  tone  set  up  by  the  vibrations  of  the 
vocal  cords,  but  in  response  to  the  rush  of  air  through  the 
cavity;  just  as  a  bottle  of  given  shape  and  size  gives  out  a 
definite  note  when  the  air  which  it  contains  is  set  in  vibra- 
tion, by  blowing  across  its  mouth.  A  whisper,  in  fact,  is 
speech  without  voice ;  the  larynx  takes  scarcely  any  part  in 
the  production  of  the  sounds ;  the  vocal  cords  remain  apart 
and  comparatively  slack ;  and  the  expiratory  blast  rushes 
through  without  setting  them  in  vibration. 

The  fundamental  tone  of  the  ' vowel-cavity'  may  be  found 
for  each  vowel  by  placing  the  mouth  in  the  position  necessary 
for  uttering  it,  then  bringing  tuning-forks  of  different  period 
in  front  of  it,  and  noting  which  of  them  sets  up  sympathetic 


268  A  MANUAL  OF  PHYSIOLOGY 

resonance  in  the  air  of  the  mouth,  and  so  causes  its  sound 
to  be  intensified.  The  fundamental  tone  is  lowest  for  u  (as 
in  lute).  Next  comes  o;  then  a  (as  in  path);  then  e;  while 
i  is  highest  of  all.  A  simple  illustration  of  this  may  be 
found  in  the  fact  that  when  the  vowels  are  whispered  in  the 
order  given,  the  pitch  rises. 

Such  is  the  explanation  of  the  difference  of  the  vowels  in  quality 
which  was  first  given  by  Helmholtz.  Universally  accepted  for  a  time, 
it  has  been  in  recent  years  assailed  by  Hermann,  who  bases  his 
criticisms  (i)  on  microscopic  examination  of  curves  obtained  by  the 
Edison  phonograph,  and  (2)  on  the  results  of  his  phono-photographic 
method.  (The  record  of  an  Edison  phonograph  is  magnified  by  a 
system  of  levers,  the  last  of  which  carries  a  small  mirror,  on  which 
a  beam  of  light  is  allowed  to  strike.  The  reflected  beam  falls  on  a 
moving  drum  covered  with  sensitive  paper.  Thus  the  movements  of 
the  mirror  are  greatly  exaggerated  and  photographed.)  Hermann 
has  come  to  the  conclusion  that  the  mouth  does  not  act  as  a  mere 
resonator,  but  that  for  each  vowel,  in  addition  to  the  fundamental 
note  due  to  the  vibration  of  the  vocal  cords,  the  pitch  of  which  is, 
of  course,  variable,  one  or,  it  may  be,  two  other  notes,  not  necessarily 
harmonics  of  the  laryngeal  note,  but  separated  from  it  by  a  constant 
or  nearly  constant  musical  interval,  are  directly  produced  by  the 
passage  of  the  expiratory  blast  through  the  mouth.  For  example, 
the  buccal  note  for  a  is  in  the  middle  of  the  second  octave  of  the 
laryngeal  note,  the  buccal  notes  for  e  in  the  beginning  of  the  second 
and  the  end  of  the  third  octave.  The  fact  that  it  is  by  no  means 
difficult  to  sing  and  whistle  at  the  same  time  shows  the  possibility  of 
Hermann's  view,  that  a  fixed  tone  can  be  generated  in  the  mouth 
by  the  intermittent  stream  of  air  issuing  from  between  the  vibrating 
vocal  cords,  just  as  a  tone  is  generated  in  a  pipe  by  blowing  into  or 
over  it  (Griitzner).  McKendrick  has  also  made  important  investiga- 
tions on  this  subject,  and  has  obtained  curves  by  enlarging  the 
phonographic  records  by  mechanical  means. 

When  u  or  o  is  sounded,  the  buccal  cavity  has  the  form  of  a  wide- 
bellied  flask,  with  a  short  and  narrow  neck  for  u,  a  still  shorter  but 
wider  neck  for  o.  For  /  the  tongue  is  raised  and  almost  in  contact 
with  the  palate,  and  the  cavity  of  the  mouth  is  shaped  like  a  flask 
with  a  long  narrow  neck  and  a  very  short  belly.  For  e  the  shape  is 
similar,  but  the  neck  is  not  so  narrow.  For  a  the  vowel- cavity  is 
intermediate  in  form  between  that  of  u  and  z,  being  roughly  funnel- 
shaped,  and  the  mouth  is  rather  widely  opened  (Figs.  96  to  98). 

When  the  vowels  are  being  uttered,  the  soft  palate  closes 
the  entrance  to  the  nasal  chambers  completely,  as  may  be 
shown  by  holding  a  candle  in  front  of  the  nose,  or  trying  to 
inject  water  through  the  nares.  If  the  cavities  of  the  nose 


RESPIRATION 


269 


are  not  completely  blocked  off,  the  voice  assumes  a  nasal 
character  in  pronouncing  certain  of  the  vowels  ;  and  in  some 
languages  this  is  the  ordinary  and  correct  pronunciation. 

Many  animals  have  the  power  of  emitting  articulated 
sounds ;  a  few  have  risen,  like  man,  to  the  dignity  of 
sentences,  but  these  only  by  imitation  of  the  human  voice. 
Both  vowels  and  consonants  can  be  distinguished  in  the 
notes  of  birds,  the  vocal  powers  of  which  are  in  general 
higher  than  those  of  mammalian  animals.  The  latter,  as  a 
rule,  produce  only  vowels,  though  some  are  able  to  form 
consonants  too. 

The  nervous  mechanism  of  voice  and  speech  will  have  to  be 


OU 


FIG.  96. 


FIG.  97. 


FIG.  98. 


again  considered  when  we  come  to  study  the  physiology  of 
the  brain  and  spinal  cord.  But  the  curious  physiological 
antithesis  between  the  functions  of  abduction  and  of  adduc- 
tion of  the  vocal  cords  may  be  mentioned  here.  The  abductor 
muscles  are  not  employed  in  the  production  of  voice;  they  are 
associated  with  the  less  specialized,  the  less  skilled  and  pur- 
posive function  of  respiration.  The  adductor  muscles  are  not 
brought  into  action  in  respiration  ;  they  are  associated  with 
the  highly-specialized  function  of  speech.  Corresponding  to 
this  difference  of  function,  we  find  that  the  adductors  only 
are  represented  in  the  cortex  of  the  brain,  the  abductors  in 
the  medulla  oblongata.  Stimulation  of  an  area  in  the  lower 
part  of  the  ascending  frontal  convolution,  near  the  fissure  of 


270  A  MANUAL  OF  PHYSIOLOGY 

Rolando,  in  the  macaque  monkey,  causes  adduction  of  the 
vocal  cords,  never  abduction.  Stimulation  of  the  medulla 
oblongata  (accessory  nucleus)  causes  abduction,  never  adduc- 
tion (Horsley  and  Semon).  The  skilled  adductor  function 
is,  therefore,  placed  under  control  of  the  cortex.  The  vitally 
important,  but  more  mechanical,  abductor  function  is 
governed  by  the  medulla.  The  abductor  movements  are 
more  likely  to  be  affected  by  organic  disease,  the  adductor 
movements  by  functional  changes.  But  the  distinction 
between  the  two  groups  of  muscles  is  not  entirely  due  to  a 
difference  of  central  connections  ;  for  Hooper  has  found  that 
in  an  animal  deeply  narcotized  with  ether,  stimulation  of 
the  recurrent  laryngeal  nerve  causes  invariably  abduction  of 
the  vocal  cords  ;  in  an  animal  slightly  narcotized,  adduction. 
On  the  other  hand,  when  the  nerve  is  cooled  the  abductors 
give  way  before  the  adductors.  The  same  is  true  when  it 
is  allowed  to  become  dry.  And  after  death  in  a  cholera 
patient  it  was  observed  that  the  posterior  crico-arytenoid, 
an  abductor  muscle,  was  the  first  of  the  intrinsic  laryngeal 
muscles  to  lose  its  excitability.  Lesions  of  the  medulla 
oblongata  are  often  accompanied  by  marked  changes  in  the 
character  of  the  voice  and  the  power  of  articulation. 

Section  or  paralysis  of  the  superior  laryngeal  nerve  causes 
the  voice  to  become  hoarse,  and  renders  the  sounding  of 
high  notes  an  impossibility,  owing  to  the  want  of  power  to 
make  the  vocal  cords  tense.  Stimulation  of  the  vagus  within 
the  skull  causes  contraction  of  the  crico-thyroid  muscle  and 
increased  tension  of  the  cords.  Section  or  paralysis  of  the 
inferior  laryngeal  nerves  leads  to  loss  of  voice  or  aphonia, 
and  dyspnoea  (Fig.  99).  Both  adductor  and  abductor 
muscles  are  paralyzed  ;  the  vocal  cords  assume  their  mean 
position — the  position  they  have  in  the  dead  body — and  the 
glottis  can  neither  be  narrowed  to  allow  of  the  production 
of  a  note,  nor  widened  during  inspiration.  It  is  said,  how- 
ever, that  young  animals,  in  which  the  structures  around  the 
glottis  are  more  yielding  than  in  adults,  can  still  utter  shrill 
cries  after  section  of  the  inferior  laryngeals,  the  contraction 
of  the  crico-thyroid  muscle  alone  being  able,  while  increasing 
the  tension  of  the  cords,  to  draw  them  together.  Strong 


RESPIRATION 


271 


stimulation  of  the  inferior  laryngeal  causes  closure  of  the 
glottis,  for  although  it  supplies  both  abductors  and  adductors, 
the  latter  prevail.  With  weak  stimulation,  and  in  young 
animals,  the  abductors  carry  off  the  victory,  and  the  glottis 
is  opened  (Risien  Russell). 

Interference  with  the  connections  on  one  side,  between 
the  higher  cerebral  centres  and  the  medulla  oblongata,  as  by 
rupture  of  an  artery  and  effusion  of  blood  into  the  posterior 
portion  of  the  internal  capsule  (giving  rise  to  hemiplegia, 
or  paralysis  of  the  opposite  side  of  the  body),  is  not  followed 


FIG.  99.— DIAGRAM  OF  VOCAL  CORDS  IN  PARALYSES  OF  THE  LARYNX. 

a,  Paralysis  of  both  inferior  laryngeal  nerves.  The  vocal  cords  have  taken  up  the 
'  mean  '  position,  b,  Paralysis  of  right  inferior  laryngeal  nerve.  An  attempt  is  being 
made  to  narrow  the  glottis  for  the  utterance  of  sound.  The  right  cord  remains  in  its 
'  mean  '  position,  c,  Paralysis  of  the  abductor  muscles  only,  on  both  sides.  The 
cords  are  approximated  beyond  the  '  mean '  position  by  the  action  of  the  adductors. 

by  loss  of  voice ;  the  laryngeal  muscles  on  both  sides  are 
still  able  to  act. 

In  stammering,  spasmodic  contraction  of  the  diaphragm 
interrupts  the  effort  of  expiration.  The  stammerer  has  full 
control  of  the  mechanism  of  articulation,  but  not  of  the 
expiratory  blast.  His  larynx  and  lips  are  at  his  command, 
but  not  his  diaphragm.  To  conquer  this  defect  he  must 
school  his  respiratory  muscles  to  calm  and  steady  action 
during  speech.  The  stutterer,  on  the  other  hand,  has  full 
control  of  the  expiratory  muscles.  His  diaphragm  is  well 
drilled,  but  his  lips  and  tongue  are  insubordinate. 


272  A  MANUAL  OF  PHYSIOLOGY 


PRACTICAL  EXERCISES  ON  CHAPTER  III. 

1 .  Tracing   of  the  Respiratory  Movements.  —  (a)   Set   up   the 
arrangement  shown  in  Fig.  100,  and  test  whether  it  is  air-tight.     Have 
also  in  readiness  an  induction  machine  and  electrodes  arranged  for 
an  interrupted  current.     Anaesthetize  a  dog  with  morphia  and  ether 
or  ACE  mixture.     Insert  a  cannula  into  the  trachea  (p.  177),  and 
connect  it  with  the  large  bottle  by  a  tube.     Connect  the  bottle  with 
a  recording  tambour  adjusted  to  write  on  a  drum,  and  regulate  the 
amount  of  the  excursion  of  the  lever  by  slackening  or  tightening  the 
screw-clamp.     Set  the  drum  off  at  slow  speed,  and  take  a  tracing. 

(6)  Then  disconnect  the  cannula  from  its  tube.  Dissect  out  the 
vagus  in  the  lower  part  of  the  neck,  pass  a  ligature  under  it,  but  do 
not  tie  it.  Connect  the  cannula  again  with  the  bottle,  and  while  a 
tracing  is  being  taken  ligature  the  vagus.  Then  stimulate  its  central 
end  with  weak  shocks,  marking  the  time  of  stimulation  on  the  drum. 
Repeat  the  stimulation  with  strong  shocks,  and  observe  the  results. 

(c)  Apply  a  strong  solution  of  potassium  chloride  with  a  camel's- 
hair  brush  to  the  central  end  of  the  vagus  while  a  tracing  is  being 
taken,  and  observe  the  effect. 

(d)  Isolate  the  sciatic  nerve  (p.  185),  ligature  it,  and  cut  below  the 
ligature.     Stimulate  its  central  end  while  a  tracing  is  being  taken. 
The  respiratory  movements  will  be  increased. 

(<?)  Disconnect  the  cannula,  and  isolate  the  vagus  on  the  other 
side.  While  a  tracing  is  being  taken,  divide  it.  The  respiratory 
movements  will, probably  at  once  become  deeper  and  less  frequent. 

(/)  Again  disconnect  the  cannula.  Isolate  the  superior  laryngeal 
branch  of  the  vagus,  which  will  be  found  coursing  inwards  to  the 
larynx  at  the  level  of  the  thyroid  cartilage.  Ligature  the  nerve,  and 
divide  it  between  the  larynx  and  the  ligature.  Reconnect  the 
cannula.  Take  a  tracing  first  with  weak  and  then  with  strong 
stimulation  of  the  central  end  of  the  superior  laryngeal. 

(g)  Insert  a  cannula  into  the  carotid  artery.  While  a  tracing  is 
being  taken,  allow  the  blood  to  flow.  Dyspnoea  and  exaggeration  of 
the  respiratory  movements  will  be  seen  when  a  considerable  quantity 
of  blood  has  been  lost.  Mark  and  varnish  the  tracings.  In  the 
whole  of  this  experiment  the  cannula  is  to  be  disconnected,  except 
when  the  lever  is  actually  writing  on  the  drum,  in  order  that  the 
period  during  which  the  animal  must  breathe  into  the  confined  spare 
of  the  bottle  may  be  diminished  as  much  as  possible. 

2.  The  Effect  of  Temperature  on  the  Respiratory  Centre — Heat 
Dyspnoea. — Set  up  an  arrangement  for  taking  a  respiratory  tracing  as 
in  i.     Anaesthetize  a  dog,  and  fasten  it,  back  downward,  on  a  holder. 
Make  an  incision  in  the  middle  line  of  the  neck,  commencing  a 
little  below  the  cricoid  cartilage,  and  extending  down  for  4  or  5 
inches.     Insert  a  cannula  into  the  trachea.     Isolate  both  carotid 
arteries  for  as  great  a  distance  as  possible.     Take  two  pieces  of  lead 
tube  about  9  inches  long,  and  bend  up  about  2  inches  at  each  end 
nearly  to  a  right  angle.     Place  one  of  the  tubes  in  contact  length- 


PRACTICAL  EXERCISES 


273 


wise  with  each  carotid,  securing  contact  by  loose  ligatures.  Support 
the  tubes  in  clamps,  so  that  the  arteries  are  not  pressed  on.  Connect 
two  adjacent  ends  of  the  tubes  by  a  short  rubber  tube.  Connect 
one  of  the  remaining  ends  to  a  funnel,  supported  on  a  stand,  and  the 


other  to  a  rubber  tube  hanging  over  the  table  above  a  lar^e  jar. 
Slip  two  or  three  folds  of  paper  between  the  tubes  and  the°  vagus 
nerves.  Heat  two  or  three  litres  of  water  to  55°  or  60°  C  Now 
connect  the  tracheal  cannula  with  the  bottle.  As 'soon  as  the  tracing 
is  under  way,  let  the  hot  water  run  through  the  funnel  and  lead  tubes 

18 


274  A  MANUAL  OF  PHYSIOLOGY 

into  the  jar.  Mark  on  the  tracing  the  point  at  which  the  circulation 
of  the  hot  water  was  begun,  and  go  on  passing  it  until  it  has 
produced  an  effect.  Then  stop  the  drum,  and  circulate  water  at  the 
ordinary  temperature  till  the  breathing  is  again  normal.  Then,  while 
a  tracing  is  being  taken,  pass  ice-cold  water  through  the  tubes,  and 
again  notice  the  effect. 

3.  Measurement  of  Volume   of  Air  inspired  or  expired — Vital 
Capacity. — A  spirometer  of  sufficient  accuracy  for  this  experiment 
can  be  made  by   removing  the    bottom  of  a   large   bottle  with  a 
capacity  of  not  less  than  4  litres.     A  good  cork,  through    which 
passes  a  glass  tube  connected  with  a  rubber  tube,  is  fitted  into  the 
neck.     The  bottle  is  then  fixed  vertically,  mouth  downwards,  the  glass 
tube   being   blocked   for   the   time,    and  graduated    by   pouring  in 
measured  quantities  of  water,  say  100  c.c.  at  a  time,  and  marking  the 
level.     The  divisions  are  then  etched  in.     If  the  cork  does  not  fit  air- 
tight, it  is  covered  with  wax.     The  bottle  is  swung  on  two  pulleys  and 
immersed,  bottom  down,  in  a  large  glass  jar  or  a  small  cask  nearly  full 
of  water.     A  smaller  bottle  may  be  used  for  the  determination  of  the 
tidal  air,  so  as  to  reduce  the  error  of  reading. 

(1)  Submerge  the  bottle  to  the  stopper,  after  opening  the  pinch- 
cock  on  the  rubber  tube.     Breathe  into  the  bottle,  close  the  cock, 
adjust  the  bottle  so  that  the  level  of  the  water  is  the  same  inside  and 
outside,  and  then  read  off  the  level.     Determine  the  volume  of  air 
expired  in  : 

(a)  A  normal  expiration  after  a  normal  inspiration  (tidal  air); 

(fr)  The  greatest  possible  expiration  after  a  normal  inspiration 
(supplemental  air) ; 

(c)  The  greatest  possible  expiration  after  the  greatest  possible 
inspiration  (vital  capacity). 

(2)  Open  the  cock,  and  raise  the  bottle  till  it  is  nearly  full  of  air. 
Determine  the  volume  of  air  inspired  in  : 

(a)  A  normal  inspiration  after  a  normal  expiration  (tidal  air) ; 

(b)  The   greatest  possible   inspiration   after  a  normal  expiration 
(complemental  air) ; 

(c)  The   greatest   possible   inspiration  after  the  greatest  possible 
expiration  (vital  capacity). 

Make  several  observations  of  each  quantity,  and  take  the  mean. 

(3)  Count  the  rate  of  respiration  for  three  minutes,  keeping  the 
breathing  as  nearly  normal  as  possible  ;  repeat  the  observation  ;  and 
from  the  mean  result  and  the  amount  of  the  tidal  air  calculate  the 
quantity  of  air  taken  into  the  lungs  in  twenty-four  hours  (pulmonary 
ventilation). 

4.  Respiratory  Pressure. — Connect  a  strong  rubber  tube  to  one 
limb  of  a  mercurial  manometer  provided  with  a  scale,     (i)  Fasten 
the  tube  with  a  little  cotton-wool  in  one  nostril,  breathe  through  the 
other  with  closed  mouth,  and  observe  the  amount  by  which  the  level 
of  the  mercury  is  altered  in  ordinary  inspiration  and  expiration. 

(2)  Repeat  the  observation  with  forced  breathing,  pinching  the 
tube  at  the  height  of  inspiration  and  expiration,  and  reading  oft  the 
maximum  inspiratory  and  expiratory  pressure. 


PRACTICAL  EXERCISES  275 

(3)  Repeat  (i)  with  the  tube  connected  to  the  mouth  by  a  glass 
tube  held  between  the  lips,  and  the  nostrils  open. 

(4)  Repeat  (2)  with  the  tube  in  the  mouth  and  nostrils  closed. 

5.  Determination  of  Carbon  Dioxide  and  Oxygen  in  Inspired  and 
Expired  Air — (i)  Estimation  of  Carbon  Dioxide. — Fill  a  burette 
with  water,  and  close  the  pinchcock  on  the  rubber  tube.  Immerse 
the  wide  end  of  the  burette  in  a  large  vessel  of  water,  and  fill  it  with 
carbon  dioxide  by  putting  into  it  below  the  water  a  tube  connected 
with  a  bottle  in  which  carbon  dioxide  is  being  evolved  by  the  action 
of  hydrochloric  acid  on  marble  chips.  See  that  gas  has  been  coming 
off  freely  from  the  bottle  for  a  little  time  before  the  tube  is  put  under 
the  burette.  Do  not  fill  the  burette  with  gas  beyond  the  graduated 
part.  Hold  the  burette  in  the  vertical  position,  its  mouth  being  still 
immersed,  make  the  level  of  the  water  the  same  inside  and  outside, 
and  read  off  the  meniscus.  Then  introduce  a  piece  of  stick  sodium 
hydrate,  close  the  burette  with  a  finger  or  the  palm  of  the  hand,  lift 
it  out  of  the  water,  and  by  a  sort  of  see-saw  movement  shake  the 
sodium  hydrate  repeatedly  from  end  to  end  of  it.  Again  immerse 
the  burette,  and  read  the  level  of  the  meniscus.  Most  of  the  gas 
will  be  absorbed.  Repeat  the  shaking.  If  the  reading  is  still  the 
same,  absorption  is  now  complete. 

(2)  Estimation  of  Oxygen  (Analysis  of  Inspired  Air).— Fill  lhe_ 
buieile  with  the  air  of  the  laboratory.     Open  the  pinchcock,   and 
immerse  the  wide  end  of  the  burette  till  the  water  reaches  the  gradua- 
tion.    Then  close  the  cock,  and  read  off  the  meniscus.     Introduce  a 
piece  of  sodium  hydrate,  and  proceed  as  in  (i).     Notice  that  there 
is  no  appreciable  absorption.     (This  method  is  not  suitable  for  the 
measurement  of  the  small  quantity  of  carbon  dioxide  in  ordinary 
air.)     Now  introduce,  under  water,  some  pyrogallic  acid.     This  can 
be  done  conveniently  by  wrapping  up  some  of  the  crystals  in  thin 
paper  so  as  to  form  a  kind  of  small  cigarette,  which  is  pushed  up  into 
the  burette.     A  little  more  sodium  hydrate  may  also  be  added,  if  the 
piece  first  introduced  is  entirely  dissolved.     Shake  as  described  in 
(i),  till  no  more  absorption  takes  place.    Then  read  off  the  meniscus 
again  (always  making  the  level  the  same  inside  and  outside  the  burette). 
The  difference  in  the  two  readings  gives  the  amount  of  oxygen  present. 
What  remains  in  the  burette  is  nitrogen  (and  a  little  argon).     Its 
amount  is,  of  course,  equal  to  the  reading  of  the  burette,  plus  the 
capacity  of  the  ungraduated  part  at  the  narrow  end  of  the  burette, 
which  must  be  determined  once  for  all  by  a  separate  measurement. 

(3)  Analysis  of  Expired  Air. — (a)  Fill  the  spirometer  with  water, 
breathe  into  it  several  times  in  your  ordinary  way,  but  be  careful  not 
to  inspire  any  air  from  the  spirometer;  then  fill  the  burette  with  the 
expired  air  from  it.      Or  simply  expire  several  times  through  the 
burette,   seeing   that  none  of  the    inspired   air  comes    through   it. 
Determine,   as  in   (i)  and  (2),  the  percentage   amount  of  carbon 
dioxide,    oxygen   and   nitrogen,     (b)   Repeat    (a)   with:  air   expired 
after  the  lungs  have  been  thoroughly  ventilated  by  taking  a  number 
of  deep  breaths  in  succession,  and  determine  whether  there  is  any 
difference  in  the  percentage  amounts. 


276 


A  MANUAL  OF  PHYSIOLOGY 


6.  Estimation  of  the  Quantity  of  Water  and  of  Carbon  Dioxide 
given  off  by  an  Animal  (Haldanes  Method), —  (i)  Connect  the 
apparatus  shown  in  Fig.  101  with  the  water-pump.  Allow  a  negative 
pressure  of  5  or  6  inches  of  water  to  be  established  in  it,  as  shown 


FIG.  101. — HALDANE'S  APPARATUS  FOR  MEASURING  THE  QUANTITY  OF  CO., 
AND  AQUEOUS  VAPOUR  GIVEN  OFF  BY  AN  ANIMAL. 

A,  chamber  into  which  the  animal  is  put  ;  i  and  4,  Woulff  s  bottles  filled  with 
soda-lime  to  absorb  carbon  dioxide  ;  2,  3,  and  5,  Woulff's  bottles  filled  with  pumice- 
stone  soaked  in  sulphuric  acid  to  absorb  watery  vapour  ;  B  glass  bell-jar  suspended  in 
water,  by  means  of  which  the  negative  pressure  is  known  ;  P,  water- pump  which  sucks 
air  through  the  apparatus  ;  i  and  a  are  simply  for  absorbing  the  carbon  dioxide  and 
water  of  the  ingoing  air. 

by  the  rise  of  water  in  the  bell-jar,  B.  Then  close  the  open  tube  of 
carbon  dioxide  bottle  i,  and  clamp  the  tube  between  the  water-pump 
and  the  bell-jar.  If  the  negative  pressure  is  maintained,  the  arrange- 
ment is  air-tight.  Now  weigh  bottle  3  and  bottles  4  and  5,  the  last 
two  together.  Place  a  cat  in  the  respiratory  chamber  A,  connect  the 


A,  soda-lime  tube  ;  B,  sulphuric 
acid  tube  ;  C,  wooden  frame,  in 
which  A  and  B  are  supported  by 
wires  d  ;  b,  wire  hook,  which  grips- 
the  glass  tube  firmly,  and  by 
means  of  which  the  tubes  are  lifted 
out  of  the  frame  in  order  to  be 
weighed  ;  a,  short  piece  of  glass 
tubing,  by  taking  out  which  the 
absorption  tubes  are  disconnected 
from  the  rest  of  the  apparatus  ;  e. 
glass  tube  going  off  to  animal 
chamber.  The  right-hand  glass 
tube  of  B  should  not  touch  the. 
sulphuric  acid  as  depicted. 


FIG.  102. — ABSORPTION  TUBES  FOR  CO2  AND  MOISTURE. 

chamber  directly  with  the  water-pump,  and  test  whether  it  is  tight. 
Then  take  the  stopper  out  of  bottle  i,  and  adjust  the  rate  at  which 
air  is  drawn  through  the  apparatus.  Let  the  ventilation  go  on  for  a 
few  minutes,  then  insert  bottles  3,  4,  and  5  again.  Note  the  time 
exactly  at  this  point,  and  after  an  hour  disconnect  3,  4,  and  5,  and 
again  weigh.  The  difference  of  the  two  weighings  of  3  shows  the 


PRACTICAL  EXERCISES  277 

quantity  of  water  given  off  by  the  animal  in  an  hour ;  the  difference 
in  the  combined  weight  of  4  and  5,  the  quantity  of  carbon  dioxide. 
Weigh  the  cat,  and  calculate  the  amount  of  water  and  of  carbon 
dioxide  given  off  per  kilo  per  hour. 

(2)  For  the  student  it  is  more  convenient  to  use  smaller  animals. 
The  mouse  may  be  taken  as  an  example  of  a  warm-blooded  animal, 
and  the  frog  of  a  cold-blooded.  Instead  of  the  Woulff's  bottles  use 
wide  test-tubes  connected  as  in  Fig.  102,  and  for  the  animal  chamber 
a  small  beaker,  closed  with  a  very  carefully-fitted  cork  which  has 
been  boiled  in  paraffin.  The  inlet  and  outlet  tubes  of  the  chamber 
are  to  be  introduced  through  this  cork.  The  holes  for  these  are  to 
be  bored  with  the  greatest  care,  and  the  tubes  to  be  put  in  while  the 
cork  is  still  hot  from  boiling  in  paraffin.  Also  insert  a  thermometer 
about  6  inches  long  registering  from  o°  C.  to  45°  C.  Modeller's  wax 
is  to  be  used  finally  to  render  all  the  junctions  air-tight. 

Add  to  the  series  of  tubes  described  in  the  apparatus  a  single 
tube  containing  baryta-water.  This  is  placed  after  the  tube  5,  and 
so  arranged  that  the  air-current  bubbles  through  the  water.  As  long 
as  the  absorption  of  carbon  dioxide  is  complete,  the  baryta-water 
remains  clear.  Beyond  this  a  water-bottle  should  be  placed  to  act 
as  a  valve  and  to  indicate  the  negative  pressure  in  the  apparatus. 
It  can  be  most  simply  constructed  by  using  a  cylinder  of  stout  glass 
tubing  in  a  wide-mouthed  bottle  containing  some  water,  the  inlet  and 
outlet  tubes  passing  through  a  paraffined  cork  which  seals  the  upper 
end  of  the  cylinder. 

Before  making  an  observation,  test  whether  the  apparatus  is  air- 
tight, as  explained  above,  after  introducing  the  animal  into  the 
chamber,  sea'in ;  the  latter  with  wax,  and  connecting  it  with  the 
absorption  tubes.  But  a  negative  pressure  of  2  or  3  inches  of  water 
is  a  sufficient  test  for  the  small  apparatus. 

To  make  an  observation,  set  the  air-current  going  at  the  desired 
rate.  Allow  it  to  run  for  a  few  minutes  till  the  carbon  dioxide,  which 
has  accumulated  during  the  testing,  has  been  swept  out.  At  a  time 
which  has  been  decided  on  and  noted,  stop  the  current  by  discon- 
necting the  water-pump.  Disconnect  and  stopper  up  the  animal 
chamber,  and  weigh  it  as  quickly  as  possible.  Connect  up  again, 
using  only  recently-weighed  absorption-tubes,  and  finally  connect 
with  the  water-pump  and  allow  the  current  to  pass  for  a  definite 
period,  say  an  hour.  If  a  consecutive  series  of  observations  is  to  be 
made,  two  sets  of  tubes  should  be  prepared  for  use  during  alternate 
periods.  Use  in  each  case  two  soda-lime  tubes,  the  most  recently 
filled  one  being  placed  second  of  the  two. 

The  soda-lime  should  not  be  too  dry,  or  absorption  is  not 
sufficiently  rapid.  The  following  facts  are  made  out  in  the  observation  : 

(a]  The  loss  of  weight  by  the  animal  chamber  (chiefly  loss  by  the 
animal),  (b]  The  gain  of  the  sulphuric  acid  tube  in  water,  (c]  The 
gain  of  the  soda-lime  tubes  in  carbon  dioxide. 

If  we  compare  total  loss  and  total  gain,  we  find  they  do  not  corre- 
spond, the  gain  being  always  greater  than  the  loss.  The  surplus  can 
only  be  oxygen  which  has  been  absorbed  by  the  animal  and  added  to 


278  A  MANUAL  OF  PHYSIOLOGY 

the  hydrogen  and  carbon  of  its  substance  to  form  water  and  carbon 
dioxide.  Calculate  the  respiratory  quotient  (p.  225). 

The  following  series  of  experiments  may  be  done  with  this 
apparatus  by  advanced  students  :  (i)  Observe  the  amount  of  gaseous 
exchange  per  kilo  and  hour  at  room  temperature  in  :  (a)  A  cold- 
blooded animal  (frog),  (d)  a  warm-blooded  animal  (mouse),  (c)  Cal- 
culate the  respiratory  quotient  in  each  case.  (2)  Observe :  (a)  The 
effect  of  exercise  in  increasing,  and  of  rest  in  diminishing,  the 
total  gaseous  exchange  ;  (/£)  the  effect  of  food  in  increasing  the 
total  gaseous  exchange ;  (c}  the  effect  of  different  kinds  of  food 
(carbo-hydrates,  proteids,  etc.)  on  the  respiratory  quotient  (p.  225). 
(3)  Observe  the  reaction  of:  (a)  A  cold-blooded  animal,  (b)  a  warm- 
blooded animal,  to  changes  in  temperature  of  the  surrounding  air,  as 
shown  in  the  rise  and  fall  of  the  gaseous  exchange.  For  this,  arrange 
round  the  beaker  a  water-jacket  through  which  a  current  of  water 
flows.  Allow  cold  water  to  flow  through  the  jacket  for  half  an  hour, 
and  read  off  the  temperature  of  the  chamber  (say  10°  C.).  For  the 
next  half-hour  heat  the  water  in  the  jacket  till  the  air  of  the  chamber 
is  at  30°  C.  Lastly,  take  another  observation  of  a  cold  period. 
Compare  the  exchange  for  the  three  periods  (p.  228). 

7.  Section  of  both  Vagi. — Proceed  as  in  experiment  24,  p.  189, 
but  use  an  ordinary  rabbit ;  and  instead  of  cutting  the  sympathetic, 
pass  threads  under  both  vagi,  divide  them,  and  sew  up  the  wound. 
An  induction  coil  is  not  required,  unless  the  student  has  any  diffi- 
culty in  deciding  which  nerve  is  the  vagus.  The  point  may  be  at 
once  settled  by  stimulating  the  nerves  before  division.  Stimulation 
of  the  vagus  will  cause  slowing  or  stoppage  of  the  heart,  and  there- 
fore of  the  pulse  in  the  carotid,  and  quickening  of  respiration. 
Stimulation  of  the  sympathetic  will  have  neither  of  these  effects. 
A  dog  may  also  be  used,  and  the  vago-sympathetics  divided.  Count 
the  pulse  and  the  rate  of  respiration  before  and  after  the  section  of 
each  nerve,  and  observe  carefully  any  change  that  may  occur.  Also 
note  whether  the  depth  of  the  breathing  is  affected.  The  animal 
must  be  looked  at  once  at  least  on  the  day  of  the  operation,  and  its 
behaviour  carefully  observed.  It  should  be  seen  daily  thereafter  so 
long  as  it  survives.  A  rabbit  does  not  usually  live  much  more  than 
twenty-four  hours. 

As  soon  after  death  as  possible,  make  an  autopsy,  observing 
especially  the  state  of  the  lungs.  Harden  portions  of  the  lungs  that 
appear  to  contain  the  most  exudation  in  Miiller's  fluid  (ten  times  as 
much  fluid  as  tissue).  Change  the  fluid  next  day,  and  again  at  the 
end  of  a  week.  In  three  or  four  weeks  wash  out  the  Miiller's  fluid 
under  the  tap,  and  transfer  the  tissue  to  90  per  cent,  alcohol.  After 
a  lew  days  it  is  to  be  prepared  for  cutting  by  being  passed  succes- 
sively through  absolute  alcohol  (two  days),  absolute  alcohol  and 
ether  mixture  (two  days),  thin  celloidin  (two  or  three  days),  thick 
celloidin  (one  day).  Fasten  on  vulcanized  wood-fibre  and  cut 
sections  with  a  sliding  microtome,  moistening  the  knife  with  80  per 
cent,  alcohol.  Stain,  mount,  and  examine  under  the  microscope. 
Note  the  exudation  in  the  alveoli,  and  make  drawings.  Write  a 
report  of  your  complete  experiment. 

• 


Plate  II 


8erouf  alveolus 


Mucous  alveolus 


Crescentt  of  Gianuzzi 


Duet 


Supporting  connective  tistue 


1.  Section  of  submaxillary  gland  showing  both  mucous  and  serous  alveoli,  x 
(Stained  with  hsematoxylin., 


Before  secretion  (retting)  Jfter  tecretion  (active) 

2.  Section  of  seroas  gland,  x  800.    (Stained  with  borax  carmine.) 


Mucous  cells 


An  otinus 


Connective  tiMut 


Intermediate  duel 
leading  from  aeini  of  gland 

to  intralobular  duct 
3.  Section  of  mucous  glat*d  (after  secretion),  X  300.    (Stained  with  picrocarmiae.) 


CHAPTER    IV. 
DIGESTION. 

IN  the  last  chapter  we  have  described  the  manner  in  which 
the  interchange  of  gases  between  the  tissues  and  the  air  is 
carried  out.  We  have  now  to  consider  the  digestion  and 
absorption  of  the  solid  and  liquid  food,  its  further  fate  in 
relation  to  the  chemical  changes  or  metabolism  of  the 
tissues,  and  finally  the  excretion  of  the  waste  products  by 
other  channels  than  the  lungs. 

Logically,  we  ought  to  take  metabolism  after  absorption 
and  before  excretion,  tracing  the  food  through  all  its  vicissi- 
tudes from  the  moment  when  it  enters  the  blood  or  lymph 
till  it  is  cast  out  as  useless  matter  by  the  various  excretory 
organs.  Unfortunately,  however,  the  steps  of  the  process 
are  as  yet  almost  entirely  hidden  from  us ;  we  know  only 
the  beginning  and  the  end.  We  can  follow  the  food  from 
the  time  it  enters  the  alimentary  canal  till  it  is  taken  up  by 
the  tissues  of  absorption  ;  and  we  have  really  a  fair  know- 
ledge of  this  part  of  its  course.  We  can  collect  the  end 
products  as  they  escape  in  the  urine,  or  in  the  breath,  or  in 
the  sweat ;  and  our  knowledge  of  them  and  of  the  manner 
in  which  they  are  excreted  is  considerable.  But  of  the 
wonderful  pathway  by  which  the  dead  molecules  of  the  food 
mount  up  into  life,  and  then  descend  again  into  death,  we 
catch  only  a  glimpse  here  and  there.  Only  the  introduction 
and  the  conclusion  of  the  story  of  metabolism  are  at  present 
in  our  possession  in  fairly  continuous  and  legible  form.  We 
will  read  these  before  we  try  to  decipher  the  handful  of  torn 
leaves  which  represents  the  rest 


280  A  MANUAL  OF  PHYSIOLOGY 

Comparative.  —  In  the  lowest  kinds  of  animals,  such  as  the 
Amoeba,  there  is  neither  mouth,  nor  alimentary  canal,  nor  anus  :  the 
food,  wrapped  round  by  pseudopodia,  is  taken  in  at  any  part  of  the 
animal  with  which  it  happens  to  come  in  contact.  A  vacuole  is 
formed  around  it.  Acid  is  secreted  into  the  vacuole,  the  food  is 
digested  within  the  cell-substance,  and  the  part  of  it  which  is  useless 
for  nutrition  is  cast  out  again  at  any  part  of  the  surface. 

Coming  a  little  higher,  we  find  in  the  Ccelenterates  a  mouth  and 
alimentary  tube,  which  opens  into  the  body-cavity,  where  a  certain 
amount  of  digestion  seems  to  take  place,  and  from  which  the  food  is 
absorbed  either  through  the  cells  of  the  endoderm,  or,  as  in  Medusa, 
by  means  of  fine  canals,  which  radiate  from  the  body-cavity  into  its 
walls,  and  form  part  of  the  so-called  gastro-vascular  system.  In  the 
Echinodermata  we  have  a  further  development,  a  complete  alimentary 
canal  with  mouth  and  anus,  and  entirely  shut  off  from  the  body- 
cavity.  In  many  Arthropods  it  is  possible  already  to  distinguish 
parts  corresponding  to  the  stomach,  and  the  small  and  large  intes- 
tines of  higher  forms,  the  digestive  glands  being  represented  by 
organs  which  in  some  groups  seem  to  be  homologous  with  the  liver, 
and  in  others  with  the  salivary  glands  of  the  higher  vertebrates.  A 
few  Molluscs  seem  in  addition  to  possess  a  pancreas. 

Among  Vertebrates  fishes  have  the  simplest,  and  birds  and  mam- 
mals the  most  complicated,  alimentary  system.  In  the  lowest  fishes 
the  stomach  is  only  indicated  by  a  slight  widening  of  the  anterior 
part  of  the  digestive  tube.  In  water-living  Vertebrates  there  are  no 
salivary  glands.  In  Birds  the  oesophagus  is  generally  dilated  to  form 
a  crop,  from  which  the  food  passes  into  a  stomach  consisting  of  two 
parts,  one  pre-eminently  glandular  (proventriculus),  the  other  pre- 
eminently muscular  (ventriculus).  Among  Mammals  a  twofold 
division  of  the  stomach  is  distinctly  indicated  in  rodents  and  cetacece, 
but  this  organ  reaches  its  greatest  complexity  in  ruminants,  which 
possess  no  fewer  than  four  gastric  pouches.  The  differentiation  of 
the  intestine  into  small  and  large  intestine  and  rectum  is  more 
distinct,  both  anatomically  and  functionally,  in  Mammals  than  in 
lower  forms ;  but  there  are  marked  differences  between  the  various 
mammalian  groups  both  in  the  relative  size  of  the  several  parts  of 
the  digestive  tube,  and  in  the  proportion  between  the  total  length  of 
the  alimentary  canal  and  the  length  of  the  body.  In  general,  the 
canal  is  longest  in  herbivora,  shortest  in  carnivora.  Thus,  the  ratio 
between  length  of  body  and  length  of  intestine  is  in  the  cat  i  :  4, 
dog  i  :  6,  man  i  :  5  or  6,  horse  1:12,  cow  i  :  20,  sheep  i  :  27.  The 
relative  capacity  of  the  stomach,  small  intestine,  and  large  intestine, 
is  in  the  dog  6  :  2  :  1*5,  in  the  horse  i  :  3*5  :  7,  in  the  cow  7:2:1. 
The  area  of  the  mucous  surface  of  the  alimentary  canal  is  very  con- 
siderable, in  the  dog  more  than  half  that  of  the  skin,  the  surface  of 
the  small  intestine  being  three  times  that  of  the  stomach  and  four 
times  that  of  the  large  intestine.  In  the  horse  the  mucous  surface 
has  twice  the  area  of  the  skin. 

Anatomy  of  the  Alimentary  Canal  in  Man. — The  alimentary  canal 
is  a  muscular  tube,  which,  beginning  at  the  mouth,  runs  under  the 


• 


DIGESTION  281 

various  names  of  pharynx,  oesophagus,  stomach,  small  intestine,  large 
intestine,  and  rectum,  till  it  ends  at  the  anus.  Its  walls  are  largely 
composed  of  muscular  fibres  ;  its  lumen  is  clad  with  epithelium,  and 
into  it  open  the  ducts  of  glands,  which,  morphologically  speaking, 
are  involutions  or  diverticula  formed  in  its  course.  In  virtue  of  its 
muscular  fibres  it  is  a  contractile  tube ;  in  virtue  of  its  epithelial 
lining  and  its  special  glands  it  is  a  secreting  tube ;  in  virtue  of  both 
it  is  fitted  to  perform  those  mechanical  and  chemical  actions  upon 
the  food  which  are  necessary  for  digestion.  Its  inner  surface  is  in 
most  parts  richly  supplied  with  bloodvessels,  and  in  special  regions 
beset  with  peculiarly-arranged  lymphatics  ;  by  both  of  these  channels 
the  alimentary  tube  performs  its  function  of  absorption.  From  the 
beginning  of  the  oesophagus  to  the  end  of  the  rectum  the  muscular 
wall  consists,  broadly  speaking,  of  an  outer  coat  of  longitudinally- 
arranged  fibres,  and  a  thicker  inner  coat  of  fibres  running  circularly 
or  transversely  around  the  tube.  Between  the  layers  lies  a  plexus  of 
non-medullated  nerves  and  nerve-cells  (Auerbach's  plexus).  In  the 
stomach  the  longitudinal  fibres  are  found  only  on  the  two  curvatures, 
and  a  third  incomplete  coat  of  oblique  fibres  makes  its  appearance 
internal  to  the  circular  layer.  In  the  large  intestine,  again,  the 
longitudinal  fibres  are  chiefly  collected  into  three  isolated  strands. 
In  the  pharynx  the  typical  arrangement  is  departed  from,  inasmuch 
as  there  is  no  regular  longitudinal  layer ;  but  the  three  constrictor 
muscles  represent  to  a  certain  extent  the  great  circular  coat.  The 
muscles  of  the  mouth  and  of  the  pharynx  are  of  the  striped  variety. 
So  is  the  muscle  of  the  upper  half  of  the  oesophagus  in  man  and  the 
cat,  and  of  the  whole  oesophagus  in  the  dog  and  the  rabbit.  In  the 
rest  of  the  alimentary  canal  the  muscle  is  smooth,  except  at  the  very 
end,  where  the  external  sphincter  of  the  anus  is  striped  In  certain 
situations  the  circular  coat  is  developed  into  a  regular  anatomical 
sphincter,  a  definite  muscular  ring,  whose  function  it  is  to  shut  one 
part  of  the  tube  off  from  another  (sphincter  pylori),  or  to  help  to 
close  the  external  opening  of  the  tube  (internal  sphincter  of  anus). 
Elsewhere  a  tonic  contraction  of  a  portion  of  the  circular  coat, 
not  anatomically  developed  beyond  the  rest,  creates  a  functional 
sphincter  (cardiac  sphincter  of  stomach). 

Throughout  the  greater  part  of  the  digestive  tract  the  peritoneum 
forms  a  thin  serous  layer,  external  to  the  muscular  coat.  Internally 
the  muscular  coat  is  separated  from  the  mucous  membrane,  the  lining 
of  the  canal,  by  some  loose  areolar  tissue  containing  bloodvessels, 
lymphatics  and  nerves  (Meissner's  plexus),  and  called  the  submucous 
coat.  Between  the  mucous  and  submucous  layers,  but  belonging  to 
the  former,  in  the  whole  canal  below  the  beginning  of  the  oesophagus, 
is  a  thin  coat  of  smooth  muscular  fibre,  the  muscularis  mucosse,  con- 
sisting in  some  parts,  e.g.,  in  the  stomach,  of  two,  or  even  three, 
layers.  Between  this  and  the  lumen  of  the  canal  lie  the  ducts  and 
alveoli  of  glands,  surrounded  by  bloodvessels  and  embedded  in 
adenoid  or  lymphoid  tissue,  which  in  particular  regions  is  collected 
into  well-defined  masses  (solitary  follicles,  Peyer's  patches,  tonsils), 
extending,  it  may  be,  into  the  submucous  tissue.  In  the  mouth, 


282  A  MANUAL  OF  PHYSIOLOGY 

pharynx  and  oesophagus,  the  glands  lie  in  the  submucosa,  as  do  the 
glands  of  Brunner  in  the  duodenum ;  everywhere  else  they  are  con- 
fined to  the  mucous  membrane  proper.  Between  the  openings  of  the 
glands  the  mucous  membrane  is  lined  with  a  single  layer  of  columnar 
epithelial  cells,  sometimes  (in  the  small  intestine)  arranged  along  the 
sides  of  tiny  projections  or  villi.  At  the  ends  of  the  alimentary  canal, 
viz.,  in  the  mouth,  pharynx  and  oesophagus,  and  at  the  anus,  the 
epithelium  is  stratified  squamous,  and  not  columnar. 

The  purpose  of  food  is  to  supply  the  waste  of  the  tissues 
and  to  maintain  the  normal  composition  of  the  body.  In 
the  body  we  find  a  multitude  of  substances  marked  off  from 
each  other,  some  by  the  sharpest  chemical  differences,  others 
by  characters  much  less  distinct,  but  falling  upon  the  whole 
into  a  few  fairly  definite  groups.  Thus,  there  are  bodies  like 
serum-albumin,  serum-globulin,  myosin,  and  so  on,  which 
are  so  much  alike  that  they  can  all  be  placed  in  one  great 
class,  as  proteids.  Then  we  have  substances  like  glycogen 
and  dextrose,  vastly  simpler  in  their  composition,  and 
belonging  to  the  group  of  carbo-hydrates.  Then,  again,  fats 
of  various  kinds  are  widely  distributed  in  normal  animal 
bodies ;  and  inorganic  materials,  such  as  water  and  salts,  are 
never  absent. 

Now,  although  it  is  by  no  means  necessary  that  a  sub- 
stance in  the  body  belonging  to  one  of  these  great  groups 
should  be  derived  from  a  substance  of  the  same  group  in  the 
food,  it  has  been  found  that  no  diet  is  sufficient  for  man 
unless  it  contains  representatives  of  all ;  a  proper  diet  must 
include  proteids,  carbo-hydrates,  fats,  inorganic  salts  and 
water.  These  proximate  principles  have  to  be  obtained 
from  the  raw  material  of  the  food-stuffs ;  it  is  the  business 
of  digestion  to  sift  them  out  and  to  prepare  them  for 
absorption.  This  preparation  is  partly  mechanical,  partly 
chemical. 

The  water  and  salts  and  some  carbo-hydrates,  such  as 
dextrose,  are  ready  for  absorption  without  change.  Fats  are, 
probably,  for  the  most  part,  only  mechanically  altered.  In- 
diffusible  carbo-hydrates,  like  starch  and  dextrin,  are  changed 
into  diffusible  sugar,  and  the  natural  proteids  into  diffusible 
peptones.  Mechanical  division  of  the  food  is  an  important 
aid  to  the  chemical  action  of  the  digestive  juices.  We  shall 
see  that  this  mechanical  division  forms  a  great  part  of  the 


DIGESTION  283 

work  of  the  stomach,  but  it  is  normally  begun  in  the  mouth, 
and  it  is  of  consequence  that  this  preliminary  stage  should 
be  properly  performed. 

I.  The  Mechanical  Phenomena  of  Digestion. 

Mastication.  —  It  is  among  the  mammalia  that  regular  Q 
mastication  of  the  food  first  makes  its  appearance  as  an 
important  aid  to  digestion.  The  amphibian  bolts  its  fly,  the 
bird  its  grain,  and  the  fish  its  brother,  without  the  ceremony 
of  chewing.  In  ruminating  mammals  we  see  mastication 
carried  to  its  highest  point ;  the  teeth  work  all  day  long, 
and  most  of  them  are  specially  adapted  for  grinding  the 
food.  The  carnivora  spend  but  a  short  time  in  mastication ; 
their  teeth  are  in  general  adapted  rather  for  tearing  and 
cutting  than  for  grinding.  Where  the  diet  is  partly  animal 
and  partly  vegetable,  as  in  man,  the  teeth  are  fitted  for  all 
kinds  of  work ;  and  the  process  of  mastication  is  in  general 
neither  so  long  as  in  the  purely  vegetable  feeders,  nor  so 
short  as  in  the  carnivora. 

In  man  there  are  two  sets  of  teeth  :  the  temporary  or  milk 
teeth,  and  the  permanent  teeth.  The  milk-teeth  are  twenty 
in  number,  and  consist  on  each  side  of  four  incisors  or  * 
cutting-teeth,  two  canines  or  tearing-teeth,  and  four  molars 
or  grinding-teeth.  The  central  incisors  emerge  at  the 
seventh  month  from  birth,  the  other  incisors  at  the  ninth 
month,  the  canines  at  the  eighteenth,  and  the  molars  at  the 
twelfth  and  twenty-fourth  month  respectively.  Each  tooth 
in  the  lower  jaw  appears  a  little  before  the  corresponding 
one  in  the  upper  jaw.  Each  of  the  milk-teeth  is  in  course 
of  time  replaced  by  a  permanent  tooth,  and  in  addition  the 
vacant  portion  of  the  gums  behind  the  milk  set  is  now  filled 
up  by  twelve  teeth,  six  on  each  side,  three  above  and  three 
below.  These  twelve  are  the  permanent  molars ;  they  raise 
the  number  of  the  permanent  teeth  to  thirty-two.  The 
permanent  teeth  which  occupy  the  position  of  the  milk 
molars  now  receive  the  name  of  premolars.  The  first  tooth 
of  the  permanent  set  (the  first  true  molar)  appears  at  the 
age  of  6J  years ;  the  last  molar,  or  wisdom  tooth,  does  not 
emerge  till  the  seventeenth  to  the  twenty-fifth  year. 


284 


A  MANUAL  OF  PHYSIOLOGY 


In  mastication  the  lower  jaw  is  moved  up  and  down,  so 
as  to  alternately  separate  and  approximate  the  two  rows  of 
teeth.  It  has  also  a  certain  amount  of  movement  from  side 
(to  side,  and  from  front  to  back.  The  masseter,  temporal 
and  internal  pterygoid  muscles  raise,  and  the  digastric,  with 
'the  assistance  of  the  mylo-  and  genio-hyoid,  depresses,  the 
lower  jaw.  The  external  pterygoids  pull  it  forward  when 
both  contract,  forward  and  to  one  side  when  only  one 
contracts.  The  lower  fibres  of  the  temporal  muscle  retract 
the  jaw.  The  buccinator  and  orbicularis  oris  muscles 
prevent  the  food  from  passing  between  the  teeth  and  the 
cheeks  and  lips.  The  tongue  keeps  the  food  in  motion, 
works  it  up  with  the  saliva,  and  finally  gathers  it  into  a 
bolus  ready  for  deglutition. 

'  That  mastication  may  be  properly  performed,  the  teeth  must  be 
sound ;  and  that  they  may  remain  sound,  they  should  be  kept  clean. 
For  the  particles  of  food  that  adhere  to  the  teeth  after  a  meal  become 
the  feeding-ground  of  bacteria,  whose  acid  products  injuriously  affect 
the  enamel,  and  often  by  corroding  it  expose  the  dentine  Entrance 
is  thus  afforded  to  the  micro-organisms  of  caries,  which,  although 
they  cannot  live  on  enamel,  with  its  small  proportion  of  organic 
matter,  flourish  upon  dentine,  and  especially  upon  the  contents  of 
the  pulp  cavity  when  this  is  at  length  opened.  In  addition  to  the 
deformity  and  the  loss  of  distinctness  in  speech  which  extensive 
destruction  of  the  teeth  entails,  a  vast  number  of  cases  of  foul 
breath  are  entirely  due  to  filthy  and  carious  teeth.  And  since  in 
most  countries  bad  breath  subtracts  more  from  the  sum  of  human 
happiness  than  bad  laws,  there  is  perhaps,  even  in  this  relation  alone, 
no  single  hygienic  measure  that  costs  so  little  and  yields  so  much 
as  the  thorough  and  systematic  cleansing  of  the  mouth.  But  the 
proper  care  of  the  teeth  is  by  no  means  of  merely  aesthetic  interest ; 
it  is  of  great  importance  for  the  maintenance  of  health.  In  certain 
cases  of  severe  and  even  serious  dyspepsia,  the  cause  of  the  mischief 
lies  no  deeper  than  the  mouth,  and  the  patient  needs,  not  physic  for 
his  stomach,  but  filling  for  his  carious  teeth.  And  although  no 
physician  at  the  present  day  can  take  all  medicine  for  his  province 
as  Bacon  took  all  knowledge,  every  man  who  busies  himself  with  the 
treatment  of  alimentary  diseases  (and  how  few  diseases  are  not  in 
some  degree  alimentary !)  should  know  enough  about  the  teeth  to  be 
able  to  tell  when  a  patient  has  mistaken  the  doctor's  door  for  the 
dentist's.' 

Deglutition. — This  act  consists  of  a  voluntary  and  an  in- 
voluntary stage.  During  the  former  the  anterior  part  of 
the  tongue  is  pressed  against  the  hard  palate  so  as  to  thrust 


DIGESTION  285 

the  bolus  through  the  isthmus  of  the  fauces.  As  soon  as 
this  has  happened  and  the  food  has  reached  the  posterior 
portion  of  the  tongue,  it  has  passed  beyond  the  control  of  the 
will,  and  the  second  or  involuntary  stage  of  the  process  begins. 
This  stage  may  be  divided  into  two  parts :  (i)  pharyngeal, 
(2)  cesophageal — both  being  reflex  acts.  During  the  first 
the  food  has  to  pass  through  the  pharynx,  the  upper  portion 
of  which  forms  a  part  of  the  respiratory  tract,  and  is  in  free 
communication  with  the  larynx  during  ordinary  breathing. 
It  is  therefore  necessary  that  respiration  should  be  inter- 
rupted and  the  larynx  closed  while  the  food  is  being  moved 
through  the  pharynx.  But  that  the  interruption  may  be 
short,  the  food  must  be  rapidly  passed  over  this  perilous 
portion  of  its  descent.  The  pharynx  is  accordingly  provided 
with  rapidly-contracting  striped  muscle ;  and  that  none  of 
its  purchase  may  be  lost,  the  pharyngeal  cavity  is  cut  off 
from  the  nose  and  mouth  as  soon  as  the  bolus  has  entered 
it.  The  soft  palate  is  raised  by  the  levator  palati ;  at  the 
same  time  the  upper  part  of  the  pharynx,  narrowed  by  the 
contraction  of  the  superior  constrictor,  comes  forward  to 
meet  the  soft  palate,  closes  in  upon  it,  and  so  prevents  the 
food  from  passing  into  the  nasal  cavities.  The  pharynx  is 
cut  off  from  the  mouth  by  the  closure  of  the  fauces  through 
the  contraction  of  the  palato-pharyngeal  muscles  which  lie 
in  their  posterior  pillars.  The  larynx  is  pulled  upwards 
and  forwards  by  the  contraction  of  the  thyro-hyoid  muscle, 
and  the  elevation  of  the  hyoid  bone  by  the  muscles  which 
connect  it  to  the  lower  jaw.  The  glottis  is  closed  by  the 
approximation  of  the  vocal  cords  and  the  arytenoid  car- 
tilages, assisted  it  may  be  by  the  folding  down  of  the 
epiglottis  like  a  lid.  But  this  organ  can  hardly  play  the  great 
part  which  has  been  assigned  to  it  in  closing  the  larynx,  since 
swallowing  proceeds  in  the  ordinary  way  when  it  is  absent. 
The  morsel  of  food,  grasped  by  the  middle  and  lower  con- 
strictors as  it  leaves  the  back  of  the  tongue,  passes  rapidly 
and  safely  over  the  closed  larynx,  the  process  being  accele- 
rated by  the  pulling  up  of  the  lower  portion  of  the  pharynx 
over  the  bolus  by  the  action  of  the  palato-  and  stylo-pharyngei. 
The  second  or  oesophageal  portion  of  the  involuntary 


286  A  MANUAL  OF  PHYSIOLOGY 

stage  is  a  more  leisurely  performance.  The  bolus  is  carried 
along  by  a  peculiar  contraction  of  the  muscular  wall  of  the 
oesophagus,  which  travels  down  as  a  wave,  pushing  the  food 
"T  before  it.  When  the  food  reaches  the  lower  end  of  the 
gullet  the  tonic  contraction  of  that  part  of  the  tube  is  for 
a  moment  relaxed,  apparently  by  reflex  inhibition,  and  the 
morsel  passes  into  the  stomach. 

Such  is  the  view  of  the  mechanism  of  deglutition  that  has  hitherto 
commanded  the  largest  amount  of  support ;  and  when  the  food  is 
of  such  consistence  and  is  swallowed  in  morsels  of  such  size  that  it 
actually  distends  the  oesophagus,  there  is  little  doubt  that  this  view 
is  substantially  correct.  On  the  other  hand,  there  are  reasons  for 
supposing  that  liquid  or  semi-solid  food  is  shot  down  to  the  bottom 
of  the  lax  oesophagus  mainly  by  the  contraction  of  the  mylo-hyoid 
muscles,  and  that  it  is  only  after  lying  there  for  about  six  seconds 
that  it  is  forced  through  the  cardiac  sphincter  into  the  stomach  by 
the  arrival  of  the  tardy  peristaltic  contraction  of  the  cesophageal  wall 
(Kronecker  and  Meltzer). 

-r  There  are  certain  remarkable  peculiarities  which  dis- 
tinguish this  peristaltic  movement  of  the  oesophagus  from 
that  of  other  parts  of  the  alimentary  canal.  It  is  far  more 
closely  related  to  the  nervous  system,  and,  unlike  the 
peristaltic  contraction  of  the  intestine,  can  pass  over  any 
muscular  block  caused  by  ligature,  section,  or  crushing,  so 
long  as  the  nervous  connections  are  intact.  But  division 
of  the  cesophageal  nerves  causes,  as  a  rule,  stoppage  of 
cesophageal  movements  ;  although  under  certain  circum- 
stances an  excised  portion  of  the  tube  may  go  on  contract- 
ing in  the  characteristic  way  after  removal  from  the  body. 
Again,  the  peristaltic  wave  when  artificially  excited  seems 
always  under  normal  conditions  to  travel  down  the  oesophagus, 
never  to  spread  upwards  or  in  both  directions,  as  may 
happen  in  the  intestine.  Stimulation  of  the  mucous  mem- 
brane of  the  pharynx  will  cause  reflex  movements  of  the 
oesophagus,  while  stimulation  of  its  own  mucous  membrane 
is  ineffective.  From  these  facts  we  learn  that  although  the 
muscle  of  the  oesophagus  may  possess  a  feeble  power  of 
spontaneous  peristaltic  contraction,  yet  this  is  usually  in 
abeyance,  or  at  least  overmastered  by  nervous  control ;  so 
that  impulses,  passing  from  a  nerve  centre  and  travelling 


DIGESTION  287 

down  in  regular  progression  along  the  cesophageal  nerves, 
excite  the  muscular  fibres  in  succession  from  the  upper  to 
the  lower  end  of  the  tube. 

The  centre  for  the  whole  involuntary  stage  (both 
pharyngeal  and  cesophageal)  of  deglutition  lies  in  the  upper 
part  of  the  medulla  oblongata,  a  little  above  the  respiratory 
centre.  When  the  brain  is  sliced  away  above  the  medulla 
deglutition  is  not  affected,  but  if  the  upper  part  of  the 
medulla  is  removed,  the  power  of  swallowing  is  abolished. 
In  man  disease  of  the  spinal  bulb  interferes  far  more  with 
deglutition  than  disease  of  the  brain  proper. 

Normally  the  afferent  impulses  to  the  centre  are  set  up  by 
the  contact  of  food  or  saliva  with  the  mucous  membrane  of 
the  posterior  part  of  the  tongue,  the  soft  palate  and  the 
fauces,  the  nerve-channels  being  the  superior  laryngeal,  the 
pharyngeal  branches  of  the  vagus,  and  the  palatal  branches 
of  the  fifth  nerve.  A  feather  has  sometimes  been  swallowed 
involuntarily  by  a  reflex  movement  of  deglutition  set  up 
while  the  soft  palate  or  pharynx  were  being  tickled  to 
produce  vomiting.  Artificial  stimulation  of  the  central  end 
of  the  superior  laryngeal  will  cause  the  movements  of  degluti- 
tion independently  of  the  presence  of  food  or  liquid  ;  but  if 
the  central  end  of  the  glosso-pharyngeal  nerve  be  stimulated 
at  the  same  time,  the  movements  do  not  occur.  The  glosso- 
pharyngeal  is  therefore  able  to  inhibit  the  deglutition  centre, 
and  it  is  probably  owing  to  the  action  of  this  nerve  that  in  a 
series  of  efforts  at  swallowing,  repeated  within  less  than  a 
certain  short  interval  (about  a  second),  only  the  last  is 
successful. 

The  efferent  nerves  of  the  reflex  act  of  deglutition  are  the 
hypoglossal  to  the  tongue  and  the  thyro-hyoid  and  other 
muscles  concerned  in  raising  the  larynx  ;  the  glosso-pharyn- 
geal, vagus,  facial  and  fifth  to  the  muscles  of  the  palate, 
fauces,  and  pharynx ;  and  the  vagus  to  the  larynx  and 
oesophagus.  Section  of  the  vagus  interferes  with  the  passage 
of  food  along  the  oesophagus  ;  stimulation  of  its  peripheral 
end  causes  cesophageal  movements. 

Movements  of  the  Stomach  and  Intestines. — Here  the  peri- 
staltic  movements  become  much  more  independent  of  the 


288  A  MANUAL  OF  PHYSIOLOGY 

nervous  system,  and  much  more  dependent  upon  the  con- 
tinuity of  the  muscular  tissue  than  in  the  oesophagus.  The 
whole  of  the  stomach  does  not  take  part  equally  in  these 
movements.  We  may  divide  the  organ,  both  anatomically 
and  functionally,  into  two  portions — a  pyloric  portion,  or 
antrum  pylori,  and  a  larger  cardiac  portion,  or  fundus.  At 
the  junction  of  the  antrum  and  the  fundus  the  circular 
muscular  coat  is  thickened  into  a  ring  called  the  '  transverse 
band,'  or  '  sphincter  of  the  antrum.'  When  the  stomach  is 
empty  it  is  contracted  and  at  rest.  A  few  minutes  after 
food  is  taken  contractions  begin  in  the  antrum,  and  run  on 
in  constricting  undulations  (in  the  cat  at  the  rate  of  six  in 
the  minute)  towards  the  pyloric  sphincter.  Feeble  at  first, 
they  become  stronger  and  stronger  as  digestion  proceeds, 
and  gradually  come  to  involve  the  portion  of  the  fundus 
next  the  sphincter  of  the  antrum,  but  apparently  their 
direction  is  always  towards  the  pylorus,  never,  in  normal 
digestion,  away  from  it.  The  food  is  thus  subjected  to 
energetic  churning  movements  in  the  pyloric  end  of  the 
stomach,  and  worked  up  thoroughly  with  the  gastric  juice. 
Kept  in  constant  circulation,  it  gradually  becomes  reduced 
to  a  semi-liquid  mass,  the  chyme,  which  is  at  intervals  driven 
against  the  pylorus  by  strong  and  regular  peristaltic  con- 
tractions of  the  lower  end  of  the  stomach,  the  sphincter 
relaxing  from  time  to  time  by  a  sort  of  reflex  inhibition  to 
admit  the  better-digested  portions  into  the  duodenum,  but 
tightening  more  stubbornly  at  the  impact  of  a  hard  and 
undigested  morsel.  The  cardiac  end,  with  the  exception  of 
the  portion  that  borders  the  transverse  band,  appears  to 
take  no  share  in  these  peristaltic  movements.  And,  indeed, 
it  is  far  more  difficult  to  cause  such  contractions  by  artificial 
stimulation  in  the  fundus  than  in  the  pylorus.  The  two 
portions  of  the  stomach  seem  to  be  partially,  or  in  certain 
animals  from  time  to  time  completely,  cut  off  from  each 
other  by  the  contraction  of  the  sphincter  of  the  antrum. 
The  fundus,  so  far  as  its  mechanical  functions  are  con- 
cerned, appears  to  act  chiefly  as  a  reservoir  for  the  food, 
which  it  gradually  passes  into  the  antrum  as  digestion  goes 
on,  by  a  tonic  contraction  of  its  walls.  These  facts  have 


DIGESTION  289 

been  mainly  ascertained  by  observations  on  animals,  such  as 
the  dog  and  the  cat,  either  by  direct  inspection  after  opening 
the  abdomen  (Rossbach),  or  in  the  intact  body  by  means  of 
the  Rontgen  rays  (Cannon).  In  the  latter  method  the  food 
is  mixed  with  subnitrate  of  bismuth,  which  is  opaque  to 
these  rays,  so  that  when  the  animal  is  looked  at  through  a 
fluorescent  screen  the  stomach  appears  as  a  dark  shadow  in 
the  field. 

The  peristaltic  movements  of  the  small  intestine  are  the 
most  typical  of  their  kind.  Normally,  the  constriction 
travels  slowly  down  the  tube,  squeezing  the  contents  before 
it,  and  the  wave  ends  at  the  ileo-csecal  valve,  which  separates 
the  small  intestine  from  the  large.  The  cause  of  this^ 
definite  direction  of  the  peristaltic  wave  is  not  understood,/ 
but  it  is  grounded  in  the  anatomical  relations  of  the  intes- 
tinal wall.  For  when  a  portion  of  the  intestine  is  resectedA 
turned  round  in  its  place  and  sutured,  so  that  what  was 
before  its  upper  is  now  its  lower  end,  the  contraction  wave 
appears  to  be  unable  to  pass,  and  the  obstruction  to  the 
onward  flow  of  the  intestinal  contents  causes  marked  dila- 
tation of  the  gut,  and  sometimes  serious  disturbance  of 
nutrition.  But  under  certain  conditions  a  reverse  or  anti- 
peristalsis  is  set  up  even  in  the  intact  body,  and  by  artificial 
stimulation  it  is  easy  to  excite  peristaltic  waves  which  travel 
in  both  directions.  The  movements  of  the  large  intestines 
do  not  differ  essentially  from  those  of  the  small.  They  start 
at  the  ileo-caecal  valve  and  travel  downwards,  but  do  not 
normally  reach  the  rectum,  which,  except  during  defsecation, 
remains  at  rest. 

Influence  of  Nerves  on  the  Gastro-intestinal  Movements. — As  T 
we  have  said,  these  movements  are  much  less  closely 
dependent  on  the  nervous  system  than  are  those  of  the 
oesophagus ;  they  can  go  on  when  the  nervous  connections 
are  cut ;  they  cannot  spread  when  the  continuity  of  the 
muscle  is  destroyed,  and  the  mere  presence  of  food  will 
excite  them  when  reflex  action  has  been  excluded  by  section 
of  the  nerves.  Nevertheless,  the  nervous  system  does 
exercise  some  influence  in  the  way  of  regulation  and  control, 
if  not  in  the  way  of  direct  initiation  of  the  movements,  and 


290  A  MANUAL  OF  PHYSIOLOGY 

the  swallowing  or  even  the  smell  of  food  has  been  observed 
to  strengthen  the  contractions  of  a  loop  of  intestine  severed 
from  the  rest,  but  with  its  nerves  still  intact.  The  vagus  is 
the  efferent  channel  of  this  reflex  action  :  stimulation  of  its 
peripheral  end  may  cause  movements  of  all  parts  of  the 
alimentary  canal  from  oesophagus  to  large  intestine,  except 
apparently  the  cardiac  end  of  the  stomach  (Meltzer),  and 
may  strengthen  movements  already  going  on ;  but  section 
of  it  does  not  stop  them,  nor  hinder  the  food  from  causing 
peristalsis  wherever  it  comes.  It  is  only  the  distant  and 
reflex  action  of  food  which  division  of  the  vagi  can  abolish ; 
and  we  do  not  know  to  what  extent  the  movements  of 
normal  digestion  are  directly  excited,  and  to  what  extent 
they  are  reflex.  The  splanchnic  nerves  contain  fibres  by 
which  the  intestinal  movements  can  be  inhibited,  but  they 
are  certainly  not  always  in  action,  for  section  of  these  nerves 
has  no  distinct  effect  upon  the  movements,  in  spite  of  the 
vascular  dilatation  which  it  causes.  On  the  other  hand, 
stimulation  of  the  peripheral  end  of  the  cut  splanchnic 
usually,  but  by  no  means  invariably,  causes  arrest  of  the 
peristalsis.  Occasionally,  however,  it  has  the  opposite 
effect.  We  have  no  evidence  that  the  ganglion-cells  in  the 
walls  of  the  alimentary  canal  are  either  automatic  or  reflex 
centres  for  its  movements. 

The  lower  part  of  the  large  intestine  is  influenced  by  the 
sacral  nerves  (second,  third  and  fourth  sacral  in  the  rabbit), 
and  by  certain  lumbar  nerves,  in  the  same  way  as  the  higher 
parts  of  the  alimentary  canal,  and  particularly  the  small 
intestine,  are  influenced  by  the  vagus  and  the  splanchnics. 
Stimulation  of  these  sacral  nerves  within  the  spinal  canal 
causes  contraction,  tonic  or  peristaltic,  of  the  descending 
colon  and  rectum;  stimulation  of  the  lumbar  nerves  or  of 
the  portions  of  the  sympathetic  into  which  their  visceral 
fibres  pass  (lumbar  sympathetic  chain  from  second  to  sixth 
ganglia,  or  the  rami  from  it  to  the  inferior  mesenteric 
ganglia)  causes  inhibition  of  the  movements,  preceded,  it 
may  be,  by  a  transient  increase. 

Stimulation  of  the  sacral  nerves  causes  or  increases  the 
contraction  of  both  coats  of  the  descending  colon  and 


DIGESTION  291 

rectum;  stimulation  of  the  lumbar  nerves  inhibits  both. 
And  in  the  small  intestine  the  same  law  holds  good  ;  the 
two  coats  are  contracted  together  by  the  action  of  the 
vagus,  or  inhibited  together  by  that  of  the  splanchnics 
(Langley).  With  the  establishment  of  these  facts  an  in- 
genious theory,  originated  by  v.  Basch  and  adopted  by 
Gaskell,  falls  to  the  ground.  They  supposed  that  the  same 
nerve  which  causes  contraction  of  the  circular  coat  in  all 
tubes  whose  walls  are  made  up  of  two  layers  of  muscle, 
also  contains  fibres  that  bring  about  inhibition  of  the 
longitudinal  coat,  and  vice  versa.  It  was  suggested  that 
in  this  way  antagonism  between  the  two  coats  was  pre- 
vented. 

Some  drugs,  such  as  strychnia,  stimulate  peristaltic  move- 
ments by  acting  through  the  central  nervous  system ;  others, 
like  nicotine  and  muscarine,  by  acting  directly  on  the  intes- 
tine. Atropia  antagonizes  the  action  of  muscarine,  and 
morphia  that  of  nicotine,  in  both  cases  by  local  influence  ; 
but  after  morphia  the  intestinal  walls  are  steadily  contracted, 
not  relaxed.  An  isolated  loop  of  intestine,  fed  with  properly 
oxygenated  blood,  remains  altogether,  or  nearly,  at  rest ;  if 
the  blood  is  allowed  to  become  venous,  movements  are  set 
up  which  much  surpass  the  normal  movements,  both  in  their 
vigour  and  in  the  speed  with  which  they  travel.  For  this 
reason  the  peristaltic  contractions  seen  on  opening  the 
abdomen  in  a  recently  killed  animal  give  an  exaggerated 
picture  of  what  actually  occurs  in  the  intact  body. 

Defaecation  is  partly  a  voluntary  and  partly  a  reflex  act. 
But  in  the  infant  the  voluntary  control  has  not  yet  been 
developed ;  in  the  adult  it  may  be  lost  by  disease  ;  in  an 
animal  it  may  be  abolished  by  operation,  and  in  each  case 
the  action  becomes  wholly  reflex.  In  the  normal  course  of 
events,  the  rectum,  which  is  empty  and  quiescent  in  the 
intervals  of  defsecation,  is  excited  to  contraction  as  soon  as 
faeces  begin  to  enter  it  through  the  sigmoid  flexure,  and  the 
sensations  caused  by  their  presence  give  rise  to  the  desire  to 
empty  the  bowels.  This  desire  may  for  a  time  be  resisted 
by  the  will,  or  it  may  be  yielded  to.  In  the  latter  case  the 
abdominal  muscles  are  forcibly  contracted,  and  the  glottis 

19—2 


292 


A  MANUAL  OF  PHYSIOLOGY 


being  closed,  the  whole  effect  of  their  contraction  is  ex- 
pended in  raising  the  pressure  within  the  abdomen  and  pelvis, 
and  so  driving  the  faeces  from  the  colon  to  the  rectum.  The 
sphincter  ani  is  now  relaxed  by  the  inhibition  of  a  centre  in 
the  lumbar  portion  of  the  spinal  cord,  through  the  activity 
of  which  the  tonic  contraction  of  the  sphincter  is  normally 
maintained.  This  relaxation  is  partly  voluntary,  the  im- 
pulses that  come  from  the  brain  acting  probably  through  the 
medium  of  the  lumbar  centre;  but  in  the  dog,  after  section 
of  the  cord  in  the  dorsal  region,  the  whole  act  of  defaeca- 
tion,  including  contraction  of  the  abdominal  muscles  and 
relaxation  of  the  sphincter,  still  takes  place,  and  here  the 
process  must  be  purely  reflex.  The  contraction  of  the 
levatores  ani  helps  to  resist  over-distension  of  the  pelvic 
floor  and  to  pull  the  anus  up  over  the  faeces  as  they  escape. 

Vomiting. — We  have  seen  that  under  normal  conditions 
the  movements  of  the  alimentary  canal  always  tend  to  carry 
the  food  in  one  definite  direction,  along  the  tube  from  the 
mouth  to  the  rectum.  The  peristaltic  waves  generally  run 
only  in  this  direction,  and,  further,  regurgitation  is  prevented 
at  three  points  by  the  cardiac  and  pyloric  sphincters  of  the 
stomach  and  the  ileo-caecal  valve.  But  in  certain  circum- 
stances the  peristalsis  may  be  reversed,  one  or  more  of  the 
guarded  orifices  forced,  and  the  onward  stream  of  the 
intestinal  contents  turned  back.  In  obstruction  of  the  bowel, 
the  faecal  contents  of  the  large  intestine  may  pass  up  beyond 
the  ileo-caecal  valve,  and,  reaching  the  stomach,  be  driven 
by  an  act  of  vomiting  through  the  cardiac  orifice  ;  in  what  is 
called  '  a  bilious  attack,'  the  contents  of  the  duodenum  may 
pass  back  through  the  pylorus  and  be  ejected  in  a  similar 
way  ;  or,  what  is  by  far  the  most  common  case,  the  contents 
of  the  stomach  alone  may  be  expelled. 

Vomiting  is  usually  preceded  by  a  feeling  of  nausea  and  a 
rapid  secretion  of  saliva,  which  perhaps  serves,  by  means  of 
the  air  carried  down  with  it  when  swallowed,  to  dilate  the 
cardiac  orifice  of  the  stomach,  but  may  be  a  mere  by-play 
of  the  reflex  stimulation  bringing  about  the  act.  The 
diaphragm  is  now  forced  down  upon  the  abdominal 
contents,  the  glottis  closed,  and  the  abdominal  muscles 


DIGESTION  293 

strongly  contracted.  At  the  same  time  the  stomach  itself, 
and  particularly  the  antrum  pylori,  contracts,  the  cardiac 
orifice  relaxes,  and  the  gastric  contents  are  shot  up  into 
the  pharynx,  and  issue  by  the  mouth  or  nose.  Either 
the  diaphragm  and  abdominal  muscles  alone,  without  the 
stomach,  or  the  diaphragm  and  stomach  together,  without 
the  abdominal  muscles,  can  carry  out  the  act  of  vomiting. 
For  an  animal  whose  stomach  has  been  replaced  by  a  bladder 
filled  with  water  can  be  made  to  vomit  by  the  administra- 
tion of  an  emetic  (Magendie) ;  and  Hilton  saw  that  a  man 
who  lived  fourteen  years  after  an  injury  to  the  spinal  cord 
at  the  height  of  the  sixth  cervical  nerve,  which  caused 
complete  paralysis  below  that  level,  could  vomit,  though 
with  great  difficulty.  In  a  young  child,  in  which  very  slight 
causes  will  induce  vomiting,  the  stomach  alone  contracts 
during  the  act.  But  in  the  adult  such  a  contraction  is 
ineffectual,  and  the  same  appears  to  be  the  case  in  animals, 
for  a  dog  under  the  influence  of  a  moderate  dose  of  curara, 
which  paralyzes  the  voluntary  muscles  but  not  the  stomach, 
cannot  vomit. 

The  nerve  centre  is  in  the  medulla  oblongata.  It  may  be 
excited  by  many  afferent  channels :  irritation  of  the  fauces 
or  pharynx,  of  the  stomach  or  intestines  (as  in  strangulated 
hernia),  of  the  liver  or  kidney  (as  in  cases  of  gallstone  or 
renal  calculi),  of  the  uterus  or  ovary,  and  of  the  brain  (as 
in  cerebral  tumour),  are  all  capable  of  causing  vomiting  by 
impulses  passing  from  them  to  the  vomiting  centre. 

The  vagus  nerve  in  man  certainly  contains  afferent  fibres 
by  the  stimulation  of  which  this  centre  can  be  excited, 
i  for  it  has  been  noticed  that  when  the  vagus  was  exposed 
in  the  neck  in  the  course  of  an  operation,  the  patient 
vomited  whenever  the  nerve  was  touched  (Boinet,  quoted 
by  Cowers).  In  meningitis,  vomiting  is  often  a  prominent 
symptom,  and  is  sometimes  due  to  irritation  of  the  vagus 
nerve  by  the  inflammatory  process. 

Some  drugs  act  as  emetics  by  irritating  surfaces  in  which 
efficient  afferent  impulses  may  be  set  up,  the  gastric  mucous 
membrane,  for  example ;  sulphate  of  zinc  and  sulphate  of 
copper  act  mainly  in  this  way.  Apomorphia,  on  the  other 


294  ^  MANUAL  OF  PHYSIOLOGY 

hand,  stimulates  the  centre  directly,  and  this  is  also  the 
mode  in  which  vomiting  is  produced  in  certain  diseases 
of  the  medulla  oblongata.  The  efferent  nerves  for  the 
diaphragm  are  the  phrenics,  for  the  abdominal  muscles  the 
intercostals.  The  impulses  which  cause  contraction  of  the 
stomach  pass  along  the  vagi.  Dilatation  of  the  cardiac 
orifice  is  brought  about  partly  by  the  shortening  of  muscular 
fibres,  which  spread  out  upon  the  stomach  from  the  lower 
end  of  the  oesophagus,  perhaps  partly  by  nervous  inhibition. 
— ^* 
— p  II.  The  Chemical  Phenomena  of  Digestion. 

The  chemical  changes  wrought  in  the  food  as  it  passes 
along  the  alimentary  canal  are  due  to  the  secretions  of 
various  glands,  which  line  its  cavities,  or  pour  their  juices 
into  it  through  special  ducts.  These  secretions  owe  their 
power  for  the  most  part  to  substances  present  in  them 
in  very  small  amount,  but  which,  nevertheless,  act  with 
extraordinary  energy  upon  the  various  constituents  of  the 
food,  causing  profound  changes  without  being  themselves 
used  up,  or  their  digestive  power  affected.  These  marvellous 
and  as  yet  mysterious  agents  are  the  unformed  or  un- 
organized ferments — unorganized  because,  unlike  some  other 
ferments,  such  as  yeast,  their  action  does  not  depend  upon 
the  growth  of  living  cells.  Their  chemical  nature  has  not 
been  exactly  made  out ;  some  of  them  at  least  do  not  appear 
to  be  proteids.  But  it  is  doubtful  whether  even  one  of  the 
ferments  of  the  digestive  juices  has  as  yet  been  satisfactorily 
isolated,  and  at  present  it  is  only  by  their  effects  that  we 
recognise  them.  Some  of  them  act  best  in  an  alkaline,  some 
in  an  acid  medium;  they  all  agree  in  having  an  'optimum' 
temperature,  which  is  more  favourable  to  their  action  than 
any  other ;  a  low  temperature  suspends  their  activity,  and 
boiling  abolishes  it  for  ever.  The  action  of  all  of  them  seems 
to  be  hydrolytic;  i.e.,  it  is  accompanied  with  the  taking  up 
of  the  elements  of  water  by  the  substance  acted  upon.  The 
accumulation  of  the  products  of  the  action  first  checks  and 
then  arrests  it. 

Beside  these  unformed  ferments,  certain  formed  ferments, 
or  micro-organisms,  are  present  in  parts  of  the  alimentary 


DIGESTION  295 

canal,  and  even  in  normal  digestion  contribute  to  the 
changes  brought  about  in  the  food ;  while  under  abnormal 
conditions  they  may  awaken  into  troublesome,  and  even 
dangerous,  activity.  It  is  possible  that  many  of  these  act 
by  producing  unorganized  ferments,  and  that  the  distinction 
between  the  two  kinds  of  ferments  is  rather  superficial. 

It  is  now  necessary  to  consider  in  detail  the  nature  of 
the  various  juices  yielded  by  the  digestive  glands,  and  the 
mechanism  of  their  secretion,  so  far  as  it  is  known  to  us. 
Since  it  is  along  the  digestive  tract  that  glandular  action 
is  seen  on  the  greatest  scale,  this  discussion  will  practically 
embrace  the  nature  of  secretion  in  general.  And  here  it 
may  be  well  to  say  that,  although  in  describing  digestion  it 
is  necessary  to  break  it  up  into  sections,  a  true  view  is  only 
got  when  we  look  upon  it  as  a  single,  though  complex, 
process,  one  part  of  which  fits  into  the  other  from  beginning 
to  end.  It  is,  indeed,  the  duty  of  the  physiologist,  wherever 
it  is  possible  to  insert  a  cannula  into  a  duct  and  to  drain  off 
an  unmixed  secretion,  to  investigate  the  properties  of  each 
juice  upon  its  own  basis ;  but  it  must  not  be  forgotten  that 
in  the  body  digestion  is  the  joint  result  of  the  chemical 
work  of  five  or  six  secretions,  the  greater  number  of  which 
are  actually  mixed  together  in  the  alimentary  canal,  and  of 
the  mechanical  work  of  the  gastro-intestinal  walls. 

*The  Chemistry  of  the  Digestive  Juices, 
(i)  Saliva. — The  saliva  of  the  mouth  is  a  mixture  of  the 
secretions  of  three  large  glands  on  each  side,  and  of  many 
small  ones.  The  large  glands  are  the  parotid,  which  opens 
by  Stenson's  duct  opposite  the  second  upper  molar  tooth ; 
the  submaxillary,  which  opens  by  Wharton's  duct  under  the 
tongue  ;  and  the  sublingual,  opening  by  a  number  of  ducts 
near  and  into  Wharton's.  The  small  glands  are  scattered 
over  the  sides,  floor,  and  roof  of  the  mouth,  and  over  the 
tongue. 

Two  types  of  salivary  glands,  the  serous  or  albuminous  and 
the  mucous,  are  distinguished  by  structural  characters  and 
by  the  nature  of  their  secretion  ;  and  the  distinction  has 
been  extended  to  other  glands.  The  parotid  of  many,  if  not 


296  A  MANUAL  OF  PHYSIOLOGY 

all,  mammals  is  a  purely  serous  gland ;  it  secretes  a  watery 
juice  with  a  general  resemblance  in  composition  to  dilute 
blood-serum.  The  submaxillary  of  the  dog  and  cat  is  a 
typical  mucous  gland ;  its  secretion  is  viscid,  and  contains 
mucin.  The  submaxillary  gland  of  man  is  a  mixed  gland ; 
mucous  and  serous  alveoli,  and  even  mucous  and  serous  cells, 
are  intermingled  in  it  (Plate  II.,  Fig.  i).  The  submaxillary 
of  the  rabbit  is  purely  serous.  The  sublingual  is  in  general  a 
mixed  gland,  but  with  far  more  mucous  than  serous  alveoli. 
The  mixed  saliva  is  a  somewhat  viscous,  colourless  liquid 
of  alkaline  reaction  and  low  specific  gravity  (average  about 
1005).  Besides  water  and  salts,  it  contains  mucin  (entirely 
from  the  submaxillary,  the  sublingual  and  the  small  mucous 
glands  of  the  mouth),  to  which  its  viscidity  is  due,  traces  of 
serum-albumin  and  sjej^mij^Lo^ljn,  (chiefly  from  the  parotid), 
(and  a  ferment — pty_alin.  The  salts  are  calcium  carbonate 
and  phosphate  (often  deposited  as  'tartar'  around  the  teeth, 
occasionally  as  salivary  calculi  in  the  glands  and  ducts), 
sodium  and  potassium  chloride,  and  usually,  but  not  always, 
a  trace  of  sulphQcyanjde  of  potassium,  detected  by  the  red 
colour  which  it  strikes  with  ferric  chloride.*  The  total 
solids  amount  only  to  five  or  six  parts  in  the  thousand.  A 
great  deal  of  carbon  dioxide  can  be  pumped  out  from  saliva, 
as  much  as  60  to  70  c.c.  from  100  c.c.  of  the  secretion,  i.e., 
more  than  can  be  obtained  from  venous  blood.  Only  a 
small  proportion  of  this  is  in  solution,  the  rest  existing  as 
carbonates.  A  very  small  quantity  of  oxygen  (about 
0*5  volume  per  cent.)  appears  also  to  be  present  even  in 
saliva  which  has  not  come  into  contact  with  the  air 
(Pfluger).  Under  the  microscope  epithelial  scales,  leucocytes 
(the  so-called  salivary  corpuscles),  bacteria,  and  portions  of 
food,  may  be  found.  All  these  things  are  as  accidental  as 
the  last — they  are  mere  flotsam  and  jetsam,  washed  by  the 
saliva  from  the  inside  of  the  mouth.  But  greater  significance 
attaches  to  certain  peculiar  bodies,  either  spherical  or  of 
irregular  shape,  that  are  seen  in  the  viscid  submaxillary 

*  The  sulphocyanide  is  absent  from  the  saliva  of  many  animals.  In 
12  dogs  the  saliva  obtained  from  the  submaxillary  gland  by  stimulation 
of  the  chorda  tympani  only  once  contained  a  trace  of  it. 


DIGESTION  297 

saliva  of  the  dog  or  cat.  They  appear  to  be  masses  of 
secreted  material.  The  quantity  of  saliva  secreted  in  the 
twenty-four  hours  varies  a  good  deal.  On  an  average  it  is 
from  i  to  2  litres.  (Practical  Exercises,  p.  374.) 

Besides  its  functions  of  dissolving  sapid  substances,  and 
so  allowing  them  to  excite  sensations  of  taste,  of  moistening 
the  food  for  deglutition  and  the  mouth  for  speech,  and  of 
cleansing  the  teeth  after  a  meal,  saliva,  in  virtue  of  its 
ferment,  ptyalin,  is  amylolytic ;  that  is,  it  has  the  power  of 
digesting  starch  and  converting  it  into  maltose^  a  reducing  ( 
sugar.  In  man  the  secretion  of  any  of  the  three  great 
salivary  glands  has  this  power,  although  that  of  the  parotid 
is  most  active.  In  the  dog,  on  the  other  hand,  parotid 
saliva  has  little  action  on  starch,  and  submaxillary  none  at 
all ;  while  in  animals  like  the  rat  and  the  rabbit  the  parotid 
secretion  is  highly  active.  In  the  horse,  sheep,  and  ox,  the 
saliva  secreted  by  all  the  glands  seems  equally  inert.  A 
watery  or  glycerine  extract  of  a  gland  whose  natural  secre- 
tion is  active  also  possesses  amylolytic  power. 

Starch- grains  consist  of  granulose  enclosed  in  envelopes 
of  cellulose.  Only  the  granulose  is  acted  upon  by  ptyalin, 
and  hence  unboiled  starch,  in  which  the  cellulose  envelopes 
are  intact,  is  but  slowly  affected  by  saliva.  When  starch  is 
boiled,  the  envelopes  are  ruptured,  and  the  granulose  passes 
into  imperfect  solution,  yielding  an  opalescent  liquid.  If  a 
little  saliva  be  added  to  some  boiled  starch  solution  which 
is  free  from  sugar,  and  the  mixture  be  set  to  digest  at  a 
suitable  temperature  (say  40°  C.),  the  solution  in  a  very  short 
time  loses  its  opalescence  and  becomes  clear.  It  still, 
however,  gives  the  blue  reaction  with  iodine;  and  Trommer's 
test  (p.  23)  shows  that  no  sugar  has  as  yet  been  formed. 
The  change  is  so  far  purely  a  physical  one ;  the  substance  in 
solution  is  soluble  starch.  Later  on  the  iodine  reaction 
passes  gradually  through  violet  into  red  ;  and  finally  iodine 
causes  no  colour  change  at  all,  while  maltose  is  found  in 
large  amount,  along  with  isomaltose,  a  sugar  having  the 
same  formula  as  maltose,  but  differing  from  it  in  the  melting 
point  of  the  crystalline  compound  formed  by  it  with  phenyL 
h^drazine  (p.  426).  Traces  of  dextrose,  a  sugar  which  rotates 


298  A  MANUAL  OF  PHYSIOLOGY 

the  plane  of  polarization  less  than  maltose,  but  has  greater 
reducing  power,  are  produced  by  the  further  action  of  the 
saliva  on  maltose  itself.  When  a  small  quantity  of  ferment 
acts  for  a  short  time,  the  production  of  isomaltose  is 
favoured.  The  production  of  maltose  and  dextrose  is 
favoured  by  the  action  of  a  large  quantity  of  ferment  for  a 
long  time  (KUlz  and  Vogel). 

The  red  colour  indicates  the  presence  of  a  kind  of  dextrin 

called  erythrodextrin  ;  the  violet  colour  shows  that  at  first 

this  is  still  mixed  with  some  unchanged  starch.     Soon  the 

erythrodextrin    disappears,   and   is   succeeded    by   another 

dextrin,  which  gives  no  colour  with  iodine,  and  is  therefore 

called    achroodextrin.     This     is    partly,    but    in    artificial 

digestion  never  completely,  converted  into  maltose,  and  can 

always  at  the  end  be  precipitated  in  greater  or  less  amount 

by  the  addition  of  alcohol  to  the  liquid.     It  is  probable  that 

a  whole  series  of  dextrins  is  formed  during  the  digestion  of 

starch.     Some  of  these  may  appear  as  forerunners  of  the 

sugar,  others  merely  as  concomitants  of  its  production.    The 

latter  may  never  pass  into  sugar;  and  it  is  certain  that  sugar 

may  appear  before  all  the  starch  has  been  converted  into 

achroodextrin.     When  the  sugar  is  removed  as  it  is  formed, 

as  is  approximately  the  case  when  the  digestion  is  performed 

in  a  dialyser,  the  residue  of  unchanged  dextrin  is  less  than 

when  the  sugar  is  allowed  to  accumulate  (Lea).    In  ordinary 

artificial  digestion,  for  instance,  under  the  most  favourable 

circumstances  at  least  12  to  15  per  cent,  of  the  starch  is  left 

as  dextrin ;  in  dialyser  digestions  the  residue  of  dextrin  may 

be  little  more  than  4  per  cent.     This  goes  far  to  explain  the 

complete  digestion  of  starch  which  apparently  takes  place  in 

the  alimentary  canal,  a  digestion  so  complete  that,  although 

soluble  starch    and  dextrin    may  be  found  in  the  stomach 

after  a  starchy  meal,  they  do  not  occur  in  the  intestine,  or 

only  in  minute  traces.     Here  the  amylolytic  ferment  of  the 

pancreatic  juice,  which,  as  we  shall  see,  is  essentially  the 

same  in  its  action  as  ptyalin,  only  more  powerful,  must  be 

able  to  effect  a  very  complete  conversion. 


DIGESTION  299 

It  is  impossible  with  our  present  knowledge  to  represent  the  entire 
process  by  a  chemical  equation.  If  we  look  only  to  the  final  product, 
the  equation 

(C6H1005).  +  \  H20  =  ?(C12H2A,) 

Starch.  Water.  Maltose. 

or 

2(CfiH100B)a  +  0H20  =  flC12H22Ou 

will  represent  the  change  in  natural  and  complete  digestion.  The 
molecule  of  starch  being  taken  as  some  unknown  multiple,  a,  of  the 
group  CGH10O5,  the  first  equation  suits  the  case  of  a  being  an  even 
number,  and  the  second  that  of  a  being  an  odd  number. 

If  we  accept  4  per  cent,  as  the  minimum  residue  of  unchanged 
dextrin  in  the  best  artificial  digestion,  or,  in  other  words,  if  we  suppose 
that  of  25  parts  of  starch  24  are  changed  into  maltose,  and  i  remains 
as  dextrin,  our  equation,  taking  the  dextrin  molecule  as  a  multiple  b 
of  C6H10O5,  will  be  : 


Starch.  Water.  Maltose.  Dextrin. 

for  the  case  where  v  is  a  whole  number.     If  7-   is  not  a  whole 
b  o 


number,  we  should  have  to  clear  of  fractions  by  multiplying  both 

sides  by  —   where 
m 

We  should  thus  get  : 


sides  by  —   where  m  is  the  greatest  common  measure  of  a  and  b. 
m 


Starch.  Water.  Maltose.  Dextrin. 

It  is  a  notable  fact  that  amylolytic  ferments  are  not 
confined  to  the  animal  body.  Diastase,  which  is  present  in 
all  sprouting  seeds,  and  may  be  readily  extracted  by  water 
from  malt,  forms  maltose  and  dextrin  from  starch.  Its 
optimum  temperature,  however,  is  about  65°  C.,  while  that 
of  ptyalin  is  about  40°  C. 

Salivary  digestion  goes  on  best  in  a  neutral  or  slightly 
alkaline  medium.  It  can,  however,  still  proceed  when  the 
medium  is  made  faintly  acid  ;  but  an  acidity  equal  to  that 
of  a  *i  per  cent,  solution  of  hydrochloric  acid  stops  it 
completely,  although  the  ferment  is  still  for  a  time  able  to 
act  when  the  acidity  is  sufficiently  reduced.  Strong  acids 
or  alkalies  permanently  destroy  it.  These  facts  are  of  con- 
sequence, for  they  show  that  in  the  mouth,  where  the 
reaction  is  alkaline,  the  conditions  are  favourable  to  salivary 


300  A  MANUAL  OF  PHYSIOLOGY 

digestion ;  while  in  the  stomach,  where,  as  we  shall  see,  it 
is  acid  during  the  greater  part  of  digestion,  the  conditions 
are  not  so  favourable,  but  may  be,  on  the  contrary,  inimical. 
Although  the  food  stays  but  a  short  time  in  the  mouth, 
there  is  no  doubt  that,  in  man  at  least,  some  of  the  starch 
is  there  changed  into  sugar  (p.  375).  But  this  does  not  seem 
to  be  the  case  in  all  animals.  Something  depends  on  the 
amylolytic  activity  of  the  saliva,  and  something  upon  the 
form  in  which  the  starchy  food  is  taken,  whether  it  is  cooked 
or  raw,  enclosed  in  vegetable  fibres  or  exposed  to  free 
admixture  with  the  secretions  of  the  mouth. 

It  is  important  to  note  here  that  hydrolytic  changes  of 
very  much  the  same  nature  as  those  produced  by  ptyalin 
i  can  be  brought  about  in  other  ways.  If  starch  is  heated  for 
a  time  with  dilute  hydrochloric  or  sulphuric  acid,  it  is 
changed  first  into  dextrin,  and  then  into  a  form  of  reducing 
sugar,  which,  however,  is  not  maltose,  but  dextrose.  If 
maltose  is  treated  with  acid  in  the  same  way,  it  is  also 
changed  into  dextrose.  When  glycogen  (p.  439)  is  boiled 
with  dilute  oxalic  acid  at  a  pressure  of  three  atmospheres, 
isomaltose  and  dextrose  are  formed  (Cremer).  We  shall  see 
later  on  that  the  action  of  other  ferments  can  also  be  to  a 
certain  extent  imitated  by  purely  artificial  means.  In  fact, 
some  of  the  ferments  accomplish  at  a  comparatively  low 
temperature  what  can  be  done  in  the  laboratory  at  a  higher 
temperature,  and  by  the  aid  of  what  we  may  call  more 
violent  methods. 

(2)  Gastric  Juice. — The  Abbe  Spallanzani,  although  not, 
perhaps,  the  first  to  recognise,  was  the  first  to  study  system- 
atically, the  chemical  powers  of  the  gastric  juice,  but  it  was 
by  the  careful  and  convincing  experiments  of  Beaumont 
that  the  foundation  of  our  exact  knowledge  of  its  composi- 
tion and  action  was  laid. 

It  is  difficult  to  speak  without  enthusiasm  of  the  work  of  Beaumont,, 
if  we  consider  the  difficulties  under  which  it  was  carried  on.  An 
army  surgeon  stationed  in  a  lonely  post  in  the  wilderness  that  was 
then  called  the  territory  of  Michigan,  a  thousand  miles  from  a 
University,  and  four  thousand  from  anything  like  a  physiological 
laboratory,  he  was  accidentally  called  upon  to  treat  a  gun-shot 
wound  of  the  stomach  in  a  Canadian  voyageur,  Alexis  St.  Martin. 


DIGESTION  301 

When  the  wound  healed  a  permanent  fistulous  opening  was  left,  by 
means  of  which  food  could  be  introduced  into  the  stomach  and  T~ 
gastric  juice  obtained  from  it.  Beaumont  at  once  perceived  the 
possibilities  of  such  a  case  for  physiological  research,  and  began  a 
series  of  experiments  on  digestion.  After  a  while,  St.  Martin,  with 
the  wandering  spirit  of  the  voyageur,  returned  to  Canada  without 
Dr.  Beaumont's  consent  and  in  his  absence.  Beaumont  traced  him, 
with  great  difficulty,  by  the  help  of  the  agents  of  a  fur-trading 
company,  induced  him  to  come  back,  provided  for  his  family  as  well 
as  for  himself,  and  proceeded  with  his  investigations.  A  second 
time  St.  Martin  went  back  to  his  native  country,  and  a  second 
time  the  zealous  investigator  of  the  gastric  juice,  at  heavy  expense, 
s-ecured  his  return.  And  although  his  experiments  were  necessarily 
less  exact  than  would  be  permissible  in  a  modern  research,  the 
modest  book  in  which  he  published  his  results  is  still  counted 
among  the  classics  of  physiology.  The  production  of  artificial 
fistulae  in  animals,  a  method  that  has  since  proved  so  fruitful,  was  first 
suggested  by  his  work. 

Gastric  juice  when  obtained  pure,  as  it  can  be  from  an 
accidental  fistula  in  man,  or  by  mechanically  stimulating  the 
mucous  membrane  of  the  stomach  of  a  fasting  dog  through 
an  artificial  gastric  fistula,  is  a  thin,  colourless  liquid  of  low 
specific  gravity  (1002  to  1005)  and  distinctly  acid  reaction. 
The  total  solids  average  about  5  parts  per  thousand,  about 
one  half  being  inorganic  salts,  chiefly  _sqdium  and  potassium 
chloride.  Two  ferments  are  present :  pepsin,  which  changes 
proteids  into  peptones ;  and  rennin.  which  curdles  milk. 
The  acidity  is  due  to  free  hydrochloric  acid,  the  proportion 
of  which  in  man  is  usually  something  like  '2  per  cent.,  but 
more  in  the  dog  ("3  to  "5  per  cent.).  It  is  said  that  in 
cancer  of  the  stomach  the  free  hydrochloric  acid  is  replaced 
by  lacticjicidj  and  it  is  known  that  in  health  some  lactic 
acid  is  often  present  when  the  stomach  contains  food,  being 
produced  from  the  carbo-hydrates  by  the  action  of  a  ferment 
or  ferments,  not  specific  to  gastric  juice,  but  found  every- 
where in  the  alimentary  canal.  That  in  normal  gastric 
juice  the  acidity  is  not  due  to  lactic  acid  can  be  shown  by 
Uffelmann's  test  (Practical  Exercises,  p.  378). 

More  than  this,  it  is  not  due  to  an  organic,  but  to  an 
inorganic  acid,  for  healthy  gastric  juice  causes  such  an 
alteration  in  the  colour  of  aniline  dyes  like  congo-red  and! 
methyl  violet,  as  would  be  produced  by  dilute  mineral  acids,/ 
and  not  by  organic  acids,  even  when  present  in  much  greater 


302  A  MANUAL  OF  PHYSIOLOGY 

strength.  Finally,  when  the  bases  and  acid  radicals  of  the 
juice  are  quantitatively  compared,  it  is  found  that  there 
is  more  chlorine  than  is  required  to  combine  with  the 
bases ;  the  excess  must  be  present  as  free  hydrochloric  acid. 
The  quantity  of  gastric  juice  secreted  is  very  great ;  it  has 
been  estimated  at  as  much  as  5  to  10  litres  in  twenty-four 
hours,  or  five  times  as  much  as  the  quantity  of  saliva 
secreted  in  the  same  time.  But  such  estimates  are  loose 
and  uncertain. 

The  great  action  of  gastric  juice  is  upon  proteids.  In  this 
two  of  its  constituents  have  a  share,  the  pepsin  and  the  free 
acid.  One  member  of  this  chemical  copartnery  cannot  act 
without  the  other ;  peptic  digestion  requires  the  presence 
both  of  pepsin  and  of  acid ;  and,  indeed,  an  active  artificial 
juice  can  be  obtained  by  digesting  the  gastric  mucous 
membrane  with  *2  per  cent,  hydrochloric  acid.  A  glycerine 
extract  of  a  stomach  which  is  not  too  fresh  also  possesses 
peptic  powers  ;  but  it  requires  the  addition  of  a  sufficient 
quantity  of  acid  to  render  them  available. 

Well-washed  fibrin  obtained  from  blood  is  a  convenient 
proteid  for  use  in  experiments  on  digestion.  Since  the 
blood  contains  traces  of  pepsin,  the  fibrin  should  be  boiled 
to  destroy  any  which  may  be  present. 

If  we  place  a  little  fibrin  in  a  beaker,  cover  it  with  *2  per 
cent,  hydrochloric  acid,  add  a  small  quantity  of  pepsin  or 
of  a  gastric  extract,  and  put  the  beaker  in  a  water-bath 
at  40°  C.,  the  fibrin  soon  swells  up  and  becomes  translucent, 
then  begins  to  be  dissolved,  and  in  a  short  time  has  dis- 
appeared (see  Practical  Exercises,  p.  377). 

If  we  examine  the  liquid  before  digestion  has  proceeded 
very  far,  we  shall  find  chiefly  acid-albumin  in  solution ; 
later  on,  chiefly  albumoses ;  and  still  later,  chiefly  peptones. 
From  this  we  conclude  that  acid-albumin  is  a  stage  in  the 
conversion  of  fibrin  into  albumose,  and  albumose  a  half-way 
house  between  acid-albumin  and  peptone. 

Similar,  but  not  identical,  intermediate  substances  occur  in  the 
digestion  of  the  other  proteids,  as  well  as  in  that  of  bodies  like 
gelatin,  which  are  not  true  proteids,  but  which  pepsin  can  digest. 
The  generic  name  of  proteose  properly  includes  all  bodies  of  the 
albumose  type,  the  term  '  albumose '  itself  being  sometimes  reserved 


DIGESTION  303 

for  such  intermediate  products  of  the  digestion  of  a.bumin ;  while 
those  of  fibrin  are  called  fibrinoses ;  of  globulin,  globuloses ;  of 
casein,  caseoses  ;  and  so  on.  Probably  the  peptones  produced  from 
different  proteids  are  also  not  absolutely  identical. 

Beyond  peptone  gastric  digestion  does  not  go.  Indeed, 
in  no  case  does  the  whole  of  the  original  proteid,  in  an 
artificial  digestion,  ever  reach  the  stage  of  peptone  ;  although 
the  pancreatic  juice,  as  we  shall  see  later  on,  can  split  up 
peptone  itself  into  substances  which  are  no  longer  proteid. 
Since  the  subject  of  proteid  digestion  must  come  up  again, 
it  will  be  well  to  postpone  any  closer  discussion  of  the 
process  till  we  can  view  it  as  a  whole.  In  the  meantime  it 
is  only  necessary  to  repeat  that  pepsin  alone  cannot  digest 
proteids  at  all.  Its  action  requires  the  presence  of  an  acid ; 
in  a  neutral  or  alkaline  medium  peptic  digestion  stops.  As 
in  the  case  of  other  ferments,  there  is  a  certain  temperature 
at  which  pepsin  acts  best,  an  '  optimum '  temperature 
(35°  to  40°  C.,  or  about  that  of  the  body).  At  o°  C.  it  is 
inactive,  except  in  cold-blooded  animals  (frog).  Boiling 
destroys  it. 

Dilute  acid  alone  does  not  dissolve  coagulated  proteids 
like  boiled  fibrin,  or  does  so  only  with  extreme  slowness. 
Uncoagulated  proteids,  however,  are  readily  changed  by  it 
into  acid-albumin ;  and  by  the  prolonged  action  of  acids, 
especially  at  a  high  temperature,  further  changes  may  be 
caused  in  all  proteids,  apparently  of  much  the  same  nature 
as  those  produced  in  peptic  digestion.  But  under  the 
ordinary  conditions  of  natural  or  artificial  gastric  digestion, 
it  may  be  said  that  the  acid  alone  does  little  until  it  is  aided 
by  the  ferment,  just  as  the  ferment  alone  does  nothing 
without  the  aid  of  the  acid.  One  striking  difference,  how- 
ever, there  is :  the  acid  is  used  up  during  the  process ;  the 
ferment  is  little,  if  at  all,  affected.  Although  hydrochloric 
acid  acts  most  powerfully,  other  acids,  such  as  lactic,  phos- 
phoric, or  sulphuric,  can  replace  it. 

The  milk-curdling  ferment,  rennin,  is  contained  in  large 
amount  in  an  extract  of  the  fourth  stomach  of  the  calf, 
which  has  long  been  used  in  the  manufacture  of  cheese. 
It  exists  in  the  healthy  gastric  juice  of  man,  but  disappears 
in  cancer  of  the  stomach  and  in  chronic  gastric  catarrh. 


304  A  MANUAL  OF  PHYSIOLOGY 

It  can  be  separated  from  pepsin  by  precipitating  an  acid 
extract  of  calf's  stomach  with  magnesium  carbonate  in 
powder,  and  some  neutral  acetate  of  lead.  The  pepsin  is 
mechanically  carried  down  with  the  precipitate,  but  most  of 
the  rennin  remains  in  solution.  The  curdling  of  milk  by 
rennin  is  essentially  a  coagulation  of  casein.  It  seems  to 
be  produced  by  the  splitting  up  of  a  more  complex  body, 
caseinogen,  into  two  substances,  one  of  which,  casein,  is 
insoluble  (in  the  presence  of  calcium  phosphate,  but  not 
otherwise),  and  forms  the  curd ;  while  the  other,  whey- 
proteidy  is  soluble,  and  passes  into  the  whey.  Dilute  acid 
will  of  itself  precipitate  casein,  and  the  presence  of  acid, 
and  particularly  hydrochloric  acid,  in  the  gastric  juice  helps 
the  action  of  the  milk-curdling  ferment.  That  a  ferment  is 
really  concerned  in  the  process  is,  however,  shown  by  the 
fact  that  the  juice,  after  being  made  neutral  or  alkaline,  still 
curdles  milk,  and  that  this  power  is  destroyed  by  boiling. 
The  optimum  temperature  is  the  same  as  that  of  the  other 
ferments  of  the  digestive  tract,  about  40°  C.  (p.  377). 

As  to  the  exact  function  which  the  milk-curdling  ferment 
of  the  gastric  juice  performs  in  digestion,  we  have  no  precise 
knowledge.  It  seems  superfluous  if  we  suppose  that  the 
free  acid  is  able  of  itself  to  do  all  that  the  ferment  does 
along  with  it.  But  there  is  evidence  that  the  curd  pro- 
duced by  the  ferment  is  more  profoundly  changed  than  the 
precipitate  caused  by  dilute  acids  ;  for  the  latter  may  be 
redissolved,  and  then  again  curdled  by  rennin,  while  this 
cannot  be  done  with  the  former.  We  may  suppose,  then, 
that  the  ferment  is  capable  of  effecting  changes  more 
favourable  to  the  subsequent  action  of  the  pepsin  upon  the 
casein  than  those  which  the  acid  alone  would  effect.  Or  it 
may  be  that  the  ferment  acts  in  the  early  stages  of  digestion 
before  much  acid  has  been  secreted.  We  do  not  know 
whether  the  curdling  of  milk  renders  it  easier  for  the 
watery  portion  to  be  absorbed  by  the  walls  of  the  stomach. 
If  this  were  the  case,  it  would  be  a  raison  d'etre  for  early 
curdling,  since  milk  is  a  very  dilute  food,  and  the  immense 
proportion  of  water  in  it  might  weaken  the  gastric  juice  too 
much  for  rapid  digestion  of  the  proteids. 


DIGESTION  305 

On  fats  and  carbo-hydrates  gastric  juice  has  no  action,  T 
although  it  will  dissolve  the  proteid  constituents  of  fat-cells, 
and  the  proteid  substances  which  keep  the  fat-globules  of 
milk  apart  from  each  other;  while  swallowed  saliva  will 
continue  to  act  on  starch  in  the  stomach,  so  long  as  the 
acidity  is  not  too  great.  Healthy  gastric  juice  has  no 
action  on  cane-sugar,  but  when  there  is  much  mucus 
present,  it  seems  to  contain  a  ferment  which  changes  this 
sugar  into  dextrose,  or  into  a  mixture  of  dextrose  and 
levulose  ('  invert  '  sugar). 

(3)  Pancreatic  Juice.  —  Pancreatic  juice,  bile,  and  intestinal 
juice,  of  which  the  first  two  only  are  important,  are  all 
mingled  together  in  the  small  intestine,  and  act  upon  the 
food,  not  in  succession,  but  simultaneously.  But  by  artificial 
fistulae  in  animals  they  can  all  be  obtained  separately  ;  and 
occasionally  some  of  them  can  be  procured  through  accidental 
fistulae  in  the  human  subject 

Pancreatic  juice,  as  obtained  from  a  dog,  by  means  of  a 
cannula  tied  in  the  duct  of  Wirsung  through  an  opening  in 
the  linea  alba,  is  a  clear,  viscid  liquid  of  distinctly  alkaline 
reaction.  It  differs  notably  from  saliva  and  gastric  juice  in 
its  high  specific  gravity  (about  1030),  and  the  large  pro- 
portion of  solids  in  it,  which  may  be  as  much  as  10  per 
cent.,  or,  roughly  speaking,  about  the  same  as  in  blood- 
plasma.  About  nine-tenths  of  the  solids  consist  of  proteids, 
and  rather  less  than  one-tenth  of  inorganic  material  (chiefly 
.sodium  carbonate,  to  which  the  alkaline  reaction  is  due,  and 
Traces  of  fats,  soaps  and  leucin  may 


also  be  present.  When  the  juice  is  heated  to  near  the 
boiling-point,  a  copious  precipitate  of  coagulated  albumin  is 
formed.  The  fresh  juice  coagulates  spontaneously,  especially 
at  a  low  temperature  ;  but  the  coagulum  is  soon  digested. 
Possibly  cold  hinders  the  destructive  power  of  the  juice  on 
the  factors  necessary  for  coagulation  more  than  it  restrains 
the  process  of  clotting.  The  quantity  of  pancreatic  juice 
secreted  during  the  twenty-four  hours  in  an  average  man 
has  been  estimated  at  200  to  300  c.c.  An  artificial  pan- 
creatic juice  can  be  made  by  extracting  the  pancreas,  which 
must  not  be  too  fresh  (p.  378),  with  water  or  glycerine. 

20 


306  A  MANUAL  OF  PHYSIOLOGY 

Pancreatic  juice  contains  four  ferments  :  (i)  A  proteolytic 
or  proteid-digesting  ferment,  trypsin  ;  (2)  an  amylolytic  fer- 
ment, amylopsin ;  (3)  a  fat-splitting  or  lipolytic  ferment, 
steapsin,  also  called  pialyn  ;  (4)  a  milk-curdling  ferment. 

The  last  cannot  be  considered  as  taking  any  practical 
share  in  digestion,  since  it  can  hardly  ever  happen  that 
milk  passes  through  the  stomach  without  being  curdled. 

Trypsin,  to  a  certain  extent,  corresponds  with  pepsin  in  its 
action  on  proteids.  But  it  has  two  remarkable  peculiarities: 
it  acts  energetically  in  an  alkaline  as  well  as  in  a  not  too 
acid  medium  (a  very  slight  amount  of  digestion  may  go  on 
in  distilled  water)  ;  and  its  action  does  not  stop  at  the 
peptone  stage — it  can  split  up  peptones  into  leucin,  tyrosin 
and  aspartic  acid,  crystalline  nitrogenous  substances  very 
different  from  proteids. 

If  fibrin  is  digested  at  a  temperature  of  40°  C.  with  a  i  per 
cent,    solution    of    sodium    carbonate,    to   which    a    little 
pancreatic  extract  or  juice  has  been   added,  along  with  a 
trace  of  thymol  to  prevent  putrefaction,  it  is  gradually  eaten 
away  without  swelling  up  and  becoming  transparent  as  it 
does  in  peptic  digestion ;  but  some  granular  debris  is  always 
left  (p.  379).     This  undigested   residue  is  soluble  in  i  per 
cent,  sodium  hydrate,  but  it  is  never  entirely  dissolved  in 
any    artificial     digestion.      In    natural    digestion,    on    the 
contrary,  it  is  never  found ;  just  as    some  dextrin  always 
remains   when    ptyalin   has   done   its    utmost    upon    starch 
:Cfl  ^      outside  the  body,  while  in  the  intestine  little  or  no  dextrin 
YH       can  be  detected.     When  the  undigested  residue  is  filtered 
c^      off,    the   solution   may   still   contain :    (i)    a    substance   or 
J^  *    substances  having  resemblances  both  to  alkali-albumin  and 
to   globulin,    (2)    albumoses,    (3)    peptone,    (4)   leucin    and 
tyrosin.     It  will  depend  on  how  far  the  digestion  has  been 
carried   whether,  and   in  what  quantity,  any  one  of  these 
bodies  is  present. 

The  order  in  which  they  'appear  and  their  relative  amount 
at  different  stages  of  the  digestion  show  that  the  alkali- 
albumin  and  albumoses  are,  like  the  acid-albumin  and 
albumoses  of  peptic  digestion,  mainly,  at  any  rate,  inter- 
mediate substances  through  which  proteid  passes  on  its 


DIGESTION  307 

way  to  peptone ;  and  there  is  no  reason  to  believe  that  up  to 
this  point  there  are  any  essential  differences  between  the 
action   of  trypsin  and   pepsin.     In   both  cases  the  action 
seems  to  consist  in  a  splitting  up  of  the  complex   proteid 
with  assumption  of  water,  so  that  each  successive  product 
is  further  hydrated  than  the  last ;  nor  is  it,  as  yet  at  least, 
possible    to    point    out    any    radical    distinction    between 
the   peptone   of    gastric    and    the    peptone   of    pancreatic 
digestion.     It  is  not  necessary  to  suppose  that  the  further 
splitting  up  of  some  of  the  peptone  by  trypsin  into  leucin 
and    tyrosin  is  an  action  differing  in  kind  so  much  as   in 
degree  from  that  which  leads  to  the  formation  of  peptone 
both    in   tryptic   and   in   gastric   digestion.     Trypsin  is   in 
almost  all  respects  a  more  powerful  ferment  than  pepsin ; 
it  can    do    most  things   which   pepsin    can    do,  and  a  few 
things   which   pepsin    cannot  do ;    but  it  can    do   nothing 
which  is  not  right  in  the  line  of  peptic  digestion.     Thus,  a 
pancreatic  digest  almost  always  contains  less  albumose  than 
a  peptic  digest ;  more  of  the  albumose  is  carried  on  to  the 
further  stage  of  peptone  by  the  more  powerful  ferment ;  but 
we  ascribe  this  not  to  a  peculiar  property,  but  to  a  more 
energetic    action   on   the    common   lines.     And   when   this 
action  suffices  to  push  the   peptone  still  farther  along  the 
downward   path,   it    is   not   necessary   to   assume   that   an 
influence  radically  different  from  that  of  pepsin  is  at  work. 
This  argument  is  strengthened  when  we  find  that  without  a 
ferment  at  all,  by  the  prolonged  action  of  various  agents 
which  cause  hydration,  such  as  dilute  acids  or  alkalies,  or 
superheated  steam,  or  oxidizing  substances  like  ozone,  albu- 
moses  and  peptones  first,  and  ultimately  leucin  and  tyrosin, 
may  be  formed  from  ordinary  proteids.     In  fact,  it  would 
seem  that  when  the  complex  proteid  molecule  is  split  up  by 
proteolytic  ferments,  or  by  other  and  not  too  violent  agents, 
there  are  certain  favourite  '  sets  '  or  combinations  into  which 
its  constituents  are  apt  to  fall,  no  matter  how  the  decom- 
position may  be  brought  about,  bodies  of  the  fatty  and  of 
the   aromatic    series   being    especially   constant    and   con- 
spicuous  among   the   products.      Leucin,    for   instance,   is 
amido-caproic  acid,  in  which  amidogen  (NH2)  has  replaced 

20 — 2 


3o8  A  MANUAL  OF  PHYSIOLOGY 

one  atom  of  hydrogen  in  the  fatty  acid,  and  tyrosin  is  an 
amidated  aromatic  acid  (p.  379).  So  we  may  perhaps  con- 
sider the  proteid  molecule  as  partly  built  up  out  of  fatty 
acid  and  aromatic  groups  united  with  amidogen. 

As  much  as  8  to  10  per  cent,  of  leucin,  and  2  to  4  per  cent,  of 
tyrosin,  may  be  produced  in  artificial  tryptic  digestion  of  fibrin  (Lea, 
Kiihne),  but  only  a  portion  (about  the  half)  of  the  peptones  formed 
ever  undergoes  this  change,  no  matter  how  long  the  digestion  may  be 
continued. 

This  and  other  facts  have  led  to  the  theory  that  every  natural 
proteid  consists  of  two  elements  as  regards  the  products  into  which 
it  may  be  split  by  digestion — a  hemi  element  and  an  anti  element. 
0  Thus,  albumin  is  supposed  to  consist  of  hemi-albumin  and  anti- 
albumin.  When  digested  by  trypsin,  the  hemi-albumin  gives  rise 
eventually  to  hemi-peptone,  and  the  ^anti-albumin  to  anti-peptone. 
The  hemi-peptone  is  comparatively  unstable,  and  is  further  split  up 
into  leucin  and  tyrosin ;  the  anti-peptone  is  comparatively  stable, 
and  resists  further  change. 

As  to  the  method  in  which  the  ferments  bring  about  these  pro- 
found changes,  and  the  role  played  by  the  auxiliary  acid  or  alkali, 
we  are  almost  completely  in  the  dark.  Wurtz  has  supposed  that 
papain,  a  ferment  obtained  from  the  juice  of  the  fruit  of  the  Carica 
papaya,  which  acts  powerfully  on  proteids  in  much  the  same  way  as 
f.  trypsin,  unites  temporarily  with  the  proteid — with  fibrin,  for  instance 
— and  after  the  hydration  of  the  latter  is  complete,  is  again  set  at 
liberty,  and  free  to  act  on  some  more  of  the  unchanged  fibrin.  He 
compares  its  action  with  that  of  some  inorganic  bodies,  such  as 
sulphuric  acid,  a  small  quantity  of  which  may  cause  the  hydration  of 
a  large  amount  of  certain  substances  by  forming  temporary  com- 
pounds with  them,  and  being  then  set  free  to  act  again.  In  peptic 
digestion,  however,  the  hydrochloric  acid  seems  certainly  to  be  used 
up.  In  the  gastric  juice  it  is  perhaps  united  to  the  pepsin  ;  and  it  is 
capable  of  forming  combinations  with  all  proteids,  the  lower  proteids, 
such  as  peptone,  combining  with  a  greater  proportion  of  the  acid 
than  the  higher,  such  as  fibrin  or  albumin. 

In  all  that  we  have  hitherto  said  regarding  tryptic  diges- 
tion we  have  supposed  that  putrefaction  has  been  entirely 
prevented.  If  no  antiseptic  is  added  to  a  tryptic  digest,  it 
rapidly  becomes  filled  with  micro-organisms,  and  emits  a 

H^CH  very  disagreeable  faecal  odour;  and  now  various  bodies 
which  are  not  found  in  the  absence  of  putrefaction  make 
their  appearance,  such  as  indol,  skatol,  and  other  sub- 

.  -  ^^  stances  to  which  the  faecal  odour  is  due.  They  are  not  true 
^CH  products  of  tryptic  digestion,  but  are  formed  by  the  putre- 

C'K        factive    micro-organisms,  which  can  themselves   break    up 


DIGESTION 


309 


proteids  into  leucin  and  tyrosin,  and  readily  change  tyrosin 
into  indol. 

Amylopsin,  the  sugar-forming  ferment  of  pancreatic  juice, 
changes  starch  into  dextrin  and  maltose,  just  as  ptyalin 
does;  but  it  is  more  powerful,  and  readily  acts  on  raw 
starch  as  well  as  boiled. 

Steapsin  splits  up  neutral  fats  into  glycerine  and  the 
corresponding  fatty  acids.  The  latter  unite  with  the  alkalies 
of  the  pancreatic  juice  and  the  bile  to  form  soaps,  which 
aid  in  the  emulsification  of  fats.  In  this  important  process, 
so  essential  to  digestion,  bile  acts  as  the  helpmate  of  pan- 
creatic juice ;  together  they  effect  much  more  than  either  or 
both  can  accomplish  by  separate  action. 

(4)  Bile. — Bile  is  a  liquid  the  colour  of  which  varies  greatly 
in  different  groups  of  animals,  and  even  in  the  same  species 
is  not  constant,  depending  on  the  length  of  time  the  bile 
has  remained  in  the  gall-bladder  and  other  circumstances. 
When  it  is  recognised  that  the  colour  depends  on  a  series  of 
pigments,  which  are  by  no  means  stable,  and  of  which  one 
can  be  caused  to  pass  into  another  by  oxidation  or  reduction, 
this  want  of  uniformity  will  be  easily  intelligible.  The  fresh 
bile  of  carnivora  is  golden  red  ;  the  bile  of  herbivorous 
animals  is  in  general  of  a  green  tint,  but,  when  it  has  been 
retained  long  in  the  gall-bladder,  may  incline  to  reddish- 
brown.  Human  bile  is  generally  described  as  being  of  a 
reddish  or  golden-yellow  colour,  but  it  is  doubtful  whether 
this  is  true  of  the  perfectly  fresh  secretion,  for  bile  flowing 
from  a  fistula  has  been  observed  to  be  green  (Robson, 
Copeman  and  Winston).  That  of  a  monkey  taken  from  the 
gall-bladder  immediately  after  death  is  dark  green,  but  if 
left  a  few  hours  in  the  gall-bladder  it  is  brown,  the  green 
pigment  having  been  reduced.  This  would  seem  to  indicate 
that  human  bile,  originally  green,  may  alter  its  colour  in  the 
interval  which  must  elapse  before  it  can  usually  be  obtained 
after  death.  Bile,  as  obtained  from  accidental  fistulae  in 
otherwise  healthy  persons,  has  a  much  lower  specific  gravity 
than  pancreatic  juice  (1008  to  1009).  The  composition  of 
human  bile  is  approximately  as  follows : 


310  A  MANUAL  OF  PHYSIOLOGY 

Water  -  .  982  parts  in  i.ooo 

r*      i  •    i 

Solids  : 

Mucin  and  pigments  -            -  1*5  \ 

Bile-salts  -  7-5 

Lecithin  and  soaps  •            •  I     Vi8        „         M 

Cholesterin  -            -          5 1 

Inorganic  salts  -  7-5] 

It  will  be  observed  that  no  proteids  are  enumerated  in 
this  table  ;  bile  contains  none,  and  it  is  unlike  all  the  other 
digestive  juices  in  this  respect. 

Mucin  is  scarcely  to  be  looked  upon  as  an  essential  constituent  of 
bile ;  it  is  not  formed  by  the  actual  bile-secreting  cells,  but  by 
mucous  glands  in  the  walls  and  goblet-cells  in  the  epithelial  lining 
of  the  larger  bile-ducts,  and  especially  of  the  gall-bladder.  The 
mucin  of  human  bile  is  a  true  mucin,  but  that  of  ox-bile  is  a  nucleo- 
albumin  (p.  17).  Although  bile  (or  at  least  free  bile-acids)  has  in 
itself  considerable  antiseptic  power,  the  mucin  causes  it  rapidly  to 
putrefy.  It  may  be  removed  by  precipitation  with  alcohol  or  dilute 
acetic  acid. 

Bile-pigments. — It  has  been  said  that  these  form  a  series,  but 
only  two  of  the  pigments  of  that  series  appear  to  be  present  m 
normal  bile,  bilirubin  and  biliverdin.  In  human  bile  as  usually 
obtained,  the  former,  in  herbivorous  bile  and  that  of  some  cold- 
blooded animals,  such  as  the  frog,  the  latter,  is  the  chief  pigment. 
But  in  fresh  human  bile  biliverdin  may  be  chiefly  present,  and 
bilirubin  can  be  extracted  in  large  amount  from  the  gallstones  of 
cattle;  while  in  the  placenta  of  the  bitch  biliverdin  is  present  in 
quantity,  although,  as  in  all  carnivora,  it  is  either  absent  from  the 
bile  or  exists  in  it  in  comparatively  small  amount.  All  these  facts 
show  that  the  two  pigments  are  readily  interchangeable. 

Bilirubin  is  best  obtained  from  powdered  red  gallstones  by  dis- 
solving the  chalk  with  hydrochloric  acid,  and  extracting  the  residue 
with  chloroform,  which  takes  up  the  pigment.  From  this  solution, 
on  evaporation,  beautiful  rhombic  tables  or  prisms  of  bilirubin 
separate  out ;  and  the  crystals  are  finer  when  the  solution  also  con- 
tains cholesterin  than  when  it  is  pure. 

Biliverdin  can  be  obtained  from  the  placenta  of  the  bitch  by 
extraction  with  alcohol.  It  is  insoluble  in  chloroform,  and  by  means 
of  this  property  it  may  be  separated  from  bilirubin  when  the  two 
happen  to  be  present  together  in  bile.  Biliverdin  can  also  be  formed 
from  bilirubin  by  oxidation.  By  the  aid  of  active  oxidizing  agents, 
such  as  yellow  nitric  acid  (which  contains  some  nitrous  acid),  a 
whole  series  of  oxidation  products  of  bilirubin  is  obtained,  beginning 
with  biliverdin,  and  passing  through  bilicyanin,  a  blue  pigment,  to 
choletelin,  a  yellow  substance.  It  is  possible  that  there  are  other 
intermediate  bodies.  This  is  the  foundation  of  Gmelin's  test  for  bile- 
pigments  (see  Practical  Exercises,  p.  380). 

The  positive  pole  of  a  galvanic  current  causes  the  same  oxidative 
changes,  the  same  play  of  colours,  while  the  reducing  action  of  the 


DIGESTION  311 

negative  pole  reverses  the  effect,  if  the  action  of  the  positive  electrode 
has  not  gone  too  far.  Starting  from  biliverdinr  the  negative  pole 
causes  the  green  to  pass  through  yellowish-green  into  golden- yellow, 
and  ultimately  into  pale  yellow,  indicating  a  series  of  bodies  formed 
by  reduction  of  the  biliverdin.  These  reactions  can  also  be  used  for 
the  detection  of  bile-pigments. 

By  the  reducing  action  of  sodium  amalgam,  or  of  tin  and  hydro- 
chloric acid,  on  bilirubin,  but  not  apparently  by  electrolysis,  hydro- 
bilirubin  is  obtained.  This  is  identical  with  the  '  febrile '  urobilin 
of  some  pathological  urines,  and  with  stercobilin,  a  pigment  found 
in  the  faeces  from  birth  onwards,  although  not  in  the  meconium 
(pp.  358,  389),  and  therefore  probably  derived  from  the  normal  bile- 
pigment  by  reduction  in  the  intestine  itself,  where  reducing  sub- 
stances due  to  the  action  of  micro-organisms  are  never  absent  in 
extra-uterine  life.  The  changes  occurring  in  oxidation  and  reduction 
of  the  bile-pigment  may  be  partially  represented  as  follows  : 

(C32H36N406)  +  02  =  (C3,H36N408),  +  202  =  (C32H36N4O12)  • 

Bilirubin.  Liliverdin.  Choletelin. 

2(C32H36N406)  -  02  +  4H20  -  2(C32H36NA.2H20). 

Bilirubin.  Hydrobilirubin. 

Judging  from  the  analogy  of  the  blood-pigment — from  which,  as 
we  shall  see,  the  bile-pigment  is  derived,  and  the  changes  in  which, 
through  oxidation  and  reduction,  have  a  certain  superficial  resem- 
blance to  those  which  bilirubin  undergoes  when  it  is  converted  into 
biliverdin,  and  which  biliverdin  undergoes  when  it  passes  back  again 
to  bilirubin — we  might  have  expected  bile  to  possess  a  characteristic 
spectrum. 

This,  however,  is  not  the  case.  The  bile  of  most  animals  shows  no 
bands  at  all.  The  fresh  bile  of  certain  animals,  the  ox,  for  instance, 
does  show  bands — a  strong  one  over  C,  and  two  weaker  bands,  one 
of  which  is  just  to  the  left  of  D,  and  the  other  to  the  right  of  it,  but 
nearer  D  than  E.  The  two  last  bands  grow  stronger  when  the  bile 
is  allowed  to  stand  for  twenty-four  hours,  and  in  about  three  days, 
in  warm  weather,  a  fourth  sharp  band  may  appear  between  C  and  B. 
But  none  of  these  bands  are  due  to  the  normal  bile-pigment,  and 
they  are  not  essentially  changed  when  this  is  oxidized  or  reduced  by 
electrolysis.  MacMunn  attributes  the  spectrum  of  the  bile  of  the  ox 
and  sheep  to  a  body  which  he  calls  cholohaematin,  and  which  does 
not  belong  to  the  bile-pigments  proper.  Of  the  derivatives  of  the 
bilirubin  set,  only  the  lowest  and  the  highest  members,  hydro- 
bilirubin  and  choletelin,  are  described  as  giving  absorption  spectra. 

The  Bile-salts. — These  are  the  sodium  salts  of  two  acids,  glyco- 
cholic  and  taurocholic.  In  human  bile  both  are  present,  but  the 
former  in  greater  quantity  than  the  latter.  In  the  bile  of  the  dog 
and  cat  only  taurocholic  acid  is  found;  in  that  of  the  carnivora 
generally  it  is  by  far  the  more  important  of  the  two  acids ;  in  the 
bile  of  herbivora  there  is  much  more  glycocholic  than  taurocholic 
acid. 

Both  acids  are  made  up  of  a  non-nitrogenous  body,  cholic  or 


312  A  MANUAL  OF  PHYSIOLOGY 

cholalic  acid,  and  a  nitrogenous  body,  glycin  in  glycocholic,  and 
V^-  -       taurin  in  taurocholic  acid. 

^  -  ^  ^^'The   decomposition   of  the   bile-acids   into   these   substances   is 
=o  rt       effected  by  boiling  them  with  dilute  acid  or  alkali,  a  molecule  of 
3         water  being  taken  up;  thus  — 

M.  HI. 


H20  -  C2H5NO2 

Glycocholic  acid.  Glycin.  Cholic  acid. 

C26H45NS07  +  H20  =  C2HrNS03  +  C24H40O5. 

Taurocholic  acid.  Taurin.  Cholic  acid. 

Taurocholic  acid  is  much  more  easily  broken  up  than  glycocholic  ; 
even  boiling  with  water  is  sufficient. 

Glycin  is  amido-acetic  acid,  taurin  is  amido-isethionic  acid,  an 
atom  of  the  hydrogen  of  the  acid  being  in  each  case  replaced  by 
NH2.  A  notable  difference  between  glycocholic  and  taurocholic 
acid  is  that  the  latter  contains  sulphur.  The  whole  of  this  belongs 
to  the  taurin. 

Traces  of  cholic  acid,  probably  formed  by  the  action  of  putre- 
factive products  on  the  bile-salts,  are  found  in  the  intestines, 
especially  in  the  lower  portion. 

Pettenkofet*  s  test  for  bile-acids  (Practical  Exercises,  p.  380),  acci- 
dentally discovered  in  examining  the  action  of  bile  upon  sugar, 
depends  upon  three  facts:  (i)  That  cholic  acid  and  furfurol  give  a 
purple  colour  when  brought  together  ;  (2)  that  the  bile-salts  yield 
cholic  acid  when  acted  upon  by  sulphuric  acid  ;  (3)  that  when  cane- 
sugar  is  decomposed  by  strong  sulphuric  acid,  furfurol  is  formed. 

Since  a  similar  colour  is  given  when  the  same  reagents  are  added 
to  a  solution  containing  albumin,  it  is  necessary  to  remove  this,  if 
present,  from  any  liquid  which  is  to  be  tested  for  bile-acids. 

Lecithin  and  cholesterin  are  by  no  means  peculiar  to  bile.  They 
are  found  in  almost  all  the  liquids  of  the  body,  and  are  especially 
important  constituents  of  the  nervous  substance.  The  former  is  a 
crystallizable  fat  of  a  peculiar  nature,  containing  nitrogen  and 
phosphorus.  It  is  unstable,  and  when  heated  with  baryta-water  it 
yields  a  soap,  barium  stearate,  which  is  precipitated,  and  two  other 
substances,  choline  and  glycero-phosphoric  acid,  which  remain  in 
solution. 

Cholesterin  is  a  triatomic  alcohol.  It  is  best  obtained  from  white 
gallstones,  of  which  it  is  the  chief,  and  sometimes  almost  the  sole, 
constituent  (see  Practical  Exercises,  p.  380). 

The  chief  inorganic  salt  of  bile  is  sodium  chloride.  The  phos- 
phoric acid  of  the  ash  comes  partly  from  the  phosphorus  of  organic 
compounds  (lecithin  and  bile-mucin),  the  sulphuric  acid  from  the 
sulphur  of  taurocholic  acid,  the  sodium  largely  from  the  bile-salts. 
Iron  is  a  notable  inorganic  constituent  of  bile,  although  it  exists  only 
in  traces,  in  the  form  of  phosphate  of  iron.  Manganese  is  also 
present.  100  c.c.  of  fresh  bile  yields  50  to  100  c.c.  of  carbon  dioxide, 
part  of  which  is  in  solution  and  part  combined  with  alkalies. 


DIGESTION  313 

The  quantity  of  bile  secreted  in  twenty-four  hours  in  an 
average  man  is  probably  from  750  c.c.  to  a  litre. 

The  great  action  of  the  bile  in  digestion  is  undoubtedly 
the  preparation  of  the  fats  for  absorption,  either  in  the  form 
of  a  mechanical  suspension  or  emulsion,  or  in  solution  as 
soaps  ;  and  this  it  accomplishes,  not  by  itself,  but  in  conjunc- 
tion with  the  pancreatic  juice. 

No  completely  satisfactory  explanation  has  been  given  of 
the  precise  nature  of  this  partnership,  but  it  is  certain  that 
the  fat-splitting  ferment  of  the  pancreatic  juice,  on  the  one 
hand,  and  the  bile-salts  on  the  other,  contribute  largely  to 
the  total  action.  An  alkaline  solution,  a  solution  of  sodium 
carbonate,  e.g.,  is  unable  of  itself  to  emulsify  a  perfectly 
neutral  oil ;  but  if  some  free  fatty  acid  be  added,  emulsifica- 
tion  is  rapid  and  complete.  Now,  there  is  no  doubt  that 
here  a  soap  is  formed  by  the  action  of  the  alkali  on  the  fatty 
acid,  and  there  is  equally  little  doubt  that  the  formation  of 
the  soap  is  an  essential  part  of  the  emulsification.  But  it  is 
not  clear  in  what  manner  the  soap  acts,  whether  by  form- 
ing a  coating  round  the  oil-globules,  or  by  so  altering  the 
surface  tension,  or  other  properties  of  the  solution  in  which 
it  is  dissolved,  that  they  no  longer  tend  to  run  together. 
However  this  may  be,  in  pancreatic  juice  we  have  the  two 
factors  present  which  this  simple  experiment  shows  to  be 
necessary  and  sufficient  for  emulsification ;  we  have  a 
ferment  which  can  split  up  neutral  fats  and  set  free  fatty 
acids,  and  an  alkali  which  can  combine  with  those  acids  to 
form  soaps.  Accordingly,  pancreatic  juice  is  able  of  itselr 
to  form  emulsions  with  perfectly  neutral  oils.  It  is  possible 
that  the  proteid  constituents  of  pancreatic  juice,  and  par- 
ticularly a  substance  resembling  alkali-albumin,  may  have  a 
share  in  emulsification.  In  bile,  on  the  contrary,  although 
the  alkali  is  present,  there  is  no  fat-splitting  ferment,  and 
according  to  the  best  experiments,  bile  alone  has  no  emulsi- 
fying power.  But  we  now  come  to  a  remarkable  fact :  this 
inert  bile  when  added  to  pancreatic  juice  greatly  intensifies 
its  emulsifying  action,  and  a  solution  of  bile-salts  has  much 
the  same  effect  as  bile  itself.  The  fact  is  undoubted,  but 
the  explanation  is  obscure.  What  it  is  that  bile  or  bile-salts 


314  A  MANUAL  OF  PHYSIOLOGY 

can  add  to  the  pancreatic  juice  which  so  increases  its  power 
of  emulsification,  we  do  not  know.  It  is  indeed  true  that 
the  bile,  in  virtue  of  its  alkaline  salts,  can,  in  presence  of  a 
free  fatty  acid,  rapidly  form  an  emulsion  But  the  pan- 
creatic juice  itself  contains  a  considerable  quantity  of  sodium 
carbonate. 

A  part  of  the  effect  of  the  bile  seems  to  be  due  to  its 
favouring  in  some  way  the  fat-splitting  action  of  the  pan- 
creatic juice.     The  capacity  of  dissolving  soaps,  which  is  a 
property  of  the  bile-salts,  would  undoubtedly  be  important 
if  it  were  definitely  proved  that  this  is  the  form  in  which 
the  chief  part  of  the  fat  is  absorbed,  as  some   have  held. 
It  would  also  be  important  on  the  emulsion  theory  of  fat 
absorption  if  it  could  be  shown  that  the  comparatively  small 
emulsifying  power  of  pancreatic  juice  by  itself  is  due  to  its 
want  of  solvent  power  for  the  soaps  which  it  forms,  and  espe- 
cially if  it  were  shown  that  soaps  such  as  the  alkaline  stear- 
ates  produced  in  the  digestion  of  ordinary  fatty  food,  which 
are  soluble  in  water,  were  much  less  soluble  in  the  pancreatic 
secretion.     However  the  mutual  action  of  the  two  juices  on 
the  digestion  of  fats  may  be  explained,  there  is  no  doubt 
that  they  are  equally  necessary.     For  in  some  diseases  of 
the  pancreas  fat  often  appears  in  the  stools,  and  this  token 
of  imperfect  digestion  of  the  fatty  food  may  be  confirmed  by 
the  wasting  of  the  patient ;  and  the  same  occurs  when  the 
bile  is  prevented  by  obstruction  of  the  duct  or  by  a  biliary 
fistula  from  entering  the  intestine.      The   white    stools   of 
jaundice  owe  their  colour,  not   merely  to   the   absence   of 
bile-pigment,  but  also  to  the  presence  of  fat.     In  suckling 
children  it  is  not  uncommon  to  see  the  fseces  white  with 
fat.      This  is  a  less  serious  symptom  than  in  adults,  and 
perhaps  betokens  merely  that  the  milk  in  the  feeding-bottle 
is  undiluted  cow's  milk,  which  is  richer  in  fat  than  human 
milk,  and  ought  to  be  mixed  with  an  equal  quantity  of  water. 
Bidder  and  Schmidt  found  that  the  chyle  in  the  thoracic 
duct  of  a  normal  dog  contained  3*2  per  cent,  of  fat.     In  a 
dog  with  the  bile-duct  ligatured  the  proportion  fell  to  o'2 
per  cent. 

Bile  has  been  credited  with  a  physical  power  of  aiding  the 


DIGESTION  315 

passage  of  fat  through  membranes,  and  it  has  been  inferred 
that  this  has  an  important  bearing  on  the  absorption  of  fat 
from  the  intestine.  But  the  inference  does  not  follow  from 
the  statement,  and  the  statement  has  been  itself  denied. 

On  proteids  bile  has  no  digestive  action.  The  addition 
of  it  to  a  gastric  digest  causes  a  precipitate  of  acid-albumin 
(parapeptone),  albumose,  and  pepsin.  The  precipitate  is 
soluble  in  excess  of  bile,  or  of  a  solution  of  bile-salts,  but  the 
pepsin  has  no  longer  any  power  of  digesting  proteids.  Part 
of  the  bile-acids  is  also  thrown  down  by  the  acid  of  the 
digest. 

It  has  been  vaguely,  and  almost  helplessly  suggested,  in  the 
laudable  endeavour  to  find  functions  for  the  bile,  that  by  neutralizing 
the  chyme  bile  prepares  it  for  the  action  of  the  pancreatic  juice. 
But  since  the  contents  of  the  small  intestine  are  acid  throughout  the 
whole  of  digestion,  it  is  evident  that  the  excess  of  bile  required  to 
neutralize  the  chyme  and  redissolve  the  precipitated  proteids  does 
not  actually  exist.  And  it  is  difficult  to  see  in  what  way  the  preci- 
pitation of  a  substance  can  prepare  the  way  for  its  digestion.  The 
whole  discussion  is,  indeed,  an  illustration  of  the  hazard  that  is  run 
in  transferring  without  great  care  the  results  of  digestion  in  vitro  to 
the  normal  and  natural  processes  in  the  alimentary  canal. 

Although  bile  has  sometimes  a  feebly  amylolytic  action,  this  is 
not  to  be  included  among  its  specific  powers,  for  a  diastatic  ferment 
in  small  quantities  is  widely  diffused  in  the  body. 

Succus  Entericus. — This  is  the  name  given  to  the  special 
secretion  of  the  small  intestine,  which  is  supposed  to  be  a 
product  of  the  Lieberkuhn's  crypts  and  of  Brunner's  glands. 
In  order  to  obtain  it  pure,  it  is  of  course  necessary  to  prevent 
admixture  with  the  bile,  the  pancreatic  juice,  and  the  food. 
This  is  done  by  dividing  a  loop  of  intestine  from  the  rest  by 
two  transverse  cuts,  the  abdomen  having  been  opened  in  the 
linea  alba.  The  continuity  of  the  digestive  tube  is  restored 
by  stitching  the  portion  below  the  isolated  loop  to  the  part 
above  it ;  one  end  of  the  loop  is  sutured  to  the  lips  of  the 
wound  in  the  linea  alba,  and  the  other  being  ligatured,  the 
whole  forms  a  sort  of  test-tube  opening  externally  (Thiry's 
fistula).  Or  both  ends  are  made  to  open  through  the 
abdominal  wound  (Vella's  fistula).  Another  method  is  to 
make  a  single  opening  in  the  intestine,  and  by  means  of  two 
indiarubber  balls,  one  of  which  is  pushed  down,  and  the 


316  A  MANUAL  OF  PHYSIOLOGY 

other  up  through  the  opening,  and  which  are  afterwards 
inflated,  to  block  off  a  piece  of  the  gut  from  communication 
with  the  rest.  The  intestinal  juice  so  obtained  is  a  thin 
yellowish  liquid  of  alkaline  reaction.  Its  specific  gravity  is 
about  1010.  It  contains  a  small  amount  of  proteids,  and 
about  the  same  proportion  of  inorganic  salts  as  most  of  the 
liquids  and  solids  of  the  body,  namely,  '7  or  '8  per  cent. ; 
but  its  composition  seems  to  be  far  from  constant.  It  has 
been  credited  with  various  digestive  powers  ;  in  fact,  accord- 
ing to  one  or  two  enthusiastic  observers,  it  would  almost 
seem  to  sum  up  in  itself  the  actions  of  all  the  other  diges- 
tive juices,  and  to  possess  besides  a  peculiar  activity  of  its 
own.  But  we  need  not  hesitate  to  say  that  in  the  work  of 
digestion  it  plays  at  most  a  very  subordinate  part.  The 
sodium  carbonate,  in  which  it  is  exceedingly  rich,  may 
form  soaps  with  fatty  acids  produced  by  the  action  of  the 
pancreatic  juice  or  of  the  fat-splitting  bacteria  in  which  the 
intestine  abounds,  and  may  thus  aid  in  the  emulsification 
of  fats.  That  a  great  deal  of  fat  may  be  split  up  in  the 
alimentary  canal  in  the  absence  both  of  bile  and  pancreatic 
juice  is  well  ascertained.  The  alkali  of  the  succus  entericus 
will  at  the  same  time  check  the  growing  acidity  of  the  in- 
testinal contents.  A  ferment  called  invertin — which  is  not 
introduced  with  the  food  or  formed  by  bacterial  action  as 
has  been  suggested,  since  it  occurs  in  the  aseptic  intestine 
of  the  new-born  child — changes  cane-sugar  into  a  mixture 
of  dextrose  and  levulose,  both  reducing  sugars,  but  rotating 
the  plane  of  polarization  in  opposite  directions,  as  indicatec 
by  their  names ;  some  maltose  may  be  changed  into  dex- 
trose. But  here  the  catalogue  of  the  powers  of  the  succus 
entericus  ceases ;  on  proteids  and  starch  it  has  little  or  no 
action. 

Having  now  finished  our  review  of  the  chemistry  of  the 
digestive  juices,  our  next  task  is  to  describe  what  is  known 
as  to  their  secretion — the  nature  of  the  cells  by  which  it  is 
effected  and  their  histological  appearance  in  activity  anc 
repose,  and  the  manner  in  which  it  is  called  forth  anc 
controlled. 


DIGESTION  317 

<=— r 

III.  The  Secretion  of  the  Digestive  Juices. 

The  digestive  glands  are  formed  originally  from  involu- 
tions of  the  mucous  membrane  of  the  alimentary  canal,  the 
salivary  glands  from  the  epiblast,  the  others  from  the  hypo- 
blast  (Chap.  XIV.).  Some  are  simple  unbranched  tubes,  in 
which  there  is  either  no  distinction  into  body  and  duct,  as 
in  Lieberkiihn's  crypts  in  the  intestines,  or  in  which  one  or 
more  of  the  tubes  open  into  a  duct,  as  in  the  glands  of  the 
cardiac  end  of  the  stomach.  Some  are  branched  tubes, 
several  of  which  may  end  in  a  common  duct ;  such  are  the 
glands  of  the  pyloric  end  of  the  stomach,  and  the  Brunner's 
glands  in  the  duodenum.  In  others  the  main  duct  ramifies 
into  a  more  or  less  complex  system  of  small  channels,  into 
each  of  the  ultimate  branches  of  which  one  or  more  (usually 
several)  of  the  secreting  tubules  or  alveoli  open.  The 
salivary  glands  and  the  pancreas  belong  to  this  class  of 
compound  tubular  or  racemose  glands,  and  so  does  the  liver 
of  such  animals  as  the  frog.  But  in  the  latter  organ  the 
typical  arrangement  is  obscured  in  the  higher  vertebrates  by 
the  predominance  of  the  portal  bloodvessels  over  the  system 
of  bile-channels  as  a  groundwork  for  the  grouping  of  the  cells. 

In  every  secreting  gland  there  is  a  vascular  plexus  outside 
the  cells  of  the  gland -tubes,  and  a  system  of  collecting 
channels  on  their  inner  surface  ;  and  in  a  certain  sense  the 
cells  of  every  gland  are  arranged  with  reference  to  the  blood- 
vessels on  the  one  hand,  and  the  ducts  on  the  other.  But 
in  the  ordinary  racemose  glands  the  blood-supply  is  mainly 
required  to  feed  the  secretion ;  the  cells  of  the  alveoli  have 
either  no  other  function  than  to  secrete,  or  if  they  have  other 
functions,  they  are  not  such  as  to  entail  a  great  disproportion 
between  the  size  of  the  cells  and  the  lumen  of  the  channels 
into  which  they  pour  their  products.  For  both  reasons  the 
relation  of  the  grouping  of  the  cells  to  the  duct-system  is 
very  obvious,  to  the  blood-system  very  obscure.  In  the  liver 
the  conditions  are  precisely  reversed.  We  cannot  suppose 
that  the  manufacture  of  a  quantity  of  bile  less  in  volume 
than  the  secretion  of  the  salivary  glands,  though  doubtless 
containing  far  more  solids,  requires  an  immense  organ  like 


318  A  MANUAL  OF  PHYSIOLOGY 

the  liver,  and  a  tide  of  blood  like  that  which  passes  through 
the  portal  vein.  And,  as  we  shall  see,  the  liver  has  other 
functions,  some  of  them  certainly  of  at  least  equal  im- 
portance with  the  secretion  of  bile,  and  one  of  them 
evidently  requiring  from  its  very  nature  a  bulky  organ. 
Accordingly,  both  the  richness  of  the  blood-supply  and  the 
size  of  the  secreting  cells  are  out  of  proportion  to  the  calibre 
of  the  ultimate  channels  that  carry  the  secretion  away. 
The  so-called  bile-capillaries,  which  represent  the  lumen  of 
the  secreting  tubules,  are  mere  grooves  in  the  surface  of 
adjoining  cells ;  and  the  architectural  lines  on  which  the 
liver  lobule  is  built  are :  (i)  the  interlobular  veins  which  carry 
blood  to  it ;  (2)  the  rich  capillary  network  which  separates 
its  cells  and  feeds  them  ;  (3)  the  central  intra-lobular  vein 
which  drains  it.  Thus  a  network  of  cells  lying  in  the  meshes 
of  a  network  of  blood-capillaries  takes  the  place  of  a  regular 
dendritic  arrangement  of  ducts  and  tubules ;  and  in  accord- 
ance with  this  the  bile  -  capillaries,  instead  of  opening 
separately  into  the  ducts,  form  a  plexus  with  each  other 
within  the  hepatic  lobule. 

The  dncts  and  secreting  tubules  of  all  glands  are  lined  by 
cells  of  columnar  epithelial  type,  but  the  type  is  most  closely 
preserved  in  the  ducts.  In  none  of  the  digestive  glands  is 
there  more  than  a  single  complete  layer  of  secreting  cells. 
But  the  alveoli  of  the  mucous  salivary  glands  show  here  and 
there  a  crescent-shaped  group  of  small  deeply-staining  cells 
(crescents  of  Gianuzzi)  outside  the  columnar  layer  (Plate  II., 
i,  3),  and  between  it  and  the  basement  membrane,  while 
the  gland-tubes  of  the  cardiac  end  of  the  stomach  have  in 
the  same  situation  a  discontinuous  layer  of  large  ovoid  cells, 
termed  parietal  from  their  position,  oxyntic  (or  acid-secreting) 
from  their  supposed  function  (Fig.  104).  The  serous  salivary 
glands,  the  pancreas,  the  pyloric  glands  of  the  stomach,  the 
Lieberkiihn's  crypts,  have  but  a  single  layer  of  epithelium  ; 
and  since  there  is  no  hepatic  cell  which  is  not  in  contact 
with  at  least  one  bile-capillary,  the  liver  may  be  regarded  as 
having  no  more.  Remarkable  histological  changes,  evidently 
connected  with  changes  in  functional  activity,  have  been 
noticed  in  most  of  the  digestive  glands.  In  discussing  these, 


DIGESTION  319 

it  will  be  best  to  omit  for  the  present  any  detailed  reference 
to  the  liver,  since,  although  there  are  histological  marks  of 
secretive  activity  in  this  gland  as  well  as  in  others,  and  of 
the  same  general  character,  they  are  accompanied,  and  to 
some  extent  overlaid,  by  the  microscopic  evidences  of  other 
functions  (p.  440).  The  serous  salivary  glands  and  the 
pancreas  can  be  taken  together ;  so  can  the  cardiac  and 
pyloric  glands  of  the  stomach ;  the  mucous  salivary  glands 
must  be  considered  separately. 

Changes  in  the  Pancreas  and  Parotid  during  Secretion. — The 
cells  of  the  alveoli  of  the  pancreas  or  parotid  during  rest,  as 
can  be  seen  by  examining  thin  lobules  of  the  former  between 


FIG.  103. — SEROUS  GLANDS  IN  'LOADED'  AND  'DISCHARGED'  STATE. 

A,  rabbit's  pancreas,  '  loaded'  (resting) ;  A',  '  discharged'  (active),  observed  in  the 
living  animal  (Kiihne  and  Lea).  B,  loaded,  B',  discharged,  alveolus  of  parotid  (fresh 
preparations),  (Langley). 

the  folds  of  the  mesentery  in  the  living  rabbit,  or  fresh 
teased  preparations  of  the  latter,  are  filled  with  fine  granules 
to  such  an  extent  as  to  obscure  the  nucleus.  In  the  parotid 
the  whole  cell  is  granular,  in  the  pancreas  there  is  still  a 
narrow  clear  zone  at  the  outer  edge  of  the  cell  which 
contains  few  granules  or  none ;  in  both,  the  divisions 
between  the  cells  are  very  indistinct,  and  the  lumen  of  the 
alveolus  cannot  be  made  out.  During  activity  the  granules 
seem  to  be  carried  from  the  outer  portion  of  the  cell  towards 
the  lumen,  and  there  discharged  ;  the  clear  outer  zone  of 
the  pancreatic  cell  grows  broader  and  broader  at  the 
expense  of  the  inner  granular  zone,  until  at  last  the  latter 
may  in  its  turn  be  reduced  to  a  narrow  contour  line  around 


320  A  MANUAL  OF  PHYSIOLOGY 

the  lumen.  In  the  uniformly  clouded  parotid  cell  a  similar 
change  takes  place;  a  transparent  outer  zone  arises ;  and, 
after  prolonged  secretion,  only  a  thin  edging  of  granules 
may  remain  at  the  inner  portion  of  the  cell.  In  both  glands 
the  outlines  of  the  cells  become  more  clearly  indicated,  and 
a  distinct  lumen  can  be  now  recognised.  The  cells  are 
smaller  than  they  are  during  rest,  and  in  the  pancreas  they 
stain  more  readily  with  carmine  and  other  protoplasmic 
dyes,  the  outer  zone  always  staining  more  deeply  than  the 
inner,  as  is  the  case  with  the  same  zone  even  m  the  resting 
pancreatic  cell  (Plate  II.,  2). 

When  the  glands  are  hardened  with  alcohol,  or  most  of  the 
ordinary  hardening  reagents,  the  appearances  in  the  serous  salivary 
cells  differ  from  those  described,  for  the  granules,  unlike  those  ot 
the  pancreatic  cells,  are  altered  by  the  treatment,  and  the  two  zones 
in  the  discharged  gland  are  not  distinguishable  by  any  difference  in 
the  depth  of  the  carmine  stain.  But  in  the  rabbit's  parotid  after  the 
scanty  secretion  caused  by  prolonged  stimulation  of  the  sympathetic 
the  whole  cell  stains  more  deeply  than  the  loaded  cell.  Its  protoplasm 
is  turbid  with  fine  and  uniformly  diffused  granules  ;  its  nucleus  is 
large  and  spherical,  and  contains  well-marked  nucleoli,  in  contrast 
to  the  pale  and  transparent  protoplasm  and  the  small  shrivelled 
nucleus  of  the  resting  cell,  in  which  nucleoli  are  indistinct  or  invisible. 
Now,  carmine  being  a  protoplasmic  dye,  it  is  fair  to  conclude  that 
depth  of  stain  is  propoitional  to  amount  of  protoplasm  present.  The 
deeper  stain  of  the  outer  rim  of  the  pancreatic  cell  during  rest  indicates 
that  here  the  protoplasm  predominates  over  the  dead  and  unstained 
products  of  its  activity,  which  are  accumulated  in  the  remainder 
of  the  cell.  The  increase  of  the  deeply-staining  zone  during  secretion 
shows  that  these  produces  are  being  moved  towards  the  lumen  of  the 
alveolus,  and  that  the  relative  amount  of  protoplasm  in  the  outer 
zone  is  being  increased,  although  the  absolute  size  of  the  cell  may  be 
diminished.  The  deeper  stain  of  the  parotid  cell  after  sympathetic 
stimulation,  as  well  as  the  changes  in  the  nucleus,  indicate  regenera- 
tion of  protoplasm  as  much  as  elimination  of  non-protoplasmic 
elements.  For  in  the  dog  changes  similar  to  those  in  the  rabbit  are 
caused,  although  the  amount  of  secretion  on  stimulation  of  the 
sympathetic  is  very  small,  and  generally  only  sufficient  to  block  the 
ducts  without  appearing  externally.  The  disappearance  of  granules 
from  without  inwards  during  activity  suggests  that  these  are  manu- 
factured products  eliminated  in  the  secretion. 

Changes  in  the  Glands  of  the  St/mach  during  Secretion. — The 
mucous  membrane  of  the  stomach  /is  covered  with  af  single  layer  of 
columnar  epithelium,  largely  consisting  of  mucigenous  goblet-cells. 
It  is  studded  with  minute  pits,  into  which  open  the  ducts  of  the 
peptic  and  pyloric  glands,  the  ducts  being  lined  with  cells  just  like 


DIGESTION 


321 


those  of  the  general  gastric  surface.  The  peptic  or  cardiac  glands 
have  short  ducts,  into  each  of  which  open  one  to  three  gland-tubes 
seldom  branched.  The  ducts  of  the  pyloric  glands  are  longer,  and 
the  secreting  tubules,  which  also  open  by  twos  OF  threes  into  the 
ducts,  are  branched.  The  secreting  parts  of  botj*  kinds  of  glands  are 
lined  by  short  columnar,  finely  granular  cellft/f  and  in  the  pyloric 
tubules  no  others  are  present.  But,  as  we  have  said,  in  the  peptic 


FIG.  104.— THE  GASTRIC  GLANDS.— On  the  left  cardiac,  right  pyloric  (Ebstein). 

glands  there  are  besides  lar/e  ovoid  cells  scattered  at  intervals  like 
beads  between  the  basement  membrane  and  the  lining  or  chief  c&ls. 

The  histological  cringes  connected  with  secretion  do  not 
differ  essentially  from  those  described  in  the  pancreas  and 
the  parotid,  but  there  is  much  greater  difficulty  in/  making 
observations  on  the  living,  or  at  least  but  slightly  altered, 
cells.  During  digestion  the  granules  seem  to  disappear  from 


21 


322  A  MANUAL  OF  PHYSIOLOGY 

the  outer  part  of  the  chief  cells  of  the  peptic  glands, 
leaving  a  clear  zone,  the  lumen  being  bordered  by  a  granular 
layer.  Or,  more  rarely,  there  may  be  a  uniform  decrease  in 
the  number  of  granules  throughout  the  qefl.  The  ovoid 
cells  swell  up,  so  as  to  bulge  out  the  menvbrana  propria,  but 
no  definite  chapges  in  their  contents,  such  as  those  observed 
in  the  other  e6lls,  have  been  made  c*ft. 

Changes  in  Mucous  Glands  during  Secretion. — In  the  mucous 
salivary  and  other  mucous  glands  similar,  but  apparently 
more  complex,  changes  occur.  During  rest  the  cells  which 
line  the  lumen  may  be  seen  in  fresh,  teased  preparations  to 
be  filled  with  granules  or  '  spherules.'  After  active  secretion 
there  is  a  great  diminution  in  the  number  of  the  granules. 
Those  that  remain  are  chiefly  collected  around  the  lumen, 
although  some  may  also  be  seen  in  the  peripheral  portion  of 
the  cell ;  and  there  is  no  very  distinct  differentiation  into 
two  zones.  That  a  discharge  of  material  takes  place  from 
these  cells  is  shown  by  their  smaller  size  in  the  active  gland. 
That  the  material  thus  discharged  is  not  protoplasmic  is 
indicated  by  the  behaviour  of  the  cells  to  protoplasmic  stains 
such  as  carmine.  The  resting  cells  around  the  lumen  stain 
but  feebly,  in  contrast  to  the  deep  stain  of  the  demilunes, 
while  the  discharged  cells  take  on  the  carmine  stain  much 
more  readily.  Further,  when  a  resting  gland  is  treated 
with  various  reagents  (water,  dilute  acids,  or  alkalies),  the 
granules  swell  up  into  a  transparent  substance  apparently 
identical  with  mucin,  which  appears  to  fill  the  meshes  of  a 
fine  protoplasmic  network  (Fig.  105). 

In  ordinary  alcohol-carmine  preparations  only  the  network  and 
nucleus  are  stained;  the  nucleus,  small  and  shrivelled,  is  situated  close 
to  the  outer  border  of  the  cell.  When  a  discharged  gland  is  treated 
in  the  same  way  there  is  proportionally  more  '  protoplasm  '  and  less 
of  the  clear  material,  what  remains  of  the  latter  being  chiefly  in  the 
inner  portion  of  the  cell,  while  the  nucleus  is  now  large  and  spherical, 
and  not  so  near  the  basement  membrane  (Plate  II.,  i  and  3). 

Everything,  therefore,  points  to  the  granules  in  what  we 
may  now  call  the  mucin-forming  cells  as  being  in  some  way 
or  other  precursors  of  the  fully-formed  mucin ;  manufactured 
during  '  rest '  by  the  protoplasm  and  partly  at  its  expense, 


DIGESTION 


323 


moved  towards  the  lumen  in  activity,  discharged  as  mucin1 
in  the  secretion.  It  has  been  asserted  that  not  only  is  the 
protoplasm  lessened  in  the  loaded  cell  and  renewed  after 
activity,  but  that  many  of  the  mucigenous  cells  may  be 
altogether  broken  down  and  discharged,  their  place  being 
supplied  by  proliferation  of  the  small  cells  of  the  demilunes. 
This  conclusion,  however,  is  not  supported  by  sufficient 
evidence.  But  the  fact  on  which  we  would  specially  insist 
is  that  the  granules  of  the  resting  mucigenous  cell  may  be 
looked  upon  as  a  mother-substance  from  which  the  mucin 
of  the  secretion  is  derived  ;  they  are  not  actual,  but  potential, 
mucin. 

So  in  the  pancreas,  the   serous   or  albuminous  salivary 


FIG.  105.— Mucous  CELLS  (FROM  SUBMAXILLARY  OF  DOG)  IN  REST 
AND  ACTIVITY  (LANGLEY). 

A,  B,  fresh;  A',  B',  after  treatment  with  dilute  acetic  acid;  A",  B",  alveoli 
hardened  in  alcohol  and  stained  with  carmine.  A,  A'  and  A"  represent  the  loaded  ; 
B,  B'  and  B",  the  discharged  condition. 

glands,  and  the  glands  of  the  stomach,  there  is  every  reason 
to  believe  that  the  granules  which  appear  in  the  intervals  of 
rest,  and  are  moved  towards  the  lumen  and  discharged 
during  activity,  are  the  precursors,  the  mother-substances,  of 
important  constituents  of  the  secretion.  These  granules  are 
sharply  marked  off  from  the  protoplasm  in  which  they  lie 
and  by  which  they  are  built  up.  By  every  mark,  by  their 
reaction  to  stains,  for  instance,  they  are  non-living  sub- 
stance, formed  in  the  bosom  of  the  living  cell  from  the  raw 
material  which  it  culls  from  the  blood,  or,  what  is  more 
likely,  formed  from  its  own  protoplasm,  then  shed  out  in 
granular  form  and  secluded  from  further  change.  The 

21 — 2 


324 


A  MANUAL  OF  PHYSIOLOGY 


proteolytic  power  of  an  extract  of  the  pancreas,  or  the 
gastric  mucous  membrane,  seems  to  be,  roughly  speaking, 
in  proportion  to  the  quantity  of  granules  present  in  the  cells. 
Therefore  it  is  concluded  that  the  granules  are  related  in 
some  way  to  trypsin  and  pepsin. 

But  we  should  greatly  deceive  ourselves  if  we  supposed 
that  granules  of  this  nature  in  gland-cells  are  necessarily 
related  to  the  production  of  ferments.  The  mucigenous 
granules  have  no  such  significance.  Most  digestive  secre- 
tions contain  proteid  constituents,  with  which  the  granules 
may  have  to  do,  as  well  as  with  ferments.  And  bile,  a 
secretion  which  contains  no  mucin,  no  proteids,  and  no 
ferments,  as  essential  constituents,  is  formed  in  cells  with 
granules  so  disposed  and  so  affected  by  the  activity  of  the 
gland  as  to  suggest  some  relation  between  them  and  the 
process  of  secretion.  In  the  liver  -  cells  of  the  frog,  in 
addition  to  glycogen  and  oil-globules,  small  granules  may 
be  seen,  especially  near  the  lumen  of  the  gland  tubules ; 
they  diminish  in  number  during  digestion,  when  the  secre- 
tion of  bile  is  active,  and  increase  when  food  is  withheld 
and  secretion  slow.  And  in  Brunner's  glands,  as  well  as  in 
the  pyloric  glands,  many  of  the  granules,  as  seen  in  fasting 
dogs  (Savas),  appear  to  be  of  fatty  nature.  It  is  possible 
that  these  represent  the  fat  which  is  known  to  be  excreted 
into  the  alimentary  canal  (pp.  371,  374,  447). 

The  granules  in  the  ferment  -  forming  glands  are  not 
composed  of  the  actual  ferments,  and,  indeed,  the  actual 
ferments  are  present  in  the  secreting  cells  only  in  small 
amount,  if  at  all,  as  is  shown  by  the  following  facts  : 

A  glycerine  extract  of  a  fresh  pancreas  has   hardly  any 
effect  on  proteids  ;  a  similar  extract  of  a  stale  pancreas  is 
very  active.      Therefore   the   fresh   pancreas   is   devoid   o 
trypsin.     But   it   contains   a  substance  which   can   readily 
be  changed  into  trypsin ;  and  this  substance  is  soluble  i 
glycerine,  for  the  inert  extract  becomes  active  when  it  i 
treated  with  dilute  acetic  acid,  or  even  when  it  is  dilute 
with  water  and  kept  at  the  body-temperature.     If  the  fres 
pancreas  be  first  treated  with  dilute  acetic  acid,  and  the 
with  glycerine,  the  extract  is  at  once  active.     All  this  g 


DIGESTION  325 

to  show  that  in  the  fresh  pancreas  not  trypsin,  but  a  mother- 
substance,  which  has  been  named  trypsinogen,  is  present, 
and  that  the  latter  yields  trypsin,  gradually  when  the  pan- 
creas is  simply  allowed  to  stand,  more  rapidly  when  the 
dilute  acid  is  used.  The  natural  secretion  of  the  gland  is 
active  when  the  gland-cells  contain  no  ferment,  therefore 
during  secretion  the  trypsinogen  must  be  changed  into 
trypsin. 

Similarly,  a  glycerine  extract  of  a  fresh  gastric  mucous 
membrane  is  inert  as  regards  proteids,  or  nearly  so.  But 
if  the  mucous  membrane  has  been  previously  treated  with 
dilute  hydrochloric  acid,  the  glycerine  extract  is  active,  as  is 
an  extract  made  with  acidulated  glycerine.  Here  we  must 
assume  the  existence  in  the  gastric  glands  of  a  mother- 
substance,  pepsinogen,  from  which  pepsin  is  formed.  Only 
the  chief  cells  of  the  cardiac,  and  the  similar  if  not  identical 
cells  of  the  pyloric  glands,  are  believed  to  manufacture  the 
pepsin-forming  substance.  The  ovoid  cells  of  the  former 
are  supposed  to  secrete  the  hydrochloric  acid.  The  evidence 
on  which  this  belief  is  based  is  as  follows  : 

The  pyloric  glands,  in  which  in  most  situations  no  ovoid  r 
cells  are  to  be  seen,  secrete  pepsin,  but  no  acid.  The  ^^^  ^// 
pyloric  portion  of  the  stomach  has  been  isolated,  the  con-  ^c^C. 
tinuity  of  the  alimentary  canal  restored  by  sutures,  and  the 
secretion  of  the  pyloric  pocket  collected.  It  was  found  to 
be  alkaline,  and  contained  pepsin.  The  glands  of  the  frog's 
oesophagus,  which  contain  only  chief  cells,  secrete  pepsin, 
but  no  acid.  It  seems  fair  to  conclude  that  the  chief  cells 
of  the  cardiac  glands  in  the  mammal  secrete  none  of  the 
free  hydrochloric  acid,  but  certainly  some  of  pepsin.  But  it 
does  not  follow  that  all  the  pepsin  is  formed  by  these  cells, 
although  it  would  seem  that  all  the  hydrochloric  acid  must 
be  secreted  by  the  only  other  glandular  elements  present, 
the  ovoid  or  '  border  '  cells.  And,  indeed,  the  glands  in 
the  fundus  of  the  frog's  stomach,  which  are  composed  only 
of  ovoid  cells,  while  secreting  much  acid,  also  form  some 
pepsin,  although  far  less  than  the  cesophageal  glands. 

Attempts  made  to  demonstrate  an  acid  reaction  in  the  border  ceils 
have  hitherto  failed,  perhaps  because  the  acid  is  poured  into  the 


326  A  MANUAL  OF  PHYSIOLOGY 

ducts  as  fast  as  it  is  formed.  But  it  should  be  mentioned  that  some 
observers  deny  that  the  acid  is  secreted  in  the  depths  of  any  cell 
from  the  chlorides  of  the  blood,  and  believe  that  it  is  formed  at  the 
surface  of  contact  of  the  stomach-wall  with  the  gastric  contents  from 
the  sodium  chloride  of  the  food  by  an  exchange  of  sodium  ions  (p.  362) 
for  hydrogen  ions  from  the  blood  or  lymph.  It  is  in  favour  of  this 
view  that  when,  instead  of  sodium  chloride,  sodium  bromide  is  given 
in  the  food,  the  hydrochloric  acid  in  the  stomach  is  to  a  large  extent 
replaced  by  hydrobromic  acid.  This  is  not  due  to  the  decomposi- 
tion of  the  bromide  by  hydrochloric  acid,  for  it  occurs  in  animals 
deprived  for  a  considerable  time  of  salts,  and  in  *  salt-hunger  '  the 

I  stomach  contains  no  acid  (Koeppe).     There  are,  however,  certain 

I  weighty  theoretical  objections  to  this  hypothesis. 

. 
The  rennet  ferment,  according  to  Langley,  is  formed  in 

the  chief  cells,  and  has  a  precursor  or  zymogen  like  the 
others. 

A  glycerine  or  watery  extract  of  the  salivary  glands  always 
contains  active  amylolytic  ferment,  if  the  natural  secretion 
is  active.  So  that  if  ptyalin  is  preceded  by  a  zymogen 
in  the  cells,  it  must  be  very  easily  changed  into  the  actual 
ferment. 

The  Quantitative  Estimation  of  Ferment  Action. — Since  we  have 
as  yet  no  certain  method  of  freeing  ferments  from  impurities,  our  only 
quantitative  test  is  their  digestive  activity.  And  since  a  very  small 
quantity  of  ferment  can  act  upon  an  indefinite  amount  of  material 
if  allowed  sufficient  time,  we  can  only  make  comparisons  when  the 
time  of  digestion  and  all  other  conditions  are  the  same.  If  we  find 
that  a  given  quantity  of  one  gastric  extract,  acting  on  a  given  weight 
of  fibrin,  dissolves  it  in  half  the  time  required  by  an  equal  amount 
of  another  gastric  extract,  or  dissolves  twice  as  much  of  it  in  a  given 
time,  we  conclude  that  the  digestive  activity  of  the  pepsin  is  twice 
as  great  in  the  first  extract  as  in  the  second,  or,  as  it  is  sometimes 
more  loosely  put,  that  the  one  contains  twice  as  much  pepsin  as  the 
other.  A  convenient  method  of  estimating  the  rate  at  which  the 
fibrin  disappears  is  to  use  fibrin  stained  with  carmine.  As  solution 
goes  on,  the  dye  colours  the  liquid  more  and  more  deeply,  and  by 
comparing  the  depth  of  colour  at  any  time  with  standard  solutions 
of  carmine,  the  quantity  of  the  dye  set  free,  and  therefore  of  the  fibrin 
digested,  can  be  approximately  arrived  at.  This  method  cannot  be 
used  for  trypsin.  As  a  test  of  the  activity  of  a  diastatic  ferment,  we 
take  the  amount  of  sugar  formed  in  a  given  time  in  a  given  quantity 
of  a  standard  starch  so  lution. 

We  have  spoken  more  than  once  of  the  gland-cells  as 
manufacturing  their  secretions.  It  is  an  idea  that  rises 


DIGESTION  327 

naturally  in  the  mind  as  we  follow  with  the  microscope  the 
traces  of  their  functional  activity.  And  when  we  compare 
the  composition  of  the  digestive  juices  with  that  of  the 
blood-plasma  and  lymph,  the  suggestion  that  the  glands 
which  produce  them  are  not  merely  passive  filters,  but 
living  laboratories,  acquires  additional  strength.  It  is 
evident  that  everything  in  the  secretion  must,  in  some  form 
or  other,  exist  in  the  blood  which  comes  to  the  gland,  and 
in  the  lymph  which  bathes  its  cells.  No  glandular  cell,  if 
we  except  the  leucocytes,  which  in  some  respects  are  to  be 
considered  as  unicellular  glands,  dips  directly  into  the  blood  ; 
everything  a  gland-cell  receives  must  pass  through  the  walls 
of  the  bloodvessels  into  the  lymph,  And  since  lymph  is 
practically  diluted  blood-plasma,  anything  which  we  find  in 
the  secretion  and  do  not  find  in  the  blood  must  have  been 
elaborated  by  the  gland  from  raw  material  brought  to  it  by 
the  latter. 

Take,  for  example,  the  saliva  or  gastric  juice.  These  liquids  both 
coutain  certain  things  that  also  exist  in  the  blood,  but  in  addition 
they  contain  certain  things  specific  to  themselves :  mucin  in  saliva, 
hydrochloric  acid  in  gastric  juice,  ferments  in  both.  It  is  true  that  a 
trace  of  pepsin  and  trace  of  a  diastatic  ferment  may  be  discovered 
in  blood  ;  but  there  is  no  reason  whatever  to  believe  that  this  is  the 
source  of  the  pepsin,  of  the  gastric  juice, 
or  the  ptyalin  of  the  salivary  glands.  On 
the  contrary,  it  is  possible  that  the  fer- 
ments of  the  blood  may  be  in  part 
absorbed  from  the  digestive  glands,  the 
rest  being  formed  by  the  leucocytes  and 
liberated  when  they  break  down.  The 
liver  affords  an  even  better  example  of 
this  '  manufacturing '  activity  of  gland- 
cells,  and  many  facts  may  be  brought 
forward  to  prove  that  the  characteristic  FIG.  106.— H^MATOIDIN. 
constituents  of  the  bile,  the  bile-pigments 

and  bile-acids,  are  formed  in  the  liver,  and  not  merely  separated 
from  the  blood.  Bile-pigment  has  indeed  been  recognised  in  the 
normal  serum  of  the  horse,  and  bile-acids  in  the  chyle  of  the  dog, 
but  only  in  such  minute  traces  as  are  easily  accounted  for  by  absorp- 
tion from  the  intestine.  Frogs  live  for  some  time  after  excision  of 
the  liver,  but  no  bile-acids  are  found  in  the  blood  or  tissues.  But  if 
the  bile-duct  be  ligatured,  bile-acids  and  pigments  accumulate  in  the 
body,  being  absorbed  by  the  lymphatics  of  the  liver,  as  was  shown 
by  Ludwig  and  Fleischl  in  the  dog.  If  the  thoracic  duct  and  the 
bile-duct  are  both  ligatured,  no  bile-acids  or  pigments  appear  in  the 


328  A  MANUAL  OF  PHYSIOLOGY 

blood  or  tissues.  In  mammals  life  cannot  be  maintained  for  any 
length  of  time  after  ligature  of  the  portal  vein,  since  this  throws 
the  whole  intestinal  tract  out  of  gear.  But  after  an  artificial 
communication  has  been  made  between  the  portal  and  the  left 
renal  vein  or  the  inferior  cava,  the  portal  may  be  tied  and  the 
animal  live  for  months  (Eck).  The  liver  can  now  be  completely 
removed,  but  death  follows  in  a  few  hours.  In  birds  there  exists 
a  communicating  branch  between  the  portal  vein  and  a  vein  (the 
renal -portal)  which  passes  from  the  posterior  portion  of  the  body 
to  the  kidney,  and  there  breaks  up  into  capillaries ;  and  not  only 
may  the  portal  be  tied,  but  the  liver  may  be  completely  destroyed 
without  immediately  killing  the  animal.  In  the  hours  of  life  that 
still  remain  to  it  no  accumulation  of  biliary  substances  takes  place 
in  the  blood  or  tissues.  A  further  indication  that  bile-pigment  is 
produced  in  the  liver  is  the  fact  that  the  liver  contains  iron  in  relative 
abundance  in  its  cells  (p.  381),  and  eliminates  small  quantities  of  iron 
in  its  secretion.  Now  bile-pigment,  which  contains  no  iron,  is 
certainly  formed  from  blood-pigment,  which  is  rich  in  iron,  for 
hoematoidin  (Fig.  106),  a  crystalline  derivative  of  haemoglobin  found 
in  old  extravasations  of  blood,  especially  in  the  brain,  is  identical  with 
bilirubin.  The  seat  of  formation  of  bile-pigment  must  therefore  be 
an  organ  peculiarly  rich  in  iron.  The  existence  of  haematoidin, 
however,  shows  that  bile-pigment  may,  under  certain  conditions,  be 
formed  outside  of  the  hepatic  cells.  The  occurrence  of  biliverdin 
in  the  placenta  of  the  bitch  points  in  the  same  direction.  But  the 
pathological  evidence  in  favour  of  the  pre-formation  of  the  biliary 
constituents  tends  rather  to  shrink  than  to  increase.  For  many  cases 
of  what  used  to  be  considered  '  idiopathic '  or  '  hsematogenic ' 
jaundice,  i.e.t  an  accumulation  of  bile-pigments  and  bile-acids  in  the 
tissues,  due  to  defective  elimination  by  the  liver,  are  now  known  to 
be  caused  by  obstruction  of  the  bile-ducts  and  consequent  re-absorp- 
tion of  bile  ('  obstructive  '  or  '  hepatogenic  '  jaundice). 

/     But  if  substances  such  as  the  ferments,  mucin,  hydrochloric 

I  acid,  the  bile-salts  and  bile-pigments,  are  undoubtedly  manu- 

I  factured  in  the  gland-cells,  it  is  different  with  the  water  and 

j  inorganic  salts  which  form  so  large  a  part  of  every  secre- 

I  tion.     No  tissue  lacks  them ;  no  physiological  process  goes 

on  without  them  ;  they  are  not  high  and  special  products. 

As  we  breathe  nitrogen  which  we  do  not  need  because  it  is 

mixed  with  the  oxygen  we  require,  the  secreting  cell  passes 

through  its  substance  water  and  salts  as  a  sort  of  by-play  or 

adjunct  to  its  specific  work.    But  this  is  not  the  whole  truth. 

The  gland-cell  is  not  a  mere  filter  through  which  water  and 

salts  pass  in  the  same  proportions  as  they  exist  in  the  liquids 

from  which  the  cell  draws  them.    The  secretions  of  different 


DIGESTION  329 

glands  differ  in  the  nature,  and  especially  in  the  relative 
proportions,  of  their  inorganic  constituents ;  and  the  secre- 
tion of  one  and  the  same  gland  is  by  no  means  constant  in 
this  respect,  as  we  shall  have  to  note  more  especially  when 
we  come  to  deal  with  the  influence  of  the  nervous  system  on 
secretion  (p.  338). 

The  proteid  substances,  such  as  serum-albumin  and 
globulin,  common  to  blood  and  to  some  of  the  digestive 
secretions,  take  a  middle  place  between  the  constituents 
that  are  undoubtedly  manufactured  in  the  cell  and  those 
which  seem  by  a  less  special  and  laborious,  though  a 
selective,  process  to  be  passed  through  it  from  the  blood. 
Their  absence  from  bile,  and,  as  we  shall  see,  from  urine, 
their  abundance  in  pancreatic  and  scantiness  in  gastric 
juice,  point  to  a  closer  dependence  upon  the  special  activity 
of  the  gland-cell  than  we  can  suppose  necessary  in  the  case 
of  the  salts. 

Although  it  is  in  the  cells  of  the  digestive  glands  that  the 
power  of  forming  ferments  is  most  conspicuous,  it  is  by  no 
means  confined  to  them.  It  seems  to  be  a  primitive,  a 
native  power  of  protoplasm.  Lowly  animals,  like  the 
amoeba,  lowly  plants,  like  bacteria,  form  ferments  within  the 
single  cell  which  serves  for  all  the  purposes  of  their  life. 
The  ferment  -  secreting  gland-cells  of  higher  forms  are 
perhaps  only  lop-sided  amoebae,  not  so  much  endowed  with 
new  properties  as  disproportionately  developed  in  one 
direction.  The  contractility  has  been  lost  or  lessened,  the 
digestive  power  has  been  retained  or  increased;  just  as  in 
muscle  the  power  of  contraction  has  been  developed,  and 
that  of  digestion  has  fallen  behind.  The  muscle-cell  and  the 
cartilage-cell  are  parasites,  if  we  look  to  the  function  of 
digestion  alone.  They  live  on  food  already  more  or  less 
prepared  by  the  labours  of  other  cells ;  and  it  is  a  universal 
law  that  in  the  measure  in  which  a  power  becomes  useless  it 
disappears.  But  the  presence  of  pepsin  in  the  white  blood- 
corpuscles,  the  parasites  as  well  as  the  scavengers  of  the 
blood,  and  of  amylolytic  ferments  in  many  tissues,  should 
warn  us  not  to  conclude  that  the  power  of  forming  ferments 
belongs  exclusively  to  any  class  of  cells.  And  it  is  possible 


330  A  MANUAL  OF  PHYSIOLOGY 


that  food-substances  absorbed  from  the  blood  are  further 
elaborated  by  ferment  action  within  the  tissues  themselves ; 
while  many  facts  show  that  the  power  of  contraction  is 
widely  diffused  among  structures  whose  special  function  is 
very  different,  and  a  few  point  to  its  possession  in  some 
degree  even  by  glandular  epithelium.  On  the  other  hand, 
it  must  be  remembered  that  none  of  the  digestive  glands 
absorb  food  directly  from  the  alimentary  canal  to  be  then 
digested  within  their  own  cell-substance ;  the  ferments 
which  they  form  do  their  work  outside  of  them  ;  their  cells 
feed  also  upon  the  blood. 

Why  are  the  Tissues  of  Digestion  not  affected  by  the  Digestive 
Ferments  ? — This  is  the  place  to  mention  a  point  which  has 
been  very  much  debated,  though  never  satisfactorily  ex- 
plained :  Why  is  it  that  the  stomach  or  the  small  intestine 
does  not  digest  itself?  This  is  really  a  part  of  a  wider 
question  :  Why  is  it  that  living  tissues  resist  all  kinds  of 
influences,  which  attack  dead  tissues  with  success  ?  The 
living  leucocyte  destroys  bacteria  by  which  the  dead 
leucocyte  is  broken  up ;  it  kills  and  digests  them  by  sub- 
stances formed  within  itself,  but  its  own  living  protoplasm 
is  not  digested.  Or  if  the  battle  goes  the  other  way,  the 
bacteria  kill  the  leucocyte,  and  break  it  up,  perhaps,  by  the 
aid  of  ferments  of  their  own  manufacture  which  affect  it  but 
not  them.  The  amoeba  digests  food  in  its  cell-substance, 
but  does  not  digest  itself.  The  pancreatic  cell  produces 
ferments  which  ruin  it  soon  after  death,  but  are  perfectly 
harmless  during  life.  The  pancreatic  juice  acts  with  great 
intensity  upon  proteids,  but  the  living  pancreas  and  the 
living  intestinal  wall  are  immune  to  it.  When  we  ascribe 
these  things  to  the  resistance  of  living  tissues,  we  play  with 
words.  And  we  have  to  inquire  whether  this  is  a  genera 
resistance  of  all  living  tissues,  or  a  specific  resistance  o 
certain  tissues  to  certain  influences;  whether  all  living 
tissues,  or  only  the  gastric  and  intestinal  walls,  are  shielded 
from  the  attack  of  the  digestive  ferments ;  and  if  all  living 
tissues  are  protected,  whether  they  are  protected  against  all 
ferments,  or  only  against  those  produced  by  themselves  or 
by  the  organism  of  which  they  form  a  part,  against  com- 


DIGESTION  331 

paratively  inactive  ferments,   or  equally  against   the    most 
powerful. 

That  all  living  tissues  cannot  withstand  the  action  of  the 
gastric  juice  has  been  shown  by  putting  the  leg  of  a  living 
frog  inside  the  stomach  of  a  dog ;  the  leg  is  gradually  eaten 
away  (Bernard).  It  is  scarcely  to  the  point  to  say  that  it 
has  first  been  killed  and  then  digested,  for  the  question  is, 
why  the  stomach-wall  is  not  first  killed  and  then  digested  ? 
When  the  wall  has  been  injured  by  caustics  or  by  an  em- 
bolus,  the  gastric  juice  acts  on  it.  But  the  living  epithelium 
that  covers  it  is  able  to  resist  the  action  of  the  acid  and 
pepsin,  which  destroy  the  tissues  of  the  frog's  leg.  The 
alkalinity  of  the  blood  has  nothing  to  do  with  the  explana- 
tion, for  the  frog's  blood  is  also  alkaline,  and  the  cells  that 
line  the  pancreatic  ducts  are  preserved  from  the  pancreatic 
juice,  which  is  intensely  active  in  an  alkaline  medium.  In 
the  gland-cells  of  the  pancreas  the  protoplasm  is,  no  doubt, 
shielded  from  digestion  by  the  existence  of  the  ferment  in 
an  inert  form  as  zymogen  ;  and  it  is  possible  that  this  is  the 
reason,  or  at  least  one  of  the  reasons,  for  the  existence  of 
the  mother-substance.  But  this  is  not  the  whole  explana- 
tion, for  the  living  frog's  leg  is  not  harmed  by  a  weakly 
alkaline  pancreatic  extract,  which  does  not  digest  the  epi- 
thelium, because  it  cannot  kill  it.  A  certain  amount  of 
protection  may  be  afforded  to  the  walls  of  the  stomach  by 
the  thin  layer  of  mucus  which  covers  the  whole  cavity,  for 
mucin  is  not  affected  by  peptic  digestion.  And  a  mucous 
secretion  seems  in  some  other  cases  to  act  as  a  protective 
covering  to  the  walls  of  hollow  viscera,  whose  contents  are 
such  as  would  certainly  be  harmful  to  more  delicate  mem- 
branes, e.g.,  in  the  urinary  bladder,  large  intestine,  and  gall- 
bladder. Still,  however  important  such  a  mechanical  pro- 
tection may  be,  it  does  not  explain  the  whole  matter,  and  it 
is  necessary  to  suppose  that  the  gastric  epithelium  has 
some  special  power  of  resisting  the  gastric  juice,  possibly  by 
turning  any  of  the  ferment  which  may  invade  it  into  an 
inert  substance  like  the  zymogen,  or  by  opposing  its  entrance 
as  the  epithelium  of  the  bladder  opposes  the  absorption  of 
urea.  That  each  membrane  becomes  accustomed,  and,  so 


332  A  MANUAL  OF  PHYSIOLOGY 

to  speak,  '  immune,'  to  the  secretion  normally  in  contact 
with  it  is  certain ;  but  this  is  not  a  general,  but  a  special, 
vital  action. 

What  living  tissues  but  the  lining  of  the  urinary  tract  or 
of  the  large  intestine  could  bear  the  constant  contact  of 
urine  or  faeces  ?  When  urine  is  extravasated  under  the  skin 
or  the  contents  of  the  alimentary  canal  burst  into  the  peri- 
toneal cavity,  they  are  still  in  contact  with  a  living  surface, 
but  with  a  surface  much  less  fitted  to  resist  them  than  that 
by  which  they  are  normally  enclosed ;  and  the  consequences 
are  often  disastrous.  Leucocytes  thrive  in  the  blood,  but 
perish  in  urine ;  blood  does  not  harm  the  living  cells  of  the 
vessels,  but  kills  a  muscle  whose  cross-section  is  dipped  into 
it.  The  defensive,  or  rather  in  some  cases  offensive,  liquids 
secreted  by  many  animals  are  harmless  to  the  tissues  which 
produce  and  enclose  them  :  a  caterpillar  investigated  by 
Poulton  secretes  a  liquid  so  rich  in  formic  acid,  that  the 
mere  contact  of  it  would  kill  most  cells.  The  so-called 
saliva  of  Octopus  macropus  contains  a  substance  fatal  to  the 
crabs  and  other  animals  on  which  it  preys.  The  blood  of 
the  viper  contains  an  active  principle  similar  to  that  secreted 
by  its  poison-glands,  but  its  tissues  are  not  affected  by  this 
substance,  so  deadly  to  other  animals. 

The  Influence  of  the  Nervous  System  on  the  Digestive  Glands. 
The  greater  part  of  our  knowledge  of  this  subject  has  been 
gained  by  the  study  of  the  salivary  glands,  and  especially 
the  submaxillary  and  sublingual,  which  lie  superficially  and 
are  easily  exposed. 

(i,  The  Influence  of  Nerves  on  the  Salivary  Glands. — All  the 
salivary  glands  have  a  double  nerve  -  supply,  from  the 
medulla  oblongata  through  some  of  the  cranial  nerves,  and 
from  the  spinal  cord  through  the  cervical  sympathetic 
(Fig.  107). 

In  the  dog  the  chorda  tympani  branch  of  the  facial  nerve  carries 
the  cranial  supply  of  the  sublingual  and  submaxillary  glands.  It 
joins  the  lingual  branch  of  the  fifth  nerve,  runs  in  company  with  it 
for  a  little  way,  and  then,  breaking  off,  after  giving  some  fibres ^  to  the 
lingual,  passes,  as  the  chorda  tympani  proper,  along  Wharton's  duct 
to  the  submaxillary  gland.  In  the  hilus  of  this  gland  most  of  its 


DIGESTION 


333 


fibres  become  connected  with  nerve-cells  and  lose  their  medulla  in 
them,  a  few  having  lost  it  before  entering  the  hilus,  and  a  few  doing 
so  deeper  in  the  gland.  The  lingual,  the  chorda  tympani  proper, 
and  Wharton's  duct  form  the  sides  of  what  is  called  the  chordo- 
lingual  triangle.  Within  this  triangle  are  situated  many  ganglion 
cells,  a  special  accumulation  of  which  has  received  the  name  of  the 
submaxillary  ganglion.  This,  however,  should  rather  be  called  the 
sublingual  ganglion,  since  its  cells,  as  well  as  the  others  in  the 
chordo-lingual  triangle,  are  the  cells  of  origin  of  neurous  (p.  639), 
which  proceed  as  non-medullated  fibres  to  the  sublingual  gland. 
The  sublingual  gland  receives  its  cerebral  fibres  partly  from 
branches  given  off  from  the  lingual  in  the  chordo-lingual  triangle 
after  the  chorda  tympani  proper  has  separated  from  it,  and  joining 
the  nerve-cells  within  that  triangle,  partly  from  the  chorda  itself  in 
the  terminal  portion  of  its  course.  These  statements  rest  on 


SM  and  SL,  submaxillary 
and  sublingual  glands ;  P, 
parotid ;  V,  fifth  nerve  ;  VII, 
facial;  GP,  glosso-pharyn- 
geal;  L,  lingual;  CT, 
chorda  tympani  ;  CL, 
chordo-lingual ;  D,  submax- 
illary (Wharton's)  duct ;  C, 
ganglion  cell  of  so-called 
submaxillary  ganglion  in 
the  chordo-lingual  triangle, 
connected  with  a  nerve  fibre 
going  to  sublingual  gland  ; 
C",  ganglion  cell  in  hilus  of 
submaxillary  gland  ;  SSP, 
small  superficial  petrosal 
branch  of  the  facial ;  OG.otic 
ganglion ;  JN,  Jacobson's 
nerve  ;  C',  ganglion  cells  in 
superior  cervical  ganglion 
(SG)  connected  with  sym- 
pathetic fibres  going  to 
parotid,  submaxillary  and 
sublingual  glands . 


FIG.  107.— SCHEME  OF  THE  NERVES  OF  THE 
SALIVARY  GLANDS. 


anatomical    and    physiological    evidence.     The    latter    we     shall 

turn  to. 

The  cerebral  fibres  for  the  parotid  (in  the  dog)  pass  from  the 

mpanic  branch  of  the  glosso-pharyngeal  (Jacobson's  nerve)  through 
connecting  filaments  to  the  small  superficial  petrosal  branch  of  the 
facial,  with  this  nerve  to  the  otic  ganglion,  and  thence  by  the 
auriculo-temporal  branch  of  the  fifth  to  the  gland. 

The  sympathetic  fibres  for  all  the  salivary  glands  appear  to  arise 
from  nerve-cells  in  the  upper  dorsal  portion  of  the  spinal  cord. 
Issuing  from  the  cord  in  the  anterior  roots  of  the  upper  thoracic 
nerves  (first  to  fifth,  but  mainly  second  thoracic  for  the  submaxillary), 
they  enter  the  sympathetic  chain,  in  which  they  run  up  to  the 
superior  cervical  ganglion.  Here  they  break  up  into  terminal  twigs, 
and  thus  come  into  relation  with  ganglion  cells,  whose  axis-cylinder 
processes  pass  out  as  non-medullated  fibres,  and,  surrounding  the 


334  A  MANUAL  OF  PHYSIOLOGY 

external  carotid,  reach  the  salivary  glands  along  its  branches. 
Langley  has  shown,  by  means  of  nicotine  (p.  157),  that  the  sym- 
pathetic fibres  for  the  submaxillary  and  sublingual,  and,  indeed,  for 
the  head  in  general  in  the  dog  and  cat,  are  connected  with  nerve- 
cells  in  this  ganglion,  but  not  between  it  and  their  termination,  or 
between  it  and  their  origin  from  the  spinal  cord. 

Stimulation  of  the  Cranial  Fibres. — When  in  the  dog  a 
cannula  is  placed  in  Wharton's  duct,  and  the  saliva  collected 
(P-  375)»  it  is  found  that  stimulation  of  the  peripheral  end  of 
the  divided  chorda  causes  a  brisk  flow  of  watery  saliva,  and 
at  the  same  time  a  dilatation  of  the  vessels  of  the  gland, 
which  we  have  already  described  in  dealing  with  vaso-motor 
nerves  (p.  155).  That  the  increased  secretion  is  not  due 
merely  to  the  greater  blood-supply,  and  the  consequent 
increase  of  capillary  pressure,  is  shown  by  the  injection  of 
atropia,  after  which  stimulation  of  the  nerve,  although  it 
still  causes  dilatation  of  the  vessels,  is  not  followed  by  a  flow 
l  of  saliva.  Further,  mere  increase  of  pressure  could  not  in 
any  case  of  itself  account  for  the  secretion,  since  it  has  been 
found  that  the  maximum  pressure  in  the  salivary  duct  may, 
during  stimulation  of  the  chorda,  much  exceed  the  arterial 
.,  blood-pressure  (Ludwig).  In  one  experiment,  for  example, 
the  pressure  in  the  carotid  of  a  dog  was  125  mm.,  in 
Wharton's  duct  195  mm.  of  mercury. 

Even  in  the  head  of  a  decapitated  animal  a  certain 
amount  of  saliva  may  be  caused  to  flow  by  stimulation  of 
the  chorda,  but  too  much  may  easily  be  made  of  this. 
And  since  the  blood  is  the  ultimate  source  of  the  secretion, 
we  could  not  expect  a  permanent  or  copious  flow  in  the 
absence  of  the  circulation,  even  if  the  gland-cells  could 
continue  to  live.  In  fact,  when  the  circulation  is  almost 
stopped  by  strong  stimulation  of  the  sympathetic,  the  flow  of 
saliva  caused  by  excitation  of  the  chorda  is  at  the  same  time 
greatly  lessened  or  arrested,  even  though  the  sympathetic 
itself  possesses  secretory  fibres.  So  that,  while  there  is  no 
doubt  that  the  chorda  tympani  contains  fibres  whose  function 
is  to  increase  the  activity  of  the  gland-cells,  its  vaso-dilator 
action  is,  under  normal  conditions,  closely  connected  with, 
and,  indeed,  auxiliary  to,  its  secretory  action,  although  the 
former  does  not  directly  produce  the  latter.  This  is  only  a 


DIGESTION  335 

particular  case  of  a  physiological  law  of  wide  application, 
that  an  organ  in  action  in  general  receives  more  blood  than  the 
same  organ  in  repose,  or,  in  other  words,  that  the  tissues  are  fed 
according  to  their  needs.  The  contracting  muscle,  the  secreting 
gland,  is  flushed  with  blood,  not  because  an  increased  blood- 
flow  can  of  itself  cause  contraction  or  secretion,  but  because 
these  high  efforts  require  for  their  continuance  a  rich  supply 
of  what  blood  brings  to  an  organ,  and  a  ready  removal  of 
what  it  takes  away. 

The  quantity  of  blood  passing  through  the  parotid  of  a 
horse  when  it  is  actively  secreting  during  mastication  may 
be  quadrupled  (Chauveau).  The  parallel  between  the 
muscle  and  the  gland  is  drawn  closer  when  it  is  stated  that 
electrical  changes  accompany  secretion  (p.  623),  and  that 
the  rate  of  production  of  carbon  dioxide  and  consumption  of 
oxygen  rises  during  activity.  The  temperature  of  the  saliva 
flowing  from  the  dog's  submaxillary  during  stimulation  of 
the  chorda  has  been  found  to  be  as  much  as  1*5°  C.  above 
that  of  the  blood  of  the  carotid,  although  with  the  gland  at 
rest  no  constant  difference  could  be  found  (Ludwig).  But 
such  measurements  are  open  to  many  fallacies  ;  and  while 
there  is  no  doubt  that  more  heat  is  produced  in  the  active 
than  in  the  passive  gland,  it  will  not  be  surprising,  when  the 
vastly  increased  blood-flow  is  remembered,  that  no  difference 
of  temperature  between  the  incoming  and  outgoing  blood  has 
been  satisfactorily  demonstrated,  although  we  must  assume 
that  such  a  difference  exists. 

How  the  secretory  fibres  of  the  chorda  end  in  the  gland 
we  do  not  know.  We  can  hardly  doubt  that  they  must  be 
connected  with  the  secreting  cells,  although  Pflliger's  obser- 
vations, which  seemed  to  establish  this  connection,  have  not 
been  confirmed.  In  the  '  salivary  glands  '  of  the  cockroach, 
however,  nerve-fibres  have  been  shown  to  end  in  the  cells. 

It  has  already  been  mentioned  that  most  of  the  fibres  of  the  chorda 
tympani  proper  become  connected  with  ganglion-cells^ and  lose  their 
medulla  inside  the  submaxillary  gland,  only  a  few  having  already  lost 
it  by  a  similar  connection  with  ganglion-cells  in  the  chordo-lingual 
triangle.  These  facts  have  been  made  out  by  means  of  the  nicotine 
method  already  described  (p.  157).  Thus,  it  is  found  that,  after  the 
injection  of  nicotine  (5  to  10  mg.  in  a  rabbit  or  cat,  40  or  50  mg.  in  a 


336  A  MANUAL  OF  PHYSIOLOGY 

dog),  stimulation  of  the  chorda  tympani  proper  or  of  the  chordo-lingual 
nerve  causes  no  secretion  from  the  submaxillary  gland ;  but  stimula- 
tion of  the  hilus  of  the  gland  is  followed  by  a  copious  secretion — as 
much,  if  the  stimulation  is  fairly  strong,  as  was  caused  by  excitation 
of  the  nerve  before  injection  of  nicotine.  That  this  is  due  neither  to 
any  direct  action  on  the  gland-cells,  nor  to  stimulation  of  the  sym- 
pathetic plexus  on  the  submaxillary  artery,  but  to  stimulation  of 
chorda  fibres  beyond  the  hilus,  is  shown  by  the  fact  that  after  atropia 
has  been  injected  in  sufficient  amount  to  paralyze  the  nerve  endings 
of  the  chorda,  but  not  of  the  sympathetic,  stimulation  of  the  hilus 
I  causes  little  or  no  flow  of  saliva.  The  application  of  nicotine  solution 
to  the  chordo-lingual  triangle  does  not  affect  the  submaxillary  secre- 
tion caused  by  stimulation  of  the  chordo-lingual  nerve,  even  in  cases 
where  a  few  secretory  fibres  for  the  submaxillary  do  not  leave  the 
chordo-lingual  nerve  in  the  chorda  tympani  proper,  but  are  given  off 
to  the  chordo-lingual  triangle.  This  shows  that  none  of  the  ganglion- 
cells  in  the  triangle  are  connected  with  the  cerebral  secretory  fibres 
of  the  submaxillary  gland.  By  observations  of  the  same  kind  they 
are  known  to  be  connected  with  fibres  going  to  the  sublingual.  In 
a  similar  way,  by  observing  the  effects  of  stimulation  of  the  chorda 
on  the  bloodvessels  before  and  after  the  application  of  nicotine,  it 
has  been  found  that  the  vaso-dilator  fibres  are  connected  with 
ganglion-cells  in  the  same  positions  as  the  secretory  fibres  (Langley). 

Stimulation  of  the  Sympathetic  Fibres. — The  sympathetic,  as 
has  been  already  indicated,  contains  both  vaso-constrictor 
and  secretory  fibres  for  the  salivary  glands.  If  the  cervical 
sympathetic  in  the  dog  is  divided,  and  the  cephalic  end 
moderately  stimulated,  a  few  drops  of  a  thick  viscid  and 
scanty  saliva  flow  from  the  submaxillary  and  sublingual 
ducts,  while  the  current  of  blood  through  the  glands  is 
diminished.  As  a  rule,  no  visible  secretion  escapes  from  the 
parotid,  but  microscopic  examination  shows  that  many  of 
the  ductules  are  filled  with  fluid,  which  is  apparently  so 
thick  as  to  plug  them  up  (Langley) ;  while  the  cells  show 
of '  activity.' 

Simultaneous  Stimulation  of  Cranial  and  Sympathetic  Fibres. — 
When  the  chorda  and  sympathetic  are  stimulated  together, 
the  former  prevails  so  far,  with  moderate  stimulation  of  the 
latter,  that  the  submaxillary  saliva  is  secreted  in  considerable 
quantity,  and  is  not  particularly  viscid  ;  it  is,  however,  richer 
in  organic  matter  than  is  the  chorda  saliva  itself.  When 
the  chorda  is  weakly,  and  the  sympathetic  strongly  excited, 
the  scanty  secretion  (if  there  is  any)  is  of  sympathetic  type, 


DIGESTION  337 

thick  and  rich  in  organic  matter.  With  strong  stimulation 
of  both  nerves,  the  secretion,  at  first  plentiful  and  watery, 
soon  diminishes,  even  below  the  amount  obtained  by 
stimulation  of  the  chorda  alone,  perhaps  because  of  the 
diminution  in  the  blood-flow  produced  by  the  vaso-con- 
strictors  of  the  sympathetic.  With  stimulation  just  strong 
enough  to  cause  secretion  when  applied  separately  to  either 
nerve,  there  is  no  secretion  when  it  is  applied  simultaneously 
to  both. 

All  this  refers  to  the  dog.  In  this  animal,  then,  there 
seems  to  be  a  certain  amount  of  physiological  antagonism 
between  the  secretory  action  of  the  two  nerves.  But  it 
differs  in  one  respect  from  the  antagonism  between  their 
vaso-motor  fibres ;  for  with  strong  stimulation  the  con- 
strictors of  the  sympathetic  always  swamp  the  dilators  of 
the  chorda,  while  the  secretory  fibres  of  the  chorda  appear 
upon  the  whole  to  prevail  over  those  of  the  sympathetic. 
And  in  all  probability  this  apparent  secretory  antagonism  is 
very  superficial ;  and  whatever  interference  there  may  be 
between  the  two  nerves,  apart  from  any  possible  effect  of 
their  vaso-motor  interference,  is  not  due  to  the  one  annulling 
the  influence  of  the  other  on  the  gland-cells,  but  to  the  cells 
being  called  by  them  to  different  labours,  in  general  com- 
plementary to  each  other,  and  only  incompatible  in  so  far  as 
the  working  power  of  the  cells  may  not  be  able  to  respond 
at  the  same  time  to  large  demands  from  both  sides.  For 
the  sympathetic  always  adds  something  to  the  common 
secretion  when  there  is  a  secretion  at  all,  this  something 
being  represented  by  an  increase  in  the  percentage  of 
organic  matter.  Not  only  so,  but  the  sympathetic  effect 
persists  after  stimulation  has  been  stopped  ;  and  excitation 
of  the  chorda  after  previous  stimulation  of  the  sympathetic 
causes  a  flow  of  saliva  richer  in  organic  matter  than  would 
have  been  the  case  if  the  sympathetic  had  not  been 
stimulated. 

Indeed,  the  distinction  between  chorda  and  sympathetic 
saliva,  which,  by  taking  account  of  the  parotid  as  well  as  the 
submaxillary  and  sublingual  glands,  has  been  generalized 
into  a  distinction  between  cerebral  and  sympathetic  saliva, 

22 


338  A  MANUAL  OF  PHYSIOLOGY 

and  which  holds  good  in  the  dog  and  the  rabbit,  breaks  down 
before  a  wider  induction.  For  in  the  cat  the  sympathetic 
saliva  of  the  submaxillary  gland,  although  much  more 
scanty,  is  more  watery  than  the  chorda  saliva  (Langley), 
which,  however,  is  by  no  means  viscid  ;  and  the  two  secre- 
tions differ  far  less  than  in  the  dog.  In  accordance  with 
this  functional  similarity,  there  is  a  much  smaller  difference 
in  the  action  of  atropia  on  the  two  sets  of  fibres  in  the  cat 
than  in  the  dog,  although  even  in  the  cat  the  sympathetic  is 
less  readily  paralyzed  than  the  chorda. 

In  their  secretory  action  there  is  not  even  an  apparent 
antagonism  in  the  cat,  with  minimal  stimulation  of  both 
nerves,  which  causes  as  much  secretion  as  would  be  pro- 
duced if  both  were  separately  excited.  Further,  even  in  the 
dog,  after  prolonged  stimulation  of  the  sympathetic,  the 
submaxillary  saliva  is  no  longer  viscid,  but  watery,  the  pro- 
portion of  solids,  and  especially  of  organic  solids,  being 
much  lessened,  as  it  also  is  in  chorda  saliva  after  long 
excitation.  When  the  cerebral  nerve  of  the  resting  gland 
is  strongly  excited,  it  is  found  that  up  to  a  certain  limit  the 
percentage  of  organic  matter  in  a  small  sample  of  saliva 
subsequently  collected  during  a  brief  weak  excitation 
increases  with  the  strength  of  the  previous  stimulation  ; 
this  is  also  true  of  the  inorganic  solids.  But  there  is  a 
striking  difference  when  the  experiment  is  made  on  a  gland 
after  a  long  period  of  activity  ;  here  increase  of  stimulation 
causes  no  increase  in  the  percentage  of  organic  material, 
while  the  inorganic  solids  are  still  increased.  In  both  cases 
the  absolute  quantity  of  water,  and  therefore  the  rate  of  flow 
of  the  secretion,  is  augmented. 

All  this  points  to  the  same  conclusion  as  the  microscopic 
appearances  in  the  gland-cells,  that  the  cells  during  rest 
manufacture  the  organic  constituents  of  the  secretion,  or 
some  of  them,  and  store  them  up,  to  be  discharged  during 
activity.  The  water  and  the  inorganic  salts,  on  the  other 
hand,  seem  rather  to  be  secreted  on  the  spur  of  the  moment, 
so  to  speak,  and  not  to  require  such  elaborate  preparation. 
And  it  has  been  stated  that  when  the  chorda  tympani  is 
stimulated  with  currents  of  varying  strength,  the  quantity  of 


DIGESTION  339 

organic  substances  in  small  samples  of  saliva  collected  from 
a  fresh  gland  is  more  nearly  proportional  to  the  rate  of 
secretion  than  is  the  quantity  of  water  and  salts,  which 
varies  also  with  the  blood-supply. 

In  order  to  explain  the  difference  between  the  cerebral  and 
sympathetic  secretion,  Heidenhain  has  supposed  the  existence  of 
two  kinds  of  secretory  fibres  :  (i)  secretory  fibres  proper,  the  excita- 
tion of  which  causes  an  actual  outpouring  of  liquid  from  the  gland- 
cells  into  the  ducts;  (2)  'trophic'  fibres,  which  not  only  promote 
the  changes  by  which  already  formed  organic  constituents  of  the 
secretion  pass  into  solution,  but  also  stimulate  the  growth  of  the 
glandular  protoplasm.  In  such  animals  as  the  dog  the  cranial  nerve 
(the  chorda  in  the  case  of  the  submaxillary  and  sublingual  glands) 
was  supposed  to  contain  many  fibres  of  group  (i),  comparatively  few 
of  group  (2)  •  and  the  sympathetic  few  of  (i)  and  more  of  (2).  Since 
these  trophic  fibres,  according  to  Heidenhain's  original  statement  of 
his  hypothesis,  possess  two  distinct  functions,  his  second  group  is 
sometimes  subdivided  into  a  set  of  katabolic  fibres  which  favour  the 
breaking  down  of  material  in  the  cell  as  a  preliminary  to  its  removal 
in  the  secretion,  and  a  set  of  anabolic  fibres  which  have  to  do  with 
the  building  up  of  fresh  substance.  But  it  must  be  remembered  that, 
although  it  may  be  convenient  for  certain  purposes  to  make  such  a 
physiological  classification,  there  is  no  proof  of  the  existence  of  any 
corresponding  anatomical  distinction ;  and  Langley  has  shown  that 
in  the  cat's  chorda  atropia  acts  simultaneously  on  all  the  secretory 
fibres ;  the  moment  it  paralyzes  one  group  all  are  paralyzed.  If  they 
were  anatomically  distinct,  it  might  have  been  supposed  that  atropia 
in  a  certain  dose  would  pick  out  one  or  other  group,  and  leave  the 
rest  still  active. 

It  is  conceivable  that  the  differences  between  chorda  and 
sympathetic  saliva  are  due,  not  to  the  nerve-fibres,  but  to 
the  end  organs  with  which  they  are  connected ;  that  is,  the 
two  nerves  may  supply,  not  the  same,  but  different  gland- 
cells.  And  it  is  well  known  that  even  after  prolonged 
stimulation  of  the  chorda  or  chordo-lingual  alone,  some 
alveoli  of  the  dog's  submaxillary  gland  remain  in  the 
'  resting  '  state ;  after  stimulation  of  the  sympathetic  alone, 
the  number  of  unaffected  alveoli  is  much  greater  ;  while  after 
stimulation  of  both  nerves,  few  alveoli  seem  to  have  escaped 
change.  However  suggestive  these  facts  may  be,  they  will 
not  as  yet  bear  the  weight  even  of  a  hypothesis  of  salivary 
secretion.  There  must  in  any  case  be  some  overlapping  in 
the  nerve-supply  ;  that  is,  some  cells  must  be  supplied  by 

22 — 2 


340  A  MANUAL  OF  PHYSIOLOGY 

both  nerves,  since  excitation  of  the  sympathetic  influences 
the  amount  of  organic  material  in  the  saliva  obtained  by 
subsequent  stimulation  of  the  chorda,  and  this  organic 
matter  certainly  comes,  for  the  most  part  at  least,  from 
substances  stored  up  in  the  cells.  And,  indeed,  we  know 
nothing  of  a  division  of  labour  between  the  cells  of  a  gland, 
except  when  there  are  obvious  anatomical  distinctions. 
Thus,  the  submaxillary  gland  in  man  contains  both  serous 
and  mucous  acini,  and  mucin-making  cells  are  scattered 
over  the  ducts  of  most  glands,  and,  indeed,  on  nearly  every 
surface  which  is  clad  with  columnar  epithelium.  In  these 
cases  we  cannot  doubt  that  one  constituent — mucin — of  the 
entire  secretion  is  manufactured  by  a  portion  only  of  the 
cells.  In  the  cardiac  glands  of  the  stomach,  too,  the  ovoid 
cells,  in  all  probability,  yield  the  whole  of  the  acid  of  the 
gastric  juice.  But,  so  far  as  we  know,  every  hepatic  cell  is 
a  liver  in  little.  Every  cell  secretes  fully- formed  bile  ;  every 
cell  stores  up,  or  may  store  up,  glycogen.  So  it  is  with 
the  secretory  alveoli  of  the  pancreas ;  one  cell  is  just  like 
another ;  all  apparently  perform  the  same  work  ;  each  is  a 
unicellular  pancreas.  (But  see  p.  473.) 

Paralytic  Secretion.  —  When  the  chorda  tympani  is  divided,  a 
slow  *  paralytic  '  secretion  from  the  submaxillary  gland  begins  in  a 
few  hours,  and  continues  for  a  long  time  accompanied  by  atrophy  of 
the  gland.  There  is  also  a  secretion  of  the  same  kind  from  the 
submaxillary  on  the  opposite  side,  but  it  is  less  copious.  This  is 
called  the  '  antilytic '  secretion,  which  is  most  pronounced  in  the 
first  few  days  after  the  operation,  and  seems  to  be  a  transient 
phenomenon.  It  can  be  at  once  abolished  by  section  both  of  the 
chorda  and  the  sympathetic  on  the  corresponding  side,  and  is  there- 
fore due  to  impulses  arising  in  the  central  nervous  system.  The 
cause  of  the  paralytic  secretion  has  not  been  fully  made  out.  If 
within  two  or  three  days  of  division  of  the  chorda  the  sympathetic 
on  the  same  side  is  cut,  the  secretion  is  greatly  diminished  or  stops 
altogether ;  and  it  is  concluded  that  up  to  this  time  it  is  maintained 
by  impulses  passing  along  the  sympathetic  to  the  gland  from  the 
salivary  centre,  the  excitability  of  which  has  been  in  some  way  in- 
creased by  division  of  the  chorda.  But  if  section  of  the  sympathetic 
is  not  performed  for  several  days,  it  has  no  effect  on  the  paralytic 
secretion,  which  at  this  stage  seems  to  depend  on  local  changes  in 
or  near  the  gland  itself,  leading  to  a  mild  continuous  excitation 
of  those  nerve-cells  on  the  course  of  the  fibres  of  the  chorda  to 
which  reference  has  already  been  made.  Section  of  the  sympathetic 


DIGESTION  341 

alone  causes  neither  secretion  nor  atrophy,  nor  does  removal  of  the 
superior  cervical  ganglion.  The  histological  characters  of  the  gland- 
cells  during  paralytic  secretion  are  those  of  '  rest.' 

Reflex  Secretion  of  Saliva.  —  The  reflex  mechanism  of 
salivary  secretion  is  very  mobile,  and  easily  set  in  action  by 
physical  and  mental  influences.  It  is  excited  normally  by 
impulses  which  arise  in  the  mouth,  especially  by  the  contact 
of  food  with  the  buccal  mucous  membrane  and  the  gustatory 
nerve-endings.  The  mere  mechanical  movement  of  the 
jaws,  even  when  there  is  nothing  between  the  teeth,  or  only 
a  bit  of  a  non-sapid  substance  like  indiarubber,  causes 
secretion.  The  vapour  of  glacial  acetic  acid  or  ether  gives 
rise  to  a  rush  of  saliva,  as  does  gargling  the  mouth  with 
distilled  water.  The  smell,  sight,  or  thought  of  food,  and 
even  the  thought  of  saliva  itself,  may  act  on  the  salivary 
centre  through  its  connections  with  the  cerebrum,  and  make 
1  the  teeth  water.'  A  copious  flow  of  saliva,  reflexly  excited 
through  the  gastric  branches  of  the  vagus,  is  a  common 
precursor  of  vomiting ;  the  introduction  of  food  into  the 
stomach  also  excites  salivary  secretion. 

In  most  animals  and  in  man  the  activity  of  the  large 
salivary  glands  is  strictly  intermittent.  But  the  smaller  glands 
that  stud  the  mucous  membrane  of  the  mouth  never  entirely 
cease  to  secrete,  and  the  same  is  the  case  with  the  parotid 
in  ruminant  animals. 

The  centre  is  situated  in  the  medulla  oblongata,  stimula- 
tion of  which  causes  a  flow  of  saliva.  The  chief  afferent 
paths  to  the  salivary  centre  are  the  Jingual  branch  of  the 
fifth  and  the  glpsso-pharyngeal ;  but  stimulation  of  many 
other  nerves  may  cause  reflex  secretion  of  saliva.  In  ex- 
perimental stimulation,  the  sole  efferent  channel  seems  to 
be  the  cerebral  nerve-supply  of  the  glands.  After  section 
of  the  chorda,  no  reflex  secretion  by  the  submaxillary  gland 
can  be  caused,  although  the  sympathetic  remains  intact. 

It  was  alleged  by  Bernard  that,  after  division  of  the 
chordo-lingual,  a  reflex  secretion  could  be  obtained  from  the 
submaxillary  gland  by  stimulating  the  central  end  of  the 
cut  lingual  nerve  between  the  so-called  submaxillary  ganglion 
and  the  tongue,  the  ganglion  being  supposed  to  act  as 


342  A  MANUAL   OF  PHYSIOLOGY 

'  centre.'  It  has  been  shown,  however,  that  this  is  not  a 
true  reflex  effect,  but  is  due,  mainly  at  least,  to  the  excitation 
of  certain  secretory  fibres  of  the  chorda  that  run  for  some 
distance  in  the  lingual,  then  bend  back  on  their  course  and 
pass  to  the  gland. 

The  salivary  centre  can  also  be  inhibited,  especially  by 
emotions  of  a  painful  kind — for  instance,  the  nervousness 
which  often  dries  up  the  saliva,  as  well  as  the  eloquence,  of 
a  beginner  in  public  speaking,  and  the  fear  which  sometimes 
made  the  medieval  ordeal  of  the  consecrated  bread  pick  out 
the  guilty. 

In  rare  cases  the  reflex  nervous  mechanism  that  governs 
the  salivary  glands  appears  to  completely  break  down  ;  and 
then  two  opposite  conditions  may  be  seen — xerostomia,  or 
'  dry  mouth,'  in  which  no  saliva  at  all  is  secreted,  and 
chronic  ptyalism,  or  hydrostomia,  where,  in  the  absence  of 
any  discoverable  cause,  the  amount  of  secretion  is  per- 
manently increased.  Both  conditions  are  more  common  in 
women  than  in  men. 

(2)  The  Influence  of  Nerves  on  the  Gastric  Glands. — Like  saliva, 
gastric  juice  is  not  secreted  continuously,  except  in  animals, 
such  as  the  rabbit,  whose  stomachs  are  never  empty.  The 
normal  and  most  efficient  stimulus  is  the  presence  of  food 
in  the  stomach.  Faintly  alkaline  liquids,  such  as  saliva, 
excite  an  active  secretion,  but  it  is  only  early  in  digestion, 
before  the  reaction  of  the  gastric  contents  has  become 
distinctly  acid,  that  swallowed  saliva  can  have  any  effect. 
Mechanical  stimulation  of  the  gastric  mucous  membrane 
causes  a  certain  amount  of  secretion,  but  not  a  great  deal. 
No  nerve  has  been  shown  with  certainty  to  have  any 
influence  over  the  gastric  glands.  So  that  at  first  thought 
there  is  much  to  suggest  that  these  are  normally  stimulated 
in  a  more  direct  manner  than  the  salivary  glands,  perhaps 
by  the  local  action  of  food  substances  reaching  the  cells  by 
a  short-cut  from  the  cavity  of  the  stomach,  or  in  a  more 
roundabout  way  by  the  blood.  And  it  might  be  very 
plausibly  argued  that  the  gastric  glands  are  favourably 
situated  for  direct  stimulation,  while  the  salivary  glands  are 
not ;  and  that  the  great  function  of  saliva  being  to  aid 


DIGESTION  343 

deglutition,  an  almost  momentary,  and  at  the  same  time  a 
perilous  act,  it  is  necessary  to  provide  by  nervous  mechanism 
for  an  immediate  rush  of  secretion  at  any  instant,  while  it  is 
not  important  whether  the  gastric  juice  is  poured  out  a  little 
sooner  or  a  little  later,  and  therefore  it  is  left  to  be  called 
forth  by  the  more  tardy  and  haphazard  method  of  local 
action.  Nevertheless,  on  looking  a  little  closer,  we  find  that 
this  does  not  exhaust  the  subject,  and  that  the  gastric  secre- 
tion can  be  influenced  by  events  taking  place  in  distant  parts 
of  the  body,  just  as  the  salivary  secretion  can.  In  a  boy 
whose  oesophagus  was  completely  closed  by  a  cicatrix,  the 
result  of  swallowing  a  strong  alkali,  and  who  had  to  be  fed 
by  a  gastric  fistula,  it  was  found  that  the  presence  of  food 
in  the  mouth,  and  even  the  sight  or  smell  of  food,  caused 
secretion  of  gastric  juice  (Richet) ;  and  in  dogs  with  the 
oesophagus  divided  so  that  nothing  could  pass  through  it  to 
the  stomach,  a  similar  result  was  obtained  (Pawlow). 

Here  there  must  have  been  some  nervous  mechanism  at 
work.  The  secretion  can  hardly  have  been  excited  by  thd 
direct  action  of  food  products  absorbed  from  the  mouth  and 
circulating  in  the  blood — an  explanation  which  has  been 
given  of  the  secretion  seen  in  an  isolated  portion  of  the 
cardiac  end  of  the  stomach  during  the  digestion  of  food  in  the 
rest.  What  the  nervous  channels  are  through  which  these 
effects  are  produced  has  not  been  clearly  made  out.  After 
division  of  the  sympathetic  fibres  going  to  the  stomach,  and 
also  the  vagi,  gastric  secretion  is  still  caused  by  the  intro 
duction  of  food  into  the  stomach,  so  long  as  the  latter  nerves 
are  cut  below  the  origin  of  their  cardiac  and  pulmonary 
branches,  and  disturbance  of  the  heart  and  respiration  thus 
avoided  (Heidenhain).  Not  only  so,  but  the  vascular 
dilatation,  which  accompanies  the  activity  of  the  gastric  as 
well  as  the  salivary  glands,  and  is  shown  by  flushing  of  the 
mucous  membrane  of  the  stomach,  is  not  interfered  with 
by  section  of  the  vagi  in  the  position  mentioned. 

The  most  probable  conclusion  would  seem  to  be  that,  while 
a  great  part  must  be  assigned  to  the  local  effects  of  the 
food,  and  the  action  of  the  products  of  digestion  absorbed 
into  the  blood  on  the  gland-cells  or  on  nervous  centres, 


344  A  MANUAL  OF  PHYSIOLOGY 

these  may  be  supplemented  and  controlled  by  a  truly  reflex 
mechanism. 

O  (3)  The  Influence  of  Nerves  on  the  Pancreas, — Our  know- 
ledge of  the  influence  of  nerves  on  the  pancreas  is  a  little 
more  definite,  but  not  much.  Stimulation  of  the  medulla 
oblongata  causes  or  increases  secretion  even  after  section  of 
the  vagi.  Stimulation  of  the  central  end  of  the  vagus  and 
of  other  nerves  inhibits  the  secretion  ;  the  inhibition  caused 
by  vomiting  is  probably  due  to  impulses  ascending  the 
vagus.  These  facts  point  to  the  existence  of  a  reflex 
mechanism,  but  neither  has  the  centre  been  located  nor 

the  afferent  and  efferent 
paths  definitely  ascer- 
tained. The  natural  secre- 
tion of  pancreatic  juice  is 
by  no  means  so  intermit- 
tent as  that  of  saliva.  In 
the  rabbit  the  pancreatic, 
like  the  gastric,  juice  flows 
continuously.  In  a  well- 

FIG.  IOS.-RATE  OF  SECRETION  OF  PAN-  fed  d°S  k  is  Probable  that 
CREATIC  JUICE.  it  seldom  stops  altogether, 

S  shows  the  variation  in  the  rate  of  secretion  for  ft  was  found   that   after 
of  the  pancreatic  juice  in  a  dog  ;  P,  the  varia- 
tion in  the  percentage  of  solids  in  the  juice,  a  meal  it  took  from  twenty 
It  will  be  seen  that  the  maxima  of  S  fall  at  the  ,  r  ,  t 
same  time  as  the  minima  of  P.     The  numbers  «>    twenty-IOUr    hOUTS     for 

fastnmeai?  horizontal  axis  ™  hours  sincc  the  the  flow  to  cease  entirely. 

It  begins  abruptly  as  soon 

as  the  food  enters  the  stomach,  probably  through  reflex 
impulses  originating  in  the  gastric  mucous  membrane,  rises 
in  two  or  three  hours  to  a  maximum,  then  falls  till  the 
fifth  or  sixth  hour,  after  which  it  mounts  again  about  the 
ninth  or  tenth  hour  to  a  second  lower  maximum,  and  then, 
gradually  diminishing,  ultimately  stops.  During  activity  the 
bloodvessels  of  the  gland  are  dilated ;  but  we  have  as  yet  no 
precise  information  as  to  the  vaso-motor  nerves  which  govern 
them.  When  the  nerves  of  the  pancreas,  which  pass  to  it 
from  the  solar  plexus  along  the  vessels,  are  divided,  'paralytic ' 
secretion  of  thin  watery  juice  takes  place.  There  is  one 
very  remarkable  difference  between  the  normal  secretion  of 


DIGESTION  345 

pancreatic  juice  and  of  saliva  :  the  pressure  of  the  latter 
in  the  submaxillary  duct  may,  as  we  have  seen,  greatly 
exceed  the  arterial  blood-pressure,  without  reabsorption  and 
consequent  oedema  of  the  gland  occurring ;  but  the  secretory 
pressure  of  the  pancreatic  cells  is  very  low,  not  more  than  a 
tenth  of  that  of  the  salivary  glands.  (Edema  begins  before  a 
manometer  in  the  duct  shows  a  pressure  of  20  mm.  of  mercury. 

(4)  The  Influence  of  Nerves  on  the  Secretion  of  Bile. — 
Although  bile  is  secreted  constantly,  it  only  passes  at 
intervals  into  the  intestine.  For  the  liver  in  many  animals, 
unlike  every  other  gland  except  the  kidney,  has  in  connection 
with  it  a  reservoir,  the  gall-bladder,  in  which  its  secretion 
accumulates,  and  from  which  it  is  only  expelled  occasionally. 
We  have  therefore  to  distinguish  the  bile-secreting  from  the 
bile-expelling  mechanism.  Of  the  direct  influence  of  nerves 
on  either  we  have  scarcely  any  knowledge,  scarcely  even 
any  guess  which  is  worth  mentioning  here.  It  is  true  the 
secretion  of  bile  may  be  distinctly  affected  by  the  section 
and  stimulation  of  nerves  which  control  the  blood-supply  of 
the  stomach,  intestines,  and  spleen,  for  the  quantity  of  blood 
passing  by  the  portal  vein  through  the  liver  depends  upon 
the  quantity  passing  through  these  organs,  and  the  rate  of 
secretion  is  closely  related  to  the  blood-supply.  In  this  way 
stimulation  of  the  medulla  oblongata,  the  spinal  cord,  and 
the  splanchnic  nerves  stops  or  slows  the  secretion  of  bile  by 
constricting  the  abdominal  vessels  ;  and  the  same  effect  can 
be  reflexly  produced  by  the  excitation  of  afferent  nerves. 

The  muscular  fibres  of  the  gall-bladder  and  the  larger 
bile-ducts  are  thrown  into  contraction  by  stimulation  of  the 
spinal  cord.  It  is  possible  that  this  takes  place  naturally  in 
response  to  reflex  impulses  from  the  mucous  membrane  of 
the  duodenum,  for  the  application  of  dilute  acid  to  the 
mouth  of  the  bile-duct  causes  a  sudden  flow  of  bile,  and  the 
acid  contents  of  the  stomach,  when  projected  through  the 
pylorus  into  the  intestine,  have  a  similar  effect. 

The  pressure  under  which  the  bile  is  secreted  is  remarkably 
small,  the  maximum  being  no  more  than  15  mm.  of  mercury. 
But  small  as  this  is,  it  is  higher  than  the  pressure  of  the 
portal  blood,  and  therefore  the  liver  ranges  itself  with  the 


346  A  MANUAL  OF  PHYSIOLOGY 

high-pressure  salivary  glands  rather  than  with  the  low- 
pressure  pancreas.  But  although  the  biliary  pressure  is  high 
relatively  to  that  of  the  blood  with  which  the  secreting  cells 
are  supplied,  it  is  absolutely  very  low  ;  and  this  is  a  point  of 
practical  importance,  for  a  comparatively  slight  obstruction 
to  the  outflow,  even  such  as  is  offered  by  a  congested  or 
inflamed  condition  of  the  duodenal  wall  about  the  mouth 
of  the  duct,  may  be  sufficient  to  cause  reabsorption  of  the 
bile  through  the  lymphatics,  and  consequent  jaundice.  Of 

course,  complete  plugging  of  the 
duct  by  a  biliary  calculus  is  a 
much  more  formidable  barrier, 
and  inevitably  leads  to  jaundice, 
just  as  ligature  of  a  salivary  duct, 
in  spite  of  the  great  secretory 
pressure,  inevitably  causes  oedema 
of  the  gland. 

When    food     passes    into    the 
stomach,  there  is  at  once  a  sharp 

rise    in  the   rate    of  secretion   of 
FIG.  109.  —  RATE  OF  SECRETION    ,..          A  .  .  ,      ,  r 

OF  BILE.  bile.    A  maximum  is  reached  from 

S  shows  how  the  rate  of  secretion    the    fourth    to    the    eighth     hour  — 
of  bile  falls  in  a  doer  when  a  biliary    ,  i      .     •  1-1       ,1         r      j    •       •        ,1 

fistula  is  first  made,  and  the  bile    that    IS,  while    the    food    IS    in    the 

intestine;  there  is  then  a  fall,  sue- 


percentage  of  solids.  The  numbers  ceeded  by  a    second   smaller  rise 

along     the     horizontal     axis     are 

quarters  of  an  hour  since  bile  began  about  the     fifteenth    Or  Sixteenth 

to  escape  through  the  fistula.     The  ,  r  ,  •    ,       ,,  ,• 

numbers  along  the  vertical  axis  refer  hour,  from    which    the  Secretion 

dedines  to  its 


Upon  the  whole,  the  curves  of 
secretion  of  pancreatic  juice  and  bile  show  a  fairly  close 
correspondence,  which  lends  additional  support  to  the  view 
derived  from  their  chemical  and  physical  properties,  that  in 
digestion  they  are  partners  in  a  common  work. 

We  do  not  know  in  what  way  the  rate  of  secretion  of  bile 
is  influenced  by  digestion,  although  it  has  been  conjectured 
that  the  first  abrupt  rise  may  be  started  by  reflex  nervous 
action,  and  that  later  on  absorbed  food  products  may  directly 
excite  the  hepatic  cells.  Rutherford  found  that  when  the 
mucous  membrane  of  the  stomach  and  duodenum  is  irritated 


DIGESTION  347 

by  a  substance  like  gamboge,  there  is  no  increase  in  the 
rate  of  secretion  of  the  bile,  notwithstanding  the  greatly 
increased  flow  of  blood  through  the  intestinal  vessels  which 
the  irritation  causes.  This  tells  in  favour  of  the  direct 
influence  of  substances  derived  from  the  food  rather  than 
of  any  important  reflex  action. 

(5)  The  Influence  of  Nerves  on  the  Secretion  of  Intestinal 
Juice. — As  to  the  influence  of  nerves  on  the  secretion  of  the 
succus  entericus,  our  knowledge  is  almost  limited  to  a  single 
experiment,  and  that  an  inconclusive  one.  Moreau  placed 
four  ligatures  on  a  portion  of  the  small  intestine,  so  as  to 
form  three  compartments  separated  from  each  other  and 
from  the  rest  of  the  gut.  The  mesenteric  nerves  going 
to  the  middle  loop  were  divided,  and  the  intestine  returned 
to  the  abdomen.  After  some  time  a  watery  secretion  was 
found  in  the  middle  compartment,  little  or  none  in  the 
others.  This  is  a  true  '  paralytic  '  secretion,  and  not  a 
mere  transudation  depending  simply  on  the  vascular  dilata- 
tion caused  by  section  of  the  vaso-constrictor  nerves,  for  it 
has  the  same  composition  and  digestive  action  as  normal 
succus  entericus  obtained  from  a  fistula. 

Effect  of  Drugs  on  the  Digestive  Secretions. — A  small  dose  of 
atropia,  as  has  been  said,  abolishes  the  secretory  action  of  the  chorda 
tympani.  This  it  does  by  paralyzing  the  nerve-endings.  The  gland- 
cells  are  not  paralyzed,  for  the  sympathetic  can  still  cause  secretion.  *> 
The  nerve-fibres  are  not  paralyzed,  because  the  direct  application  of 
atropia  does  not  affect  them;  nor  is  the  seat  of  the  paralysis  the 
ganglion-cells  on  the  course  of  the  fibres,  for  stimulation  between 
those  cells  and  the  gland-cells  is  ineffective.  Pilocarpine  is  the 
physiological  antagonist  of  atropia,  and  restores  the  secretion  which 
atropia  has  abolished.  In  small  doses  it  causes  a  rapid  flow  of 
saliva,  its  action  being  certainly  a  peripheral  action,  and  probably  an 
action  on  the  nerve-endings,  for  it  persists  after  all  the  nerves  going 
to  the  salivary  glands  have  been  divided,  and  after  the  ganglion-cells 
have  been  paralyzed  by  nicotine.  Atropia  and  pilocarpine  act 
similarly  on  some  of  the  other  digestive  glands,  the  former  paralyzing 
the  pancreatic  secretion,  the  latter  increasing  the  secretion  of  gastric, 
and  probably  of  intestinal,  juice;  but  atropia  does  not  stop  the 
secretion  caused  by  division  of  the  intestinal  nerves.  Physostigmine 
and  muscarine  act  on  the  whole  like  pilocarpine. 

The  action  of  a  host  of  drugs  on  the  secretion  of  bile  has  been 
investigated  by  various  observers,  but  till  something  like  unanimity 
has  been  reached,  it  would  not  be  profitable  to  go  into  details  here. 


348  A  MANUAL  OF  PHYSIOLOGY 


only  real  cholagogues  at  present  positively  known  appear  to  be 
t?  *he  salts  of  the  bil^'acids,  and  the  less  effective  salol  and  salicylate  of 
^  sodium.  The  former  when  giver,  by  themselves  or  in  the  bile  cause 
not  only  an  increase  in  the  volume  of  the  biliary  secretion,  but  also  an 
increase  in  its  solids.  The  latter,  while  increasing  the  flow,  seem  to 
diminish  the  concentration  of  the  bile.  The  injection  of  haemoglobin 
into  the  blood-stream,  or  its  liberation  there  by  substances,  such  as 
toluylene-diamin  and  arseniuretted  hydrogen,  which  cause  solution 
of  the  corpuscles,  leads  to  an  increased  secretion  of  bile-pigment  as 
well  as  a  more  rapid  flow  of  bile. 

Summary.  —  Here  lei  us  sum  up  the  most  important  points 
relating  to  the  secretion  of  the  digestive  juices.  They  are 
all  formed  by  the  activity  of  gland-cells  originally  derived  from  the 
epithelial  lining  of  the  alimentary  canal.  The  organic  constituents 
or  their  precursors  (including  the  mother-substances  of  the  ferments) 
are  prepared  in  the  intervals  of  rest  —  absolute  in  some  glands, 
relative  in  others  —  and  stored  up  in  the  form  of  granules,  which 
during  activity  arc  moved  towards  the  lumen  of  the  gland  tubules, 
and  there  discharged. 

The  nerves  of  the  salivary  glands  are,  as  regards  their  origin, 
(a)  cerebral,  (b)  sympathetic  ;  the  former  group  is  vaso-dilator, 
the  latter  vaso-  constrictor  —  both  arc  secretory.  Secretion  of  saliva 
depends  strictly  on  the  nervous  system.  That  nerves  influence  the 
gastric  and  pancreatic  secretions  is  made  out,  but  nothing  definite 
is  known  as  to  the  nervous  paths.  As  regards  the  intestinal 
glands  and  the  liver,  it  has  not  been  proved  that  their  secretive 
activity  is  at  all  under  the  control  of  the  nervous  system,  except 
in  so  far  as  the  latter  may  indirectly  govern  it  through  the  blood- 
supply,  although  various  circumstances  suggest  the  probability  of  a 
more  direct  action.  In  all  the  glands  the  blood-flow  is  increased 
during  activity  —  in  some  (salivary  glands)  this  is  known  to  be 
caused  through  nerves.  In  the  salivary  glands  electromotive 
changes  accompany  the  active  state,  while  more  heat  is  produced, 
more  carbon  dioxide  given  off,  and  more  oxygen  used  up,  during 
secretion  than  during  rest.  In  the  other  glands  we  may  assume 
that  the  same  occurs. 

IV.  Digestion  as  a  Whole. 

Having  discussed  in  detail  the  separate  action  of  the 
digestive  secretions,  it  is  now  time  to  consider  the  act 
of  digestion  as  a  whole,  the  various  stages  in  which  are 


DIGESTION  349 

co-ordinated  for  a  common  end.  The  solid  food  is  more  or 
less  broken  up  in  the  mouth  and  mixed  with  the  saliva, 
which  its  presence  causes  to  be  secreted  in  considerable 
quantity.  Liquids  and  small  solid  morsels  are  shot  down 
the  open  gullet  without  contraction  of  the  constrictors  of 
the  pharynx,  and  reach  the  bottom  of  the  oesophagus  in  a 
comparatively  short  time  (TV  second)  ;  while  a  good-sized 
bolus  is  grasped  by  the  constrictors,  then  by  the  cesophageal 
walls,  and  passed  along  by  a  more  deliberate  peristaltic  con- 
traction. Beaumont  saw,  in  the  case  of  St.  Martin,  that 
the  cesophageal  orifice  of  the  stomach  contracted  firmly 


FIG.  no. — SECRETION  OF  PEPSIN. 

C  shows  the  quantity  of  pepsin  in  the  mucous  membrane  of  the  cardiac  end  of  the 
stomach  at  different  times  during  digestion  ;  P,  the  quantity  of  pepsin  in  the  mucous 
membrane  of  the  pyloric  end  ;  S,  the  quantity  of  pepsin  in  the  secretion  of  the  cardiac 
glands.  The  numbers  marked  along  the  horizontal  axis  are  hours  since  the  last  meal. 
About  five  hours  after  the  meal  S  reaches  "its  maximum.  From  the  very  beginning  of 
the  meal  C  falls  steadily  down  to  the  tenth  hour,  and  then  begins  to  rise,  i.e.,  the  gland- 
cells  of  the  cardiac  end  of  the  stomach  become  poorer  in  pepsin  as  secretion  proceeds. 

after  each  morsel  was  swallowed,  and  so  did  the  gastric 
walls  in  the  neighbourhood  of  the  fistula  when  food  was 
introduced  by  this  opening.  Two  sounds  may  be  heard  in 
man  on  listening  in  the  region  of  the  stomach  or  oesophagus 
during  deglutition  of  liquids,  especially  when,  as  generally 
happens,  they  are  mixed  with  air.  The  first  sound  occurs 
at  once,  and  is  supposed  to  be  due  to  the  sudden  squirt  of 
the  liquid  along  the  gullet ;  the  second,  which  is  heard  after 
a  distinct  interval  (six  seconds),  seems  to  be  caused  by  the 


550  A  MANUAL  OF  PHYSIOLOGY 

forcing  of  the  fluid  through  the  cardiac  orifice  of  the  stomach 
by  the  contraction  of  the  oesophagus. 

Chemical  digestion  in  man  begins  already  in  the  mouth,  a 
part  of  the  starch  being  there  converted  into  dextrins  and 
sugar  (maltose),  as  has  been  shown  by  examining  a  mass  of 
food  containing  starch  just  as  it  is  ready  for  swallowing 
(p.  375).  This  process  is  no  doubt  continued  during  the 
passage  of  the  food  along  the  oesophagus. 

The  first  morsels  of  a  meal  which  reach  the  stomach  find 
it  free  from  gastric  juice,  or  nearly  so.  They  are  alkaline 
from  the  admixture  of  saliva  ,  and  the  juice  which  is  now 
beginning  to  be  secreted,  in  response  to  the  presence  of  the 
food,  and  to  reflex  excitement  starting  in  the  mouth,  is  foi 
a  time  neutralized,  and  amylolytic  digestion  still  permitted 
to  go  on.  For  about  fifteen  minutes  after  digestion  has 
begun  there  is  no  free  hydrochloric  acid  in  the  stomach, 
although  some  is  combined  with  proteids,  and  at  least 
during  this  period  the  ptyalin  of  the  swallowed  saliva  will  be 
able  to  act,  in  spite  of  the  lactic  acid  produced  during  the  first 
part  of  the  digestive  period  by  the  action  of  the  Bacillus  acidi 
lactici  on  the  carbo-hydrates  of  the  food.  But  as  the  meal 
goes  on,  the  successive  portions  of  food  which  arrive  in  the 
stomach  will  find  the  conditions  less  and  less  favourable  for 
amylolytic  digestion ;  and,  upon  the  whole,  a  considerable 
proportion  of  the  starches  must  escape  complete  conversion 
into  sugar  until  they  are  acted  upon  by  the  pancreatic  juice. 
This  is  particularly  the  case  with  unboiled  starch,  as  con- 
tained in  vegetables  which  are  eaten  raw;  and,  indeed,  we 
know  that  sometimes  a  certain  amount  of  starch  may  escape 
even  pancreatic  digestion,  and  appear  in  the  faeces.  Mean- 
while, even  during  the  short  amylolytic  stage  of  gastric 
digestion,  pepsin  and  hydrochloric  acid  are  already  being 
poured  forth  ;  the  latter  is  entering  into  a  peculiar  combina- 
tion with  the  proteids  of  the  food  ;  and  before  the  end  of  an 
ordinary  meal  peptic  digestion  is  in  full  swing.  The  move- 
ments of  the  pyloric  end  of  the  stomach  increase,  and  eddies 
are  set  up  in  its  contents,  which  carry  the  morsels  of  food 
with  them,  and  throw  them  against  its  walls.  In  this  way 
not  only  are  the  contents  thoroughly  mixed,  and  fresh 


DIGESTION  351 

portions  of  food  constantly  brought  into  contact  with  the 
gastric  juice  secreted  mainly  in  the  more  passive  cardiac 
end,  but  a  certain  amount  of  mechanical  disintegration  is 
brought  about ;  and  this  is  aided  by  the  digestion  of  the 
gelatin-yielding  connective  tissue  which  holds  together  the 
fibres  of  muscle  and  the  cells  of  fat,  and  the  digestible 
structures  in  vegetable  tissue  which  enclose  starch  granules. 
If  milk  has  formed  a  portion  of  the  meal,  the  casein  will 
have  been  curdled  soon  after  its  entrance  into  the  stomach, 
by  the  action  of  the  rennet  ferment  alone  when  the  milk 
has  been  taken  at  the  beginning  of  digestion  before  the 
gastric  contents  have  become  distinctly  acid,  by  the  acid  and 
rennin  together  when  it  has  been  taken  later.  The  casein 
and  other  proteids  of  milk,  like  the  myosin  and  other 
proteids  of  meat,  and  the  globulins,  phytovitellins,  and 
other  proteids  of  bread  and  of  vegetable  food  in  general,  are 
all  acted  upon  by  the  pepsin  and  hydrochloric  acid,  yield- 
ing ultimately  peptones;  while  variable  quantities  of  acid- 
albumin  and  proteoses  may  escape  this  final  change,  and 
pass  on  as  such  into  the  duodenum.  In  the  dog,  indeed,  a 
meal  of  flesh  has  been  found  to  be  almost  entirely  digested 
to  the  peptone  stage  while  still  in  the  stomach,  leaving  little 
for  the  pancreatic  juice  to  do.  But  we  may  safely  assume 
that,  in  the  case  of  a  man  living  on  an  ordinary  mixed  diet, 
much  of  the  food  proteids  passes  through  the  pylorus 
chemically  unchanged,  or  having  undergone  only  the  first 
steps  of  hydration.  For,  even  a  few  minutes  after  food  has 
been  swallowed,  the  pyloric  sphincter  may  relax  and  allow 
the  stomach  to  propel  a  portion  of  its  contents  into  the  in- 
testine ;  and  such  relaxations  occur  at  intervals  as  digestion 
goes  on,  although  it  is  not  for  several  hours  (three  to  five) 
that  the  greater  portion  of  the  food  reaches  the  duodenum. 
During  this  period  the  acidity  has  at  first  been  constantly 
increasing,  although  for  about  half  an  hour  after  the  short 
amylolytic  stage  the  hydrochloric  acid  has  combined,  as  it  is 
formed,  with  the  proteids  of  the  food.  The  combination, 
however,  does  not  prevent  it  from  causing  an  acid  reaction, 
although  up  to  this  time  no  free  acid  is  present.  Then  comes 
a  stage  where  the  hydrochloric  acid  has  so  much  increased 


352 


A  MANUAL  OF  PHYSIOLOGY 


that,  after  combining  with  all  the  proteids,  some  of  it 
remains  over  as  free  acid.  The  lactic  acid  now  rapidly 
disappears  from  the  stomach  ;  and  after  a  time  the  total 
acidity  begins  to  fall,  the  fully-digested  proteids  being  con- 
tinually absorbed  in  the  form  of  peptones,  which  are  only 
found  in  traces,  if  at  all,  in  the  chyme.  This  fall  continues 
till  the  third  or  fourth  hour,  the  proportion  of  free  to  com- 
bined acid  continuing,  nevertheless,  to  rise,  since  nearly  all 
that  is  now  secreted  remains  free.  Easily-diffusible  bodies, 
such  as  sugars  and  some  of  the  organic  crystalline  con- 
of  meat,  e.g.,  jcreatm,  will  also  pass  through  the 
gastric  mucous  membrane  into  the  blood.* 

*  Seventeen  dogs,  after  twenty-four  hours'  fast,  were  fed  with  a  meal 
of  raw  maize-starch,  minced  meat,  and  milk.  They  were  caused  to 
vomit,  after  an  interval  varying  from  fifteen  minutes  to  five  and  three- 
quarter  hours,  by  the  subcutaneous  injection  of  2  milligrammes  of 
apomorphine.  The  results  of  an  examination  of  the  vomit  are  embodied 
in  the  following  table  : 


Time  between 
Feeding  and 
Vomiting, 

Time  between 
Injection  of 
Amorphine 
and  Vomiting, 

Amount  of 
Reducing 
Sugar 
found. 

Acid 
Albumin. 

Albumose. 

Muscle  Fibres. 

Peptone 

in  minutes. 

in  minutes. 

15 

7 

Fair 

Present 

Trace 

Well  preserved 

None 

15 

12 

Marked 

j? 

Present 

57 

Trace 

20 

15 

)> 

Much 

Much 

)) 

None 

60 

25 

Trace 

Trace 

Present 

Present 

5) 

75 

14 

•>•> 

None 

» 

Swollen,  striation 

often  lost 

90 

20 

Much 

Much 

Trace 

Present 

None 

90 

2 

„ 

» 

Much 

»» 

90 

3 

Present 

Present 

Present 

it 

105 

None 

T) 

» 

j» 

120 

— 

Present 

1) 

n 

n 

150 

10 

Trace 

None 

jj 

Few 

150 

M 

Present 

Present 

» 

Much  broken 

down 

I5C 

10 

Trace 

Trace 

Much 

— 

9» 

150 

10 

Much 

j> 

» 

— 

Trace 

210 

— 

— 

Present 

Present 

Present 

Trace 

300 

— 

Trace 

i) 

5> 

Scarcely  any 

»» 

345 

— 

Present 

)» 

» 

Greatly  changed 

None 

Starch  granules  and  fat  globules  were  found  in  every  case.  The  reac- 
tion was  always  acid,  as  is  generally  the  case  in  the  dog  even  twenty-four 
hours  after  a  meal. 

Six  other  dogs,  after  a  twenty-four  hours'  fast,  were  fed  with  raw  starch 
and  lard.  In  twenty  minutes  apomorphine  was  injected.  It  acted  in 
from  three  to  five  minutes.  In  no  case  was  any  sugar  found  in  the  vomit 


DIGESTION  353 

The  substances  which  reach  the  duodenum  are:  (i)  thej 
whole  of  the  fats,  with  no  chemical  and  little  physical  change. 
But  the  partial  digestion  in  the  stomach  of  the  envelopes 
and  protoplasm  of  the  cells  of  adipose  tissue,  and  of  the 
proteid  which  keeps  the  fat  of  milk  in  emulsion,  prepares 
the  fats  for  what  is  to  follow  in  the  intestine.  (2)  All 
the  proteids  which  have  not  been  carried  to  the  stage  of 
peptone,  and  perhaps  some  peptone.  (3)  All  the  starch 
and  dextrins — and  glycogen,  if  any  be  present — which  have 
not  been  converted  into  maltose,  and  possibly  a  little 
maltose.  (4)  Elastin,  nuclein,  cellulose,  and  other  sub- 
stances not  digestible  or  digestible  only  with  difficulty  in 
gastric  juice.  (5)  The  constituents  of  the  gastric  juice 
itself,  including  pepsin.  The  ptyalin  of  the  saliva  has  been 
already  digested  and  destroyed. 

It  must  be  remembered  that  all  this  time,  even  from  the 
beginning  of  digestion,  a  certain  amount  of  pancreatic  juice 
has  been  finding  its  way  into  the  duodenum  in  response  to 
that  distant  action  of  the  food  which  we  have  discussed, 
and  the  reflex  nature  of  which  we  have  not  been  able  either 
definitely  to  admit  or  altogether  to  reject.  The  secretion  of 
bile,  too,  always  going  on,  has  quickened  its  pace,  and  the 
gall-bladder  is  getting  more  and  more  full  as  the  meal 
proceeds  and  gastric  digestion  begins.  When  the  acid 
chyme,  a  grayish  liquid,  turbid  with  the  debris  of  animal 
and  vegetable  tissues — with  muscular  fibres,  fat  globules, 
starch  granules,  and  dotted  ducts — gushes  through  the 
pylorus  and  strikes  the  duodenal  wall,  a  rush  of  bile  takes 
place,  which  perhaps  precipitates  some  of  the  soluble  consti- 
tuents— parapeptones,  proteoses  (albumoses),  and  pepsin — as 
a  granular  coating  on  the  surface  of  the  mucous  membrane. 
The  pepsin,  although  afterwards  redissolved  along  with  the 
rest  of  the  precipitate,  is  thus  rendered  inert,  and  prevented 
from  destroying  the  trypsin  already  present  in  the  duodenum, 
as  it  would  otherwise  do,  since  the  reaction  of  the  chyme 

This  is  interesting  in  connection  with  the  well-known  fact  that  dog's 
saliva  usually  contains  no  ptyalin.  In  saliva  obtained  from  twelve  dogs 
by  stimulation  of  the  chorda  tympani,  the  presence  of  a  diastatic 
ferment  was  only  once  made  out. 

23 


354  A  MANUAL  OF  PHYSIOLOGY 

still  remains  acid.     By-and-by,  as  bile  and  pancreatic  juice 
continue  to  be  poured  out,  the  reaction  becomes  less  acid 
though  never  alkaline  unless  for  a  short  time  in  the  duo- 
denum, and  the  trypsin  begins  its  work  upon  the  proteids. 
The  undigested  proteids  are  all  carried  on  to  the  stage  of 
X  peptone,  much  of  this  being  absorbed  as  it  is  formed,  some 
^    even  in  perfectly  normal  digestion,  in  the  dog  at  least,  being 
furthersplit  up  into  leucin  and  tyrosin. 

^Tct t^iff+'Cl™* -»  f °«^      f^T^ 

J  The  common   statement  that   the  contents  of  the  intestine  are 

alkaline  requires  to  be  qualified  by  reference  to  the  indicator  used. 
The  reaction  in  the  duodenum,  as  tested  by  litmus,  may  possibly 
become  alkaline  for  a  time,  when  the  inflow  of  bile  and  pancreatic 
juice  is  at  its  height ;  but  the  chyme  soon  becomes  acid  again,  and 
its  acidity  continually  increases  as  it  passes  down  the  gut.     In  the 
lower  end  of  the  small  intestine  the  reaction  may  again  become 
alkaline.    To  phenolphthalein,  which  is  very  sensitive  to  weak  organic 
/s          acids,  the  reaction  is  acid  throughout  the  whole  intestine.    But  methyl 
orange,  which  readily  reacts  to  inorganic  acids,  gives  no  indication 
of  their  presence,  but  shows,  on  the  contrary,  an  alkaline  reaction 
from  duodenum  to  caecum,  caused  probably  by  the  alkaline  salts  of 
organic  acids  (Moore  and  Rockwood).     The  acidity  of  the  intestinal 
^contents  appears  to  be  largely  due  to  the  lactic  acid  produced  by  the 
•  H  action  of  micro-organisms  on  the  carbo-hydrates,  and  the  fatty  acids 
set  free  from  the  fats  by  the  action  of  the  steapsin  of  the  pancreatic 
juice  and  the  fat-splitting  bacteria.     So  that  although  trypsin,  like 
pepsin,  performs  its  work,  for  the  most  part,  at  any  rate,  in  an  acid 
medium,  the  cause  of  the  acidity  and  the  character  of  the  medium 
are  by  no  means  alike.    We  are  not,  however,  without  other  examples 
of  digestive  juices  destined  to  act  in  a  medium  with  an  opposite 
reaction  to  their  own.     The  'saliva'  of  Octopus  macropus,  strongly 
acid  though  it  is,  contains  a  proteolytic  ferment  which  in  vitro  acts, 
like  trypsin,  better  in  a  neutral  or  alkaline  than  in  an  acid  solution. 
The  pepsin  of  the  (in  itself)  alkaline  secretion  of  the  pyloric  end  of 
the  stomach  becomes  a  constituent  of  the  acid  gastric  juice ;  and  it 
may,  perhaps,  be  considered  a  morphological  accident,  so  to  speak, 
that  the  oxyntic  cells  of  the  cardiac  end  should  mingle  their  acid 
products  with  the  (presumedly)  alkaline  secretion  of  the  chief  cells 
in  the  lumen  of  each  gland-tube,  instead  of  being  massed  as  a 
separate  organ  with  a  special  duct. 

In  the  lower  portions  of  the  small  intestine  bacteria  of 
various  kinds  are  present  and  active ;  and  it  is  not  unlikely 
that  even  throughout  its  whole  length  a  certain  range  of 
action  is  permitted  to  them,  checked  by  the  acidity  of  the 
chyme,  and  perhaps  by  the  antiseptic  properties  of  the  bile. 


DIGESTION  355 

The  stomach,  with  its  acid  contents,  forms  during  the 
greater  part  of  gastric  digestion  a  valve  or  trap  to  cut  off 
the  upper  end  of  the  intestine  from  the  bacteria-infested 
regions  of  the  mouth  and  pharynx,  and  to  destroy  the 
micro-organisms  swallowed  with  the  food  and  saliva.  The 
occasional  presence  in  vomited  matter  of  sarcinae  or 
regularly  arranged  groups  of  micrococci,  generally  four  to  a 
group,  shows  that  under  abnormal  conditions  the  gastric 
contents  are  not  perfectly  aseptic ;  and  even  from  a  normal 
stomach  active  micro-organisms  of  various  kinds  can  be 
obtained.  But  upon  the  whole  there  is  no  doubt  that  the 
acidity  of  the  gastric  juice  is  an  important  check  on  bacterial 
activity  during  the  first  part  of  digestion,  and  in  the  upper 
portion  of  the  alimentary  canal. 

And,  indeed,  Koch  has  shown  that  the  acidity  of  the  gastric 
juice  of  a  guinea-pig  is  sufficient  to  kill  the  comma  bacillus 
of  cholera.  Normal  guinea-pigs  fed  with  cholera  bacilli 
were  unaffected.  But  if  the  gastric  juice  was  neutralized 
by  an  alkali  before  the  administration  of  the  bacilli  the 
guinea-pigs  died. 

It  has  been  supposed  by  some  that  this  bactericidal  action 
is  the  chief  function  of  the  stomach,  and  the  question  has 
been  asked,  why  we  should  attribute  any  digestive  im- 
portance to  the  secretion  of  that  viscus,  since  the  pancreatic 
juice  can  do  all  that  the  gastric  juice  does,  and  some  things 
which  it  cannot  do.  Further,  it  has  been  shown  that  a  dog 
may  live  five  years  after  complete  excision  of  the  stomach, 
comport  himself  in  all  respect  like  a  normal  dog,  and 
when  killed  for  autopsy  show  every  organ  in  perfect  health 
(Czerny).  Recently,  too,  the  stomach  has  been  excised  in 
man  with  a  successful  result.  But  if  this  is  to  be  admitted 
as  evidence  against  the  digestive  function  of  the  stomach,  it 
is  just  as  good  evidence  against  the  bactericidal  function, 
particularly  as  it  has  in  addition  been  shown  that  even 
putrid  flesh  has  no  harmful  effect  on  a  dog  after  excision  of 
the  stomach,  any  more  than  on  a  normal  dog.  And,  indeed, 
the  reasoning  is  fallacious  which  assumes  that  what  may 
happen  under  abnormal  conditions  must  happen  when  the 
conditions  are  normal.  For  nothing  is  impressed  more  often 

23 — 2 


356  A  MANUAL  OF  PHYSIOLOGY 

on  the  physiological  observer  than  the  extraordinary  power  of 
adaptation,  of  making  the  best  of  everything,  which  the 
animal  organism  possesses.  Doubtless,  a  dog  without  a 
stomach  will  use  to  the  best  advantage  the  digestive  fluids 
that  remain  to  him ;  and  the  pancreatic  juice  may  be 
adequate  to  the  task  of  complete  digestion.  So,  too,  a  man 
from  whom  the  surgeon  has  removed  a  kidney,  or  a  testicle, 
or  a  lobe  of  the  thyroid  gland,  may  be  in  no  respect  worse 
off  than  the  man  who  possesses  a  pair  of  these  organs. 
But  what  do  we  deduce  from  this  ?  Not,  surely,  that  the 
excised  thyroid,  or  testicle,  or  kidney  was  useless,  or  the 
gastric  juice  inactive,  but  that  the  organism  has  been  able  to 
compensate  itself  for  their  loss. 

The  lower  end  of  the  small  intestine  is  not  cut  off  by  any 
bacteria-proof  barrier  from  the  large  intestine,  in  which 
putrefaction  is  constantly  going  on.  So  that  micro-organisms 
may  be  able  to  work  their  way  above  the  ileo-caecal  valve, 
even  against  the  downward  peristaltic  movement.  But  even 
if  this  were  not  the  case,  a  few  bacteria  or  their  spores, 
passing  through  the  stomach  with  the  food,  would  be  enough 
to  set  up  extensive  changes  as  soon  as  they  reached  a  part 
of  the  alimentary  canal  where  the  conditions  were  favourable 
to  their  development.  Indeed,  from  the  time  when  the  first 
micro-organism  enters  the  digestive  tube  soon  after  birth,  it 
is  never  free  from  bacteria  ;  and  their  multiplication  in  one 
part  of  it  rather  than  another  depends  not  so  much  on  the 
number  originally  present  to  start  the  process,  as  on  the 
conditions  which  encourage  or  restrain  their  increase. 

The  fats  are  in  part  broken  up  into  their  fatty  acids  and 
glycerine  by  the  fat-splitting  ferment  of  the  pancreatic  juice. 
The  acids  will  form  soaps  with  alkalies  wherever  they  meet 
them  in  the  intestinal  contents,  or  even  in  the  mucous 
membrane.  A  portion  of  those  soluble  soaps  may  be  imme- 
diately absorbed ;  the  rest  may  aid  in  the  emulsification  of 
that  unknown  but  probably  large  balance  of  the  fats  which 
is  not  chemically  decomposed.  The  starch  and  dextrine 
which  have  escaped  the  action  of  the  saliva  are  changed  into 
maltose  by  the  pancreatic  juice.  A  little  dextrine  may  be 
absorbed  as  such  (Bleile). 


DIGESTION  357 

The  succus  entericus  plays  no  very  important  part, 
although,  as  an  alkaline  liquid,  it  doubtless  aids  in  lessening 
the  acidity  of  the  chyme  and  establishing  the  reaction 
favourable  to  intestinal  digestion.  It  will  invert  any  cane- 
sugar  which  may  reach  the  intestine ;  but  it  cannot  be 
doubted  that  cane-sugar  may  be  absorbed  by  the  stomach, 
being  inverted  either  by  a  ferment  in  the  mucus  lining  that 
viscus,  or  on  its  way  through  the  gastric  walls. 

Upon  the  whole  no  great  amount  of  water  is  absorbed  in 
the  small  intestine,  or  at  least  the  loss  is  balanced  by  the 
gain,  for  the  intestinal  contents  are  as  concentrated  in  the 
duodenum  as  in  the  ileum.  But  as  soon  as  they  pass  beyond 
the  ileo-caecal  valve,  water  is  rapidly  absorbed,  and  the 
contents  thicken  into  normal  faeces,  to  which  the  chief  con- 
tribution of  the  large  intestine  is  mucin,  secreted  by  the  vast 
number  of  goblet-cells  in  its  Lieberkiihn's  crypts. 

Bacterial  Digestion. — So  far  we  have  paid  no  attention  to 
other  than  the  soluble  ferments  of  the  digestive  tract.  It 
is  now  necessary  to  recognise  that  the  presence  of  bacteria 
is  an  absolutely  constant  feature  of  digestion  ;  and  although 
their  action  must  in  part  be  looked  upon  as  a  necessary  evil 
which  the  organism  has  to  endure,  and  against  the  conse- 
quences of  which  it  has  to  struggle,  it  is  not  unlikely  that  in 
part  it  may  be  ancillary  to  the  processes  of  aseptic  digestion. 
But  bacteria  are  not  essential,  as  some  have  supposed.  For 
it  has  been  shown  that  a  young  guinea-pig,  taken  by 
Caesarean  section  from  its  mother's  uterus  with  elaborate 
antiseptic  precautions,  and  fed  in  an  aseptic  space  on  sterile 
milk,  grew  apparently  as  fast  as  one  of  its  sisters  brought 
up  in  the  orthodox  microbic  way.  The  alimentary  canal 
remained  free  from  bacteria  (Nuttall  and  Thierfelder). 

Among  the  more  important  actions  of  bacteria  on   the 

^proteid  food-products  in   the  intestines  may  be  mentioned 

^  the  formation  of  jndoL  phenol,  and  skatol.  the  first  having 

tyrosin  for  its  precursor,   and  being  itself  after  absorption 

-  the  precursor  of  the  indican  in  the  urine ;  the  second  being 

^to  a  small  extent  thrown  out  with  the  faeces,  but  chiefly 

absorbed  and  eliminated  by  the  kidneys  as  an  aromatic  com- 

pound  of  sulphuric  acid ;  the  third  passing  out  mainly  in 


358  A  MANUAL  OF  PHYSIOLOGY 

the  faeces.  From  carbo-hydrates  lactic  acid  is  formed  in 
increasing  amount  as  the  lower  portion  of  the  intestine  is 
reached,  so  that  the  reaction,  which  is  acid  in  the  upper  part 
of  the  tube,  owing  to  the  acidity  of  the  chyme,  in  spite  of 
the  outflow  of  bile  and  pancreatic  juice  remains  acid  in  the 
ileum.  In  the  dog,  indeed,  on  a  flesh  diet,  and  therefore 
under  conditions  which  leave  little  scope  for  lactic  acid 
fermentation,  the  reaction  of  the  whole  of  the  small  intestine 
has  been  found  acid.  But  this  is  perhaps  not  constantly  the 
case ;  and  when  it  does  occur,  it  may  be  connected  with  the 
very  thorough  and  almost  exhaustive  digestion  of  proteids, 
which,  as  we  have  already  mentioned,  the  stomach  of  the 
dog  is  of  itself  able  to  accomplish,  so  that  little  being  left 
for  the  intestine  to  do,  little  of  the  alkaline  digestive  juices 
is  poured  into  it,  and  this  little  is  swamped  by  the  acid 
gastric  contents. 

The  large  intestine  is  the  chosen  haunt  of  the  bacteria  of 
the  alimentary  canal ;  they  swarm  in  the  faeces,  and  by  their 
influence,  especially  in  the  caecum  of  herbivora,  but  also  to 
a  small  extent  in  man,  even  cellulose  is  broken  up,  the 
final  products  being  carbon  dioxide  and  marsh  gas.  The 
contents  of  the  large  bowel  are  generally  acid  from  the 
products  of  putrefaction,  although  the  wall  itself  is 
alkaline. 

Faeces. — In  addition  to  mucin,  secreted  mainly  by  the  large 
intestine,  the  faeces  consist  of  indigestible  remnants  of  the 
food,  such  as  elastic  fibres,  spiral  vessels  of  plants,  and  in 
general  all  vegetable  structures  chiefly  composed  of  cellulose. 
They  are  coloured  with  a  pigment,  stercobilin,  derived  from 
the  bile  pigments.  Stercobilin  is  identical  with  '  febrile ' 
urobilin,  with  the  urobilin  which  forms  a  common,  though  not 
an  invariable,  constituent  of  bile  itself,  and  probably  with  the 
urobilin  of  normal  urine.  No  bilirubin  or  biliverdin  occurs 
in  normal  faeces,  although  pathologically  they  may  be  present. 
The  dark  colour  of  the  faeces  with  a  meat  diet  is  due  to 
haematin  and  sulphide  of  iron,  the  latter  being  formed  by 
the  action  of  the  sulphuretted  hydrogen  which  is  constantly 
present  in  the  large  intestine  on  the  organic  compounds 
of  iron  contained  in  the  food  or  in  the  secretions  of  the 


DIGESTION  359 

alimentary  canal.*  A  small  amount  of  altered  bile  acids  and 
their  products  is  also  found  ;  and  in  respect  to  these,  and  to 
the  altered  pigments,  bile  is  an  excretion.  And  although  its 
important  function  in  digestion,  and  the  fact  that  the  greater 
part  of  the  bile  salts  is  reabsorbed,  show  that  in  the  adult 
it  is  very  far  from  being  solely  a  waste  product,  the  equally 
cogent  fact,  that  the  intestine  of  the  new-born  child  is  rilled 
with  what  is  practically  concentrated  bile  (meconium),  proves 
that  it  is  just  as  far  from  being  purely  a  digestive  juice. 
Skatol  and  other  bodies,  formed  by  putrefactive  changes  in 
the  proteids  of  the  food,  are  also  present  in  the  faeces,  and 
are  responsible  for  the  faecal  odour.  Masses  of  bacteria  are 
invariably  present.  Of  the  inorganic  substances  in  faeces 
the  numerous  crystals  of  triple  phosphate  are  the  most 
characteristic.  When  the  diet  is  too  large,  or  contains  too 
much  of  a  particular  kind  of  food,  a  considerable  quantity 
of  digestible  material  may  be  found  in  the  faeces,  e.g., 
muscular  fibres  and  fat.  But  it  should  be  remembered  that 
under  all  circumstances  the  composition  of  the  faeces  differs 
from  that  of  the  food.  The  intestinal  contribution  is  always 
an  important  one,  although  relatively  more  important  with 
a  flesh  than  with  a  vegetable  diet. 

*  It  was  supposed  by  Bunge  that  only  such  organic  compounds  of  iron 
could  be  absorbed,  and  that  the  undoubted  benefit  derived  from  the 
administration  of  inorganic  iron  compounds,  such  as  ferric  chloride,  in 
anaemia,  was  due  not  to  their  direct  absorption,  but  to  their  shielding  the 
organic  compounds  from  the  attack  of  the  sulphuretted  hydrogen.  But 
this  theory  has  been  shown  to  be  inconsistent  with  the  facts.  For 
instance,  while  iron  accumulates  in  the  liver  of  an  animal  to  which 
inorganic  salts  of  iron  are  given,  it  does  not  accumulate  when  salts  of 
manganese  are  substituted,  although  these  are  equally  decomposed  by 
sulphuretted  hydrogen.  Stockman,  from  careful  estimations  of  the 
quantity  of  iron  in  a  number  of  actual  dietaries,  concludes  that  the 
greater  part  of  it  must  be  retained  in  the  body  and  used  over  and  over 
again.  +£ 


CHAPTER    V  . 
ABSORPTION. 

Physical  Introduction — Diffusion. — When  a  solution  of  a  substance 
is  placed  in  a  vessel,  and  a  layer  of  water  carefully  run  in  on  the  top 
of  it,  it  is  found  after  a  time  that  the  dissolved  substance  has  spread 
itself  through  the  water,  and  that  the  composition  of  the  mixture  is 
uniform  throughout.  The  result  is  the  same  when  two  solutions 
containing  different  proportions  of  the  same  substance,  or  containing 
different  substances,  are  placed  in  contact.  The  phenomenon  is 
called  diffusion.  The  time  required  for  complete  diffusion  is  com- 
paratively short  in  the  case  of  a  substance  like  hydrochloric  acid  or 
sodium  chloride,  exceedingly  long  in  the  case  of  albumin  or  gum. 
In  both  it  is  more  rapid  at  a  high  temperature  than  at  a  low. 

Osmosis. — If  the  solution  be  separated  from  water  by  a  membrane 
absolutely  or  relatively  impermeable  to  the  dissolved  substance,  but 
permeable  to  water,  water  passes  through  the  membrane  into  the 
solution.  This  phenomenon  is  called  osmosis.  E.g.,  a  membrane  of 
ferrocyanide  of  copper,  nearly  impermeable  to  cane-sugar,  can  be 
formed  in  the  pores  of  an  unglazed  porcelain  pot  by  allowing  potas- 
sium ferrocyanide  and  cupric  sulphate  to  come  in  contact  there.  If 
the  pot  is  filled  with,  say.  a  i  per  cent,  solution  of  cane-sugar,  closed 
by  a  suitable  stopper,  connected  to  a  manometer,  and  then  placed 
in  a  vessel  of  water,  water  passes  into  it  till  the  pressure  indicated 
by  the  manometer  rises  to  a  certain  height.  With  a  2  per  cent, 
solution  it  reaches  twice  this  height,  and  in  general  the  osmotic 
pressure,  as  it  is  called,  is  in  any  solution  proportional  to  the 
molecular  concentration*  of  the  solution,  or,  in  other  words,  to  the 
number  of  molecules  of  the  dissolved  substance  in  a  given  volume 
of  the  solution.  If  in  this  sentence  we  substitute  '  gaseous 
pressure'  for  'osmotic  pressure,'  and  'gas7  for  'solution,'  we  have 
a  statement  of  Boyle's  law,  which  asserts  that  the  pressure  of  a 
gas  is  proportional  to  its  density.  And,  indeed,  it  has  been 
shown  that  the  osmotic  pressure  of  the  dissolved  substance  is  the 

*  The  molecular  concentration  is  strictly  defined  as  the  number  of 
grammes  of  the  dissolved  substance  in  a  litre  of  the  solution  divided  by  the 
gramme-molecular  weight.  The  gramme-molecular  weight,  or  gramme- 
molecule,  is  the  number  of  grammes  corresponding  to  the  molecular 
weight.  Thus,  the  gramme-molecular  weight  of  sodium  chloride  (NaCl)  is 
58'36  grammes,  and  of  cane-sugar  (Ci2H.>.Oii),  342  grammes. 


Fitftw 


Fat  globule  in  central  lacteal 


. 


"  -#«*  globules  passing  through 


*<*&  •'-.  * 

? 

^.         V    ,"  V^^    ^  .    ^Ks-   • 


Circular  mutcukw 
coat 


1.  Section  of  frog's  intestine  to  show  absorption  of  fat,  X 
(Stained  with  picroearmine  and  oaraic  acid.V 


Filii 


More  Highly  magnified 
•portion  of  vilfat 


Goblet  cell  with  fl*g  of  mucin 


Capillary  plexu* 


A  LieberJeuhn'n  crypt 


Circular  muscular  eoat 


Longitudinal  mtucular  coat 
2.  Section  of  small  intestine.    Blood-vessels  injected. 
(Stained  with  hsematozyiin  and  eosin.) 


ABSORPTION  361 

same  as  the  pressure  that  would  be  exerted  by  a  gas,  say  hydrogen, 
if  all  the  water  were  removed,  and  a  molecule  of  hydrogen  substituted 
for  each  molecule  of  the  substance,  or  as  would  be  exerted  by  the 
substance  itself  if,  after  removal  of  the  solvent,  it  could  be  left  as  a 
gas  filling  the  same  volume.  And  the  osmotic  pressure  of  a  solution 
of  one  substance  is  the  same  as  that  of  a  solution  of  any  other 
substance  which  contains  in  a  given  volume  the  same  number  of 
molecules  of  the  dissolved  substance.  In  other  words,  the  osmotic 
pressure  is  not  dependent  on  the  nature,  but  on  the  molecular  con- 
centration, of  the  substance.  The  analogy  of  the  laws  of  osmotic  to 
those  of  gaseous  pressure  becomes  still  more  obvious  when  it  is 
added  that  the  osmotic  pressure  of  a  substance  with  any  given 
molecular  concentration  is  proportional  to  the  absolute  temperature  ; 
and  that  when  a  solution  contains  more  than  one  dissolved  substance, 
the  total  osmotic  pressure  is  the  sum  of  the  partial  osmotic  pressures 
which  each  substance  would  exert  if  it  were  present  alone  in  the 
same  volume  of  the  solution. 

The  osmotic  pressure  of  a  solution  may  reach  an  enormous  amount. 
Thus,  a  i  per  cent,  solution  of  cane-sugar  has  a  pressure  at  o°  C.  of 
493  mm-  of  mercury.  A  10  per  cent,  solution  of  cane-sugar  would  have 
an  osmotic  pressure  of  more  than  six  atmospheres,  and  a  17  per  cent, 
solution  of  ammonia  a  pressure  of  no  less  than  224  atmospheres. 
The  osmotic  pressure  must  be  due  to  the  kinetic  energy  of  the 
moving  molecules.  Where  the  molecules  are  hindered  from  passing 
a  bounding  membrane,  the  pressure  exerted  by  their  impacts  on  the 
boundary  is  greater  than  where  the  membrane  is  easily  permeable, 
because  in  the  latter  case  many  of  the  molecules  pass  through, 
carrying  with  them  their  kinetic  energy.  The  pressure  must  be  still 
less  when  a  dissolved  substance  diffuses  freely  into  water ;  but  how- 
ever small  it  may  become,  it  is  in  the  osmotic  pressure  of  the 
molecules  of  the  dissolved  substance  that  the  force  which  causes 
diffusion  must  be  sought. 

In  practice  it  is  inconvenient,  and  in  many  cases  impossible,  to 
directly  measure  the  osmotic  pressure  by  means  of  a  non-permeable 
or  semi-permeable  membrane  like  ferrocyanide  of  copper.  Recourse 
is  therefore  had  to  indirect  methods.  Of  these,  one  of  the  most 
generally  used  depends  on  the  fact  that  the  freezing  point  of  a 
solution  is  lower  than  that  of  the  solvent ;  for  example,  salt  water 
freezes  at  a  lower  temperature  than  fresh  water.  The  amount  by 
which  the  freezing-point  is  lowered  depends  on  the  molerular  con- 
centration of  the  dissolved  substance,  to  which,  as  we  have  seen,  the 
osmotic  pressure  is  also  proportional.  When  a  gramme-molecule  of 
a  substance  is  dissolved  in  a  litre  of  water,  the  freezing-point  is 
lowered  by  i'8°  C.  ;  the  osmotic  pressure  is  22*35  atmospheres 
(16,986  mm.  of  mercury).  It  is  therefore  easy  to  calculate  the 
osmotic  pressure  of  any  solution  if  we  know  the  amount  by  which  its 
freezing-point  is  lowered.  A  i  per  cent,  solution  of  cane-sugar,  for 
example,  would  freeze  at  about  -0*052°  C.  Its  osmotic  pressure 

=  — —  x  16,986  =  490  mm.  of  mercury, 
i  '8 


362  A  MANUAL  OF  PHYSIOLOGY 

The  osmotic  pressure  of  different  solutions  may  also  be  compared 
by  observing  the  effect  produced  on  certain  vegetable  and  animal 
cells.  When  a  solution  with  a  greater  osmotic  pressure  than  the 
cell-sap  (a  hyperisotonic  solution]  is  left  for  a  time  in  contact  with 
certain  cells  in  the  leaf  of  Tradescantia  discolor,  plasmolysis  occurs — 
that  is,  the  protoplasm  loses  water  and  shrinks  away  from  the  cell- 
wall.  If  the  osmotic  pressure  of  the  solution  is  lower  than  that  of 
the  coloured  cell-sap  (Jiypoisotonic  solution),  no  shrinking  of  the 
protoplasm  takes  place.  By  using  a  number  of  solutions  of  the  same 
substance  but  of  different  strength,  two  can  be  found,  the  stronger  of 
which  causes  plasmolysis,  and  the  weaker  not.  Between  these  lies 
the  solution  which  is  isotonic  with  the  cell-sap — that  is,  has  the  same 
molecular  concentration  and  osmotic  pressure.  The  strength  of  an 
isotonic  solution  of  some  other  substance  can  then  be  determined  in 
the  same  way  with  sections  from  the  same  leaf. 

Animal  cells  (red  blood-corpuscles)  may  also  be  employed,  the 
liberation  of  haemoglobin  or  the  swelling  of  the  corpuscles,  as 
measured  by  the  haematocrite  (p.  35),  being  taken  as  evidence  that 
the  solution  in  contact  with  them  is  hypoisotonic  to  the  contents  of 
the  corpuscles.  If  the  corpuscles  shrink,  the  solution  is  hyperisotonic 
to  their  contents.  But  since  the  cells  are  much  more  permeable  to 
certain  substances  than  to  others,  this  method  does  not  always  yield 
trustworthy  results. 

Electrolytes. — We  have  said  that  the  osmotic  pressure  is  propor- 
tional to  the  concentration  of  the  solution,  but  this  statement  must  now 
be  qualified.  For  certain  compounds,  including  all  inorganic  salts  and 
many  organic  substances,  the  osmotic  pressure  decreases  less  rapidly 
than  the  theoretical  molecular  concentration  as  the  solution  is  diluted. 
The  explanation  appears  to  be  that  in  solution  some  of  the  molecules 
of  these  bodies  are  broken  up  into  simpler  groups  or  single  atoms, 
called  ions.  Each  ion  exerts  the  same  osmotic  pressure  as  the 
molecule  did  before.  The  proportion  between  the  average  number 
of  these  dissociated  molecules  and  of  ordinary  molecules  is  constant 
for  a  given  concentration  of  the  solution  and  a  given  temperature. 
But  as  the  solution  is  diluted,  the  proportion  of  dissociated  mole- 
cules becomes  greater.  The  bodies  which  behave  in  this  way  are 
electrolytes — that  is,  their  solutions  conduct  a  current  of  electricity  ; 
bodies  which  do  not  exhibit  this  behaviour  do  not  conduct  in 
solution.  And  there  are  many  reasons  for  believing  that  the  dis- 
sociation of  the  electrolytes  is  the  essential  thing  in  electrolytic 
conduction.  We  may  suppose  that  in  a  solution  of  an  electrolyte — 
sodium  chloride,  for  instance — a  certain  number  of  the  molecules 
fall  asunder  into  a  kation  (Na),  carrying  a  charge  of  positive 
electricity,  and  an  anion  (Cl),  carrying  an  equal  negative  charge. 
These  electrical  charges,  it  must  be  remembered,  are  not  created  by 
the  passage  of  a  current  through  the  solution.  We  do  not  know  how 
they  arise,  but  the  ions  must  be  supposed  to  be  electrically  charged 
at  the  moment  when  the  molecule  is  broken  up.  And  the  ions  of 
different  substances  must  each  be  supposed  to  carry  the'  same 
quantity  of  electricity.  But  since  they  are  all  wandering  freely  in 


ABSORPTION  363 

the  solution,  no  excess  of  negative  or  of  positive  electricity  can 
accumulate  at  any  part  of  it — in  other  words,  no  difference  of  potential 
can  exist.  When  electrodes  connected  with  a  voltaic  battery  are 
dipped  into  a  solution  of  an  electrolyte,  a  difference  of  potential 
(p.  518),  an  electrical  slope,  is  established  in  the  liquid,  and  the 
positively  charged  kations  are  compelled  to  wander  towards  the 
negative  pole,  the  negatively  charged  anions  towards  the  positive 
pole.  In  this  way  that  movement  of  electricity  which  is  called 
a  current  is  maintained  in  the  solution.  It  is  clear  that  the  greater 
the  number  of  ions,  and  the  faster  they  move  in  the  solution,  the 
greater  will  be  the  quantity  of  electricity  carried  to  the  electrodes 
in  a  given  time,  when  the  difference  of  potential  between  the 
electrodes,  or  the  steepness  of  the  electric  slope,  remains  constant. 
In  other  words,  the  specific  conductivity  of  a  solution  of  an  electrolyte 
varies  as  the  number  of  dissociated  molecules  in  a  given  volume  and 
the  speed  of  the  ions.  It  increases  up  to  a  certain  point  with  the 
concentration,  because  the  absolute  number  of  dissociated  molecules 
in  a  given  volume  increases.  The  molecular  conductivity — that  is,  the 
conductivity  per  molecule,  or,  strictly,  the  ratio  of  the  specific  con- 
ductivity to  the  molecular  concentration,  increases  with  the  dilution, 
because  the  relative  number  of  dissociated  molecules,  as  compared 
with  undissociated,  increases.  At  a  certain  degree  of  dilution  the 
molecular  conductivity  reaches  its  maximum,  for  all  the  molecules 
are  dissociated.  The  ratio  of  the  molecular  conductivity  of  any  given 
solution  to  this  maximum  or  limiting  value  is  therefore  a  measure  of 
the  proportion  between  the  number  of  dissociated  and  the  total  number 
of  molecules.  The  molecular  conductivity  of  the  salts  dissolved  in 
the  liquids  of  the  animal  body,  for  the  degree  of  dilution  in  which 
they  exist  there,  is  such  that  we  must  assume  them  to  be  for  the  most 
part  dissociated. 

Absorption  of  the  Food. — In  the  preceding  chapter  we 
have  traced  the  food  in  its  progress  along  the  alimentary 
canal,  and  sketched  the  changes  wrought  in  it  by  diges- 
tion. We  have  next  to  consider  the  manner  in  which  it  is 
absorbed.  Then,  for  a  reason  which  has  already  been 
explained,  instead  of  following  its  fate  within  the  tissues, 
until  it  is  once  more  cast  out  of  the  body  in  the  form  of 
waste  products,  it  will  be  best  to  drop  the  logical  order  and 
pick  up  the  other  end  of  the  clue — in  other  words,  to 
pass  from  absorption  to  excretion,  from  the  first  step  in 
metabolism  to  the  closing  act,  and  afterwards  to  return  and 
fill  in  the  interval  as  best  we  can. 

And  here,  first  of  all,  it  should  be  remembered  that  the  epithelial 
surfaces,  through  which  the  substances  needed  by  the  organism 
enter  it,  and  waste  products  leave  it,  are,  physiologically  considered, 
outside  the  body.  The  mucous  membranes  of  the  alimentary, 


3^4 


A  MANUAL  OF  PHYSIOLOGY 


respiratory  and  urinary  tracts  are  in  a  sense  as  much  external  as  the 
fourth  great  division  of  the  physiological  surface,  the  skin.  The  two 
latter  surfaces  are  in  the  mammal  purely  excretory.  Absorption  is 
the  dominant  function  of  the  alimentary  mucous  membrane,  but  a 
certain  amount  of  excretion  also  goes  on  through  it.  The  pulmonary 
surface  both  excretes  and  absorbs,  and  that  in  an  equal  measure. 
But  it  is  by  no  means  necessary  that  the  surface  through  which 
oxygen  is  taken  in  and  gaseous  waste  products  given  off  should  be 
buried  deep  in  the  body,  and  communicate  only  by  a  narrow  channel 
with  the  exterior.  In  the  frog  the  skin  is  largely  an  absorbing  as 
well  as  an  excreting  surface ;  oxygen  passes  freely  in  through  it,  just 
as  carbon  dioxide  passes  freely  out.  In  most  fishes,  and  many  other 

gill-bearing  animals,  the  whole 
gaseous  interchange  takes  place 
through  surfaces  immersed  in  the 
surrounding  water,  and  therefore 
distinctly  external.  In  certain  forms 
it  has  even  been  shown  that  the 
alimentary  canal  may  serve  con- 
spicuously for  absorption  and  ex- 
cretion of  gaseous,  as  well  as  liquid 
and  solid  substances.  Still  lower 
down  in  the  animal  scale,  the  sur- 
face of  a  single  tube  may  perform 
all  the  functions  of  digestion,  ab- 
sorption and  excretion.  Lower  still, 
and  even  this  tube  is  wanting,  and 
everything  passes  in  and  out  through 
an  external  surface  pierced  by  no 
permanent  openings. 

Indeed,   even   in  man  the  func- 

Carbon  c,   nitrogen   n,  hydrogen  h,    tions     of     the     various      anatomical 

±3^:kT?±«Mi  ^visions  of  the  physiological  sur- 
renal  epithelium  ;  A,  the  alimentary  face  are  not  quite  sharply  marked 
canal ;  S,  the  skin.  off  frOm  each  other.  Though 

gaseous    interchange    goes    on   far 

more  readily  through  the  pulmonary  membrane  than  anywhere  else, 
swallowed  oxygen  is  easily  enough  absorbed  from  the  alimentary 
canal  and  carbon  dioxide  given  off  into  it ;  and  to  a  small  extent 
these  gases  can  also  pass  through  the  skin.  Though  water  is  ex- 
creted chiefly  by  the  skin,  the  pulmonary  and  the  urinary  surfaces, 
and  on  the  whole  absorbed  chiefly  from  the  digestive  tract,  there  is 
no  surface  which  in  the  twenty-four  hours  pours  out  so  much  water 
as  the  mucous  membrane  of  the  stomach.  Under  normal  condi- 
tions, it  is  true,  by  far  the  greater  part  of  this  is  reabsorbed  in  the 
intestine,  yet  in  diarrhoea,  whether  natural  or  caused  by  purgatives, 
the  intestines  themselves  may,  instead  of  absorbing,  contribute 
largely  to  the  excretion  of  water.  Again,  although  the  solids  of  the 
excreta  are  normally  given  off  in  far  the  greatest  quantity  in  the 
urine  and  faeces  (only  part  of  the  latter  is  truly  an  excretion,  since 


FIG.    in.— DIAGRAM    OF  ABSORP- 
TION AND  EXCRETION. 


e 


ABSORPTION  365 

much  of  the  faeces  of  a  mixed  diet  has  never  been  physiologically 
inside  the  body  at  all),  yet  salts  are  constantly,  and  urea  occasionally, 
found  in  the  excretions  of  the  skin,  and  of  the  respiratory  tract. 
Further,  although  the  solids  and  liquids  of  the  food  are  usually  taken 
in  by  the  alimentary  mucous  surface,  it  is  possible  to  cause  sub- 
stances of  both  kinds  to  pass  in  through  the  skin  ;  and  a  certain 
amount  of  absorption  may  also  take  place  through  the  urinary 
bladder.  So  that  really  it  may  be  considered,  from  a  physiological 
point  of  view,  as  more  or  less  an  accident  that  a  man  should  absorb 
his  food  by  dipping  the  villi  of  his  intestine  into  a  digested  mass, 
rather  than  by  dipping  his  fingers  into  properly  prepared  solutions, 
as  a  plant  dips  its  roots  among  the  liquids  and  solids  of  the  soil ;  or 
that  he  should  draw  air  into  organs  lying  well  in  the  interior  of  his 
thorax,  instead  of  letting  it  play  over  special  thin  and  highly  vascular 
portions  of  his  skin ;  or  that  the  surface  by  which  he  excretes  urea 
should  be  buried  in  his  loins,  instead  of  lying  free  upon  his  back. 

It  has  been  already  explained  that,  although  digestion  is 
a  necessary  preliminary  to  the  absorption  of  most  of  the 
solids  of  the  food,  we  are  not  to  suppose  that  all  the  food 
must  be  digested  before  any  of  it  begins  to  be  absorbed.  On 
the  contrary,  the  two  processes  go  on  together.  As  soon  as 
any  peptone  has  been  formed  from  the  proteids,  or  sugar 
from  the  starch,  they  begin  to  pass  out  of  the  alimentary 
canal ;  and  by  the  time  digestion  is  over,  absorption  is  well 
advanced. 

Even  in  the  mouth  it  has  already  begun,  and  it  is  con- 
tinued with  far  greater  rapidity  in  the  stomach.  Here 
peptones,  sugar,  and  diffusible  substances  like  alcohol,  and 
the  extractives  of  meat,  which  form  an  important  part  of 
most  thin  soups  and  of  beef-tea,  are  undoubtedly  absorbed.* 
But  it  is  in  the  small  intestine  that  absorption  reaches  its 
height.  The  mucous  membrane  of  this  tube  offers  an 
immense  surface,  multiplied  as  it  is  by  innumerable  villi, 
and  by  the  valvulae  conniventes.  Here  the  whole  of  the  fat, 
much  sugar  and  peptone,  certain  products  of  the  further 
action  of  the  unformed  and  formed  ferments  of  the  intestine 
on  the  food,  and  certain  constituents  of  the  bile  are  taken  in. 

*•  The  following  table  illustrates  the  rapidity  of  absorption  of  cane- 
sugar.  After  a  twenty-four  hours'  fast,  nineteen  dogs  were  fed  with 
known  amounts  of  cane-sugar,  and  killed  after  an  interval  varying  from 
thirty  minutes  to  four  hours.  The  contents  of  the  stomach  and  intestines 
were  separately  collected,  and  the  amount  of  sugar  (estimated  as  glucose) 
determined  before  and  after  boiling  with  hydrochloric  acid.  In  the  first 
sixteen  experiments  the  sugar  was  given  in  the  form  of  a  10  per  cent. 


366 


A  MANUAL  OF  PHYSIOLOGY 


In  the  large  intestine,  as  has  been  already  said,  water  and 
soluble  salts  are  chiefly  absorbed 

What  now  is  the  mechanism  by  which  these  various 
products  are  taken  up  from  the  digestive  tube,  and  what 
paths  do  they  follow  on  their  way  to  the  tissues  ? 

Theories  of  Absorption.  —  Not  so  very  long  ago  it  was  supposed  by 
many  that  the  processes  of  diffusion,  osmosis  and  filtration  offered  a 
tolerably  complete  explanation  of  physiological  absorption.  At  that 
time  the  dominant  note  of  physiology  was  an  eager  appeal  to 
chemistry  and  physics  to  '  come  over  and  help  it ';  and  as  new  facts 
were  discovered  in  these  sciences  they  were  applied,  with  a  confidence 
that  was  almost  naive,  to  the  problems  of  the  animal  organism.  The 
phenomena  of  the  passage  of  liquids  and  dissolved  solids  through 
animal  membranes,  upon  which  the  work  of  Graham  had  cast  so 
much  light,  seemed  to  find  their  parallel  in  the  absorptive  processes 
of  the  alimentary  canal.  And  when  digestion  was  more  deeply 
studied,  facts  appeared  which  seemed  to  show  that  its  whole  drift 
was  to  increase  the  solubility  and  difTusibility  of  the  constituents  of 
the  food.  But  as  time  went  on,  and  more  was  learnt  of  the  phenomena 
of  absorption  and  the  powers  of  cells,  these  crude  physical  theories 
broke  down,  and  discarded  '  vitalistic  '  hypotheses  began  once  more 
to  arouse  attention.  Then  came  the  recent  investigations  of  De 
Vries,  Van't  Hoff,  and  others  in  the  domain  of  molecular  physics, 
which  gave  to  our  notions  of  osmosis  the  precision  that  was  wanted 
before  its  relation  to  many  physiological  processes  could  be  profitably 
discussed.  At  the  present  time  it  must  be  admitted  that  we  possess 
no  explanation  of  absorption  which  is  more  than  a  confession  of 
ignorance,  and  does  not  itself  need  to  be  explained.  Some  physiolo- 
gists, impressed  with  the  vast  progress  of  physics  and  chemistry,  and 
especially  with  the  strides  that  have  recently  been  made  in  the  study 

solution,  in  the  last  three  in  the  solid  state,  a  little  lard  being  always 
mixed  with  it  to  render  it  more  palatable. 


. 

Found  in 

Found  in 

. 

Found  in 

Found  in 

>  -• 

£j  . 

Stomach, 

Intestine, 

JJ  c 

v2  § 

Stomach 

Intestine, 

fl 

"g"§-|         »n  grm. 

in  grm. 

>3)M 

>  2*'g 

in  grm. 

in  grin. 

Is 

M 

1  j-2:  Glu- 
'-'  "^        cose. 

Cane- 
sugar. 

Glu- 
cose. 

Cane- 
sugar. 

r 

•"  J3.S 

Glu- 
cose. 

Cane- 
sugar. 

Glu- 
cose. 

Cane- 
sugar. 

5 

30      o 

1-66 

0 

0 

8 

1  80 

-277 

0 

O 

O 

5 

30 

0 

0 

0 

0 

7  '5     240 

O 

0 

O 

0 

10 

30       o 

Trace 

0 

O 

7  '5 

240 

0 

O 

O 

O 

5 

90  \    o 

n 

0 

O 

7'5 

240 

0 

0 

•15 

0 

5 

90 

0 

0 

0 

O 

7'5 

240 

0 

0 

o 

O 

10 

90 

O 

0 

O 

O 

7  '5 

240 

0 

0 

0 

0      S 

ii 

90 

0 

0 

0 

0 

20 

60 

3-61 

12-89 

o 

°)   gfg' 

7'5 

105 

O 

o 

0 

O 

20 

120 

I  '2 

13*3 

•25 

I3-3 

I05 

•58 

0 

0 

0 

50 

120 

**3 

18-2 

4-5 

1-18  )•§ 

25 

1  2O          O 

o 

O 

'83 

1 

(/) 

ABSORPTION  367 

of  osmosis,  believe  that  as  our  knowledge  of  these  sciences  increases, 
it  will  become  possible  to  explain  on  physical  principles  all  the 
peculiar  phenomena  which  we  observe  in  the  passage  of  substances 
through  the  walls  of  the  alimentary  canal.  Others,  taking  account  of 
the  number  and  nature  of  these  peculiarities,  oppressed  with  the 
perennial  paradox  of  vital  action,  incline  to  the  less  sanguine  view, 
that  after  all  physical  explanations  have  been  exhausted,  the  real 
secret  of  the  cell  will  still  lurk  in  some  ultimate  *  vital '  property  of 
structure  or  of  function,  and  still  elude  our  search.  Both  the 
optimist  and  the  pessimist,  the  adherent  of  the  physical  and  the 
adherent  of  the  vitalistic  hypothesis,  admit  that  the  phenomena  of 
absorption  are  essentially  connected  with  the  cells  that  line  the 
alimentary  canal.  And  the  one  must  confess  what  the  other  pro- 
claims, that  while  the  processes  carried  on  in  these  cells  are  definite, 
well  ordered,  and  evidently  guided  by  laws,  these  laws  have  as  yet 
denied  themselves  to  the  modern  physiologist,  with  chemistry  in  one 
hand  and  physics  in  the  other,  as  they  denied  themselves  to  his  pre- 
decessor, equipped  only  with  his  scalpel,  his  sharp  eyes,  and  his 
mother-wit.  So  that  in  the  present  state  of  our  knowledge  all  we 
can  really  say  is  that,  while  absorption  is  certainly  aided  by  physical 
processes  like  osmosis,  it  is  at  bottom  the  work  of  cells  with  a 
selective  power  which  we  do  not  understand,  and  which  is  probably 
peculiar  to  living  structures.  Thus,  when  the  cells  that  line  the  intes- 
tine are  injured  or  destroyed,  absorption  from  it  is  diminished  or 
abolished.  And  in  their  normal  state  they  do  not  take  up  indis- 
criminately all  kinds  of  diffusible  substances,  nor  absorb  those  which 
they  do  take  up  in  the  direct  ratio  of  their  diffusibility,  nor  do  they 
reject  everything  which  does  not  diffuse.  Albumin,  for  example,! 
which  does  not  pass  through  dead  animal  membranes,  is  to  a  certain; 
extent  taken  up  from  a  loop  of  intestine  without  change.  And  it  hasj 
been  shown  that  the  water,  organic  and  inorganic  solids  of  the  serum 
of  an  animal  are  absorbed  from  a  loop  of  its  intestine  when  the 
pressure  in  the  capillaries  of  the  intestinal  wall  is  considerably  greater 
than  in  the  cavity  of  the  gut.  Since  the  serum  in  the  intestine  is 
isotonic  with  the  plasma  in  the  capillaries,  the  absorption  cannot  be 
due  to  osmosis  or  diffusion.  Nor  can  it  be  due  to  filtration,  since 
the  slope  of  pressure  is  from  the  capillaries  to  the  lumen  of  the  gut 
(Waymouth  Reid).  It  is  therefore  extremely  difficult  to  reconcile 
this  experiment  with  any  physical  theory  of  absorption. 

But  if  it  be  true  that  the  action  of  the  columnar  epithelium  of  the 
intestinal  mucous  membrane  is  governed  by  a  secretive  and  selective 
power,  that  makes  use  of  purely  physical  processes,  but  is  not 
mastered  by  them,  the  possibility  must  be  admitted  that  in  the  cells 
of  endothelial  type  which  line  the  serous  cavities,  the  lymphatics,  the 
bloodvessels,  the  alveoli  of  the  lungs,  and  the  Bowman's  capsules 
of  the  kidney  (p.  395),  the  element  of  secretion  is  less  marked,  and 
more  overshadowed  by  the  physical  factors.  And  it  may  very  plausibly 
be  urged  that  changes  of  considerable  physiological  complexity  can 
only  be  wrought  on  substances  that  have  to  pass  through  a  cell  of 
considerable  depth,  while  a  mere  film  of  protoplasm  suffices  for,  and 


368 


A  MANUAL  OF  PHYSIOLOGY 


indeed  favours,  mechanical  filtration  and  diffusion.  We  have  already 
seen  (p.  242),  in  the  case  of  the  lungs,  that  whatever  the  complete 
explanation  may  be  of  the  gaseous  exchange  which  takes  place 
through  the  alveolar  membrane,  physical  diffusion  undoubtedly  plays 
a  certain  part.  We  shall  see,  too  (p.  403).  that  in  the  case  of  the 
kidney  the  endothelium  of  the  Bowman's  capsule,  although  by  no 
means  devoid  of  selective  power,  does  seem  to  have  allotted  to  it  a 
simpler  task  than  falls  to  the  share  of  the  'rodded'  epithelium. 
Further,  it  has  been  stated  that  interchange  between  blood-serum, 
circulated  artificially  in  the  vessels  of  dogs  and  rabbits  which  have 
been  dead  for  hours,  and  liquids  introduced  into  the  peritoneal 

cavity,  is  essentially  the  same  as 
in  the  living  animal,  and  can  be 
explained  on  purely  physical 
principles  (Hamburger).  Ligation 
of  the  thoracic  duct  has  little 
effect  on  the  fate  of  liquids  injected 
into  serous  cavities,  since  the 
bloodvessels  play  the  chief  part  in 
their  absorption,  just  as  strychnia, 
when  injected  under  the  skin — i.e., 
into  the  lymph-spaces  of  areolar 
tissue — is  taken  up  by  the  blood 
and  does  not  appear  in  the  lymph. 
And  if  substances  can  pass,  by 
physical  processes  alone,  from  the 
serous  cavities,  which  are  really 
FIG.  112. -VERTICAL  SECTION  OF  A  expanded  lymph-spaces,  into  the 

blood,    and   from   the    blood    into 
serous  cavities,  it  is  natural  to  in- 


a 


VILLUS  (CAT)  x  300. 

a,  layer  of  columnar  epithelium  cover- 

ing  the  vilius— the  outer  edge  of  the  quire  whether  anything  else  is  con- 
cells  is  striated  ;  b,  central  lacteal  of  rernef}  ;n  tup  noccoaP  of  rhp  rnn 
vilius  ;  c,  unstriped  muscular  fibres ;  d,  ce.rnea  m  l  e  passage  Ot  tfte  COn- 

mucin-forming  goblet-cell.  stituents  of  the  lymph  through  the 

capillary  walls. 

Formation  of  Lymph. — The  teaching  of  Ludwig,  that  filtration  is 
the  great  factor  in  the  formation  of  lymph,  was  called  in  question  by 
Heidenhain,  whose  theory  of  secretion  at  first  bade  fair  to  totally 
supplant  the  older  view.  But  a  reaction  has  set  in.  A  zealous  band 
of  investigators  has  revived  the  old  doctrine  of  filtration,  and  a  con- 
troversy has  sprung  up  which  has  yielded  a  rich  harvest  of  new  facts 
and  new  ideas,  but  as  yet  shows  no  sign  of  coming  to  an  end.  One  of 
the  strongest  arguments  in  favour  of  the  secretion  theory  has  been 
the  existence  of  substances  which,  when  injected  into  the  blood, 
increase  the  flow  of  lymph,  without  affecting  appreciably  the  arterial 
pressure.  Heidenhain  divides  these  so-called  lymphagogues  into  two 
classes  :  (i)  substances  like  peptone,  leech-extract,  extract  of  crayfish, 
egg-albumin,  etc.,  which  cause  not  only  an  increase  in  the  rate  of 
flow,  but  an  increase  in  the  specific  gravity  and  total  solids  of  the 
lymph ;  (2)  crystalloid  substances,  like  sugar,  salt,  etc.,  which  cause 
an  increased  flow  of  lymph  more  watery  than  normal.  Starling  has 


ABSORPTION  369 

shown  that  although  the  lymphagogues  of  the  second  class  do  not 
raise  the  arterial  pressure,  they  do,  by  attracting  water  from  the 
tissues  and  thus  causing  hydraemic  plethora  (an  excess  of  blood  of 
low  specific  gravity),  bring  about  a  marked  rise  of  venous,  and  there- 
fore, what  is  the  important  thing  for  lymph  filtration,  of  capillary 
pressure.  The  action  of  the  first  class  of  lymphagogues,  which 
cannot  be  explained  in  this  way  because  the  pressure  in  the  capillaries 
is  not  increased,  he  attributes  to  an  injurious  effect  on  the  capillary 
endothelium  (and  especially  on  the  endothelium  of  the  capillaries  of 
the  liver,  since  nearly  the  whole  of  the  increased  lymph-flow  comes 
from  that  organ),  which  increases  its  permeability.  Starling's  expla- 
nation is  supported  by  various  facts,  but  it  is  not  easy  to  distinguish 
an  increase  of  permeability  produced  by  lymphagogues  from  an 
increase  of  secretive  activity  of  the  endothelial  cells.  Hamburger, 
too,  has  brought  forward  results  which  it  is  difficult  to  reconcile  with 
a  theory  of  filtration  even  for  the  second  class  of  lymphagogues. 
Further,  Heidenhain  has  shown  that  some  time  after  injection  of  a 
crystalloid  substance,  like  sugar,  into  the  blood,  a  greater  percentage 
of  the  substance  may  be  found  in  the  lymph  than  in  the  blood. 
Now,  when  a  mixture  of  crystalloids  and  colloids  is  filtered  through 
a  thin  membrane,  the  percentage  of  crystalloids  in  the  filtrate  is 
never,  at  most,  greater  than  in  the  original  liquid  (Cohnstein).  And 
although  Cohnstein  states  that  if  time  enough  be  allowed,  the 
maximum  concentration  of  sodium  chloride  in  the  lymph,  after  intra- 
venous injection,  becomes  approximately  the  same  as  the  maximum 
in  the  blood,  this  fact  does  not  enable  us  to  decide  against  the 
secretion  and  in  favour  of  the  filtration  hypothesis.  Lazarus-Barlow 
argues  strongly  against  the  physical  view,  and  points  out,  among 
other  interesting  conclusions,  that  the  maximum  outflow  of  lymph 
from  the  thoracic  duct  does  not  occur  at  the  time  of  maximum  intra- 
venous pressure,  and  that  in  the  great  majority  of  his  experiments 
the  injection  of  a  concentrated  solution  of  sodium  chloride,  glucose 
or  urea  into  a  vein  was  followed,  not  by  an  initial  diminution  in  the 
outflow  of  lymph  (as  might  have  been  expected  if  the  exchange  of 
water  between  the  blood  and  the  tissue  spaces  was  regulated  solely 
by  differences  in  osmotic  pressure),  but  by  an  immediate  increase. 

To  sum  up,  we  may  say  that  the  general  trend  of  research  is  at 
present  in  the  direction  of  abridging  to  a  certain  extent  the  field  of 
specific  vital  action  so  far  as  the  capillary  endothelium  is  concerned,  and 
of  enlarging  the  '  sphere  of  influence  '  of  the  more  purely  physical  pro- 
cesses of  filtration  and  osmosis. 

It  ought  to  be  remembered  in  this  whole  discussion  that  the 
epithelium  of  ordinary  glands  derives  its  supplies  of  material  from 
the  lymph.  The  vicissitudes  of  blood-pressure  affect  it  only  in  a 
secondary  and  indirect  manner.  On  the  other  hand,  the  endothelial 
cells  which  have  to  do  with  the  formation  of  lymph  are  in  direct 
contact  with  the  blood,  And  it  is  interesting  to  observe  that  in  this 
respect  the  glomeruli  of  the  kidney  and  the  alveoli  of  the  lungs  (if  the 
endothelial  lining  of  Bowman's  capsule  and  the  alveolar  membrane 

24 


370  A  MANUAL  OF  PHYSIOLOGY 

are  assumed  to  be  complete)  take  a  middle  place  between  the  glands 
proper  and  the  quasi-glandular  capillaries. 

The  increase  in  the  quantity  of  chyle  flowing  from  the  thoracic 
duct  during  digestion  may  be,  on  the  mechanical  theory,  associated 
with  the  dilatation  of  the  intestinal  arterioles  and  the  consequent 
increase  of  blood-pressure  in  the  capillaries  of  the  splanchnic  area  in 
general,  and  of  the  liver  in  particular.  But  it  may  be  equally  well 
harmonized  with  the  doctrine  of  secretion.  In  consequence  of  the 
quickened  flow  of  lymph  the  number  of  lymphocytes  in  the  blood  is 
increased  during  digestion,  a  fact  which  ought  to  be  remembered  in 
enumerating  the  corpuscles  for  clinical  purposes. 

Absorption  of  Fat. — It  has  been  already  mentioned  that 
some  of  the  fat  is  split  up  in  the  intestine  into  glycerine 
and  fatty  acids,  but  how  much  undergoes  this  change  is 
unknown.  It  is  believed  by  some  that  the  whole  of  the  fat 
is  so  split  up,  to  be  absorbed  in  the  form  of  soaps,  or  of  free 
fatty  acids,  or  of  both.  If  this  be  the  case,  neutral  fat  must 
again  be  built  up  in  the  epithelial  cells,  covering  the  villi 
from  the  absorbed  fatty  acids  or  soaps.  For  if  an  animal  is 
killed  during  digestion  of  a  fatty  meal,  these  cells  are  found 
to  contain  globules  of  different  sizes,  which  stain  black  with 
osmic  acid,  are  dissolved  out  by  ether,  leaving  vacuoles  in 
the  cell  substance,  and  are  therefore  fat  (Plate  III.,  i).  But 
the  usual  view  is  that  the  greater  portion  of  the  fat  escapes 
decomposition,  and  is  absorbed  in  a  state  of  fine  division  by 
the  epithelial  cells.  It  is  not  known  in  what  manner  the 
cells  take  up  the  emulsified  fat  from  the  intestine,  but  it 
certainly  passes  into  them,  and  not  between  them.  When 
fat  is  found  in  the  cement  substance  between  the  cells,  it  has 
been  mechanically  squeezed  out  of  them  by  the  shrinking  of 
the  villi  in  preparation.  Leucocytes  have  been  asserted  to 
be  the  active  agents  in  the  absorption  of  fat.  They  have 
been  described  as  pushing  their  way  between  the  epithelial 
cells,  fishing,  as  it  were,  for  tatty  particles  in  the  juices  of 
the  intestine,  and  then  travelling  back  to  discharge  their 
cargo  into  the  lymph.  This  view,  however,  is  erroneous. 

But  although  the  leucocytes  do  not  aid  in  the  absorption 
of  fat  from  the  intestine,  they  appear  to  take  it  up  from 
the  epithelial  cells,  conveying  it  through  the  spaces  of 
the  network  of  adenoid  tissue  that  occupies  the  interior  of 
the  villus,  to  discharge  it  into  the  central  lacteal,  where  it 


ABSORPTION  371 

mingles  with  the  lymph  and  forms  the  so-called  molecular 
basis  of  the  chyle.  A  part  of  the  fat  reaches  the  lacteal  in 
some  other  way,  without  being  carried  by  the  leucocytes. 
The  contraction  of  the  smooth  muscular  fibres  of  the  villus 
and  the  peristaltic  movements  of  the  intestinal  walls  alter 
the  capacity  of  the  lacteal  chamber,  and  so  alternately  fill  it 
from  the  lymph  of  the  adenoid  reticulum,  and  empty  it  into 
the  lymphatic  vessel  with  which  it  is  connected.  By  this 
kind  of  pumping  action  the  passage  of  fat  and  other  sub- 
stances into  the  lymphatics  is  aided.  In  the  dog  no  fat 
is  absorbed  by  the  bloodvessels,  except  perhaps  a  small 
quantity  in  the  form  of  soaps  ;  it  nearly  all  goes  into  the 
lacteals,  and  thence  by  the  general  lymph  stream  through 
the  thoracic  duct  into  the  blood.  And  in  man  the  chyle 
collected  from  a  lymphatic  fistula  contained  a  large  propor- 
tion of  the  fat  given  in  the  food  (Munk).  But  this  ban 
statement  would  be  misleading  if  we  did  not  add  that  the  fat 
taken  in  can  never  be  entirely  recovered  in  the  chyle  collected 
from  the  thoracic  duct.  A  portion  of  it  disappears,  and  its 
fate  is  unknown.  And  even  after  ligature  of  the  thoracic  duct 
a  large  proportion  of  a  meal  of  fatty  acids  is  absorbed  from 
the  intestine,  by  what  channel  is  uncertain  (Frank).  ^ 

A  dog  normally  absorbs  9 — 21  per  cent,  of  the  fat  in  a  ^ 
meal  in  three  to  four  hours;  21 — 46  per  cent,  in  seven 
hours;  and  86  per  cent,  in  eighteen  hours  (Harley).  After 
•excision  of  the  pancreas  not  only  is  the  absorption  of  fat 
abolished,  but  more  fat  can  be  recovered  from  the  intestine 
than  is  given  in  the  food.  This  at  first  sight  paradoxical 
result  is  explained  by  the  well-established  fact  that  a  certain 
amount  of  fat  is  normally  excreted  into  the  intestine. 

Absorption  of  Water,  Salts,  and  Sugar. — The  water,  salts, 
and  sugar  pass  normally  into  the  rootlets  of  the  portal  vein, 
not  into  the  chyle,  for  no  increase  in  the  quantity  of  these 
substances  flowing  through  the  thoracic  duct  takes  place 
during  digestion,  while  the  sugar  in  the  portal  blood  is 
increased  after  a  starchy  meal.  In  man  not  i  per  cent,  of 
the  sugar  corresponding  to  the  carbo-hydrates  of  the  food 
could  be  recovered  in  the  chyle  escaping  from  a  lymphatic 
fistula.  But  when  a  large  amount  of  a  dilute  solution  of 

24-2 


372  A  MANUAL  OF  PHYSIOLOGY 

sugar  is  introduced  into  the  intestine  some  of  it  is  taken 
up  by  the  lacteals. 

Absorption  of  Proteids. — The  proteids  of  the  food  and 
their  digested  products  also  pass  directly  into  the  blood- 
capillaries  which  feed  the  portal  system.  For  it  has  been 
shown  that  after  ligature  of  the  thoracic  duct  proteid  sub- 
stances are  still  absorbed  from  the  intestine,  and  the  urea 
corresponding  to  their  nitrogen  appears  in  the  urine.  And 
the  proteids  in  the  lymph  flowing  from  a  lymphatic  fistula 
in  man  were  not  found  to  be  sensibly  increased  during  the 
digestion  of  proteid  food  (Munk). 

Although  a  certain  amount  of  egg-albumin,  myosin,  alkali- 
albumin,  and  other  proteid  substances  can  be  absorbed  as 
such  by  the  small,  and  even  by  the  large  intestine,  there  can 
be  no  doubt  that  the  greater  part  of  the  proteids  of  the 
food  is  first  changed  into  peptones.  But  peptones  are  either 
not  found  at  all  in  the  blood  or  only  in  small  amount,  and, 
indeed,  when  injected  into  the  blood  they  are  excreted  in 
the  urine.  When  injected  in  larger  amount  they  pass  also 
into  the  lymph,  from  which  they  gradually  reach  the  blood 
again,  and  are  eventually,  as  before,  eliminated  by  the 
kidneys.  The  clear  inference  is  that  when  absorbed  from 
the  alimentary  canal  they  must  be  changed  into  one  or  both 
of  the  chief  proteids  of  blood  and  chyle  (serum-albumin  and 
serum-globulin)  in  their  passage  through  its  walls.  And 
it  has  actually  been  shown  that  during  the  digestion  of  a 
proteid  meal  the  mucosa  of  the  stomach  and  intestine 
contains  peptone,  while  none  is  present  in  the  muscular 
coat  or  in  any  other  organ.  The  peptone  rapidly  disappears 
from  a  portion  of  the  mucous  membrane  kept  at  a  tempera- 
ture of  about  40°  C.  outside  of  the  body ;  but  not  if  it  has 
been  thrown  into  boiling  water  immediately  after  excision, 
nor  even  if  it  has  been  heated  to  60°  C.  for  a  few  minutes. 
Now,  a  temperature  of  60°  C.  does  not  destroy  an  un- 
organized ferment,  but  kills  a  living  cell.  The  regenera- 
tion of  peptone  must  therefore  presumably  take  place  in 
cells,  and  the  only  available  cells  in  this  locality  are  those 
which  line  the  intestine,  or  the  leucocytes  which  wander 
between  them.  Accordingly,  both  have  been  credited  with 

Jii 


ABSORPTION  373 

the  power  of  absorbing  and  transforming  peptone,  but  the 
balance  of  evidence  is  in  favour  of  the  epithelial  cells.  We 
cannot,  however,  as  in  the  case  of  the  fat,  single  out  any 
particular  tract  of  these  cells  as  alone  engaged  in  the 
absorption  of  peptone,  or,  indeed,  of  the  diffusible  sub- 
stances in  general.  In  all  likelihood  the  cells  covering  the 
villi  are  actively  concerned,  but  there  is  no  valid  reason  for 
denying  a  share  to  the  general  lining  of  the  stomach  and 
small  intestine,  even  including  the  Lieberkiihn's  crypts, 
which  morphologically  form  a  kind  of  inverted  villi.  It  is, 
indeed,  true  that  the  crypts  do  not  take  part  in  the  absorp- 
tion of  fat,  for  no  granules  blackened  by  osmic  acid  occur  in 
them  during  digestion  of  a  fatty  meal.  But  this  is  a  ground 
for  attributing  to  them  other  absorptive  functions  rather 
than  for  altogether  denying  to  them  a  share  in  absorption, 
especially  as  it  seems  unlikely  that  the  secretion  of  the 
comparatively  scanty  and  relatively  unimportant  succus 
entericus  should  engross  the  whole  activity  of  such  an 
extensive  sheet  of  cells.  Even  the  large  intestine,  which 
possesses  Lieberkiihn's  crypts  but  no  villi,  is  able  to  absorb 
not  only  peptones  and  sugar,  but  also  undigested  proteids ; 
and  although  these  are  powers  which  can  be  rarely  exercised 
in  normal  digestion,  they  form  the  physiological  basis  of  the 
important  method  of  treatment  by  nutrient  enemata. 

We  may  add  to  the  proof  of  the  varied  powers  of  the  cells 
of  the  intestinal  wall  given  by  the  change  which  peptones 
undergo  in  their  passage  through  them,  the  fact,  already 
mentioned,  that  cane-sugar  does  not  pass  into  the  blood  as 
such  unless  large  quantities  are  given,  but  is  first  converted 
into  dextrose,  even  in  the  absence  of  an  inverting  ferment, 
and  the  remarkable  discovery  of  Munk,  that  fatty  acids  given 
by  the  mouth  appear  in  the  lymph  of  the  thoracic  duct  as 
neutral  fats,  having  somewhere  or  other,  in  all  probability 
on  their  way  through  the  epithelium  of  the  gut,  been  com- 
bined with  glycerine,  although  no  free  glycerine  is  known  to 
occur  in  the  body. 

Since,  however,  the  amount  of  neutral  fat  recovered  from 
the  thoracic  duct  is  not  equivalent  to  more  than  one-third 
of  the  fatty  acids  given,  it  has  been  suggested  that  this 


374  A  MANUAL  OF  PHYSIOLOGY 

synthesis  of  fat  is  only  apparent,  and  that  the  whole  of  the 
fat  which  appears  in  the  chyle  after  a  meal  of  fatty  acids 
comes  from  the  fat  excreted  into  the  intestine  (Frank), 
which  is  increased  when  fatty  acids  are  given  by  the  mouth. 
But  the  suggestion  is  more  ingenious  than  the  evidence 
advanced  in  its  support  is  convincing. 


PRACTICAL  EXERCISES  ON  CHAPTERS  IV.  AND  V. 

i.  Saliva. —  Collection  and  Microscopic  Examination  of  Saliva. — 
Chew  a  piece  of  paraffin-wax,  or  inhale  ether  or  the  vapour  of  strong 
acetic  acid.  The  flow  of  saliva  is  increased.  Collect  it  in  a  porcelain 
capsule.  Examine  a  drop  under  the  microscope.  It  may  contain  a 
few  flat  epithelial  scales  from  the  mouth  and  a  few  round  granular 
bodies,  the  salivary  corpuscles,  the  granules  in  which  often  show  a 
lively,  dancing  movement  (Brownian  motion).  Filter  the  saliva  to 
free  it  from  air-bubbles,  and  perform  the  following  experiments : 

(a)  Test  the  reaction  with  litmus  paper.     It  is  usually  alkaline. 
An  acid  reaction  may  indicate  that  bacterial  processes  are  abnormally 
active  in  the  mouth. 

(b)  Add  dilute  acetic  acid.     A  precipitate  indicates  the  presence 
of  mucin  (p.  296).     Filter. 

j  (c)  Add  a  drop  or  two  of  silver  nitrate  solution,  A  precipitate 
soluble  in  ammonia,  insoluble  in  nitric  acid,  proves  that  chlorides 
are  present. 

(d)  Add  to  another  portion  a  few  drops  of  dilute  ferric  chloride. 
and  the  same  quantity  to  as  much  distilled  water  in  a  control  test- 
tube.    A  red  coloration  is  obtained,  due  to  the  presence  of  potassium 
sulphocyanide  (KCNS).      The   colour   is   discharged  by  mercuric 
chloride.     This  reaction  is  not  given  by  the  saliva  of  most  animals, 
nor  by  that  of  some  men. 

(e)  To  the  filtrate  from  (b)  add  Millon's  reagent.     A  red  coloration 
or  precipitate  shows  that  proteid  is  present. 

(/)  Take  some  boiled  starch  mucilage,  and  test  it  for  reducing 
sugar  by  Trommer's  test  (p.  23).  If  no  sugar  is  found,  take  three 
test-tubes,  label  them  A,  B,  and  C,  and  nearly  half  fill  each  with  the 
boiled  starch.  To  A  add  a  little  saliva,  to  B  some  saliva  which  has 
been  boiled,  to  C  an  equal  volume  of  0*4  per  cent,  hydrochloric  acid 
and  a  little  saliva  which  has  been  neutralized,  so  as  to  make  the 
strength  of  the  acid  in  the  mixture  0*2  per  cent.,  or  the  same  as  that 
of  the  gastric  juice.  Put  the  test-tubes  into  a  water-bath  at  about 
40°  C.  In  a  few  minutes  test  the  contents  for  reducing  sugar. 
Abundance  will  be  found  in  A,  none  in  B  nor  in  C.  In  B  the 
ferment  ptyaltn  has  been  destroyed  by  boiling ;  in  C  its  action  has 
been  inhibited  by  the  acid.  If  the  test-tubes  have  been  left  long 
enough  in  the  bath,  n6  blue  colour  will  be  given  by  A  on  the 


PRACTICAL  EXERCISES  375 

addition  of  iodine,  but  a  strong  blue  colour  by  B  and  C  ;  i.e.,  the 
starch  will  have  completely  disappeared  from  A. 

(g)  Put  some  starch  in  a  test-tube,  add  a  little  saliva,  and  hold  in 
the  hand  or  place  in  a  bath  at  40°  C.  On  a  porcelain  slab  place 
several  separate  drops  of  dilute  iodine  solution.  With  a  glass  rod 
add  a  drop  of  the  mixture  in  the  test-tube  to  one  of  the  drops  of 
iodine  at  intervals  as  digestion  goes  on.  At  first  only  the  blue  colour 
given  by  starch  will  be  seen ;  a  little  later  a  violet  colour,  due  to  the 
presence  of  erythrodextrin  in  addition  to  some  unaltered  starch.  A 
little  later  the  colour  will  be  reddish,  the  starch  having  disappeared, 
and  the  erythrodextrin  reaction  being  no  longer  obscured.  Later  still 
no  colour  reaction  will  be  obtained,  the  erythrodextrin  having  under- 
gone further  changes,  and  only  sugar  (maltose,  isomaltose,  and 
perhaps  a  trace  of  dextrose)  and  achroodextrin — a  kind  of  dextrin 
which  gives  no  colour  with  iodine — being  present. 

(h)  Put  a  little  distilled  water  in  a  porcelain  capsule,  and  bring  the 
water  to  the  boil.  Now  put  into  the  mouth  some  boiled  starch 
paste,  and  move  it  about  as  in  mastication.  After  half  a  minute  spit 
the  starch  out  into  the  boiling  water.  Divide  the  water  into  two 
portions.  Test  one  for  sugar,  and  the  other  for  starch.  Repeat  the 
experiment,  but  keep  the  starch  two  minutes  in  the  mouth.  Report 
the  result. 

(/)  Starch  solution  to  which  saliva  has  been  added  is  placed  in  a 
dialyser  tube  of  parchment  paper  for  twenty-four  hours.  At  the  end 
of  that  time  the  dialysate  (the  surrounding  water)  should  be  tested 
for  sugar  and  for  starch.  Sugar  will  probably  be  found,  but  no 
starch.  If  no  reaction  for  sugar  is  obtained,  the  dialysate  should  be 
concentrated  on  the  water-bath,  and  again  tested. 

2.  Stimulation  of  the  Chorda  Tympani. — (i)  Having  previously 
studied  the  anatomy  of  the  mouth  and  submaxillary  region  in  the  dog 
by  dissecting  a  dead  animal  (Fig.  115,  p.  383),  put  a  good-sized  dog 
under  morphia.  Set  up  an  induction-machine  for  a  tetanizing  current 
(p.  175),  and  connect  it  with  fine  electrodes.  Fasten  the  dog  on  the 
holder,  give  ether  if  necessary,  and  insert  a  cannula  in  the  trachea 
(p.  177).  Then  make  an  incision  3  or  4  inches  long,  through 
skin  and  platysma  muscle,  along  the  inner  border  of  the  lower  jaw, 
beginning  about  the  angle  of  the  mouth,  and  continuing  backwards 
towards  the  angle  of  the  jaw.  Ligature  doubly,  and  divide  such 
branches  of  the  jugular  vein  as  come  in  the  way,  except  those 
belonging  to  the  submaxillary  gland.  Feel  for  the  facial  artery,  so 
as  to  be  able  to  avoid  it.  Divide  the  digastric  muscle  about  its 
anterior  third,  and  clear  it  carefully  from  its  attachments.  The 
broad,  thin  mylo-hyoid  muscle  will  now  be  seen  with  its  motor  nerve 
lying  on  it.  Divide  the  muscle  about  its  middle  at  right  angles  to 
its  fibres,  and  raise  it  carefully.  The  lingual  nerve  will  be  seen 
emerging  from  under  the  ramus  of  the  jaw.  It  runs  transversely 
towards  the  middle  line,  and  then,  bending  on  itself,  passes  forwards 
parallel  to  the  larger  hypoglossal  nerve.  In  its  transverse  course  the 
lingual  will  be  seen  to  cross  the  ducts  of  the  submaxillary  and  sub- 
lingual  glands.  These  structures  having  been  identified,  the  lingual 


376  A  MANUAL  OF  PHYSIOLOGY 

nerve  is  to  be  ligatured  before  it  enters  the  tongue  and  cut  peri- 
pherally to  the  ligature.  Then  a  suitable  glass  cannula  with  a 
rectangular  elbow  is  to  be  inserted  into  the  submaxillary  duct  (the 
larger  of  the  two),  just  as  if  it  were  a  bloodvessel  (p.  58).  The 
lingual  is  now  to  be  lifted  by  means  of  the  ligature,  and  traced  back 
towards  the  jaw  till  its  chorda  tympani  branch  is  seen  coming  off  and 
running  backwards  along  the  duct.  The  chordo-lingual  nerve 
(Fig.  107,  p.  333)  is  then  to  be  cut  centrally  to  the  origin  of  the 
chorda  tympani,  which  can  now  be  easily  laid  on  electrodes  by 
means  of  the  ligature  on  the  lingual.  On  stimulating  the  chorda, 
the  flow  of  saliva  through  the  cannula  will  be  increased.  The 
current  need  not  be  very  strong.  If  the  flow  stops  after  a  short  time, 
it  can  be  again  caused  by  renewed  stimulation  after  a  brief  rest.  A 
quantity  of  saliva  may  thus  be  collected,  and  the  experiments  already 
made  with  human  saliva  repeated. 

(2)  Expose  the  vago-sympathetic  nerve  in  the  neck  on  the  same 
side ;  ligature  it ;  divide  below  the   ligature,  and   note   the   effect 
produced  by  stimulation  of  the  upper  end  on  the  flow  of  saliva. 

(3)  Set    up    another    induction-machine,    and    connect   it   with 
electrodes.     Stimulate  the  chorda,  and  note  the  rate  of  flow  of  the 
saliva.     Then,  while  the  chorda  is  still  being  excited,  stimulate  the 
vago-sympathetic  and  observe  the  effect.     If  the  experiment  is  suc- 
cessful, finish  by  stimulating   the  chorda  for  a  long  time.     Then 
harden  both  submaxillary  glands  in  absolute  alcohol,  make  sections, 
stain  with  carmine  and  compare  them. 

3.  Effect  of  Drugs  on  the  Secretion  of  Saliva. — (i)  Proceed  as 
in  2  (i),  but,  in  addition,  insert  a  cannula  into  the  femoral  vein,  and 
while  the   chorda  is  being  stimulated  inject  into  the  vein,  in  the 
manner  described  on  p.  177,  TO  to  15  milligrammes  of  sulphate  of 
atropia.     This  will  stop  the  flow  of  saliva,  and  abolish  the  effect  of 
stimulation  of  the  chorda. 

(2)  Now  empty  the  cannula  in  the  submaxillary  duct  by  means  of 
a  feather,  and  fill  it  with  a  2  per  cent,  solution  of  pilocarpine  nitrate 
by  means  of  a  fine  pipette.  Then,  attaching  a  small  syringe  to  the 
cannula,  force  into  the  duct  about  \  c.c.  of  the  solution.  Dis- 
connect the  syringe.  Secretion  of  saliva  will  again  begin,  and 
stimulation  of  the  chorda  will  again  cause  an  increase  in  the  flow. 
But  after  a  few  minutes  the  action  of  the  atropia  will  reassert  itself 
and  the  flow  will  stop.  Renewed  secretion  may  be  caused  by  a  fresh 
injection  of  pilocarpine. 

4.  Gastric  Juice — (a)  Preparation  of  Artificial   Gastric  Juice. — 
Take  a  portion  of  the  pig's  stomach  provided,  strip  off  the  mucous 
membrane  (except  that  of  the  pyloric  end),  cut  it  into  small  pieces 
with  scissors,  and  put  it  in  a  bottle  with  fifty  times  its  weight  of 
0*4  per  cent,  hydrochloric  acid.     Label  and  put  in  a  bath  at  40°  C. 
for  twelve  hours.     Then  filter. 

(b)  Take  another  portion  of  the  mucous  membrane,  cut  it  into 
pieces,  and  rub  up  with  clean  sand  in  a  mortar.  Then  put  it  in  a 
small  bottle,  cover  it  with  glycerine,  label,  and  set  aside  for  two  or 
three  days.  The  glycerine  extracts  the  pepsin. 


PRACTICAL  EXERCISES  377 

\  (f)  Take  five  test-tubes,  A,  B,  C,  D,  E,  and  in  each  put  a  little 
washed  and  boiled  fibrin.  To  A  add  a  few  drops  of  glycerine-  £u> 
extract  of  pig's  stomach,  and  fill  up  the  test-tube  with  0-2  per  cent, 
hydrochloric  acid.  To  B  add  glycerine  extract  and  distilled  water ; 
to  C  glycerine  extract  and  i  per  cent,  sodium  carbonate ;  to  D 
0-2  per  cent,  hydrochloric  acid  alone ;  to  E  glycerine  extract  which 
has  been  boiled,  and  0-2  per  cent,  hydrochloric  acid. 

Put  up  another  set  of  five  test-tubes  in  the  same  way,  except  that  a 
few  drops  of  a  watery  solution  of  a  commercial  pepsin  are  substituted 
for  the  glycerine  extract.  Label  the  test-tube  A',  B',  C',  D',  E'. 

Into  another  test-tube  put  a  little  fibrin,  and  fill  up  with  the 
filtered  acid  extract  from  (a).  Label  it  F.,t  Place  all  the  test-tubes 
in  a  tumbler,  and  set  them  in  a  water-bath^at  40  t$. 

After  a  time  the  fibrin  will  have  almost  completely  disappeared  in 
A,  A',  and  F,  but  not  in  the  other  test-tubes.     Filter  the  contents  of 
A,  A',  and  F.  **Y(xf\ji     r^~  O^v^xt/c^^   "*A-  **JL    ^~ZL^<^<J-^(^O 
{^)-  Test  the  filtrate  for  the  produces  of  gastric  digestion  : 

(a)  Neutralize  a  portion  carefully  with  dilute  sodium 
hydrate.  A  precipitate  of  acid-albumin  may  be 
thrown  down.  Filter. 

(ft)  To  a  portion  of  the  filtrate  from  (a)  add  excess  of 
sodium  hydrate  and  a  drop  or  two  of  very  dilute 
copper  sulphate.  A  rose  colour  indicates  the 
presence  of  proteoses  or  peptones.  The  cupric 
sulphate  must  be  very  cautiously  added,  because  an 
excess  gives  a  violet  colour,  and  thus  obscures  the 
rose  reaction.  If  still  more  cupric  sulphate  be 
added,  blue  cupric  hydrate  is  thrown  down,  and 
nothing  can  be  inferred  as  to  the  presence  or  the 
nature  of  proteids  in  the  liquid. 

(y)  Heat  another  portion  of  the  filtrate  from  (a)  to  30°  C., 
and  add  crystals  of  ammonium  sulphate  to  satura- 
tion. A  precipitate  of  proteoses  (albumoses)  may 
be  obtained.  Filter  off. 

(8)  Add  to  the  filtrate  from  (y)  a  trace  of  cupric  sulphate 
and  excess  of  sodium  hydrate.  A  rose  colour  in- 
dicates that  peptones  are  present.  More  sodium 
hydrate  must  be  added  than  is  sufficient  to  break 
up  all  the  ammonium  sulphate,  for  the  biuret 
reaction  requires  the  presence  of  free  fixed  alkali. 
A  strong  solution  of  the  sodium  hydrate  should 
therefore  be  used,  or  the  stick  caustic  soda.  The 
addition  of  ammonium  sulphate  will  cause  the  red 
colour  to  disappear;  so  will  the  addition  of  an 
acid.  Sodium  hydrate  will  bring  it  back.  Ammonia 
does  not  affect  the  colour. 

(e)  To  some   milk  in  a  test-tube   add  a  drop  or  two  of  rennet 
extract,  and  place  in  a  bath  at  40°  C.     In  a  short  time  the  milk  is 
curdled  by  the  rennin. 
5-    ( i )  To  obtain  Normal  Chyme. — Inject  subcutaneously  into  a 


378  A  MANUAL  OF  PHYSIOLOGY 

dog,  one  and  a  half  hours  after  a  meal  of  meat,  2  mg.  of 
apomorphine.  One-half  of  one  of  the  ordinary  tabloids  is  enough. 
Collect  the  vomit. 

(2)  To  obtain  Pure  Gastric  Juice. — Put  a  fasting  dog  under  ether, 
and  fasten  on  the  holder.     Clip  the  hair  and  shave  the  skin  in  the 
middle   line   below   the    sternum.      Make   a   longitudinal   incision 

through  the  skin  and  subcutaneous  tissue 
from  the  xiphoid  cartilage  downwards  for 
3  or  4  inches.  The  linea  alba  will  now 
be  seen  as  a  white  mesial  streak,  Open 
the  abdomen  by  an  incision  through  it. 
Pull  over  the  stomach  towards  the  right, 
stitch  it  to  the  abdominal  wall,  open  it,  and 
FIG.  113.— STOMACH-  insert  a  stomach-cannula  (Fig.  113).  By 
CANNULA.  mechanically  stimulating  the  mucous 

membrane  of  the  stomach  with  a  feather, 

or  by  the  introduction  of  pieces  of  indiarubber,  a  flow  of  gastric 

juice  can  be  caused. 

(3)  (a)  Test  the  proteolytic  and  milk-curdling  powers  of  the  nitrate 
from  the  chyme  obtained  in  (i),  and  of  the  pure  juice  obtained 
in  (2).     Both  will  dissolve  fibrin,  but  probably  neither  will  curdle 
milk  when  neutralized.      For    the    gastric  juice  of  many  animals 
contains  no  rennin,  although  the  fully-formed  ferment  or  its  zymogen 
may   be   present  in  the   gastric   mucous   membrane.      The  rennet 
ferment  is  active  in  an  acid  or  neutral,  but  inactive  in  an  alkaline 
medium.      Examine   a   drop  of  the   unfiltered   chyme   under  the 
microscope.     Partially  digested  fragments  of  the  food  will  be  seen  — 
muscular  fibres,  or  fat  cells.     Filter,  and  proceed  as  in  4  (d}. 

(4)  Test  the  filtrate  from  the  chyme  and  the  gastric  juice  for 
lactic  acid  by  Ueffelmann's  test,  and  for  hydrochloric  acid  by  Giins- 
burg's  reagent. 

Ueffelmann's  Test  for  Lactic  Acid. — The  reagent  is  a  dilute  solu- 
tion of  carbolic  acid  to  which  a  trace  of  ferric  chloride  has  been 
added  (say  a  drop  of  a  i  per  cent,  ferric  chloride  solution  to  5  c.c. 
of  a  i  per  cent,  carbolic  acid  solution).  The  blue  colour  of  the 
mixture  is  turned  yellow  by  lactic  acid,  but  not  by  dilute  hydro- 
chloric acid ;  normal  healthy  gastric  juice  does  not  affect  it,  there- 
fore its  acidity  is  not  caused  by  free  lactic  acid. 

Giinsburg's  Reagent  for  Free  Hydrochloric  Acid  in  Gastric  Juice 
is  made  by  dissolving  2  parts  of  phloroglucinol  and  i  part  of  vanillin 
in  30  parts  by  weight  of  absolute  alcohol.  A  few  drops  of  the  reagent 
are  added  to  a  few  drops  of  the  filtered  gastric  juice  in  a  small 
porcelain  capsule,  and  the  whole  evaporated  to  dryness  over  a  small 
bunsen  flame.  If  free  hydrochloric  acid  is  present,  a  carmine-red 
residue  is  left.  If  all  the  hydrochloric  acid  is  united  to  proteids  in 
the  stomach  contents,  the  reaction  does  not  succeed.  It  is  also 
hindered  by  the  presence  of  leucin. 

6.  Pancreatic  Juice. — (a)  Take  a  piece  of  the  pancreas  of  an  ox 
or  dog  which  has  been  kept  twenty-four  hours  at  the  temperature  of 
the  laboratory,  and  make  a  glycerine  extract  in  the  same  way  as  in 


PRACTICAL  EXERCISES  379 

the  case  of  the  pig's  stomach  4,  (a).     Put  in  a  small  bottle,  and  set 
aside  for  a  day  or  two. 

(b)  Put  a  little  fibrin  into  each  of  six  test-tubes,  A,  B,  C,  D,  E,  F. 
To  A  add  a  few  drops  of  glycerine  extract  of  pancreas,  and  fill  up 
with  i  per  cent,  sodium  carbonate  solution ;  to  B  add  glycerine 
extract  and  distilled  water;  to  C  glycerine  extract  and  excess  of 
OT  per  cent,  hydrochloric  acid;  to  D  i  per  cent,  sodium  carbonate 
alone ;  to  E  i  per  cent,  sodium  carbonate  in  which  a  few  drops 
of  glycerine  extract  of  pancreas  has  been  previously  boiled ; 
to  F  glycerine  extract  and  excess  of  0-4  per  cent,  hydrochloric 
acid. 

Set  up  six  test-tubes,  A',  B',  C',  D',  E',  F',  in  the  same  way,  but 
substitute  a  few  drops  of  a  solution  of  commercial  pancreatin  for  the 
glycerine  extract.  Put  all  the  test-tubes  in  a  tumbler,  and  place  in 
a  bath  at  40°  C.  The  fibrin  will  be  gradually  eaten  away  in  A  and  A' 
by  the  action  of  the  trypsin,  but  will  not  swell  up  or  become  clear 
before  disappearing,  as  it  does  in  dilute  hydrochloric  acid  with 
glycerine  extract  of  stomach.  Filter  the  contents  of  these  test-tubes. 
Neutralize  the  filtrate  with  dilute  acid ;  a  precipitate  will  consist  of 
alkali-albumin.  If  such  a  precipitate  is  obtained,  filter  it  off  and  test 
the  filtrate  for  proteoses  and  peptones  as  in  4  (d\  p.  377.  Digestion 
will  also  have  taken  place  in  C  and  C',  but  not  in  the  other  test- 
tubes  (pp.  306,  354). 

(f)  Leucin  and  Tyrosin. — If  pancreatic  digestion  be  allowed  to  go 
on  for  some  time,  part  of  the  peptone  first  formed  may  be  broken  up 
into  leucin  and  tyrosin.  If  the  *  digest '  be  neutralized  to  separate 
alkali-albumin,  then  filtered,  and  the  filtrate  concentrated  and  allowed 
to  stand,  a  crop  of  tyrosin  crystals  will  separate  out,  since  tyrosin 
is  only  slightly  soluble  in  watery  solutions  of  neutral  salts.  These 
crystals  having  been  filtered  off,  the  proteoses  (albumoses)  and 
peptones  can  be  precipitated  together  by  alcohol,  and  afterwards 
separated,  if  that  is  desired,  by  redissolving  the  precipitate  in  water 
and  throwing  down  the  proteoses  by  saturation  with  ammonium 
sulphate.  The  alcoholic  filtrate  will  contain  any  leucin  that  may  be 
present,  since  that  body  is  moderately  soluble  in  alcohol,  as  well  as 
traces  of  tyrosin,  which,  however,  is  much  less  soluble  in  this  medium. 
On  concentration,  crystals  of  both  substances  will  be  obtained. 
Tyrosin  crystallizes  characteristically  from  animal  liquids  in  beautiful 
silky  needles  united  into  sheaves,  leucin  in  the  form  of  indistinct 
fatty-looking  balls,  often  marked  with  radial  striae  and  coloured  with 
pigment  (Figs.  122  and  123,  p.  394). 

(d)  Add  a  few  drops  of  the  glycerine  extract  to  a  test-tube  con- 
taining starch  mucilage,  which  has  been  previously  found  free  from 
reducing  sugar.  Put  in  a  bath  at  40°  C.  After  a  short  time  abund- 
ance of  reducing  sugar  will  be  found,  owing  to  the  action  of  the 
ferment,  amylopsin. 

7.*  To  obtain  Normal  Pancreatic  Juice. — (a)  Give  a  rabbit  f  grm. 
chloral  hydrate  per  rectum.     Put  on  a  holder.     Open  the  abdominal 
cavity  by  an  incision  in  the  linea  alba   2\  inches  long.     Pull  the 
*  This  experiment  is  only  suitable  for  advanced  students. 


:w     i   3  7tf 


380  A  MANUAL  OF  PHYSIOLOGY 

duodenum,  which  will  be  found  in  the  right  hypcchondrium,  through 
the  wound,  and  follow  it  down  till  its  mesentery  prevents  it  from 
coming  out  any  farther.  Here  the  pancreatic  duct  will  be  found. 
'  Resect  2  inches  of  the  intestine  at  this  point,  leaving  the 
mesenteric  attachment,  tie  the  cut  ends  of  the  intestine  above  and 
below,  and  drop  them  in  the  cavity,  bringing  the  resected  portion 
through  the  wound.'  Open  the  resected  piece  of  intestine  opposite 
the  mesenteric  attachment,  and  spread  it  out  on  the  abdominal  wall. 
Clamp  the  ends  to  stop  haemorrhage.  Push  into  the  pancreatic  duct 
a  small  glass  cannula  through  the  papilla  on  which  the  duct  opens. 
The  juice  begins  to  flow  immediately,  and  the  flow  lasts  four  to  six 
hours,  although  it  is  slow,  and  only  a  comparatively  small  quantity 
can  be  collected.  The  exposed  intestine  must  be  kept  moist  by 
pads  of  cotton-wool  soaked  in  normal  saline  (Rachford).  The 
animal  must  be  killed  as  soon  as  the  flow  has  ceased.  The  juice 
has  an  alkaline  reaction. 

(b)  With  the  juice  so  obtained  perform  the  following  experiments 
to  demonstrate  its  fat-splitting  action  \  Shake  a  little  of  it  with  neutral 
olive-oil ;  the  oil  becomes  acid  owing  to  the  formation  of  fatty  acid- 
Take  with  a  pipette  a  drop  of  the  oil  from  the  surface  of  the  mixture 
of  oil  and  pancreatic  juice,  and  put  it  on  a  J  per  cent,  solution 
of  sodium  carbonate   in  a  watch-glass.     An   emulsion  is    formed. 
Sodium  carbonate  and  neutral  olive-oil  do  not  form  an  emulsion ; 
some  fatty  acid  must  be  present. 

8.  Bile. — (a)  Test  the  reaction  of  ox  bile.     It  is  alkaline. 

(fr)  Add  dilute  acetic  acid.  A  precipitate  of  bile-mucin  (really 
nucleo-albumin)  falls  down.  Some  of  the  bile-pigment  is  also  pre- 
cipitated. Filter. 

(c)  Dilute  the  filtrate  from  (b).     Put  a  little  of  it  into  a  porcelain 
capsule,  add  a  few  drops  of  strong  sulphuric  acid,  and  a  drop  or 
two  of  a  dilute  solution  of  cane-sugar      A  purple  colour  appearing 
at  once,  or  after  gentle  heating,  shows  the  presence  of  bile-acids 
(Pettenkofer's  reaction).     Examine  the  purple  liquid  in  a  test-tube 
with  a  spectroscope  (p.  62).     Two  absorption  bands  are  seen,  one 
between  D  and  E,  the  other  between  E  and  F. 

(d)  Add  yellow  nitric  acid  (containing  nitrous 
acid)  to  a  little  bile  on  a  white  porcelain-slab. 
A  play  of  colours,  beginning  with  green  and 
running  through  blue  to  yellow  and  yellowish- 
brown,  indicates  the  presence  of  bile-p:gment 
(Gmelin's  reaction). 

(e)  Cholesterin    (Fig.    114). — Preparation. — 
Extract    a   powdered    gallstone   (preferably   a 
white  one)  with  hot  alcohol  and  ether  in  a  test- 
tube.     Heat  the  test-tube  in  warm  water.     Put 

FIG.  ii4.-CHOLEs-      a  drop  of  the  extract  on  a  siide.     Flat  crystals 

of  cholesterin,  often  chipped  at  the  corners, 
separate  out.  Carefully  allow  a  drop  of  strong  sulphuric  acid  and  a 
drop  of  dilute  iodine  to  run  under  the  cover-glass.  A  play  of  colours 
— violet,  blue,  green,  red — is  seen. 


PRACTICAL  EXERCISES  381 

Evaporate  a  drop  of  the  solution  of  cholesterin  in  a  small  porcelain 
capsule,  add  a  drop  of  strong  nitric  acid,  and  heat  gently  over  a 
flame.  A  yellow  stain  is  left,  which  becomes  red  when  a  drop  of 
ammonia  is  poured  on  it  while  it  is  still  warm. 

(/)  Preparation  of  Bile  Salts  from  Bile. — Evaporate  bile  to  a 
small  bulk,  mix  the  residue  with  animal  charcoal,  dry  to  a  paste  at 
1 00°  C.,  extract  with  absolute  alcohol,  and  precipitate  the  solution 
with  ether.  The  bile-salts  separate  as  a  mass  of  needle-shaped 
crystals,  often  in  sheaf-like  bundles.  On  dissolving  the  crystals  in 
water,  and  adding  dilute  sulphuric  acid  to  displace  the  bile-acids,  the 
latter  are  precipitated  as  crystalline  needles. 

(g)  To  demonstrate  the  Presence  of  Iron  in  the  Liver  Cells. — Steep 
sections  of  liver  in  a  solution  of  potassium  ferrocyanide,  and  then  in 
dilute  hydrochloric  acid.  They  become  bluish  from  the  formation 
of  prussian  blue.  A  fine-pointed  glass  rod  or  a  platinum  lifter  should 
be  used  in  manipulating  the  sections.  A  steel  needle  cannot  be 
employed.  Mount  in  glycerine  or  Farrant's  solution.  Blue  granules 
may  be  seen  under  the  microscope  in  some  of  the  hepatic  cells. 

(h}  To  some  starch,  shown  to  be  free  from  sugar,  add  a  little  bile, 
and  place  in  a  bath  at  40°.  After  a  time  test  for  reducing  sugar. 
Report  the  result. 

9.  Microscopical  Examination   of  FsBces. — Examine   under   the 
microscope  the  slides  provided.     Draw,  and  as  far  as  possible  deter- 
mine the  nature  of,  the  objects  seen  (p  358). 

10.  Absorption  of  Fat. — Feed  a  rat  or  frog  with  fatty  food;  kill 
the  rat  in  three  or  four  hours,  the  frog  in  two  or  three  days.     Strip 
off  tiny  pieces  of  the  mucous  membrane  of  the  small  intestine,  and 
steep  them  in  \  per  cent,  solution  of  osmic  acid  for  forty-eight  hours. 
Then  tease  fragments  of  the  mucous  membrane  in  glycerine,  take  off 
the  glycerine  with  blotting-paper,  mount  in  Farrant,  and  examine 
under  the  microscope.     Other  portions  of  the  mucous  membrane 
may  be  hardened  for  a  fortnight  in  a  mixture  of  2  parts  of  Miiller's 
fluid  and  i  part  of  a  i  per  cent,  solution  of  osmic  acid.     Sections 
are  then  made  with  a  freezing  microtome  after  embedding  in  gum. 
No  process  must  be  used  by  which  the  fat  would  be  dissolved  out 
(Schafer). 

ii. ;  Time  required  for  Digestion  and  Absorption  of  various  Food 
Substances. — Feed  three  dogs,  A,  B  and  C,  which  have  previously 
fasted  for  twenty-four  hours,  with  a  meal  containing  starch  (proved 
to  be  free  from  sugar),  lard  and  meat. 

(i)  After  fifteen  minutes  inject  subcutaneously  into  A  2  c.c.  of  a 
o'i  per  cent,  solution  of  apomorphine.  Note  the  time  which  elapses 
before  the  animal  vomits.  Collect  the  vomit. 

(a)  Examine  a  little  of  it  under  the  microscope,  and  make  out  fat 
globules,  muscular  fibres  and  starch  granules.  The  latter  can  be 

*  Experiments  11  and  12  are  conveniently  done  in  a  class  by  assigning 
each  of  the  three  animals  to  a  separate  set  of  students.  The  contents  of 
the  stomach  and  intestine  are  divided  into  three  portions,  so  that  each 
set  has  a  sample  from  each  dog. 


382  A  MANUAL  OF  PHYSIOLOGY 

recognised  by  their  being  coloured  blue  by  a  drop  or  two  of  iodine 
solution. 

(&)  Filter  the  chyme,  mixing  it,  if  necessary,  with  a  little  water, 
and  test  it  as  in  4  (d)  for  the  products  of  digestion.  In  addition,  test 
for  starch,  dextrin  and  reducing  sugar. 

(2)  One  and  a  quarter  hours  after  the  meal  inject  apomorphine 
into  dog  B,  and  proceed  as  in  (i). 

(3)  Two  and  a  half  hours  after  the  meal  inject  apomorphine  into 
dog  C,  and  proceed  as  in  (i).     Compare  the  results  from  the  three 
specimens  of  chyme. 

12*  Quantity  of  Cane-sugar  inverted  and  absorbed  in  a  Given 
Time. — Take  three  dogs,  A,  B  and  C,  which  have  fasted  for  twenty- 
four  hours.  Feed  A  and  B  with  50  c.c.  of  a  standard  solution  of  cane- 
sugar  (about  a  10  per  cent,  solution),  and  some  lard  to  render  the 
sugar  more  palatable.  If  the  dogs  have  been  kept  without  water  for 
a  day  they  will  more  readily  take  the  sugar  solution.  Feed  C  with 
10  grammes  of  powdered  cane-sugar  mixed  with  lard,  the  mixture 
being  rolled  into  little  balls. 

(1)  After  half  an  hour  put  A  under  chloroform  or  the  ACE  mixture  ; 
fasten  it  on  a  holder,  open  the  abdomen  in  the  linea  alba,  lift  a  loop 
of  the  small  intestine  gently  up   and   observe  the   lacteals  in  the 
mesentery.     Now  kill  the  animal,  tie  the  oesophagus,  place  double 
ligatures  on  the  pyloric  end  of  the  stomach  and  the  lower  end  of  the 
small  intestine,  and  divide  between  them.     Cut  out  the  stomach  and 
intestine ;  wash  their  contents  into  separate  vessels,  and  test  the  re- 
action with  litmus-paper.    Add  water  and  rub  up  thoroughly.    Filter. 
Wash  the  residue  repeatedly  with  small  quantities  of  water,  and  pass 
all  the  washings  through  the  filter.    Make  up  each  of  the  two  filtrates 
to  200  c.c. 

(a)  Examine  the  residue  microscopically  for  fat. 

(b)  Test  the  filtrates  from  the  contents  of  the  stomach  and  intes- 
tines qualitatively  for  glucose  by  Trommer's  (p.  23)  and  the  phenyl- 
hydrazine  test  (p.  426). 

(c)  If  no  reducing  sugar  is  present,  add  to  20  c.c.  of  each  filtrate 
i  c.c.  of  hydrochloric  acid,  boil  for  half  an  hour,  and  again  test  for 
reducing  sugar.     If  it  is  now  found,  some  cane-sugar  is  present. 

(d)  If  reducing  sugar  is  found,  estimate  its  amount  as  glucose  by 
Fehling's  solution  (p.  427)  in  a  measured  quantity  of  the  filtrate 
before  and  after  boiling  with  one-twentieth  of  its  volume  of  hydro- 
chloric acid. 

(<?)  Estimate  in  the  same  way  the  amount  of  the  glucose  in  the 
standard  solution  of  cane-sugar  after  inversion,  and  before  inversion 
if  it  gives  the  qualitative  test  for  reducing  sugar  before  it  has  been 
boiled  with  acid. 

From  the  data  obtained  (and  taking  95  parts  of  cane-sugar  as 
equal  to  100  parts  of  glucose)  calculate  the  amount  of  cane-sugar 
absorbed,  left  unchanged,  and  inverted,  though  not  absorbed. 

(2)  One  and   a   half  hours  after    the  meal  anaesthetize  B,   and 
proceed  as  in  (i). 

*  See  note,  p.  381. 


PRACTICAL  EXERCISES 


383 


(3)  Two  hours  after  the  meal  proceed  in  the  same  way  with  C. 
Compare  your  results. 

13.  Auto-digestion  of  the  Stomach. — In  some  of  the  previous 
experiments  the  stomach  of  an  animal  killed  during  digestion  should 
be  removed  from  the  body  after  double  ligation  of  oesophagus  and 
duodenum,  and  placed   in  a  water-bath  at  40°  C.     After  several 
hours  the  contents  should  be  washed  out,  and  the  mucous  membrane 
examined.     It  may  be  entirely  eaten  away  in  parts. 

14.  Time  required  for  Food  to  pass  through  the  Alimentary 
Canal. — Feed   a   dog   with   bones.     Keep   in   a   special  cage,  and 
observe  how  long  it  takes  before  the  easily-recognised  white  bone- 
faeces  appear. 


Submaxillary        Carotid 
Gland.  Artery. 


Chorda 
Tympani. 


Digastric 
Muscle  (cut). 


Lingual 
Nerve. 


W  barton's 
Duct. 


FIG.  1 1 5.— DISSECTION  FOR  STIMULATION  OF  CHORDA  TYMPASJ 
(AFTER  BERNARD). 


CHAPTER    VI. 
EXCRETION. 

WE  have  now  followed  the  ingoing  tide  of  gaseous,  liqui< 
and  solid  substances  within  the  physiological  surface  of  the 
body.  There  we  leave  them  for  the  present,  and  turn  to  the 
consideration  of  the  channels  of  outflow,  and  the  waste 
products  which  pass  along  them.  In  a  body  which  is 
neither  increasing  nor  diminishing  in  mass  the  outflow  must 
exactly  balance  the  inflow  ;  all  that  enters  the  body  must 
sooner  or  later,  in  however  changed  a  form,  escape  from  it 
again.  In  the  expired  air,  the  urine,  the  secretions  of  the 
skin,  and  the  fasces,  by  far  the  greater  part  of  the  waste  pro- 
ducts is  eliminated.  Thus  the  carbon  of  the  absorbed  solids 
of  the  food  is  chiefly  given  off  as  carbon  dioxide  by  the  lungs  ; 
the  hydrogen,  as  water  by  the  kidneys,  lungs  and  skin,  along 
with  the  unchanged  water  of  the  food  ;  the  nitrogen,  as  urea 
by  the  kidneys.  The  faeces  in  part  represent  unabsorbed 
portions  of  the  food.  A  small  and  variable  contribution  to 
the  total  excretion  is  the  expectorated  matter,  and  the  secre- 
tions of  the  nasal  mucous  membrane  and  lachrymal  glands. 
Still  smaller  and  still  more  variable  is  the  loss  in  the  form  ol 
dead  epidermic  scales,  hairs  and  nails.  The  discharges  from 
the  generative  organs  are  to  be  considered  as  excretions 
with  reference  to  the  parent  organism,  and  so  is  the  milk 
and  even  the  foetus  itself,  with  respect  to  the  mother. 

Excretion  by  the  lungs  and  in  the  faeces  has  been  already 
dealt  with.  All  that  is  necessary  to  be  said  of  the  expectora 
tion  and  the  nasal  and  lachrymal  discharges  is  that  th< 
first  two  generally  contain  a  good  deal  of  mucin,  and  an 
produced  in  small  mucous  and  serous  glands,  the  cells 


Plate  IV. 
3.  Crystals  of  phenyl  glucosazone  from  urine, 


lan'it 


rlobular  artery 


Malpighian  Ivft 


1.  Crystals  of  uric  acid 
from  urine. 


4.  Section  of  cortex  of  injected  kidney.  2.  Crystala  of  ammonium  urate 

from  urine. 


6.  Section  of  medulla  of  injected  kidney 
showing  vasa  recta  and  collecting  tubules. 


West. Newman  ciir  lifh. 


EXCRETION  385 

which  are  of  the  same  general  type  as  those  of  the  mucous 
and  serous  salivary  glands.  The  lachrymal  glands  are 
serous  like  the  parotid  ;  and  the  tears  secreted  by  them 
contain  some  albumin  and  salts,  but  little  or  no  mucin.  The 
sexual  secretions  and  milk  will  be  best  considered  under 
reproduction  (Chap.  XIV.),  so  that  there  remain  only  the 
urine  and  the  secretions  of  the  skin  to  be  treated  here. 

I.  Excretion  by  the  Kidneys. 

The  Chemistry  of  the  Urine.  —  Normal  urine  is  a  clear 
yellow  liquid  of  acid  reaction,  and  with  an  average  specific 
gravity  of  about  1020,  the  usual  limits  being  1015  and  1025, 
although  when  water  is  taken  in  large  quantities,  or  long 
withheld,  the  specific  gravity  may  fall  to  1005,  or  even  less, 
or  rise  to  1035,  or  even  more.  The  quantity  passed  in 
twenty-four  hours  is  very  variable,  and  is  especially 
dependent  on  the  activity  of  the  sweat-glands,  being,  as  a 
rule,  smaller  in  summer  when  the  skin  sweats  much,  than 
in  winter  when  it  sweats  little.  The  average  quantity  for 
an  adult  male  is  1200  to  1500  c.c.  (say,  40  to  50  oz.).* 

Composition  of  Urine. — It  is  essentially  a  solution  of  urea 
and  inorganic  salts,  the  proportion  of  the  latter  being  about  IA/LC  ^  = 
i'5  per  cent.,  or  double  the  usual  amount  in  physiological 
solids  and  liquids.     Besides  urea,  there  are  other  nitrogenous 
^bodies  in  much  smaller  quantity,  such  asjiric  acid  and  the 
-allied  xanthin  bases.  Jiy^urkjuui  and  kreatinin.     Some  of  I ,    \ 
these  at  least  are  products  of  the  metabolism  of  proteids 
within  the  tissues ;  and  besides  the  inorganic  salts  there  areTT^f-^Xt 
certain  organic  bodies — indol,  phenol,  pyrokatechin,  skatol 
—united  with  sulphuric  acid,  which  are  primarily  derived  c^ 
'"  from  the  products  of  the  putrefaction  of  proteids  within  the 
^digestive  tube.     In  tabular  form  the  composition  of  urine, 

The  average  quantity  of  urine  varies  not  only  with  the  season,  but 


1166  c.c.  The  highest  average  in  any  one  individual  for  the  observation 
period  was  1487  c.c.  (for  seven  days),  and  the  lowest  743  c.c.  (for  eight 
days).  The  greatest  quantity  passed  in  any  one  period  of  twenty-four 
hours  was  2286  c.c.  (by  the  individual  whose  average  was  the  highest). 
The  smallest  quantity  passed  in  twenty-four  hours  was  650  c.c.  (by 
individual  whose  average  was  the  lowest). 


386 


A  MANUAL  OF  PHYSIOLOGY 


and  the  total  excretion  by  an  average  man  of  70  kilos,  may 
be  given  thus  : 

Per  1000.  In  24  hours. 

-  960  1440  grammes 

-  40  60 


Water 
Solids 

Urea  - 

Uric  acid  and  xanthin  bases 

Hippuric  acid 

Kreatinin 

Sodium 

Potassium 

Ammonia 

Calcium  and  magnesium 

Chlorine 

Phosphoric  acid 

Sulphuric  acid 

Mucus,  pigment,  etc. 


20 


r8 


o«5 

10 

2'5 

075 
075 
7 
3'5 

2 


3275  grammes. 


26' 5  grammes. 


The  acidity  of  urine  is  not  due  to  free  acid,  for  the  tests  which 
reveal  the  presence  of  free  acid  in  a  mixture,  such  as  the  precipitation 
of  sulphur  on  the  addition  of  sodium  hyposulphite,  and  the  change 
of  colour  of  many  organic  substances,  give  a  negative  result  when 
applied  to  urine.  The  acidity  is  chiefly  due  to  the  acid  phosphates 
of  sodium  and  potassium ;  in  a  less  degree  to  dissolved  carbon 
dioxide.  That  a  considerable  proportion  of  the  phosphoric  acid  is 
normally  present  in  the  form  of  acid  sodium  phosphate  (NaH2PO4) 
is  shown  by  the  fact  that  barium  chloride  usually  precipitates  only 
about  40  per  cent,  of  the  phosphoric  acid,  leaving  the  rest  in  solution. 
Now,  barium  chloride  does  not  cause  a  precipitate  in  a  dilute  solution 
of  acid  sodium  phosphate,  but  does  precipitate  the  disodium-hydrogen 
phosphate  (Na2HPO4).  The  acidity  is  estimated  by  running  into  a 
given  quantity  of  urine  a  dilute  solution  of  sodium  hydrate,  which  has 
been  previously  titrated  with  a  pure  acid  solution  (say,  oxalic  acid) 
of  known  strength,  until  a  neutral  reaction  is  just  obtained.  From 
the  amount  of  sodium  hydrate  required  the  acidity  can  be  calculated 
in  terms  of  the  standard  acid.  Normally  the  acidity  of  urine  is  about 
equal  to  that  of  a  o'  i  per  cent,  solution  of  sulphuric  acid.  It  diminishes 
I  distinctly,  or  even  gives  place  to  alkalinity,  during  digestion  when 
!"<*-  tU^£A~  the  acid  of  the  gastric  juice  is  being  secreted,  and  varies  with  the 
( quantity  of  vegetable  food  in  the  diet.  The  urine  of  herbivora  is 
alkaline,  and  turbid  from  precipitated  carbonates  and  phosphates  of 
earthy  bases,  while  that  of  carnivora  and  of  fasting  herbivora,  which 
are  living  on  their  own  tissues,  is  strongly  acid  and  clear.  Normal 
human  urine  may  deposit  urates  soon  after  discharge,  as  they  are 
more  soluble  in  warm  than  in  cold  water.  They  carry  down  some 
of  the  pigment,  and  therefore  usually  appear  as  a  pink  or  brick-red 
sediment.  When  urine  is  allowed  to  stand  after  being  voided,  what 
is  generally  described  as  '  acid  fermentation '  occurs.  The  acidity 
gradually  increases,  owing  apparently  to  the  formation  of  lactic  acid ; 
acid  sodium  urate  is  produced  from  the  neutral  urate,  and  comes  down 
in  the  form  of  amorphous  granules,  while  the  liberated  uric  acid  is 
deposited  often  in  'whetstone'  crystals,  coloured  yellow  by  the  pigmen 


EXCRETION 


387 


(Fig.  116  ;  Plate  IV.,  i).  Calcium  oxalate  may  also  be  thrown  down 
as  '  envelope,  X  b,  or,  less  frequently,  'sand-glass'  crystals,  c (Fig.  117). 
If  the  urine  is  allowed  to  stand  for  a  few  days,  especially  in  a  warm 
place,  or  in  a  place  where  urine  is  decomposing,  the  reaction  becomes 
ultimately  strongly  alkaline,  owing  to  the  formation  of  ammonium 
carbonate  from  urea  by  the  action  of  micro-organisms  (Micrococcus 
ure<z>  Bacterium  urea,  and  others)  which  reach  it  from  the  air,  and 


FIG.  116.—  Ufcic  ACID. 


FIG.  117.— CALCIUM  OXALATE. 


produce  a  soluble  ferment,  in  whose  presence  the  urea  is  split  up 
under  absorption  of  water.     Thus  : 

CON2H4  +  2  H2O     =     (NH4)2CO3. 

Urea.  Ammonium  carbonate. 

The  substances  insoluble  in  alkaline  urine  are  thrown  down,  the 
deposit  containing  ammonio-magnesic  or  triple  phosphate^  formed 
by  the  union  of  ammonia  with  the  magnesium  phosphate  present  in 
fresh  urine,  and  precipitated  as  clear  crystals  of  '  knife-rest '  or  *  coffin- 
lid  '  shape  (Fig.  118),  along  with  amorphous  earthy  phosphates,  and 
often  acid  ammonium  urate  in 
the  form  of  dark  balls  occa- 
sionally covered  with  spines 
(Plate  IV.,  2). 

It  is  only  in  pathological  con- 
ditions that  this  alkaline  fermen- 
tation takes  place  within  the 

bladder.  The  reaction  of  the  FIG.  118.— TRIPLE  PHOSPHATE. 
urine  can  readily  be  made  alka- 
line by  the  administration  of  alkalies,  alkaline  carbonates,  or  the 
salts  of  vegetable  acids  like  malic,  citric,  and  tartaric  acid,  which 
are  broken  up  in  the  body  and  form  alkaline  carbonates  with  the 
alkalies  of  the  blood  and  lymph.  It  is  not  so  easy  to  increase  the 
acidity  of  the  urine,  although  mineral  acids  do  so  up  to  a  certain 
limit.  If  the  administration  of  acid  be  pushed  farther,  ammonia  is 
split  off  from  the  proteids,  and  is  excreted  in  the  urine  as  the 
ammonium  salt  of  the  acid. 

Urea,  CO(NH2)2,  is  the  form  in  which  by  far  the  greater  part  of 
the  nitrogen  is  discharged  from  the  body.  Its  amount  is  as  im- 
portant a  measure  of  proteid  metabolism  as  the  quantity  of  carbon 
dioxide  given  out  by  the  lungs  is  of  the  oxidation  of  carbonaceous 
material.  It  is  soluble  in  water  and  in  alcohol,  and  crystallizes  from 

25—2 


A  MANUAL  OF  PHYSIOLOGY 


its  solutions  in  the  form  of  long  colourless  needles,  or  four-sided 
prisms  with  pyramidal  ends  (p.  419). 

Uric  acid  (C5H4N4O3)  exists  in  large  amount  in  the  urine  of  birds. 
The  excrement  of  serpents  consists  almost  entirely  of  uric  acid.  In 
man  and  mammals  the  quantity  is  comparatively  small  in  health,  but 
is  increased  after  a  meal,  particularly  one  containing  substances  rich 
in  nucleo-proteids,  e.g.,  the  thymus  of  the  calf. 

The  xanthin  bases  are  a  group  of  substances  allied  to  uric  acid, 
and  including,  besides  xanthin  itself  (C5H4N4O2),  hypoxanthin 
(C5H4N4O),  guanin  and  other  bodies.  They  exist  in  very  small 
amount  in  urine,  but,  like  uric  acid,  are  increased  in  amount  by  the 
ingestion  of  nucleo-proteids. 

Hippuric  acid  (C9H9NO3)  occurs  in  considerable  quantity  in  the 
urine  of  herbivora;  in  the  urine  of  carnivora  and  of  man  only  in 
traces  ;  in  that  of  birds  not  at  all.  It  is  much  more  dependent  on 
the  presence  of  particular  substances  in  the  food  than  the  other 
organic  constituents  of  urine.  Anything  which  contains  benzoic 


FIG.  119.— KREATIN. 


FIG.  120.— KREATININ-ZINC-CHLORIDE. 


acid,  or  substances  which  can  be  readily  changed  into  it  (such  as 
cinnamic  and  quinic  acids),  causes  an  increase  of  the  hippuric  acid  in 
urine.  In  fact,  one  of  the  best  ways  of  obtaining  the  latter  is  from 
the  urine  of  a  person  to  whom  benzoic  acid  is  given  by  the  mouth  ; 
the  sweat  may  also  in  this  case  contain  a  trace  of  hippuric  acid. 
Chemically  it  is  a  conjugated  acid  formed  by  the  union  of  benzoic 
acid  and  glycin.  Thus  : 


CrH602 

Benzoic  acid. 


C2H5N02 

Glycin. 


C9H9N03 

Hippuric  acid. 


H2O. 

Water. 


Benzoic  acid,  therefore,  meets  glycin  in  the  body,  and  combines  with 
it,  as  fatty  acids  meet  glycerine  and  combine  with  it.  But  neither 
free  glycin  nor  free  glycerine  have  been  detected  in  the  blood  or 
tissues  (p.  424). 

Kreatinin  (C4H7N3O)  has  only  been  found  as  a  constant  con- 
stituent in  the  urine  of  man  and  a  few  other  mammals.    It  is  possibly 


EXCRETION  389    0 

the  form  in  which  the  kreatin  of  muscle  leaves  the  body.  Its  formula 
differs  from  that  of  kreatin  only  in  possessing  the  elements  of  one 
molecule  of  water  less ;  and  kreatinin  can  be  obtained  by  boiling 
kreatin  with  dilute  sulphuric  acid,  then  neutralizing  with  barium 
carbonate,  filtering,  evaporating  the  filtrate  to  dryness  on  the  water- 
bath,  and  extracting  the  residue  with  alcohol.  From  its  alcoholic 
solution  it  crystallizes  in  colourless  prisms.  It  forms  crystalline 
compounds  with  zinc  chloride  and  other  salts  (p.  424). 

Pigments  of  Urine. — The  pigments  of  urine  have  not  hitherto 
been  exhaustively  studied ;  but  we  already  know  that  normal  urine 
contains  several,  and  pathological  urines  probably  additional,  pig- 
mentary substances.  The  best-known  pigments  in  normal  urine  are 
urochrome,  the  yellow  substance  which  gives  the  liquid  its  ordinary 
colour ;  uroerythrin,  the  pink  pigment  which  often  colours  the 
deposits  of  urates  that  separate  even  from  healthy  urine ;  and 
urobilin,  sometimes  termed  normal  urobilin,  to  distinguish  it  from 
the  so-called  febrile  urobilin,  which,  as  has  been  already  mentioned, 


FIG.  121. — PEPSIN  IN  URINE.        DIASTATIC  FERMENT  IN  URINE, 
Ax  DIFFERENT  TIMES  OF  THE  DAY  (HOFFMANN). 

is  identical  with  the  faecal  pigment  stercobilin,  and  occurs  not  only 
in  many  febrile  conditions,  but  also  in  cases  with  no  fever,  such  as 
functional  derangements  of  the  liver,  dyspepsia,  chronic  bronchitis, 
and  valvular  diseases  of  the  heart.  Normal  and  febrile  urobilin  are 
said  to  present  certain  spectroscopic  differences,  but  are  probably 
one  and  the  same  substance. 

The  pigments  of  the  blood  and  bile  and  some  of  their  derivatives 
are  of  common  occurrence  in  the  urine  in  disease,  ffamatopor- 
phyrin  has  not  only  been  found  in  some  pathological  conditions,  but 
appears  to  be  constantly  present  in  minute  traces  in  normal  urine. 
In  paroxysmal  hsemoglobinuria,  methamoglobin  is  found  in  the  urine 
in  large  amount ;  and  it  is  worthy  of  note  that  it  is  not  formed  in  the 
urine  after  secretion,  but  is  already  present  as  such  when  it  reaches 
the  bladder. 

Ferments. — The  urine  contains  traces  of  proteolytic  and  amylolytic 
ferments  (Fig.  121). 

Of  the  inorganic  constituents  of  urine  the  most  important 


39o  A  MANUAL  OF  PHYSIOLOGY 

and  most  easily  estimated  are  the  chlorine,  phosphoric  acid, 
and  sulphuric  acid. 

Chlorine.— Much  the  greater  part  of  the  chlorine  is  united  with 
sodium,  a  smaller  amount  with  potassium.  The  chlorides  of  the 
urine  are  undoubtedly  to  a  great  extent  derived  directly  from  the 
chlorides  of  the  food,  and  have  not  the  same  metabolic  significance 
as  the  organic,  and  even  as  some  of  the  other  inorganic  consti- 
tuents. But  it  is  noteworthy  that  in  certain  diseased  conditions  the 
chlorine  may  disappear  entirely  from  the  urine,  or  be  greatly 
diminished,  e.g.,  in  pneumonia,  and  in  general  in  cases  in  which 
much  material  tends  to  pass  out  from  the  blood  in  the  form  of 
effusions  (p.  416). 

Phosphoric  Acid.— The  phosphoric  acid  of  the  urine  is  chiefly 
derived  from  the  phosphates  of  the  food,  but  must  partly  come  from 
the  waste  products  of  tissues  rich  in  phosphorus-containing  sub- 
stances, such  as  lecithin  and  nuclein.  The  phosphoric  acid  is  united 
partly  with  alkalies,  especially  as  acid  sodium  phosphate,  and  partly 
with  earthy  bases,  as  phosphates  of  calcium  and  magnesium.  The 
earthy  phosphates  are  precipitated  by  the  addition  of  an  alkali  to 
urine,  or  in  the  alkaline  fermentation.  In  some  pathological  urines 
they  come  down  when  the  carbon  dioxide  is  driven  off  by  heating ;  a 
precipitate  of  this  sort  differs  from  heat-coagulated  albumin  in  being 
readily  soluble  in  acids  (p.  417). 

Sulphuric  Acid.  —  This  is  only  to  a  slight  extent  derived  from 
ready-formed  sulphates  in  the  food.  The  greater  part  of  it  is  formed 
by  oxidation  of  the  sulphur  of  proteids.  About  nine-tenths  of  the 
sulphuric  acid  of  normal  urine  are  united  to  alkalies ;  the  other  tenth 
is  combined,  in  the  form  of  ethereal  sulphates,  with  aromatic  bodies 
derived  from  the  putrefaction  of  proteids  in  the  intestine.  Such  are 
potassium -phenyl-sulphate  (C6H5KSO4),  potassium -kresyl- sulphate 
(C7H7KSO4),  potassium-indoxyl-sulphate  (C8H6NKSO4),  potassium- 
skatoxyl-sulphate  (C9H8NKSO4),  and  two  double  sulphates  of  potas- 
sium and  pyrocatechin.  Most  of  those  aromatic  compounds  are 
present  in  greater  amount  in  the  urine  of  the  horse  than  in  the  normal 
urine  of  man  ;  but  in  disease  the  quantity  in  the  latter  may  be  much 
increased;  and  to  a  certain  extent  it  must  be  looked  upon  as  an 
index  of  the  intensity  of  putrefactive  processes  in  the  intestine  and  of 
absorption  from  it.  Munk  made  the  curious  observation  that  in  the 
urine  of  a  starving  dog  the  phenol-forming  substances  are  absent, 
while  in  the  urine  of  a  starving  man  they  are  present  in  abnormally 
large  amount.  The  indigo-forming  substances  ('  indican '),  on  the 
other  hand,  are  in  hunger  excreted  in  considerable  quantity  by  the 
dog,  and  not  at  all  by  man  (p.  418). 

Phenol  and  kresol  can  easily  be  obtained  from  horse's  urine  by 
mixing  it  with  strong  hydrochloric  acid,  and  distilling.  These  aromatic 
bodies  pass  over  in  the  distillate.  Pyrocatechin  remains  behind, 
and  can  be  extracted  by  ether ;  it  gives  a  green  colour  with  ferric 
chloride,  which  becomes  violet  on  the  addition  of  sodium  carbonate. 

A  small  amount  of  phosphorus  and  of  sulphur  may  appear  in  the 


EXCRETION  391 

urine  in  less  oxidized  forms  than  phosphoric  and  sulphuric  acids. 
Such  sulphur  compounds  are  potassium  sulphocyanide,  which  is 
probably,  in  part  at  least,  derived  from  that  of  the  saliva ;  and  ethyl 
sulphide,  a  substance  with  a  penetrating  odour,  which  appears  to  be 
a  constant  constituent  of  dogs'  urine  (Abel). 

Thiosulphuric  acid   (H2S2O3)  occurs  almost  constantly  in  cat's 
urine,  often  in  dog's.     It  is  not  free,  but  combined  with  bases. 

The  Urine  in  Disease. — Although,  strictly  speaking,  a  truly  T 
pathological  urine  has  no  place  in  physiology,  the  line  which 
separates  the  urine  of  health  from  that  of  disease  is  often 
narrow,  sometimes  invisible ;  while  the  study  of  abnormal 
constituents  is  not  only  of  great  importance  in  practical 
medicine,  but  throws  light  upon  the  physiological  processes 
taking  place  in  the  kidney,  and  upon  the  general  problems  of 
metabolism.  Even  in  health  the  quantity  of  the  urine,  its 
specific  gravity,  its  acidity,  may  vary  within  wide  limits.  A 
hot  day  may  increase  the  secretion  of  sweat,  and  correspond- 
ingly diminish  the  secretion  of  urine,  and  the  deficiency  of 
water  may  lead  to  a  deposit  of  brick-red  urates.  A  meal 
rich  in  fruit  or  vegetables  may  render  the  urine  alkaline,  and 
its  alkalinity  may  determine  a  precipitate  of  earthy  phos- 
phates. But  neither  the  scanty  acid  urine,  with  its  sediment 
of  urates,  nor  the  alkaline  urine  with  its  sediment  of  phos- 
phates, comes  under  the  heading  of  pathological  urines ; 
the  deviation  from  the  normal  does  not  amount  to  disease. 
The  maximum  deviation  from  the  line  of  health  is  the  total 
suppression  of  the  urine.  If  this  lasts  long,  a  train  of 
symptoms,  of  which  convulsions  may  be  one  of  the  most 
prominent,  and  which  are  grouped  under  the  name  of 
uraemia,  appears.  At  length  the  patient  becomes  comatose, 
and  death  closes  the  scene.  Suppression  of  urine  may  be 
the  consequence  of  many  pathological  conditions,  but  there 
is  one  case  on  record  which,  in  the  human  subject,  in  effect, 
though  not  in  intention,  belongs  to  experimental  physiology. 
A  surgeon  diagnosed  a  floating  kidney  in  a  woman.  With 
a  natural  impatience  of  loose  odds  and  ends  of  this  sort,  he 
offered  to  remove  it,  and  in  an  evil  hour  the  patient  con- 
sented. The  surgeon,  a  perfectly  skilful  man,  who  acted  for 
the  best,  and  to  whom  no  blame  whatever  attached,  carried 
the  kidney  to  a  well-known  pathologist  for  examination. 


392  A  MANUAL  OF  PHYSIOLOGY 

The  latter,  to  the  horror  of  the  operator,  suggested,  from 
the  appearance  of  the  organ,  that  it  was  the  only  kidney 
the  woman  possessed.  This  turned  out  to  be  the  fact. 
Not  a  drop  of  urine  was  passed.  Apart  from  this  ominous 
symptom,  all  went  well  for  seven  or  eight  days ;  but  then 
ursemic  troubles  came  on,  and  the  patient  died  on  the 
eleventh  or  thirteenth  day  after  the  operation.  The  autopsy 
showed  that  her  only  kidney  had  been  taken  away. 

In  disease  the  urine  may  contain  abnormal  constituents, 
or  ordinary  constituents  in  abnormal  amounts.  Of  the 
normal  constituents  which  may  be  altered  in  quantity,  the 
most  important  are  the  water,  the  inorganic  salts,  the  urea, 
the  uric  acid,  and  the  aromatic  substances. 

Water.  —  A  marked  and  persistent  diminution  in  the 
quantity  of  urine,  that  is  to  say,  practically  in  the  water,  with 
or  without  an  increase  in  the  specific  gravity,  is  suggestive 
of  disorganization  of  the  renal  epithelium.  In  some  infective 
diseases  the  kidney  is  liable  to  be  secondarily  involved,  its 
secreting  cells  being  perhaps  crippled  in  the  attempt  to 
eliminate  the  bacterial  poisons.  In  the  form  of  parenchy- 
matous  or  tubal  nephritis  which  so  frequently  complicates 
scarlet  fever,  the  quantity  of  urine  has  in  some  cases  fallen 
to  50  or  60  c.c.  in  the  twenty-four  hours. 

In  interstitial  nephritis,  on  the  other  hand,  where  the 
structural  changes  in  the  tubules  are  for  a  long  time  at  least 
comparatively  circumscribed,  the  quantity  of  urine  is  often 
increased,  seldom  diminished.  In  these  cases  the  increase 
in  the  blood-pressure,  associated  with  hypertrophy  of  the 
heart,  may  be  considered  responsible  for  the  exaggerated 
renal  secretion.  In  diabetes  mellitus  the  quantity  of  urine 
is  greatly  increased,  perhaps  in  some  cases  because  more 
urea  is  excreted  than  normal  and  urea  acts  as  a  diuretic, 
perhaps  also  because  the  elimination  of  sugar  draws  with  it 
an  increased  excretion  of  water  to  hold  it  in  solution. 

Inorganic  Salts.— The  changes  in  the  quantity  of  the  in- 
organic constituents  of  the  urine  in  disease  are  not,  in  the 
present  state  of  our  knowledge,  of  as  much  importance  as 
the  changes  in  the  organic  constituents.  The  chlorides  may 
totally  disappear  from  the  urine  in  pneumonia,  and  their 


EXCRETION  393 

reappearance  after  the  crisis  is,  so  far  as  it  goes,  a  favour- 
able symptom.  In  most  cases  in  which  the  quantity  of  the 
urine  is  markedly  lessened,  all  the  inorganic  substances  are 
diminished  in  amount. 

Urea. — The  quantity  of  urea  is,  as  a  rule,  increased  in 
fever,  either  absolutely  or  in  proportion  to  the  amount  of 
nitrogen  in  the  food.  In  the  interstitial  varieties  of  kidney 
disease  the  urea  is  usually  not  diminished,  but  when  the 
stress  of  the  change  falls  on  the  tubules  (parenchymatous 
nephritis),  it  is  distinctly  decreased — it  may  be  even  to  one- 
twentieth  of  the  normal. 

Uric  acid  is  diminished  in  the  urine  in  gout  (perhaps  to 
one-ninth  of  the  normal),  not  only  during  the  paroxysms, 
but  in  the  intervals.  It  accumulates  in  the  blood  and  tissues, 
and,  as  sodium  urate,  may  form  concretions  in  the  joints, 
the  cartilage  of  the  ear,  and  other  situations.  Watson 
relates  the  case  of  a  gentleman  who  used  to  avail  himself  of 
his  resources  in  this  respect  by  scoring  the  points  at  cards 
on  the  table  with  his  chalky  knuckles.  In  leukaemia  the 
quantity  of  uric  acid  and  xanthin  bases  in  the  urine  is 
greatly  increased. 

The  aromatic  bodies,  of  which  indoxyl  may  be  taken  as  the 
type,  are  increased  when  the  conditions  of  disease  favour 
the  growth  of  bacteria  in  the  intestine,  e.g.,  in  cholera,  acute 
peritonitis,  carcinoma  of  the  stomach.  A  marked  increase 
in  the  amount  of  the  *  paired  '  sulphuric  acid  in  the  urine  is 
to  be  taken  as  an  indication  that  the  bacteria  are  gaining 
the  upper  hand  in  the  intestinal  tract ;  a  marked  diminution 
is  usually  a  sign  that  the  battle  has  begun  to  turn  in  favour 
of  the  organism  (Practical  Exercises,  p.  418). 

Sugar,  proteids,  the  pigments  of  bile  and  blood,  or  their  derivatives, 
are  the  most  important  abnormal  substances  found  in  solution  in  the 
urine.  Toxalbumins  produced  by  bacterial  action  have  also  been 
demonstrated  in  the  urine  in  certain  diseases,  as  in  erysipelas  (Brieger 
and  Wassermann).  Red  blood  -  corpuscles  and  leucocytes  (pus 
corpuscles,  white  blood-corpuscles,  mucus  corpuscles)  are  the  chief 
organized  deposits ;  but  spermatozoa  may  occasionally  be  found,  as 
well  as  pathogenic  bacteria,  e.g.,  the  typhoid  bacillus ;  and  in  disease 
of  the  kidney  casts  of  the  renal  tubules  are  not  uncommon.  These 
tube-casts  may  be  composed  chiefly  of  red  blood-corpuscles,  or  of 
leucocytes,  or  of  the  epithelium  of  the  tubules,  sometimes  Uttily 


394 


A  MANUAL  OF  PHYSIOLOGY 


degenerated,  or  of  structureless  proteid,  or  of  amyloid  substance. 
Abnormal  crystalline  substances,  such  as  leucin,  tyrosin,  and  cystin, 
may  be  on  rare  occasions  found  in  urinary  sediments  ;  but  generally 
the  unorganized  deposits  of  pathological  urine  consist  of  bodies 
actually  present  in,  or  obtainable  from,  the  normal  secretion,  but 
present  in  excess,  either  absolutely,  or  relatively  to  the  solvent  power 
of  the  urine. 

Sugar. — In  diabetes  mellitus,  although  the  quantity  of  urine  is 
usually  much  increased,  its  specific  gravity  is  above  the  normal ;  and 
this  is  due  chiefly  to  the  presence  of  sugar  (glucose),  which  generally 
amounts  to  i  to  5  per  cent.,  but  may  in  extreme  cases  reach  10  or 
even  15  per  cent.,  more  than  half  a  kilogramme  being  sometimes 
given  off  in  twenty-four  hours. 

The  name  of  the  tests  for  glucose  is  legion.     They  are  mostly 


FIG.  122. — LEUCIN  CRYSTALS. 


FIG.  123.— TYROSIN  CRYSTALS. 


founded  on  its  reducing  action  in  alkaline  solution.  Hydrated  oxide 
of  bismuth  (Boettcher),  salts  of  gold,  platinum  and  silver,  indigo 
(Mulder),  and  a  host  of  other  substances,  are  reduced  by  glucose, 
and  may  be  used  to  show  its  presence.  The  reduction  of  cupric 
salts  (Trommer)  and  the  formation  of  crystals  of  phenyl-glucosazone 
(Plate  IV.,  3)  are  perhaps  the  best  established  tests.  (See  Practical 
Exercises,  p.  426). 

Proteids.  —  Serum-albumin  and  serum-globulin  are  the  proteids 
most  commonly  found  in  pathological  urine.  Both  are  coagulated 
by  heating  the  urine,  slightly  acidulated,  if  it  is  not  already  acid,  or 
by  the  addition  of  strong  nitric  acid  in  the  cold.  Proteoses  (albu- 
moses)  and  peptones  are  also  occasionally  present,  and  may  be 
recognised  by  the  tests  given  in  the  Practical  Exercises  (p.  424). 

The  pigments  of  blood  and  bile  may  be  detected  by  the  char- 
acters described  in  treating  of  these  substances;  the  spectrum  of 
oxyhsemoglobin,  or  methsemoglobin,  or  any  of  the  other  derivatives 
of  haemoglobin,  with  the  formation  of  hsemin  crystals,  would  afford 
proof  of  the  presence  of  the  former,  and  Gmelin's  test  of  the  latter. 
The  red  blood-corpuscles,  seen  with  the  microscope,  are  the  most 
decisive  evidence  of  the  presence  of  blood,  as  leucocytes  in  abundance 
are  of  the  presence  of  pus.  It  should  be  remembered  that  pus  in 
the  urine  of  women  has  sometimes  no  significance  except  as  showing 
that  there  has  been  an  admixture  of  leucorrheal  discharge  from  the 
vagina.  (See  Practical  Exercises,  pp.  62,  66,  380). 


EXCRETION  395 

The  Secretion  of  the  Urine. — We  have  now  to  consider  the 
mechanism  by  which  the  urine  is  formed  in  the  kidney 
from  the  materials  brought  to  it  by  the  blood.  And  here  the 
same  questions  arise  as  have  already  been  discussed  in  the 
case  of  the  salivary  and  other  digestive  glands :  (i)  Are  the 
urinary  constituents,  or  any  of  them,  present  as  such  in  the 
blood  ?  (2)  If  they  do  exist  in  the  blood,  are  they  separated 
from  it  by  processes  mainly  physical  or  mainly  vital — in 
other  words,  by  filtration  and  diffusion,  or  by  the  selective 
action  of  living  cells  ?  In  the  case  of  the  digestive  juices 
it  has  been  seen  that  some  constituents  are  already  present 
in  the  blood,  but  that  physical  laws  alone  cannot  explain  the 
proportions  in  which  they  occur  in  the  secretions,  nor  the 
conditions  under  which  they  are  separated ;  while  other 
constituents — and  these  the  more  specific  and  important — 
are  manufactured  in  the  gland-cells. 

In  the  kidneys  the  conditions  seem  at  first  sight  favourable 
to  physical  filtration,  as  opposed  to  physiological  secretion. 
Urine  has  been  described  as  essentially  a  solution  of  urea 
and  salts,  and  both  are  ready  formed  in  the  blood.  The 
arrangement  of  the  bloodvessels,  too,  suggests  an  apparatus 
for  filtering  under  pressure. 

Bloodvessels  and  Secreting  Tubules  of  Kidney. — The  renal  artery 
splits  up  at  the  hilus  into  several  branches,  which  pass  in  between 
the  Malpighian  pyramids,  and  form  at  the  boundary  of  the  cortex 
and  medulla  vascular  arches,  from  which  spring,  on  the  one  side,  inter- 
lobular  arteries  running  up  into  the  cortex  between  the  pyramids  of 
Ferrein,  and,  on  the  other,  vasa  recta  running  down  into  the  boundary 
layer  of  the  medulla.  The  interlobular  arteries  give  off  at  intervals 
afferent  vessels;  each  of  these  soon  breaks  up  into  a  glomerulus  or 
tuft  of  vascular  loops,  which  gather  themselves  up  again  into  a  single 
•efferent  vessel  of  somewhat  smaller  calibre  than  the  afferent.  The 
glomerulus  is  fitted  into  a  cup  or  capsule  (of  Bowman),  which  is 
•closely  reflected  over  it,  except  where  the  afferent  and  efferent  vessels 
pass  through,  and  forms  the  begimyng  of  a  urinary  tubule.  If  we 
suppose  the  tuft  pushed  into  the  blind  end  of  the  tubule  so  as  to 
indent  it,  it  will  be  easily  understood  that  the  single  layer  of  flattened 
•epithelium  reflected  on  the  glomerulus  is  continuous  with  that  lining 
the  capsule,  which  in  its  turn  is  continuous  with  the  epithelial  layer 
of  the  rest  of  the  urinary  tubule.  This  has  been  divided  by  histo- 
logists  into  a  number  of  parts  which  it  is  unnecessary  to  enumerate 
here,  further  than  to  say  that  the  urinary  tubule  proper  begins  in  the 
•cortex  in  Bowman's  capsule  and  the  proximal  convoluted  tubule 


396 


A  MANUAL  OF  PHYSIOLOGY 


(with  its  continuation,  the  spiral  tubule),  and  ends  in  the  cortex  with 
the  distal  convoluted  tubule,  the  connection  between  the  two  being 
made  by  a  long  loop  (Henle's)  with  a  descending  and  an  ascending 
limb  (Fig.  124). 

•  The  distal  convoluted  tube  joins  by  means  of  the  short  connecting 
tubule  one  of  the  straight  tubules  which  form  the  pyramids  of 
Ferrein  in  the  cortex,  and  which  run  down  into  the  medulla,  always 


Vessels   of  yhmerulu 


/ 
Proximal 


j  7~/~  ~Glo  m  eru  lu  s   with 
II  Bowman's  cafisule 


Medulla 


a  pyrami    o    erret* 


I  Collecting  tulule 


FIG.  124.— DIAGRAM  OF  BLOODVESSELS  AND  TUBULES  IN  THE  KIDNEY. 
The  arrows  show  the  direction  in  which  the  urine  flows. 

uniting  into  larger  and  larger  tubes  as  they  go,  until  at  length  they 
open  as  ducts  of  Bellini  on  the  apex  of  a  papilla.  The  two  con- 
voluted tubules  and  the  ascending  limb  of  Henle's  loop  are  lined  by 
similar  epithelial  cells  with  granular  contents  and  a  striated  or 
'  rodded'  appearance.  We  shall  see  directly  that  this  morphological 
agreement  is  the  index  of  a  functional  likeness.  The  blood-supply 
of  the  tubules,  especially  of  the  convoluted  portions,  is  exceedingly 
rich,  the  efferent  vessels  of  the  glomeruli  breaking  up  around  them 


EXCRETION  397 

into  a  close-meshed  network  of  capillaries,  from  which  the  blood  is 
collected  into  interlobular  veins  running  parallel  to  the  interlobular 
arteries  between  the  pyramids  of  Ferrein.  The  straight  tubules  of 
the  medulla  are  also  surrounded  by  capillaries  given  off  from  straight 
arteries  (arterise  rectae)  running  down  into  it  partly  from  the  arterial 
arches  and  partly  from  efferent  vessels  of  the  glomeruli  nearest  the 
boundary  layer,  the  blood  passing  away  by  straight  veins  (venae 
rectae),  which  join  the  veins  accompanying  the  arterial  arches.  The 
greater  part  of  the  blood  going  through  the  kidney  has  to  pass 
through  two  sets  of  capillaries,  one  in  the  glomeruli,  the  other  around 
the  tubules.  Even  the  portion  of  it  which  does  not  go  through  the 
glomeruli  has  for  the  most  part  a  long  route  to  traverse  in  narrow 
arterioles  and  venules  to  and  from  its  capillary  distribution.  And 
the  mean  circulation-time  through  the  kidney  has  been  found  to  be 
longer  than  that  through  most  other  organs. 

Theories  of  Renal  Secretion. — To  come  back  to  our  problem 
of  the  nature  of  renal  secretion,  the  anatomical  structure 
of  the  kidney  might  be  expected  to  throw  light  upon  the 
question.  And,  indeed,  it  was  on  a  purely  histological  foun- 
dation that  Bowman  established  his  famous  '  vital '  theory  of 
renal  secretion.  Impressed  with  the  resemblance  between  the 
renal  epithelium  and  the  epithelial  cells  of  other  glands,  and 
with  the  distribution  of  the  bloodvessels  in  the  kidney,  he 
came  to  the  conclusion  that  the  characteristic  constituents 
of  urine,  including  urea,  were  secreted  from  the  blood  by 
the  tubules.  To  the  Malpighian  bodies  he  assigned  what 
he  doubtless  considered  the  humbler  office  of  separating 
water  from  the  blood  for  the  solution  of  the  all-important 
solids.  To  Ludwig,  on  the  other  hand,  with  his  whole 
attention  fastened  on  the  mechanical  factors  by  which  the 
flow  of  urine  could  be  influenced,  the  tubules  seemed  of 
secondary  importance,  while  the  glomeruli  appeared  a  com- 
plete apparatus  for  filtering  urine  from  the  blood  into  Bow- 
man's capsule.  He  saw  that  the  efferent  vessel  was  smaller 
than  the  afferent ;  that  it  was  therefore  easier  for  blood  to 
come  to  the  glomerulus  than  to  get  away  from  it,  and  that 
the  pressure  in  the  capillaries  of  the  tuft  must  be  higher 
than  in  ordinary  capillaries,  because  the  resistance  beyond 
them  in  the  comparatively  narrow  efferent  vessel,  and 
especially  in  the  second  plexus,  is  greater  than  the  resist- 
ance beyond  a  single  capillary  network.  And  experimental 


398  A  MANUAL  OF  PHYSIOLOGY 

investigation  soon  showed  him  that  the  rate  at  which  urine 
was  formed  could  be  greatly  influenced  by  changes  in  the 
blood-pressure. 

On  such  considerations,  Ludwig  founded  th6  'mechanical' 
theory  of  urinary  excretion,  which,  although  in  a  much 
modified  form,  still  divides  with  the  vital  theory  the 
allegiance  of  physiologists.  It  is  impossible  here  to  enter 
in  detail  into  a  controversy  that  has  extended  over  half  a 
century  and  produced  an  extensive  literature.  The  result 
of  the  discussion  has  been,  in  our  opinion,  to  establish  in 
its  essential  principles  the  '  vital '  theory  of  Bowman,  or  at 
least  to  show  that  no  purely  mechanical  theory  as  yet  con- 
structed will  account  for  all  the  facts. 

Ludwig  supposed  that  the  urine,  qualitatively  complete 
in  all  its  constituents,  was  simply  filtered  through  the 
glomeruli ;  but  as  the  proportion  of  salts,  and  especially  of 
urea,  is  very  far  from  being  the  same  in  urine  as  in  blood, 
he  further  assumed  that  the  liquid  which  passes  into  Bow- 
man's capsule  is  exceeding  dilute,  and  that  absorption  of 
water,  and  perhaps  of  other  constituents,  takes  place  in  its 
passage  along  the  renal  tubules.  The  great  length  of  these 
tubules,  as  compared  with  those  of  most  other  glands, 
might  seem  to  indicate  a  long  sojourn  of  the  urine  in  them, 
and  the  probability  of  important  changes  being  caused  in 
its  passage  along  them.  But  if  we  consider  the  immense 
length  (60  to  70  cm.)  of  the  seminal  tubules  and  of  their 
gigantic  ducts  (epididymis  6  metres),  where,  of  course, 
absorption  of  water  on  a  large  scale  is  out  of  the  question, 
it  will  be  granted  that  little  can  be  built  upon  the  mere 
length  of  the  renal  tubules.  On  the  other  hand,  the  salivary 
glands,  where  there  are  no  glomeruli,  secrete  as  much  water 
as  the  kidneys  are  supposed  to  filter;  and  the  pancreas, 
whose  capillaries  form  the  first  of  a  double  set,  and  there- 
fore in  this  respect  correspond  to  the  renal  glomeruli, 
secretes  less  water  than  the  liver,  whose  capillaries  corre- 
spond to  the  low-pressure  plexus  around  the  convoluted 
tubules  of  the  kidney.  So  that  deductions  drawn  from  the 
anatomical  relations  of  the  bloodvessels  are  not  in  this  case 
of  much  value,  unless  supported  by  physiological  results. 


EXCRETION 


399 


Tried  by  the  latter  test,  the  mechanical  theory  breaks  down 
for  the  kidney,  as  it  does  for  other  glands. 

In  the  first  place,  the  absence  from  urine  of  the 
and  sugar  of  the  blood  under  normal  circumstances — if'  ^A 
infinitesimal  quantities  of  these  substances,  as  some  have7 
asserted,  are  really  to  be  found  in  healthy  urine,  it  makes 
no  difference  to  the  argument — and  the  elimination  by  the 
kidney  of  egg-albumin,  peptone,  and  other  bodies  when 
injected  into  the  veins,  show  a  selective  power  inexplicable 
except  by  reference  to  the  vital  activity  of  cells.  Urea  and 
sugar,  both  highly  diffusible  substances,  circulate  side  byl 
side  in  the  bloodvessels  of  the  kidney.  The  one  is  taken 
and  the  other  left.  The  urea  is  a  waste-product  of  no 
further  use  in  the  economy.  The  sugar  is  a  valuable  food- 
substance.  The  kidney  selects  with  unerring  certainty  the 
urea,  of  which  only  4  parts  in  10,000  are  present  in  the 
blood,  but  rejects  the  sugar,  of  which  there  is  five  times 
as  much. 

Egg-albumin  injected  into  the  blood  passes  through  the 
renal  circulation  side  by  side  with  the  serum-albumin  of 
the  plasma.  Both  are  indiffusible  through  membranes,  and 
to  the  chemist  the  differences  between  them  may  appear 
superficial  and  minute.  But  the  kidney  does  not  hesitate 
for  an  instant.  The  egg-albumin  is  promptly  excreted 
as  a  foreign  substance;  the  serum -albumin  passes  on 
untouched. 

Not  only  does  the  kidney  exercise  a  power  of  qualitative 
selection  ;  it  also  takes  cognizance  of  the  quantitative  com- 
position of  the  blood.  So  long  as  there  is  less  sugar  in  the 
plasma  than  about  3  parts  in  1,000,  it  is  refused  passage 
into  the  renal  tubules.  But  when  this  limit  is  passed,  and 
the  proportion  of  sugar  in  the  blood  becomes  excessive,  the 
kidney  begins  to  excrete  sugar,  and  continues  to  do  so  till 
the  balance  is  redressed. 

The  advocates  of  the  theory  of  filtration,  driven  from  one 
position  to  another,  have  made  their  firmest  stand  on  the 
excretion  of  the  inorganic  constituents  of  the  urine.  But 
even  here  the  theory  has  at  length  become  untenable ;  and 
there  is  little  more  reason  to  believe  that  the  copious  flow  of 


400  A  MANUAL  OF  PHYSIOLOGY 

urine  which  follows  the  absorption  of  a  large  quantity  of 
water  is  due  to  a  mere  process  of  nitration  than  there  is  to 
believe  that  nitration,  and  not  selective  secretion,  is  the 
cause  of  the  gush  of  saliva  which  precedes  vomiting,  or  the 
sudden  outburst  of  sweat  on  sudden  and  severe  exertion. 
It  is  true  that  the  direct  introduction  of  water  into  the 
blood,  or  its  attraction  from  the  lymph  spaces  when  the 
osmotic  pressure  of  the  blood  is  increased  by  the  injection 
of  substances  like  urea,  sugar  and  sodium  chloride,  may 
cause  a  condition  of  hydrcemic  plethora,  and  that  this  plethora 
may  sometimes  be  associated  with  an  increase  of  pressure  in 
the  capillaries  in  general,  and  therefore  in  the  vessels  of  the 
Malpighian  tuft.  It  may  also  be  admitted  that  such  an 
increase  of  pressure  might  be  accompanied  by  an  increased 
nitration  of  water  and  salts  into  the  Bowman's  capsule. 
But  who  will  believe  that  the  addition  of  a  tumbler  of  water, 
absorbed  from  the  alimentary  canal,  to  5^  litres  of  blood 
circulating  in  a  system  of  vessels  whose  capacity  can  and 
does  vary  within  wide  limits,  should  cause  in  the  capillaries 
of  the  kidney  an  increase  of  pressure  exactly  proportional  to 
the  increase  in  the  elimination  of  water  in  the  urine,  lasting 
for  the  same  time  and  disappearing  at  the  moment  when 
the  normal  composition  of  the  blood  is  restored  ?  Nor  is 
it  easier  to  explain  on  any  nitration  hypothesis  how  it  is 
that  in  a  starving  animal,  the  quantity  of  inorganic  sub- 
stances eliminated  in  the  urine  drops  almost  to  zero,  while 
the  proportional  amount  in  the  blood  and  tissues  is  little, 
if  at  all,  affected.  Such  facts  suggest  that  the  secreting 
cells  of  the  kidney  are  stimulated  by  the  contact  of  blood 
or  lymph  in  which  the  normal  constituents  are  present  in 
too  small  or  in  too  great  amount,  and  that  the  strength 
of  the  stimulus  is  proportional  to  the  degree  of  deficiency 
or  excess. 

But,  secondly,  there  is  positive  proof  that  the  '  rodded ' 
epithelium  of  the  tubules,  which  no  one  supposes  to  be 
abandoned  more  to  mere  physical  influences  than  the 
epithelium  of  the  salivary  glands,  plays  a  part  in  the 
secretion  of  some  of  the  urinary  constituents.  For  Bowman 
saw  crystals  of  uric  acid  in  the  epithelium  of  the  convoluted 


EXCRETION  401 

tubules  of  birds.  Heidenhain  found  that  urate  of  soda  and 
indigo-carmine  injected  into  the  blood  of  a  rabbit  are 
excreted  by  the  epithelium  of  the  convoluted  tubules  and 
the  ascending  part  of  Henle's  loop.  And  Nussbaum's  experi- 
ments, although  not  perhaps  quite  conclusive,  have  made  it 
probable  that  in  the  frog  urea  is  actually  separated  by  the 
epithelium  of  the  tubules. 

The  experiments  of  Heidenhain  and  Nussbaum  deserve  more 
detailed  description.  The  former  injected  indigo-carmine 
into  the  blood  of  rabbits  and  after  a  variable  time  killed 
them,  cut  out  the  kidneys, 
and  flushed  them  with  alcohol. 
His  results  were  as  follows  : 
(i)  When  the  spinal  cord  was 
cut  before  the  injection  in  order 
to  reduce  the  blood-pressure, 
the  blue  granules  were  found  in 
the  'rodded'  epithelium  of  the 
convoluted  tubules  and  the 
ascending  limb  of  Henle's  loop, 
and  in  the  lumen  of  the  tubules,  AFTER  INJECTION  INTO  BLOOD. 

but    nowhere     else.       The     renal        The  cortex  between  a  and   b  and 

between  c  and  d  was  cauterized  before 
COrtex    was      Coloured     blue,    the  injection.      In  the   black   wedge- 


(2)  When  the  spinal  cord  was 
not  cut,  the  pigment  was  found 
in  the  medulla  and  pelvis  of  the 
kidney,  as  well  as  in  the  cortex,  but  always  in  the  lumen 
of  the  tubules,  and  not  in  the  epithelium,  except  in  the 
situations  mentioned.  (3)  If  a  portion  of  the  cortex  of  the 
kidney  had  been  cauterized  with  nitrate  of  silver  before 
injection  of  the  pigment,  the  spinal  cord  being  left  intact, 
a  wedge  of  the  renal  substance,  corresponding  to  this  area, 
remained  coloured  only  in  the  cortex,  although  the  rest 
was  blue  in  the  medulla  also.  The  rodded  epithelium  was 
filled  with  blue  granules  as  before  (Fig.  125). 

(i)  shows  that  the  epithelium  is  capable  of  excreting 
some  substances  at  least.  (2)  appears  to  show  that  when 
the  blood-pressure  is  normal  water  is  poured  out  from  some 
part  of  the  tubule,  and  washes  the  pigment  separated  by  the 

26 


I 


402  A  MANUAL  OF  PHYSIOLOGY 

'  rodded  '  epithelium  down  towards  the  papillae.  (3)  suggests 
that  it  is  through  the  glomeruli  that  most  of  the  water 
passes.  For  cauterization  has  not  destroyed  the  power  of 
the  epithelium  to  excrete  pigment,  and  therefore,  presumably, 
would  not  have  destroyed  its  power  to  excrete  water  if  it 
possessed  this  power  in  any  great  degree  ;  and  the  glomeruli 
and  their  capsules  are  the  only  other  part  of  the  renal 
mechanism  which  can  have  been  affected.  The  fact  that 
in  birds  and  serpents,  whose  urine  is  solid  or  semi-solid,  the 
glomeruli  are  smaller  than  in  mammals  is  corroborative 
evidence  that  the  glomeruli  have  to  do  with  the  excretion  of 
water. 

An  attempt  has  recently  been  made  by  Sobieranski,  on  the  strength 
of  a  reinvestigation  of  the  microscopical  appearances  presented  by 
the  kidney  after  injection  of  pigments  into  the  blood,  to  revive 
Ludwig's  theory  that  absorption  takes  place  from  the  tubules.  He 
asserts  that,  although  pigment  granules  are  found  in  the  rodded 
epithelium,  they  are  always  near  the  lumen  of  the  tubule,  never  near 
the  basement  membrane.  From  this  he  concludes  that  the  pigment 
is  not  passed  through  the  cells  from  the  blood,  but  absorbed  by  thei 
from  the  tubules  after  excretion  by  the  glomeruli.  It  cannot,  hov 
ever,  be  admitted  that  his  observations  are  decisive. 

Nussbaum's  experiments  were  founded  on  the  anatomic; 
fact  that  the  kidney  of  batrachians,  and,  indeed,  that  of  fishes 
and  ophidia  as  well,  has  a  double  blood-supply.  The  renal 
artery  gives  off  afferent  vessels  to  the  glomeruli,  and  the 
vena  advehens  or  renal  portal  vein  breaks  up,  like  the 
portal  vein  in  the  liver,  into  a  plexus  of  capillaries  sur- 
rounding the  tubules,  with  which  plexus  the  efferent  arterioles 
of  the  glomeruli  communicate.  By  tying  the  renal  arteries 
in  the  frog,  Nussbaum  thought  he  could  at  will  stop  the 
circulation  in  the  glomeruli,  and  he  found  that  after  this  was 
done,  sugar,  peptones  and  egg-albumin,  injected  into  the 
blood,  no  longer  passed  into  the  urine,  although  they  readily 
did  so  when  the  arteries  were  not  tied.  Urea,  however,  was 
still  eliminated  by  the  kidneys  after  ligature  of  the  renal 
arteries,  and  water  along  with  it.  He  concluded  that  the 
Malpighian  corpuscles  have  the  power  of  excreting  water, 
sugar,  peptone,  and  albumin,  while  the  epithelium  of  the 
tubules  excretes  urea  as  well  as  water. 


>t  tne 


EXCRETION  403 

Adami  has  since  shown  that  the  circulation  in  the  glomeruli 
is  not  wholly  stopped  by  Nussbaum's  operation,  for  there  is 
a  certain  amount  of  anastomosis  between  the  arteries  of  the 
generative  organs  and  the  renal  arteries.  He  therefore 
suggests  that  the  water  secreted  during  the  elimination  of 
urea  after  ligature  of  the  renal  arteries  may  really  come 
through  the  Malpighian  tufts.  At  the  same  time,  this 
objection  does  not  touch  the  conclusion  of  Nussbaum,  that 
the  glomeruli  are  alone  concerned  in  the  separation  of  the 
other  bodies  mentioned.  For  his  operation,  whether  it  com- 
pletely cut  off  the  circulation  in  the  tufts  or  not,  interfered 
with  it  so  much  as  to  stop  the  excretion  of  these  substances, 
while  leaving  the  epithelium  of  the  tubules  as  able  to  con- 
tinue that  function,  if  it  possessed  it,  as  it  was  before. 
Adami  himself  has  shown  that  haemoglobin  when  free  in  the 
blood-plasma  is  excreted  by  the  glomeruli,  even  when  the 
renal  artery  has  been  ligatured,  and  that  menisci  of  this  sub- 
stance may  be  coagulated  within  the  lumen  of  the  Bowman's 
capsules  by  plunging  the  kidney  into  boiling  water.  In  the 
dog,  too,  haemoglobin  is  excreted  by  the  glomeruli,  and  may 
be  washed  out  of  the  capsule  by  the  increased  quantity  of 
water  secreted  when  sodium  nitrate  is  administered.  This 
shows  that  a  diuretic  may  act  upon  the  glomerular  epithelium, 
which  is  thus  brought  into  line  with  the  '  rodded  '  epithelium 
of  the  tubules. 

What,  then,  is  the  significance  of  the  peculiar  arrangement  of  the 
glomerular  bloodvessels,  if  the  epithelium  of  the  capsules  has  secretive 
powers  like  that  of  ordinary  glands  ?  It  is  difficult  to  believe  that 
these  unique  vascular  tufts  have  not  a  near  and  important  relation  to 
the  renal  function ;  but  it  is  by  no  means  clear  what  that  relation  is. 
The  secretion  of  water,  and  even  its  rapid  secretion,  is  not  at  all 
bound  up  with  any  set  arrangement  of  bloodvessels.  Gland-cells  all 
over  the  body  secrete  water  under  the  most  varied  conditions  of 
blood-pressure,  although  a  comparatively  high  pressure  is  upon  the 
whole  favourable  to  a  copious  outflow. 

But  the  kidney  has,  as  we  now  know,  other  functions  than  mere 
excretion  (p.  472).  And  it  may  be  that  the  simplest  part  of  the  latter 
process,  the  elimination  of  water  and  salts,  is  largely  thrown  upon 
the  Malpighian  corpuscles,  as  a  physiologically  cheaper  machine 
than  the  epithelium  of  the  tubules,  which  is  left  free  for  more  complex 
labours.  These  may  include  not  only  the  separation  of  nitrogenous 
metabolites,  but  perhaps  the  building  up  of  urea,  or  of  less  completely 

26 — 2 


404  A  MANUAL  OF  PHYSIOLOGY 

metabolized  substances  which  precede  it,  into  higher  combinations, 
and  the  consequent  regulation  of  the  quantity  of  urea  finally  excreted, 
and  the  ultimate  proteid  waste  which  this  expresses.  The  epithelium 
of  the  glomerulus,  being  a  less  highly  organized  and  less  delicately 
selective  mechanism  than  that  of  the  convoluted  tubules,  may  more 
easily  respond  to  increase  of  blood-pressure  by  increased  secretion. 
At  the  same  time,  placed  as  it  is  at  the  last  flood-gate  of  the  circula- 
tion, where  the  escape  of  anything  valuable  means  probably  its  total 
loss,  the  glomerular  epithelium  may  be  endowed  with  a  general  power 
of  resistance  to  transudation,  which  renders  a  comparatively  high 
blood-pressure  a  necessary  condition  of  its  acting  at  all.  And  as  a 
matter  of  fact,  water  ceases  to  be  secreted  by  the  kidney  long  before 
the  blood-pressure  in  the  glomeruli  can  have  fallen  below  that  which 
suffices  for  the  highest  activity  of  the  liver.  Perhaps,  however,  the 
high  minimum  pressure  required  (30  to  40  mm.  of  mercury  in  the 
dog)  is  merely  the  necessary  consequence  of  the  long  and  difficult 
path  which  most  of  the  blood  going  through  the  kidney  has  to  take, 
and  that  a  sufficient  blood-flow  cannot  be  kept  up  with  less.  It  may 
be,  too,  that  the  comparatively  small  surface  of  the  glomeruli, 
restricted  in  order  to  leave  room  for  the  more  highly  organized  parts 
of  the  renal  mechanism,  entails  the  more  intense  and  concentrated 
activity,  which  the  high  blood-pressure  renders  possible,  and  the 
simplicity  of  work  and  organization  renders  harmless. 

This  brings  us  to  a  second  suggestion  as  to  the  meaning  of  the 
double  capillary  supply  of  the  kidney,  namely,  that  the  more  highly 
organized  parts  of  the  renal  tubules  are  shielded  from  an  excessive 
blood-pressure  by  the  interposition  of  the  glomeruli  as  a  block.     This 
may  be  either  because  the  epithelium  of  the  tubules  would  not  perform 
its  proper  work  so  well  under  a  high  blood-pressure,  or  because  there 
would  be  a  danger  of  substances  which  ought  to  be  retained  being 
cast  out  into  the  urine.     In  this  connection  it  is  interesting  to  note 
that  the  specific  constituents  of  urine  are  separated  by  epithelium 
vtv/y       surrounded  by  capillaries  of  the  second  order,  and  therefore  with  a 
,  '         smaller  blood-pressure  than  exists  in  the  capillaries  of  most  glands, 
Jttvs-h  while  the  same  is  true  of  bile,  another  proteid-free  secretion.     The 
0          sweat-glands,  too,  the  second  great  outgate  of  liquid  excretion,  are 
surrounded  by  capillaries  separated  from  the  main  arterial  branch  by 
a  rete  mirabile  corresponding  to  a  glomerulus. 

The  maximum  secretory  pressure  in  the  kidney,  as  shown 
by  a  manometer  tied  into  the  divided  ureter,  is  about 
60  mm.  of  mercury  in  the  dog,  or  less  than  half  that  of 
saliva.  If  the  escape  of  the  urine  is  opposed  by  a  greater 
pressure  than  this,  or  if  the  ureter  is  tied,  the  kidney 
becomes  oedematous.  Whether  the  oedema  is  due  to  re- 
absorption  of  urine  or  to  the  pouring  out  of  lymph  owing  to 
the  pressure  of  the  dilated  tubules  on  the  veins  has  not  been 
definitely  settled.  It  has  been  already  pointed  out  th 


EXCRETION  405 

there  is  no  necessary  relation  between  the  blood-pressure  in 
the  capillaries  of  a  gland  and  its  secretory  pressure ;  and,  so 
far  as  this  goes,  water  might  just  as  well  be  secreted  at  a 
pressure  of  60  mm.  of  mercury  from  the  low-pressure  blood 
of  the  second  set  of  renal  capillaries  as  from  the  high- 
pressure  blood  of  the  glomeruli. 

The  Influence  of  the  Circulation  on  the  Secretion  of  Urine, — 
Although  the  activity  of  no  organ  in  the  body  is  governed 
more  by  the  indirect  effects  of  nervous  action  than  that  of 
the  kidney,  no  proof  has  yet  been  given  of  the  existence  of 
secretory  fibres  for  it  comparable  to  those  of  the  salivary 
glands.  All  the  changes  in  the  rate  of  renal  secretion  which 

B,  metal  box  in 
two  halves  opening 
on  the  hinge  H ; 
M,  thin  membrane ; 
A,  space  filled  with 
oil ;  O,  organ  en- 
closed in  onco- 
meter ;  V,  vessels  of 
organ  ;  A  tube  for 
filling  instrument 
with  oil  ;  T,  tube 
connected  with  D, 
which  opens  into 
cylinder  C  ;  C  is 
also  filled  with  oil ; 
P,  piston  attached 
by  E  to  a  writing 
lever. 

FIG.  126. — DIAGRAM  OF  ORGAN -PLETHYSMOGRAPH  OR  ONCOMETER. 

follow  the  section  or  stimulation  of  nerves  can  be  explained 
as  the  consequences  of  the  rise  or  fall  of  local  or  general 
blood-pressure,  and  of  the  corresponding  variations  in  the 
velocity  of  the  blood  in  the  renal  vessels. 

The  best  way  to  study  variations  in  the  calibre  of  the  renal  vessels 
is  the  plethysmographic  method,  and  the  oncometer  of  Roy  is  a 
plethysmograph  adapted  to  the  kidney.  It  consists  of  a  metal 
capsule  lined  with  a  loose  membrane,  between  which  and  the  metal 
there  is  a  space  filled  with  oil.  The  two  halves  of  the  capsule  open 
and  shut  on  a  hinge  ;  and  the  kidney,  when  introduced  into  it,  is 
surrounded  on  all  sides  by  the  membrane,  the  vessels  and  ureter 
passing  out  through  an  opening.  The  oil-space  is  connected  with  a 
cylinder  also  filled  with  oil,  above  which  a  piston,  connected  with  a 
lever,  moves.  The  lever  registers  on  a  drum  the  changes  in  the 
volume  of  the  kidney,  i.e.,  practically  the  changes  in  the  quantity  of 
blood  in  it,  and  therefore  in  the  calibre  of  its  vessels. 

Nerves  of  the  Kidney. — Both  vaso-constrictor  and  vaso-dilator 


406  A  MANUAL  OF  PHYSIOLOGY 

fibres  for  the  renal  vessels,  but  most  clearly  the  former,  have  been 
shown  to  leave  the  cord  (in  the  dog)  by  the  anterior  roots  of  the  sixth 
thoracic  to  second  lumbar  nerves,  and  especially  of  the  last  three 
thoracic.  They  run  in  the  splanchnics,  and  then  through  the  renal 
plexus — around  the  renal  artery — into  the  kidney.  The  vaso- 
constrictors predominate,  so  that  the  general  effect  of  stimulation  of 
the  nerve-roots,  the  splanchnics,  or  the  renal  nerves  is  shrinking  of 
the  kidney,  with  diminution  or  cessation  of  the  secretion  of  urine. 
But  slow  rhythmical  stimulation  of  the  roots  causes  increase  of 
volume,  the  dilators  being  by  this  method  excited  in  preference  to 
the  constrictors. 

Section  of  the  renal  nerves  is  followed  by  relaxation  of  the 
small  arteries  in  the  kidney,  and  consequent  swelling  of  the 
organ.  The  flow  of  urine  is  greatly  increased,  and  some- 
times albumin  appears  in  it,  the  excessive  pressure  in  the 
capillaries  (particularly  in  those  of  the  glomeruli)  being 
supposed  to  favour  the  escape  of  substances  to  which  the 
renal  epithelium  refuses  a  passage  under  normal  conditions. 

The  recent  investigations  of  Berkely  have  shown  that  the 
renal  nerves,  entering  at  the  hilum,  branch  repeatedly,  so 
as  to  form  a  wide-meshed  plexus  around  the  arteries,  and 
accompany  them  even  to  their  finest  ramifications  in  the 
cortex.  No  nerve-fibres  have  as  yet  been  seen  on  the  veins 
in  the  kidney-substance  or  on  the  straight  arteries.  Coming 
off  from  the  nerves  surrounding  the  arteries  are  fine  fibres 
which  are  distributed  to  the  convoluted  tubules,  and  are 
perhaps  secretory  nerves.  Some  of  them  terminate  in 
globular  ends,  others  in  fine  threads  that  pass  through  the 
membrana  propria. 

It  is  often  assumed  that  the  renal  nerves  affect  chiefly 
the  afferent  arterioles  of  the  glomeruli ;  but  there  seems  to 
be  no  experimental  ground  for  this  view,  which  is  merely  a 
doctrinaire  deduction  from  Ludwig's  filtration  theory.  For 
if  that  theory,  or  any  modification  of  it  which  postulates  a 
close  connection  between  the  blood-pressure  in  the  glome- 
rular  capillaries  and  the  rate  of  secretion  of  urine,  be  accepted, 
it  is  evidently  an  advantage  that  there  should  be  no  similar 
influence  on  the  efferent  arterioles,  since  constriction  of 
both  would  not  necessarily  cause  any  fall,  nor  dilatation  of 
both  any  rise,  of  intra-glomerular  pressure.  Heidenhain's 
suggestion,  that  the  velocity  of  the  blood-flow,  and  not  the 


EXCRETION  407 

pressure  in  the  glomeruli,  is  the  determining  factor  in 
urinary  secretion,  does  not  require  any  arbitrary  restriction 
of  the  tract  influenced  by  the  renal  vaso-motor  nerves.  If 
both  afferent  and  efferent  vessels  were  constricted,  the  blood- 
flow  would  be  diminished ;  if  both  were  relaxed,  it  would  be 
increased  ;  if  only  the  vas  afferens  were  affected,  the  changes 
would  be  in  the  same  sense,  although  less  marked,  since  the 
total  alteration  of  resistance  would  be  less. 

An  experiment  which  is  sometimes  quoted  as  a  decisive 
test  of  the  relative  importance  of  changes  in  the  rate  of  flow, 


FIG.  127. — NERVES  OF  KIDNEY  (BERKELY). 

(16)  medium-sized  artery  with  its  nerve-plexus  ;  A,  terminal  knobs ;  B,  aberrant 
branch  ending  in  terminal  knob  E;  the  dotted  lines  outline  the  artery.  (17)  Nerve- 
fibres  surrounding  a  Bowman's  capsule,  which  is  indicated  by  a  dotted  line  ;  some  of 
the  endings  are  close  to  the  membrane  ;  (18)  convoluted  tubule  shown  in  outline  with 
fine  nerve-fibres  on  it,  which  seem  to  enter  the  basement  membrane. 

and  in  the  pressure  of  the  blood  within  the  glomeruli,  is  that 
of  tying  the  renal  vein.  This  undoubtedly  does  not  lower  the 
intra-glomerular  pressure — on  the  contrary,  it  must  increase 
it — but  the  secretion  of  urine  stops.  If  the  venous  outflow 
from  the  kidney  is  only  partially  interfered  with,  the  flow  of 
urine  is  immediately  diminished,  but  the  administration  of 
a  diuretic  like  potassium  nitrate  causes  an  increase.  It  is 
suggested  that  in  these  experiments  the  secretion  stops  or 
slackens  because  an  active  circulation,  and  not  a  high 


4o8  A  MANUAL  OF  PHYSIOLOGY 

blood-pressure,  is  its  necessary  condition.  The  conclusion 
is  probably  correct,  but  the  experiment  does  not  prove  it. 
For  few  glands  can  go  on  performing  their  function  after  the 
circulation  has  ceased.  The  kidney  must  be  able  to  feed 
itself  in  order  to  continue  its  work ;  and  it  might  be  urged 
that  if  the  blood  in  the  glomeruli  could  be  kept  at  the  normal 
standard  of  arterial  blood,  secretion  might  still  go  on  after 
ligature  of  the  renal  vein. 

According  to  Ludwig,  indeed,  the  experiment  really  teaches 
that  the  liquid  part  of  the  urine  is,  at  any  rate,  not  separated 
by  the  epithelium  of  the  tubules,  since  the  blood-pressure 
in  the  capillaries  around  the  tubules  must  rise  very  greatly 
after  ligature  of  the  vein,  and  yet  secretion  is  stopped.  It 
might  equally  well  be  argued,  however,  that  the  renal  epi- 
thelium normally  secretes  water  under  a  low  blood-pressure, 
but  is  disorganized  under  the  excessive  and  entirely  un- 
accustomed pressure  which  follows  the  closure  of  the  vein. 
But  the  whole  discussion  is  an  illustration — and  this  is  the 
reason  we  have  gone  into  it  so  fully — of  the  complexity,  the 
many-sidedness  of  physiological  phenomena,  even  when 
reduced  by  well-planned  experiments  to  their  simplest  terms, 
and  the  unconscious  bias  which  theory  sometimes  gives  to 
even  the  most  acute  and  original  minds  in  interpreting  the 
results  of  observation. 

It  is  not  only  through  nerves  directly  governing  the  calibre 
of  the  vessels  of  the  kidney  that  the  rate  of  urinary  secretion 
can  be  affected.  Any  change  in  the  general  blood-pressure, 
if  not  counteracted  by,  still  more  if  conspiring  with,  simul- 
taneous local  changes  in  the  renal  vessels,  may  be  followed 
by  an  increased  or  diminished  flow  of  urine ;  and  the  law 
which  explains  all  such  variations,  or  at  least  serves  to  sum 
them  up,  is  that  in  general  an  increase  in  the  rate  of  the  blood- 
flow  through  the  kidney  is  followed  by  an  increase  in  the  rate  of 
'  secretion.  It  will  be  remarked  that  this  is  the  converse  of 
the  great  law,  of  which  we  have  already  seen  so  many  illus- 
trations, that  functional  activity  increases  blood-flow.  It  is 
probable  that  this  law  holds  for  the  kidney  as  well  as  for 
other  organs,  but  that  the  influence  of  activity  on  blood- 
supply  is  subordinated  to  that  of  blood-supply  on  activity, 


EXCRETION  409 

while  in  most  tissues,  as  in  the  muscles,  the  opposite  is  the 
case.  It  is  evident  that  an  increase  in  the  blood-flow  would 
favour  the  secretory  activity  of  the  renal  cells,  since  the 
average  concentration  of  the  blood  presented  to  them  as 
regards  those  constituents  which  they  select  would  remain 
relatively  high  in  its  circuit  through  the  kidney.  The 
*  stimulus '  to  secretion  would,  therefore,  be  relatively 
intense. 

Destruction  of  the  medulla  oblongatav(^->  of  the  vaso- 
motor  centre),  or  section  of  the  cord  below  it,  diminishes 
the  secretion  of  urine,  because  the  arterial  pressure  is 
lowered  so  much  as  to  over-compensate  the  dilatation  of  the 
renal  vessels,  which  the  operation  also  brings  about.  If  the 
blood-pressure  falls  below  40  mm.  of  mercury,  the  secretion 
is  abolished.  Stimulation  of  the  medulla  or  cord  also 
lessens  the  flow  of  urine  by  constricting  the  arterioles  of  the 
kidney  so  much  as  to  over-compensate  the  rise  of  general 
blood-pressure,  caused  by  the  constriction  of  small  vessels 
throughout  the  body. 

If  the  renal  nerves  have  been  cut,  stimulation  of  the 
medulla  oblongata  increases  the  urinary  secretion,  because 
now  the  rise  of  general  blood-pressure  is  no  longer  counter- 
balanced by  constriction  of  the  renal  vessels.  Puncture  of  a 
certain  part  of  the  floor  of  the  fourth  ventricle  may  produce 
a  copious  flow  of  urine,  perhaps  by  destroying  the  portion 
of  the  vaso-motor  centre  governing  the  renal  nerves,  while 
the  rest  remains  uninjured  and  keeps  up  the  general  blood- 
pressure,  but  possibly  by  stimulating  a  secretory  '  centre.' 

Section  of  the  splanchnic  nerves  causes  a  fall  of  arterial 
pressure,  which  is,  however  (in  animals  like  the  dog,  in 
which  compensation  soon  takes  place),  more  than  balanced 
by  the  simultaneous  dilatation  of  the  renal  vessels,  and 
therefore  for  some  time  the  flow  of  urine  is  increased,  but 
not  so  much  as  when  the  renal  nerves  alone  are  cut.  In  the 
rabbit  there  is  no  increase.  On  the  other  hand,  stimulation 
of  the  splanchnics  stops  the  urinary  secretion,  because  the 
general  rise  of  pressure  is  not  enough  to  make  up  for  the 
•constriction  of  the  renal  vessels. 


410  A  MANUAL  OF  PHYSIOLOGY 

Diuretics  are  substances  that  increase  the  flow  of  urine.  Some  of 
them  appear  to  act  mainly  by  increasing  the  general  blood-pressure, 
others  mainly  by  a  direct  influence  on  the  secreting  mechanism. 
Digitalis  is  a  representative  of  the  first  class  ;  urea  and  caffein  belong 
to  the  second.  The  action  of  digitalis  is  to  strengthen  the  beat  of 
the  heart,  which  is  at  the  same  time  somewhat  slowed,  and  to  con- 
strict the  arterioles.  Both  effects  contribute  to  the  increase  of 
pressure.  It  is  possible  that  in  addition  this  drug  directly  stimulates 
the  renal  epithelium.  Caffein^  when  injected  into  the  blood,  affects 
the  pressure  but  little.  It  causes  dilatation  of  the  renal  vessels  after 
a  passing  constriction,  and  an  increase  in  the  flow  of  urine  after  a 
temporary  diminution.  The  vascular  dilatation  is  not  the  chief 
reason  for  the  diuretic  effect,  for  the  latter  is  still  obtained  when  the 
vaso-motor  mechanism  has  been  paralyzed  by  chloral  hydrate,  and 
even  after  the  secretion  of  urine  has  been  stopped  by  the  fall  of 
pressure  consequent  on  section  of  the  spinal  cord.  Caffein,  there- 
fore, acts  directly  on  the  renal  epithelium.  The  action  of  urea, 
potassium  nitrate,  and  the  saline  diuretics  is  probably  also  a  direct 
action  on  the  secreting  structures,  although  some  have  supposed  that 
their  primary  effect  is  to  cause  vaso-dilatation  in  the  kidney,  and  a 
consequent  local  increase  in  the  capillary  pressure. 

Summary. — Our  knowledge  of  renal  secretion  may  be  thus 
summed  up :  The  water  and  salts  of  the  urine  are  partly,  and 
perhaps  chiefly,  separated  by  the  glomeruli ;  the  process  is  not  a 
physical  filtration,  but  a  true  secretion.  Substances  like  sugar, 
peptone,  egg-albumin,  and  hemoglobin  when  injected  into  the  blood 
are  excreted  by  the  glomeruli :  so  probably  is  the  sugar  of  diabetes. 
Urea,  uric  acid,  and  presumably  the  other  organic  constituents  of 
normal  urine,  with  a  portion  of  the  water  and  salts,  are  excreted 
by  the  physiological  activity  of  the  'rodded*  epithelium  of  the 
renal  tubules.  The  rate  of  secretion  of  urine  rises  and  falls  with 
the  pressure,  and  probably  still  more  with  the  velocity ,  of  the 
blood  in  the  renal  vessels.  No  secretory  nerves  for  the  kidney 
have  been  definitely  found  ;  the  effects  of  section  or  stimulation  of 
nerves  on  the  secretion  can  all  be  explained  by  the  changes  pro- 
duced in  the  renal  blood-flow.  Some  diuretics  act  by  increasing 
the  blood-flow,  others  directly  on  the  epithelium  of  the  tubules. 

Micturition. — The  urine,  like  the  bile,  is  being  constantly 
formed ;  although  secretion  varies  in  its  rate  from  time  to 
time,  it  never  ceases.  Trickling  along  the  collecting  tubules, 
the  urine  reaches  the  pelvis  of  the  kidney,  from  which  it  is 
propelled  along  the  ureters  by  peristaltic  contractions  of 
their  walls,  and  drops  from  their  valve-like  orifices  into  the 


EXCRETION  411 

bladder.  When  this  becomes  distended,  rhythmical  peri- 
staltic contractions  are  set  up  in  it,  and  notice  is  given  of  its 
condition  by  a  characteristic  sensation,  which  is  perhaps 
aided  by  the  squeezing  of  a  few  drops  of  urine  past  the 
tonically  contracted  circular  fibres  that  form  a  sphincter 
round  the  neck  of  the  bladder,  and  into  the  first  part  of  the 
urethra.  The  desire  to  empty  the  bladder  can  be  resisted 
for  a  time,  as  can  the  desire  to  empty  the  bowel.  If  it  is 
yielded  to,  the  smooth  muscular  fibres  in  the  wall  of  the 
viscus  are  thrown  into  contraction.  This  is  aided  by  an 
expulsive  effort  of  the  abdominal  muscles.  The  sphincter 
vesicae  is  relaxed  ;  and  the  urine  is  forced  along  the  urethra, 
its  passage  being  facilitated  by  discontinuous  contractions 
of  the  ejaculator  urinse  muscle,  which  also  serve  to  squeeze 
the  last  drops  of  urine  from  the  urethral  canal  at  the  com- 
pletion of  the  act. 

The  pressure  in  the  bladder  of  a  man  may  be  made  as  high 
as  10  cm.  of  mercury  during  the  act  of  micturition ;  about 
half  this  amount  is  due  to  the  contraction  of  the  vesical  walls 
alone,  the  rest  to  the  contraction  of  the  abdominal  muscles. 

Although  the  whole  performance  seems  to  us  to  be  com- 
pletely voluntary,  there  are  facts  which  show  that  it  is  at 
bottom  a  reflex  series  of  co-ordinated  movements,  that  can 
be  started  by  impulses  passing  to  a  centre  in  the  spinal 
cord  from  above  or  from  below — from  the  brain  or  from  the 
bladder.  In  dogs,  with  the  spinal  cord  divided  at  the  upper 
level  of  the  lumbar  region,  micturition  takes  place  regularly 
when  the  bladder  is  full,  and  can  be  excited  by  such  slight 
stimuli  as  sponging  of  the  skin  round  the  anus  (Goltz). 
Here,  of  course,  the  act  is  entirely  reflex ;  and  the  centre 
is  situated  at  the  level  of  the  fifth  lumbar  nerves.  The 
efferent  nerves  of  the  bladder,  like  those  of  the  rectum, 
come  partly  from  the  cord  directly  through  the  sacral  nerves, 
and  partly  through  the  lumbar  sympathetic  chain  (second  to 
sixth  ganglia).  The  sacral  fibres  are  connected  with  nerve 
cells  in  the  hypogastric  plexus,  and  the  sympathetic,  partly 
at  least,  in  the  inferior  mesenteric  ganglia.  This  anatomi- 
cal coincidence  acquires  interest  in  view  of  the  striking 
physiological  similarity  between  the  processes  of  micturition 


412  A  MANUAL  OF  PHYSIOLOGY 

and  defaecation,  a  similarity  which  is  emphasized  by  the  fact 
that  the  latter  is  almost  invariably  accompanied  by  the 
former.  An  important  difference,  however,  is  that  the  will 
can  far  more  readily  set  in  motion  the  machinery  of  micturi- 
tion than  that  of  defaecation  ;  a  man  can  generally  empty 
his  bladder  when  he  likes,  but  he  cannot  empty  his  bowels 
when  he  likes. 

Sometimes  in  disease,  and  especially  in  disease  of  the 
spinal  cord,  the  mechanism  of  micturition  breaks  down ; 
the  bladder  is  no  longer  emptied ;  it  remains  distended  with 
urine,  which  dribbles  away  through  the  urethra  as  fast  as 
it  escapes  from  the  ureters.  To  this  condition  the  term 
incontinence  of  urine  is  properly  applied. 

Reflex  emptying  of  the  bladder,  without  an  act  of  will  or 
during  unconsciousness,  is  not  true  incontinence.  The  in- 
voluntary micturition  of  children  during  sleep,  for  example, 
is  a  perfectly  normal  reflex  act,  although  more  easily  excited 
and  less  easily  controlled  than  in  adults. 

II.  Excretion  by  the  Skin. 

Besides  permitting  of  the  trifling  gaseous  interchange 
already  referred  to  (p.  258),  the  skin  plays  an  important  part 
in  the  elimination  of  water  by  the  sweat-glands. 

Sweat  is  a  clear  colourless  liquid,  alkaline  when  pure,  and 
consisting  chiefly  of  water  with  small  quantities  of  salts, 
neutral  fats,  and  volatile  fatty  acids,  and,  under  certain  con- 
ditions at  least,  the  merest  traces  of  proteids  and  urea.  It 
is  secreted  by  simple  gland-tubes,  which  form  coils  lined 
with  a  single  layer  of  columnar  epithelium,  in  the  sub- 
cutaneous tissue,  with  long  ducts  running  up  to  the  surface 
through  the  true  skin  and  epidermis.  Unless  collected  from 
the  parts  of  the  skin  on  which  there  are  no  hairs,  such  as 
the  palm,  it  is  apt  to  be  mixed  with  sebum,  a  secretion 
formed  by  the  breaking  down  of  the  cells  of  the  sebaceous 
glands,  which  open  into  the  hair  follicles,  and  consisting 
chiefly  of  fats,  soaps,  and  salts. 

Although  it  is  only  occasionally  that  sweat  collects  in 
visible  amount  on  the  skin,  water  is  always  being  given  off 


EXCRETION  413 

in  the  form  of  vapour.  This  invisible  perspiration  leaves 
behind  it  on  the  skin,  or  in  the  glands,  the  whole  of  the 
non-volatile  constituents,  which  may  be  to  some  extent 
reabsorbed ;  and  since  even  the  visible  perspiration  is  in 
large  part  evaporated  from  the  very  mouths  of  the  glands  in 
which  it  is  formed,  the  sweat  can  hardly  be  considered  a 
vehicle  of  solid  excretion,  even  to  the  small  extent  indicated 
by  its  chemical  composition. 

The  total  quantity  of  water  excreted  by  the  skin,  and  the 
relative  proportions  of  visible  and  invisible  perspiration,  vary 
greatly.  A  dry  and  warm  atmosphere  increases,  and  a 
moist  and  cold  atmosphere  diminishes  the  total,  and,  within 
limits,  the  invisible  perspiration.  Visible  sweat — given  the 
condition  of  rapid  heat-production  in  the  body  as  in  mus- 
cular labour — is  more  readily  deposited  on  freely  exposed 
surfaces  when  the  air  is  moist  than  when  it  is  dry.  The  air 
in  contact  with  surfaces  covered  by  clothing  is  never  far 
from  being  saturated  with  watery  vapour.  Here,  accordingly, 
a  comparatively  slight  increase  in  the  activity  of  the  sweat- 
glands  suffices  to  produce  more  water  than  can  be  at  once 
evaporated  ;  and  the  excess  appears  as  sweat  on  the  skin, 
to  be  absorbed  by  the  clothing  without  evaporation,  or  to  be 
evaporated  slowly,  as  the  pressure  of  the  aqueous  vapour 
gradually  diminishes  in  consequence  of  diffusion. 

The  quantity  of  sweat  given  off  by  a  man  in  twenty-four 
hours  varies  so  much  that  it  would  not  be  profitable  to  quote 
here  the  numerical  results  obtained  under  different  conditions 
of  temperature  and  humidity  of  the  air.  It  is  enough  to  say 
that  the  excretion  of  water  from  the  skin  is  of  the  same 
order  of  magnitude  as  that  from  the  kidneys :  a  man  loses 
upon  the  whole  as  much  water  in  sweat  as  in  urine.  But  it 
is  to  be  carefully  noted  that  these  two  channels  of  outflow 
are  complementary  to  each  other;  when  the  loss  of  water  by 
the  skin  is  increased,  the  loss  by  the  kidneys  is  diminished, 
and  vice  versa. 

The  Influence  of  Nerves  on  the  Secretion  of  Sweat. — The 
sweat-glands  are  governed  directly  by  the  nervous  system  ; 
and  though  an  actively  perspiring  skin  is,  in  health,  a 
flushed  skin,  the  vascular  dilatation  is  a  condition,  and  not 


414  A  MANUAL  OF  PHYSIOLOGY 

the  chief  cause  of  the  secretion.  Stimulation  of  the  peri- 
pheral end  of  the  sciatic  nerve  causes  a  copious  secretion  of 
sweat  on  the  pad  and  toes  of  the  corresponding  leg  of  a 
young  cat,  and  this  although  the  vessels  are  generally  con- 
stricted by  excitation  of  the  vaso-motor  nerves.  Not  only 
so,  but  when  the  circulation  in  the  foot  is  entirely  cut  off  by 
compression  of  the  crural  artery  or  by  amputation  of  the 
limb,  stimulation  of  the  sciatic  still  calls  forth  some  secretion. 
As  in  the  case  of  the  salivary  glands,  injection  of  atropia 
abolishes  the  secretory  power  of  the  sciatic,  while  leaving 
its  vaso-motor  influence  untouched  ;  and  pilocarpin  stimu- 
lates secretion  chiefly  by  direct  action  on  the  cells  of  the 
sweat-glands,  or  nerve  fibres  within  them. 

That  the  sweating  caused  by  a  high  external  temperature 
is  normally  brought  about  by  nervous  influence,  and  not  by 
direct  action  on  the  secreting  cells,  is  shown  by  the  following 
experiments.  One  sciatic  nerve  is  divided  in  a  cat,  and  the 
animal  is  put  into  a  hot-air  chamber.  No  sweat  appears 
on  the  foot  whose  nerve  has  been  cut,  but  the  other  feet  are 
bathed  in  perspiration.  Similarly,  a  venous  condition  of 
the  blood  (in  dyspnoea)  causes  sweating  in  the  feet  whose 
nerves  have  not  been  divided,  but  none  in  the  other  foot ; 
and  stimulation  of  the  central  end  of  the  cut  sciatic  has 
the  same  effect.  All  this  points  to  the  existence  of  a  reflex 
mechanism ;  and  it  is__certain  that  dyspnoea  acts  by  direct 
stimulation  of  the  centre  or  centres.  The  vaso-motor 
centre  is  at  the  same  time  stimulated,  and  the  bloodvessels 
constricted,  as  in  the  cold  sweat  of  the  death  agony.  Fear 
may  also  cause  a  cold  sweat,  impulses  passing  from  the 
cerebral  cortex  to  the  vaso-motor  and  sweat  centres. 

The  exact  position  and  number  of  the  sweat  centres  have  not  been 
settled.  It  is  possible  that  a  general  sweat-centre  exists  in  the 
medulla  oblongata,  but  its  existence  has  never  been  definitely  proved. 
On  the  other  hand,  it  is  known  that  in  the  cat  there  are  at  least  two 
spinal  centres,  one  for  the  fore-limbs  in  the  lower  part  of  the  cervical 
cord,  and  another  for  the  hind-limbs  where  the  dorsal  portion  of  the 
cord  passes  into  the  lumbar.  That  this  latter  centre  does  not  exist  or  is 
comparatively  inactive  in  man,  is  indicated  by  the  following  case.  A 
man  fell  from  a  window  and  fractured  his  backbone  at  the  fifth  dorsal 
vertebra.  The  lower  half  of  the  body  was  paralyzed  for  a  time,  but 


EXCRETION  415 

recovered.  Ultimately,  however,  the  paralysis  returned  ;  and  shortly 
before  his  death  (twenty-one  years  after  the  accident)  it  was  noticed 
that  a  copious  perspiration  broke  out  several  times  on  the  upper  part 
of  the  body,  while  the  lower  portion  remained  perfectly  dry.  If  there 
is  any  spinal  centre  in  man,  it  appears  to  lie  above  the  fifth  spinal 
segment.  For  it  was  seen  in  a  professional  diver  who  fractured  his 
neck  at  that  level,  and  lived  three  months  after  the  accident,  that 
sweat  frequently  appeared  on  the  parts  of  the  body  above  the  lesion, 
but  never  below.  At  the  autopsy  the  whole  thickness  of  the  cord, 
except  perhaps  a  small  portion  of  the  anterior  columns,  was  found 
destroyed. 

The  secretory  fibres  for  the  fore-limbs  (in  the  cat)  leave  the  cord 
in  the  anterior  roots  of  the  fourth  to  ninth  thoracic  nerves.  They 
pass  by  white  rami  communicantes  to  the  sympathetic  chain,  in  which 
they  reach  the  ganglion  stellatum,  where  they  are  all  connected  with 
nerve-cells.  Then,  as  non-medullated  fibres,  they  gain  the  brachial 
nerves  by  the  grey  rami,  and  run  in  the  radial  and  ulnar  to  the  pads 
of  the  feet.  The  fibres  for  the  hind-limbs  leave  the  cord  in  the 
anterior  roots  of  the  twelfth  thoracic  to  the  third  lumbar  nerves,  pass 
by  the  white  rami  to  the  sympathetic  ganglia,  in  which  they  form 
connections  with  ganglion  cells,  then,  as  non-medullated  fibres,  run 
along  the  grey  rami,  and  are  distributed  to  the  foot  in  the  sciatic. 

The  evidence  of  the  direct  secretory  action  of  nerves  on 
the  sweat  glands  is  singularly  striking  and  complete,  in  con- 
trast to  what  we  know  of  the  kidney.  In  the  latter,  blood- 
flow  is  the  important  factor ;  increased  blood-flow  entails 
increased  secretion.  In  the  former,  the  nervous  impulse  to 
secretion  is  the  spring  which  sets  the  machinery  in  motion  ; 
vascular  dilatation  aids  secretion,  but  does  not  generally  cause 
it.  It  would,  however,  be  easy  to  lay  too  much  stress  on  this 
distinction,  for  in  the  horse  the  mere  dilatation  of  the  blood- 
vessels of  the  head  after  section  of  the  cervical  sympathetic 
has  been  found  to  be  accompanied  by  increased  secretion  of 
sweat,  and  urinary  secretion  can  certainly  be  affected  by 
the  direct  action  of  various  substances  on  the  secretory 
mechanism,  independently  of  vascular  changes.  But  the 
broad  difference  stands  out  clearly  enough,  and  the  reason 
of  it  lies,  perhaps,  in  the  essentially  different  purpose  of  the 
two  secretions.  The  water  of  the  urine  is  in  the  main  a 
vehicle  for  the  removal  of  its  solids  ;  the  solids  of  the  sweat 
are  accidental  impurities,  so  to  speak,  in  the  water.  The 
kidney  eliminates  substances  which  it  is  vital  to  the  organism 
to  get  rid  of;  the  sweat-glands  pour  out  water,  not  because  it 


416  A  MANUAL  OF  PHYSIOLOGY 

is  in  itself  hurtful,  not  because  it  cannot  pass  out  by  other 
channels,  but  because  the  evaporation  of  water  is  one  of  the 
most  important  means  by  which  the  temperature  of  the 
body  is  controlled.  In  short,  urine  is  a  true  excretion, 
sweat  a  heat-regulating  secretion.  No  hurtful  effects  are 
produced  when  elimination  by  the  skin  is  entirely  prevented 
by  varnishing  it,  provided  that  the  increased  loss  of  heat  is 
compensated.  A  rabbit  with  a  varnished  skin  dies  of  cold, 
as  a  rabbit  with  a  closely-clipped  or  shaven  skin  does ;  sup- 
pression of  the  secretive  function  of  the  skin  has  nothing  to 
do  with  death  in  the  first  case  any  more  than  in  the  second. 


PRACTICAL  EXERCISES  ON  CHAPTER  VI. 
Urine. 

For  most  of  the  experiments  human  urine  is  employed — in  the 
quantitative  work  the  mixed  urine  of  the  twenty-four  hours.  Urine 
may  also  be  obtained  from  animals.  In  rabbits  pressure  on  the 
abdomen  will  empty  the  bladder.  Dogs  may  be  taught  to  micturate 
at  a  set  time  or  place,  or  kept  in  a  cage  arranged  for  the  collection  of 
urine.  Or  a  catheter  may  be  used  (p.  429). 

1.  Specific  Gravity. — Pour  the  urine  into  a  glass  cylinder,  and 
remove  froth,  if  necessary,  with  filter-paper.      Place  a  urinometer 
(Fig.  128)  in  the  urine,  and  see  that  it  does  not  come  in  contact 
with  the  side  of  the  vessel.     Read  off  on  the  graduated  stem  the 
division  which  corresponds  with  the  bottom  of  the  meniscus.     This 
gives  the  specific  gravity. 

2.  Reaction. — Test  with  litmus-paper.      Generally  the  litmus  is 
reddened,  but  occasionally  in  health  the  urine  first  passed  in  the 
morning  is  alkaline.     Sometimes  urine  has  an  amphicroic  reaction, 
i.e.,  affects  both  red  and  blue  litmus  paper.     This  is  the  case  when 
there  is  such  a  relation  between  the  bases  and  acids  that  both  acid 
and  '  neutral '  (dibasic)  phosphates  are  present  in  certain  proportions. 
The  acid  phosphate  reddens  blue  litmus,  and  the  '  neutral '  phosphate 
turns  red  litmus  blue. 

3.  Chlorides — (a)   Qualitative   Test. — Add  a  drop  of  nitric  acid 
and  a  drop  or  two  of  silver  nitrate  solution.     A  white  precipitate 
soluble  in  ammonia  shows  the  presence  of  chlorides.     The   nitric 
acid  is  added  to  prevent  precipitation  of  silver  phosphate. 

(V)  Quantitative  Estimation. — The  quantitative  estimation  of  tfa 
chlorine  in  urine  without  previous  evaporation  and  incineration  i 
best  made  by  one  of  the  modifications  of  Volhard's  method.  I 
depends  upon  the  complete  precipitation  of  the  chlorine  combined 
with  the  alkaline  metals,  and  also  of  sulphocyanic  acid,  by  silver 


PRACTICAL  EXERCISES 


FIG.  128.— URINO- 

METER. 


from  a  solution  containing  nitric  acid   in   excess ;    and  avoids  the 

error  introduced  into  simpler  methods,  like  Mohr's,  by  the  union  of 

some  of  the  silver  with  other  substances  than  chlorine.     A  given 

quantity  of  a  standard  solution  of  silver  nitrate  (more  than  sufficient 

to  combine  with  all  the  chlorine)  is  added  to 

a  given  volume  of  urine.     The  excess  of  silver 

is  now  estimated  by  means  of  a  standard  solution 

of  ammonium  sulphocyanide.    A  solution  of  the 

double  sulphate  of  iron  and  ammonium  (known 

as  iron-ammonia-alum)  is  taken  as  the  indicator, 

since  a  ferric  salt  does  not  give  the  usual  red  colour 

with  a  sulphocyanide  so  long  as  any  silver  in  the 

solution  is  uncombined  with  sulphocyanic  acid. 

To  carry  out  the  method,  put  10  c.c.  of  urine, 
which  must  be  free  from  albumin,  in  a  stoppered 
flask,  with  a  mark  corresponding  to  100  c.c. 
Add  50  c.c.  of  water,  4  c.c.  of  pure  nitric  acid 
(specific  gravity  1*2),  and  15  c.c.  of  the  standard 
silver  solution  (of  which  i  c.c.  corresponds  to 
•01  gramme  NaCl,  or  "00607  gramme  Cl) ; 
shake  well,  fill  with  water  to  the  mark,  and 
again  shake.  After  the  precipitate  has  settled, 
filter  it  off.  Take  50  c.c.  of  the  filtrate,  add 
5  c.c.  of  a  concentrated  solution  of  iron-am- 
monia-alum, and  run  in  from  a  burette  the  standard  solution  of 
ammonium  sulphocyanide  until  a  weak  but  permanent  red  coloration 
appears.  2  c.c.  of  the  sulphocyanide  solution  correspond  exactly 
to  i  c.c.  of  the  silver  solution,  so  as  just  to  allow  of  the  end  reaction 
with  the  iron  solution  being  seen,  and  no  more. 

Suppose  x  c.c.  of  the  sulphocyanide  solution  are  required,  then 
the  chlorine  in  TO  c.c.  of  urine  evidently  corresponds  to  (15-^) 
•o'oi  gramme  NaCl. 

4.  Phosphates— (i)  Qualitative  Tests.— (a)  Render  the  urine  alka- 
line with  ammonia.  A  precipitate  of  earthy  phosphates  (calcium 
and  magnesium  phosphates)  falls  down.  Filter.  To  the  filtrate  add 
magnesia  mixture  (a  mixture  of  sulphate  or  chloride  of  magnesium, 
ammonium  chloride  and  ammonia) ;  a  precipitate  shows  the  presence 
of  alkaline  phosphates  (sodium,  potassium,  or  ammonium  phos- 
phates). The  precipitate  is  ammonio-magnesic  or  triple  phosphate. 
{b}  Add  to  urine  half  its  volume  of  nitric  acid  and  a  little  molybdate 
of  ammonium,  and  heat.  A  yellow  precipitate  of  ammonium  phospho- 
molybdate  shows  that  phosphates  are  present. 

(2)  Quantitative  Estimation. — The  quantitative  estimation  of  phos- 
phoric acid  in  urine  is  best  done  volumetrically,  by  titration  with  a 
standard  solution  of  uranium  nitrate,  using  ferrocyanide  of  potassium 
as  the  indicator.  Uranium  nitrate  gives  with  phosphates,  in  a  solu- 
tion containing  free  acetic  acid,  a  precipitate  with  a  constant  pro- 
portion of  phosphoric  acid.  As  soon  as  there  is  more  uranium  in 
the  solution  than  is  required  to  combine  with  all  the  phosphoric  acid, 
-a  brown  colour  is  given  with  potassium  ferrocyanide,  due  to  the 

27 


41 8  A  MANUAL  OF  PHYSIOLOGY 

formation  of  uranium  ferrocyanide.  In  carrying  out  the  method, 
5  c.c.  of  a  mixture  of  acetic  acid  and  sodium  acetate  (there  are 
10  grammes  of  sodium  acetate  and  10  grammes  of  glacial  acetic  acid 
in  i oo  c.c.  of  the  mixture)  are  added  to  50  c.c.  of  urine,  which  is 
then  heated  in  a  beaker  on  the  water-bath  to  about  80°  C.  The 
standard  uranium  solution  (which  contains  35-5  grammes  of  uranium 
nitrate  in  the  litre,  and  i  c.c.  of  which  corresponds  to  0-005  gramme 
P?O5)  is  now  run  in  from  a  burette,  until  a  drop  of  the  urine  gives, 
with  a  drop  of  potassium  ferrocyanide  solution,  on  a  porcelain  slab, 
a  brown  colour.  Uranium  acetate  may  be  used  instead  of  uranium 
nitrate,  but  the  latter  keeps  best. 

5.  Sulphates — (i)  Qualitative   Test. —  Add   to  urine  a  drop  of 
hydrochloric  acid  and   then  a  few  drops  of  barium  chloride.     A 
white  precipitate   comes   down,   showing   that   inorganic   sulphates 
are  present.      The  hydrochloric  acid  prevents  precipitation  of  the 
phosphates. 

(2)  Quantitative  Estimation  of  the   Sulphuric  Acid  united  with 
Inorganic  Bases. — Acidulate  100  c.c.  of  albumin-free  urine  with  acetic 
acid,  add  excess  of  barium  chloride,  and  heat  on  the  water-bath  till 
the  precipitate  has  settled ;  filter  through  an  ash-free  filter,  wash  the 
precipitate  with  water,  with  dilute  hydrochloric  acid,  then  again  with 
water.     Dry,  incinerate  in  a  platinum  dish,  and  weigh.     From  the 
weight  of  barium  sulphate  the  inorganic  sulphuric  acid  is  easily  cal- 
culated (SO4  in  i  gramme  of  barium  sulphate  =  0-41 187  gramme). 

(3)  Quantitative   Estimation   of  the  Sulphuric  Acid  united  with 
Aromatic  Bodies  (aromatic  or  organic  sulphuric  acid). — Add  to  the 
nitrate  and  the  washings  from  (2)  a  little  hydrochloric  acid,  and  heat 
in  order  to  break  up  the  aromatic  sulphates.     The  elements  of  water 
are  thus  taken  up  by  these  salts ;  and  the  sulphuric  acid  is  able  to- 
unite  with  the  barium.     Add  more  barium  chloride  if  necessary,  and 
treat  the  precipitate  as  before.     Its  weight  after  incineration  gives  the 
quantity  of  barium  sulphate  corresponding  to  the  sulphuric  acid  of  the 
aromatic  compounds. 

6.  Indoxyl  can  be  oxidized  into  indigo,  and  so  estimated. 

A  qualitative  test  is  the  following  :  Ten  c.c.  of  horse's  urine  is- 
mixed  with  10  c.c.  of  strong  hydrochloric  acid,  and  a  dilute  solution 
of  sodium  hypochlorite  added  drop  by  drop ;  a  bluish  colour  appears 
if,  as  is  generally  the  case,  indoxyl  is  present,  indigo  (C1GH10N2O2> 
being  formed  by  the  oxidizing  action  of  the  hypochlorite  on  the 
indoxyl,  the  compound  of  which  with  sulphuric  acid  has  been  broken 
up  by  the  hydrochloric  acid.  The  number  of  drops  of  the  hypo- 
chlorite required  to  give  the  maximum  change  of  colour  is  deter- 
mined. Then  the  experiment  may  be  repeated  by  dropping  this 
quantity  of  hypochlorite  into  10  c.c.  of  the  hydrochloric  acid,  and 
adding  10  c.c.  of  the  urine.  The  urine  must  be  free  from  albumin. 
If  too  much  hypochlorite  be  added,  the  indigo  is  itself  oxidized. 
In  performing  the  test  in  human  urine,  which  contains  a  smaller 
quantity  of  the  indigo-forming  substance,  the  urine  should  first 
be  concentrated.  If  the  faint  blue  liquid  be  shaken  up  with  a 
few  drops  of  chloroform,  the  latter  takes  up  the  colour,  which 


PRACTICAL  EXERCISES  419 

is  thus  rendered  more  evident.  The  skatoxyl  of  urine  can  also  be 
oxidized  to  indigo,  but  it  is  present  in  far  smaller  amount.  The 
average  quantity  of  indigo  obtained  from  a  litre  of  horse's  urine  is 
about  150  milligrammes ;  from  a  litre  of  human  urine,  not  a  twentieth 
of  that  quantity. 

7.  Urea  —  (i)  Preparation. — Urea  can  be  obtained  from  dog's 
urine  by  evaporating  it  to  a  syrup,  extracting  with  absolute  alcohol, 
evaporating  most  of  the  alcohol,  and  allowing  the  mass  to  crystallize. 
Or  human  urine  may  be  concentrated  to  a  small  bulk,  cooled  to  o°, 
and  mixed  with  excess  of  strong  pure  nitric  acid.  A  mass  of  rhombic 
or  six-sided  tabular  crystals  of  nitrate  of  urea  separates.  From  the 
nitrate,  after  purification,  urea  itself  is  obtained  by  addition  of  barium 
carbonate  till  carbon  dioxide  ceases  to  be  given  off.  What  remains 
is  a  mixture  of  urea  and  barium  nitrate,  from  the  dry  residue  of  which 
urea  can  be  dissolved  out  by  alcohol  (Hoppe-Seyler). 

Urea  can  also  be  obtained  artificially  by  heating  its  isomer,  ammo- 
nium cyanate  (NH4  -  O  -  CN),  to  100°  C.  This  reaction  is  of  great 
historical  interest,  as  it  forms  the  final  step  in  Wohler's  famous 
synthesis  of  urea,  the  first  example  of  a  complex  product  of  the 
activity  of  living  matter  being  formed  from  the  ordinary  materials  of 
the  laboratory. 

Urea  is  also  formed  when  ammonia  is  allowed  to  act  on  carbonyl 
chloride.  Thus:  COC12  +  4NH3  =  CO.2(NH2)  +  2NH4C1. 

(2)  Decomposition  of  Urea. — Heated  dry  in  a  test-tube,  it  gives  off 
ammonia.     The  residue  contains  biuret,  which,  when  dissolved  in 
water,  gives  a  rose  colour,  with  a  trace  of  cupric  sulphate  and  excess 
of  sodium  hydrate  (or  of  the  hydrates  of  certain  other  metals  of  the 
alkalies  and  alkaline  earths,  p.  20).     Some  proteids — peptones  and 
albumoses — in  the  presence  of  the  same  reagents,  give  a  similar 
colour,  the  so-called  biuret  reaction. 

Heated  in  watery  solution  in  a  sealed  tube  to  180°  C.,  urea  is 
entirely  split  up  into  carbon  dioxide  and  ammonia,  a  change  which 
can  also  be  brought  about,  as  already  mentioned,  by  the  action  of 
micro-organisms.  Nitrous  acid,  hypochlorous  acid,  and  salts  of  hypo- 
bromous  acid  carry  the  decomposition  still  further,  carbon  dioxide, 
nitrogen,  and  water  being  the  products  of  their  oxidizing  action  on 
urea.  Thus  :  CO.2(NH2)  +  sNaBrO  =  3NaBr  +  2H2O  +  CO2  +  N2. 

(3)  Quantitative  Estimation  —  The  Hypobromite  Method.  —  This 
reaction  is  the  basis  of  a  method  for  the  quantitative  estimation  of 
urea  in  urine.     The  urea  is  split  up  by  sodium  hypobromite,  and 
the  carbon  dioxide  being  absorbed  by  the  excess  of  sodium  hydrate 
used  in  preparing  the  hypobromite,  the  nitrogen  is  collected  over 
water  in  an  inverted  burette.     It  is  easy  to  calculate  the  weight  of 
urea  corresponding  to  a  given  volume  of  nitrogen  measured  at  a 
given  temperature  and  pressure.     The  nitrogen  of  urea  is  f-f,  or  -^ 
of  the  whole  molecular  weight.     Now,  i  c.c.  of  N  weighs,  at  760 
millimetres  of  mercury  and  o°  C.,  '00125  gramme.    Therefore,  i  c.c. 
of  N  corresponds  to  -00125  x  -1T5-  =  '00268  gramme  urea.     Suppose, 
now,  that  i  c.c.  of  urine  was  found  to  yield  10  c.c.  of  N  measured  at 
17°  C.  and  750  millimetres  barometric  pressure.   Since  a  gas  expands 

27 — 2 


42O 


A  MANUAL  OF  PHYSIOLOGY 


part  of  its  volume  at  o°  for  every  degree  above  o°,  we  must 
correct  the  apparent  volume  of  the  nitrogen  by  multiplying  by  f-J^. 
Since  the  volume  of  a  gas  is  inversely  proportional  to  the  pressure, 
we  must  further  multiply  by  •£££.  Thus  we  get  ioxf^f  x|££  = 

Wur=9'29  c-c-  as  the  volume  of 
the  nitrogen  reduced  to  o°  C.  and 
760  millimetres  of  mercury.  Multi- 
plying this  by  '00268,  we  get  '0249 
gramme  urea  for  i  c.c.  urine,  which 
for  the  daily  yield  of  1,200  c.c. 
would  correspond  to  29^88  grammes 
urea. 

As  a  matter  of  fact,  however,  it 
has  been  found  that  there  is  always 
a  deficiency  of  nitrogen,  that  is,  a 
given  quantity  of  urea  yields  less 
than  the  estimated  amount  of  gas. 
A  gramme  of  urea  in  urine,  instead 
of  giving  off  373  c.c.  of  nitrogen, 
gives  only  354  c.c.  at  o°  C.  and 
760  millimetres  pressure.  We  must 
therefore  take  i  c.c.  of  N  as  corre- 
sponding to  '00282  gramme,  instead 
of  -00268  gramme  urea.  But  it  is 
affectation  to  make  this  correction 
if,  as  is  constantly  done  in  hospitals, 
the  temperature  is  not  taken  into 
account. 

A  convenient  apparatus  for  clini- 
cal use  is  shown  in  Fig.  129. 
Five  c.c.  of  urine  is  put  into  the 
thimble  A,  which  is  then  set  in  the 
small  bottle  B.  In  B,  15  c.c.  of  a 
solution  made  by  adding  bromine 
to  ten  times  its  volume  of  40  per  cent,  sodium  hydrate  solution  has 
already  been  placed.  The  cork  through  which  the  connecting  tube 
C  passes  is  now  carefully  fixed  in  B,  the  graduated  tube  D  is  im- 
mersed in  the  water  contained  in  the  cylinder  E,  and  the  stopcock 
F  being  open  to  the  air,  the  level  of  the  water  in  it  is  read  off.  The 
stopcock  having  been  closed  to  the  air  and  opened  to  tube  C,  the 
bottle  B  is  tilted  so  that  the  urine  in  the  thimble  is  gradually  mixed 
with  the  hypobromite  solution,  and  the  nitrogen  given  off  is  added 
to  the  air  in  the  graduated  tube  and  its  connections.  The  level  of 
the  water  in  the  tube  is  therefore  depressed.  WThen  gas  ceases  to  be 
given  off,  and  a  short  time  has  been  allowed  for  the  whole  to  cool, 
the  tube  is  raised  till  the  level  of  the  water  is  once  more  the  same 
inside  and  out.  The  level  is  again  read  off;  the  difference  of  the 
two  readings  gives  the  volume  of  nitrogen  at  the  temperature  of  the 
air  and  the  barometric  pressure.  An  ordinary  burette  may  also  be 
used,  the  tube  C  being  closed  by  a  pinchcock.  A  second  short  tube 


FIG.  129.— HYPOBROMITE  METHOD 
OF  ESTIMATING  UREA. 

F  is  a  stopcock  which  may  be  turned 
so  as  to  place  the  interior  of  the  cylinder 
D  either  in  communication  with  the 
external  air,  or  with  the  bottle  B, 
through  the  tube  C. 


PRACTICAL  EXERCISES  421 

passing  through  the  cork  of  B  is  left  open  till  the  cork  has  been 
adjusted,  and  then  closed. 

8.  Estimation  of  the  Total  Nitrogen. — It  is  often  more  important 
to  determine  the  total  nitrogen  of  the  urine  than  the  urea  alone ; 
and  this  is  conveniently  done  by  Kjeldahl's  method  (or  some  modifi- 
cation of  it),  which  can  also  be  applied  to  the  estimation  of  the 
nitrogen  in  the  faeces,  or  in  any  of  the  solids  or  liquids  of  the  body. 
It  depends  on  the  oxidation  of  the  nitrogenous  matter  in  such  a 
way  that  the  nitrogen  is  all  represented  as  ammonia.  The  ammonia 
is  then  distilled  over,  collected  and  estimated,  and  from  its  amount 
the  nitrogen  is  easily  calculated.  In  urine  the  method  can  be  carried 
out  by  adding  to  a  measured  quantity  of  it  (say  5  c.c.)  four  times 
its  volume  of  strong  sulphuric  acid,  and  boiling  in  a  long-necked 
flask  (capacity  200  c.c.),  after  the  addition  of  a  globule  of  mercury 
(about  o-i  c.c),  which  hastens  oxidation  and  obviates  bumping.  A 
part  of  the  mercuric  sulphate  formed  remains  in  solution ;  the  rest 
forms  a  crystalline  deposit.  The  heating  should  continue  for  half  an 
hour,  or  until  the  liquid  is  decolourized.  This  completes  the  process 
of  oxidation ;  and  the  next  step  is  to  liberate  the  ammonia  from  the 
substances  with  which  it  is  united  in  the  solution,  and  to  distil  it 
over.  Dilute  the  liquid  with  water,  after  cooling,  up  to  about  150  c.c., 
and  pour  into  a  larger  long-necked  flask.  Add  enough  of  a  solution 
of  sodium  hydrate  (specific  gravity  about  1-25)  to  render  the  liquid 
alkaline,  avoiding  excess,  as  this  favours  bumping.  The  proper 
quantity  can  be  found  by  determining  beforehand  how  much  of  the 
alkali  is  needed  to  neutralize  the  acid  used  for  oxidation,  and  this 
amount  should  be  added.  Bumping  may  further  be  prevented  by 
the  addition  of  a  little  granulated  zinc.  Shake  the  flask  two  or  three 
times.  Add  also  about  1 2  c.c.  of  a  concentrated  solution  of  potassium 
sulphide  (i  part  to  i|  parts  water),  which  favours  the  setting  free  of 
the  ammonia  from  the  amido-compounds  of  mercury  that  have  been 
formed  during  oxidation.  Commercial  '  liver  of  sulphur '  will  do 
quite  well.  Immediately  connect  the  distilling-flask  with  the  worm, 
as  shown  in  Fig.  130,  and  distil  the  ammonia  over  into  50  c.c.  of 
standard  (decinormal)  sulphuric  acid  contained  in  a  flask  into  which 
a  glass  tube  connected  with  the  lower  end  of  the  worm  dips.  Heat 
the  distilling  flask  at  first  gently,  then  strongly,  and  boil  for  three- 
quarters  of  an  hour,  or  until  about  two-thirds  of  the  liquid  has  passed 
over.  Then  lift  the  tube  out  of  the  standard  acid,  and  continue  the 
distillation  for  two  or  three  minutes  longer.  The  ammonia  is  now  all 
ur.ited  with  the  sulphuric  acid.  The  quantity  of  potassium  or  sodium 
hydrate  required  to  neutralize  a  given  volume  of  this  solution,  before 
and  after  the  ammonia  has  been  passed  into  it,  is  estimated  by 
titration ;  from  the  difference  the  amount  of  ammonia  is  calculated. 

In  titrating,  a  decinormal  solution  of  potassium  hydrate  may  be 
used  (i.e.,  a  solution  containing  5-6  grammes  in  1,000  c.c.),  and  the 
strength  of  this  solution,  as  well  as  of  the  decinormal  sulphuric  acid 
solution,  may  be  controlled  by  titration  with  a  decinormal  solution  of 
sodium  carbonate  (Na2CO3)  (5-3  grammes  in  1,000  c.c.)  or  of  oxalic 
acid  (6 -3  grammes  in  i}oooc.c.).  One  c.c.  of  any  one  of  these  solutions 


422  A  MANUAL  OF  PHYSIOLOGY 

is  equivalent  to  i  c.c.  of  any  other.  A  little  methyl  orange  solution 
is  added  to  the  standard  sulphuric  acid  before  titration,  to  serve  as 
indicator.  The  potassium  hydrate  is  added  till  the  pink  tinge  gives 
place  to  a  permanent  but  just  recognisable  yellow.  One  c.c.  of  deci- 
norrnal  sodium  or  potassium  hydrate  =  '0014  gramme  nitrogen. 

9.  Uric  Acid — (i)  Preparation. — Uric  acid  can  be  prepared  in  a 
pure  form  from  serpents'  excrement,  by  dissolving  it  in  dilute  sodium 
hydrate,  and  filtering.  The  filtrate  contains  sodium  urate,  which  is 
precipitated  by  a  current  of  carbon  dioxide.  The  uric  acid  is  set 
free  by  boiling  the  precipitate  with  dilute  hydrochloric  acid,  and  is 
deposited  as  a  colourless  crystalline  powder  on  cooling. 


FIG.  130. — ARRANGEMENT  FOR  DISTILLATION  IN  ESTIMATION  OF  TOTAL 

NITROGEN. 

(2)  Qualitative    Test  for    Uric   Acid — Murexide   Test. — A    small 
quantity  of  uric  acid  or  one  of  its  salts  is  heated  with  a  little  dilute 
nitric  acid.     The  colour  of  the  residue  left  by  evaporation  becomes 
yellow,  and  then  red,  and  on  the  addition  of  ammonia  changes  to 
deep  purple-red.     Potassium  or  sodium  hydrate  changes  the  yellow  to 
violet.    The  purple-red  substance  is  murexide  or  ammonium  furfurate, 
which  is  also  formed  by  the  action  of  nitric  acid  and  ammonia  on 
theobromine  (dimethylxanthin),  the  alkaloid  of  cocoa,  and  theine  or 
caffeine  (trimethylxanthin),  the  alkaloid  of  tea  and  coffee. 

(3)  Quantitative  Estimation — (a)  by  Precipitation  and  Weighing. — 
Uric  acid  is  precipitated  like  grains  of  cayenne  pepper  on  the  sides 
and  bottom  of  the  vessel  in  which  urine,  strongly  acidulated  with 
pure   hydrochloric  acid,  is  allowed  to  stand   for  forty-eight  hours. 
By  collecting  the  crystals  from  a  measured  quantity  of  urine  (say 


PRACTICAL  EXERCISES  423 

200  c.c.  with  10  c.c.  hydrochloric  acid  added)  on  a  small  weighed 
filter,  washing  the  precipitate  on  the  filter  with  as  small  a  quantity  of 
water  as  possible  (not  more  than  30  c.c.),  drying  at  110°  C,  and 
weighing,  an  estimate  may  be  made  of  the  amount  of  uric  acid  present 
(Heintz).  Notwithstanding  that  the  pigment  carried  down  with  the 
uric  acid  is  added  to  the  weight  of  the  latter,  this  method  gives 
results  somewhat  too  small,  as  a  portion  of  the  uric  acid  is  left  in 
solution. 

(b)  The  Silver  Method  of  estimating  Uric  Add. — Salkowski  has 
therefore  devised  a  method  founded  on  the  precipitation  of  the  uric 
acid  with  an  ammoniacal  silver  solution.  This,  in  one  or  other  of 
the  modified  forms  which  have  been  introduced  by  E.  Ludwig  and 
Haycraft  respectively,  is  probably  the  most  accurate  method  at 
present  at  our  disposal ;  and  of  the  two  modifications  we  may  say 
that  Ludwig's  is  the  more  exact,  but  Haycraft's  the  less  tedious. 

Haycraft's  method  (with  certain  alterations  by  Herrmann)  is  as 
follows  :  50  c.c.  of  urine  are  mixed  with  5  c.c.  of  a  magnesia  mixture* 
and  5  c.c.  of  an  ammoniacal  silver  solution.!  The  mixed  precipitate 
of  urate  of  silver  and  ammonio-magnesium  phosphate  is  allowed  to 
settle.  The  clear  liquid  is  filtered  by  means  of  a  suction-pump 
through  an  asbestos  or  glass-wool  filter.  About  4  grammes  sodium 
bicarbonate  in  substance  are  sprinkled  on  the  filter,  and  the  filtration 
of  the  precipitate  and  the  rest  of  the  liquid  proceeded  with.  The  pre- 
cipitate is  washed  on  the  filter  with  water  containing  ammonia,  until 
the  filtrate  gives  no  precipitate  either  on  the  addition  of  hydrochloric 
acid  or  of  silver  nitrate  and  nitric  acid.  The  precipitate  is  then  dis- 
solved in  pure  nitric  acid,  and  the  silver  in  it  estimated  by  titration 
with  ammonium  sulphocyanide  (Volhard's  method,  p.  417).  On  the 
assumptions  (which,  however,  are  by  no  means  granted  by  all  chemists 
who  have  studied  the  question)  that  the  uric  acid  combines  only  with 
the  silver,  and  the  silver  only  with  the  uric  acid,  and  that  the  com- 
pound formed  has  a  constant  composition,  the  amount  of  silver  enables 
us  to  calculate  the  quantity  of  uric  acid  present.  If  the  ammonium 
sulphocyanide  solution  is  made  of  centinormal  strength  (so  that  i  c.c. 
of  it  corresponds  to  i  c.c.  of  a  silver  solution  containing  17  grammes 
AgNOg  m  tne  litre),  i  c.c.  of  it  will  correspond  to  00168  gramme 
uric  acid.  The  method  is  not  suitable  for  urine  containing  a  great 
deal  of  uric  acid. 

(c}  Estimation  of  Uric  Acid  by  Precipitation  as  Ammonium  Urate 
—Whitney's  Modification  of  Hopkin's  Method. — Thirty  grammes  of 
ammonium  chloride  are  added  to  100  c.c.  of  urine.  After  two  hours 
the  precipitate  is  filtered  off  and  washed  on  the  filter  with  a  saturated 
solution  of  ammonium  chloride.  Filter  and  precipitate  are  placed  in 

*  The  magnesia  mixture  is  made  by  dissolving  100  grammes  crystal- 
lized magnesium  chloride  in  water,  then  adding  excess  of  ammonium 
chloride  and  as  much  ammonia  as  is  necessary  to  impart  a  distinct  odour 
to  the  liquid.  The  solution  is  then  made  up  to  i  litre. 

I  The  ammoniacal  silver  solution  is  made  by  dissolving  26  grammes 
silver  nitrate  in  excess  of  ammonia,  and  making  up  with  distilled  water 
to  i  litre. 


424  A  MANUAL  OF  PHYSIOLOGY 

an  Erlenmeyer  flask,  and  treated  with  10  c.c.  of  a  decinormal  solution 
of  hydrochloric  acid.  The  volume  is  made  up  to  about  50  c.c.  with 
distilled  water.  The  liquid  is  then  heated  to  boiling  to  decompose 
the  ammonium  urate,  and  the  excess  of  hydrochloric  acid  is  estimated 
by  titration  with  a  decinormal  solution  of  sodium  hydrate,  methyl 
orange  being  used  as  indicator.  If  x  is  the  number  of  c.c.  of  the 
sodium  hydrate  solution  used,  then  (  lo-x)  x  -0168  is  the  amount  in 
grammes  of  the  uric  acid  in  100  c.c.  of  urine. 

10.  Kreatinin. — Qualitatively,  kreatinin  may  be  recognised  in  very 
small  amounts  by  WeyFs  test.     A  few  drops  of  a  dilute  solution  of 
sodium  nitro-prusside  are  added  to  urine,  and  then  dilute  sodium 
hydrate.     A  ruby-red  colour  appears,  which  soon  turns  yellow.     If 
the  urine  is  now  acidified  with  acetic  acid  and  heated,  it  becomes 
first  greenish  and  then  blue. 

Kreatinin  forms  crystalline  compounds  with  various  acids  and 
salts,  of  which  the  most  important  is  kreatinin-zinc-chloride,  formed 
on  the  addition  of  zinc  chloride  to  an  alcoholic  or  watery  solution  of 
kreatinin,  often  in  the  shape  of  beautiful  thick-set  rosettes  of  needles. 
Neubauer  has  made  this  reaction  the  basis  of  a  method  for  the 
quantitative  estimation  of  kreatinin  (Fig.  120,  p.  388). 

11.  Hippuric  Acid. — From  horse's  or  cow's  urine  hippuric  acid  is 
prepared  by  evaporating  to  a  small  bulk,  and  adding  strong  hydro- 
chloric acid.     The  crystalline  precipitate  is  washed  with  cold  water, 
then  dissolved  in  hot  water,  and  filtered  hot.     Hippuric  acid  separates 
out  from  the  filtrate  in  the  cold  in  the  form  of  long  four-sided  prisms 
with  pyramidal  ends.     Heated  dry  in  a  test-tube,  the  crystals  melt, 
and  benzoic  acid  and  oily  drops  of  benzonitrile,  a  substance  with  a 
smell  like  that  of  oil  of  bitter  almonds,  are  formed. 

ABNORMAL   SUBSTANCES    IN   URINE. 

12.  Proteids — (i)    Qualitative    Tests. — (a)   Boil   and   add  a  few- 
drops  of  nitric  acid.      A  precipitate  on  boiling,  increased  or  not 
affected  by  the   acid,  shows   the  presence   of  coagulable   proteids 
(serum-albumin  or  globulin).     A   precipitate   of  earthy   phosphates 
sometimes  forms  on  boiling.     It  can  be  distinguished  from  a  pre- 
cipitate of  proteids  by  dissolving  on  the  addition  of  acid. 

(&}  Heller  s  Test. — Put  some  nitric  acid  in  a  test-tube.  Pour 
carefully  on  to  the  surface  of  the  acid  a  little  urine.  A  white  ring  at 
the  junction  of  the  liquids  indicates  the  presence  of  albumin,  globulin 
(or  albumose?).  When  this  test  is  performed  with  undiluted  urine, 
uric  acid  may  be  precipitated  and  cause  a  brown  colour  at  the  junc- 
tion. A  similar  ring  may  be  found  in  the  absence  of  proteids  when 
the  test  is  made  on  the  urine  of  a  patient  who  has  been  taking 
copaiba. 

(c)  Filter  some  urine,  and  add  to  the  filtrate  excess  of  acetic  acid 
and  a  few  drops  of  potassium  ferrocyanide.     If  proteids  are  present 
a  precipitate  forms. 

(d)  Test  for  Globulin  in  Urine. — Serum-globulin  probably  never 
occurs  in  urine  apart  from  serum-albumin.     It  may  be  detected  by 


PRACTICAL  EXERCISES  425 

Kauder's  test.  Make  the  urine  alkaline  with  ammonia,  let  it  stand 
for  an  hour  and  filter.  Half  saturate  the  filtrate  with  ammonium 
sulphate,  i.e.,  add  to  it  an  equal  volume  of  a  saturated  solution  of 
ammonium  sulphate.  Serum-globulin  is  precipitated,  serum-albumin 
is  not. 

(e)  Test  for  Albumose  in  Urine  (Albumosuria\ — Coagulable  proteids 
are  removed  by  boiling  the  urine  (acidulated  if  necessary),  and  filtering 
off  the  precipitate  if  any.  The  filtrate  is  neutralized.  If  a  further 
precipitate  falls  down  it  is  filtered  off,  the  clear  filtrate  is  heated  in  a 
beaker  placed  in  a  boiling  water-bath,  and  saturated  with  crystals  of 
ammonium  sulphate.  A  precipitate  indicates  that  albumoses  (pro- 
teoses)  are  present.  A  slight  precipitate  might  possibly  be  due  to  the 
formation  of  ammonium  urate.  A  further  test  may  be  performed  on 
the  original  urine  if  it  is  free  from  coagulable  proteids,  or  on  the 
filtrate  after  their  removal.  Add  a  few  drops  of  pure  nitric  acid.  If 
albumoses  are  present,  a  precipitate  is  thrown  down  which  disappears  on 
heating,  and  reappears  on  cooling  the  test-tube  at  the  cold-water  tap. 

(/)  Test  for  Peplone  in  Urine  (Peptonuria). — Place  some  of  the 
urine  in  a  beaker  on  a  boiling  water-bath  for  thirty  minutes,  and 
saturate  with  ammonium  sulphate  crystals.  Then  boil  over  a  small 
flame  or  in  an  air-bath  for  half  an  hour.  All  the  proteids,  including 
peptones,  are  precipitated.  But  the  peptones  can  still  be  redissolved 
by  water,  the  others  not.  Filter  hot.  Wash  the  precipitate  on  the 
filter  with  a  boiling  saturated  solution  of  ammonium  sulphate.  Then 
extract  the  residue  with  cold  water,  filter,  and  test  the  filtrate  by  the 
biuret  test  (addition  of  very  dilute  cupric  sulphate  and  excess  of 
sodium  hydrate).  A  rose  colour  indicates  the  presence  of  peptone 
(p.  377,  (S)),  but  if  the  reaction  is  only  a  faint  one,  it  may  be  due  to 
urobilin  (Stokvis). 

(2)  Quantitative  Estimation  of  Coagulable  Proteids  (Serum- 
Albumin  and  Globulin) — (a)  Gravimetric  Method. — Heat  50  to  100 
c.c.  of  the  urine  to  boiling,  adding  a  dilute  solution  (2  per  cent.)  of 
acetic  acid  by  drops  as  long  as  the  precipitate  seems  to  be  increased. 
Filter  through  a  weighed  filter.  Wash  the  precipitate  on  the  filter 
with  hot  water,  then  with  hot  alcohol,  and  finally  with  ether.  Dry 
in  an  air-bath  at  110°  C,  and  weigh  between  watch-glasses  of  known 
weight. 

(b]  Method  of  Roberts  and  Stolnikow  (modified  by  Brandberg). — 
This  method  is  founded  on  the  fact  that  the  time  taken  for  the  white 
ring  to  appear  in  Heller's  test  depends  on  the  proportion  of  coagulable 
proteid  present.  It  has  been  found  that  when  i  part  of  albumin  is 
contained  in  30,000  parts  of  an  albuminous  solution  (0-0033  Per  cent.), 
the  ring  appears  in  two  and  a  half  to  three  minutes.  The  amount  of 
dilution  of  the  urine  which  is  necessary  to  delay  the  formation  of  the 
ring  for  this  length  of  time  is  what  has  to  be  determined.  To  do 
this,  proceed  as  follows  :  Dilute  a  portion  of  the  urine  (say  5  c.c.)  ten 
times;  that  is,  add  to  it  nine  times  its  volume  of  distilled  water  (45  c.c. ) 
from  a  burette.  Place  some  pure  nitric  acid  in  a  test-tube  with  a 
pipette,  taking  care  not  to  wet  the  sides  of  the  test-tube  with  the 
acid.  Now  run  on  to  the  surface  of  the  nitric  acid  some  of  the 


426  A  MANUAL  OF  PHYSIOLOGY 

diluted  urine,  and  note  the  interval  that  elapses  before  formation 
of  the  white  ring.  If  it  is  more  than  three  minutes,  the  diluted  urine 
contains  less  than  i  part  in  30,000,  and  the  undiluted  urine  less 
than  i  part  in  3,000  (i.e.,  less  than  '033  per  cent.)  of  coagulable 
proteid,  and  the  experiment  must  be  repeated  with  urine  diluted 
to  a  smaller  extent.  If  the  ring  appears  after  a  shorter  interval 
than  three  minutes,  the  diluted  urine  contains  more  than  i  part  in 
30,000  (the  original  urine  more  than  '033  per  cent.),  and  must  be 
further  diluted.  Fill  a  burette  with  the  diluted  urine.  Run  i  c.c.  of 
it  into  a  test-tube  and  add  9  c.c.  of  distilled  water.  Repeat  the 
test  with  this  second  dilution.  If  the  ring  appears  at  a  longer 
interval  than  three  minutes,  the  twice-diluted  urine  contains  less  than 
i  part  of  albumin  in  30,000,  and  the  original  undiluted  urine  less 
than  i  part  in  300,  i.e.,  less  than  0*33  per  cent.  So  far,  then, 
we  have  found,  let  us  suppose,  that  the  proportion  of  albumin  in  the 
original  urine  lies  between  0*033  an^  °'33  P^1"  cent.  Now  run  i  c.c. 
of  the  urine  of  the  first  dilution  (the  urine  diluted  ten  times)  into 
a  test-tube,  and  add  4  c.c.  of  distilled  water,  i.e.,  dilute  again  five 
times.  If  this  gives  the  white  ring  in  Heller's  test  in  three  minutes, 

the  original  urine  will  contain   i  part  of  albumin  in    — » *•*•»  in 

10  x  5 

600  parts,  or  0*16  per  cent.  If  the  interval  is  longer  or  shorter  than 
three  minutes,  the  urine  of  the  first  dilution  (i  to  10)  must  be  diluted 
less  or  more  than  five  times  until  the  interval  amounts  to  about 
three  minutes.  The  total  dilution  corresponding  to  a  percentage  of 
0*0033  of  albumin  is  thus  known,  and  the  percentage  in  the  undiluted 
urine  can  be  easily  calculated. 

13.  Sugar— (i)  Qualitative  Tests— (a)  Trommels  Test.—  See  p.  23. 
It  is  to  be  remarked  that  some  substances  present  in  small  amount 
in  normal  urine  reduce  cupric  sulphate,  e.g.,  uric  acid  and  kreatinin, 
but  this  action  is  so  slight  that  it  can  cause  no  error  in  the  test,  as 
usually  performed.  Glycuronic  acid,  which  is  said  to  occur  even  in 
normal  urine  in  very  slight  traces,  and  which  also  reduces  cupric 
salts,  appears  in  considerable  amount  after  the  administration  of 
chloroform,  chloral,  nitro-toluol  and  other  substances.  If  less  than 
o'5  per  cent,  of  sugar  is  present  in  the  urine,  no  precipitate  of  cuprous 
oxide  will  be  formed  till  the  urine  is  cooled.  The  test  may  also  be 
performed  with  Fehling's  solution. 

(&)  ^Phenyl-hydrazine  Test. — This  test  depends  upon  the  fact  that 
phenyl-hydrazine  forms  with  sugars  such  as  glucose,  maltose,  isomal- 
tose,  etc.,  but  not  with  cane-sugar,  characteristic  crystalline  substances 
(phenyl-glucosazone,  phenyl-maltosazone,  etc.)  which  can  be  recog- 
nised under  the  microscope,  and  are  distinguished  from  each 
other  by  melting  at  different  temperatures.  Phenyl-glucosazone 
(C18H22N4O4)  melts  at  205°  C.  To  perform  the  test  for  glucose  in 
the  urine,  proceed  thus  :  Put  5  c.c.  of  urine  in  a  test-tube,  add 
i  decigramme  of  hydrochlorate  of  phenyl-hydrazine  ('twice  as  much 
as  will  lie  on  the  point  of  a  knife-blade  ' — v.  Jaksch),  and  one  and  a 
half  times  as  much  sodium  acetate  as  is  taken  of  the  phenyl-hydrazine 
salt.  Heat  the  test-tube  in  a  boiling  water-bath  for  half  an  hour. 


PRACTICAL  EXERCISES 


427 


Then  cool  at  the  tap  and  examine  the  yellow  crystalline  deposit 
under  the  microscope  (Plate  IV.,  3).  Very  minute  traces  of  sugar 
can  be  detected  in  this  way  (as  little  as  0*1  per  cent,  in  urine). 
Often  in  normal  urine  yellow  crystals  are  deposited  during  the  first 
fifteen  minutes'  heating.  They  must  not  be  mistaken  for  glucosazone. 
They  probably  consist  of  a  compound  of  glycuronic  acid  and  phenyl- 
hydrazine.  They  are  changed  as  the  heating  goes  on  into  an 
amorphous  brownish-yellow  precipitate  (Abel). 

(c)  The  Yeast  Test  is  an  important  confirmatory  test  for  distin- 
guishing the  fermentable  sugars  from  other  reducing  substances,  but  it 
is  not  very  delicate,  and  will  with  difficulty  detect  sugar  when  less  than 
0*5  per  cent,  is  present.  It  can  be  performed  thus  :  A  little  yeast 
(the  tablets  of  compressed  yeast  do  very  well)  is  added  to  a  test-tube 
half  filled  with  urine.  The  test-tube  is  then  filled  up  with  mercury, 
closed  with  the  thumb,  and  inverted  over  a  dish  containing  mercury. 
The  dish  may  be  placed  on  the  top  of  a  water-bath  whose  temperature 
is  about  40°  C.  After  twenty-four  hours  the  sugar  will  have  been 
broken  up  into  alcohol  and  carbon  dioxide.  The  latter  will  have 
collected  above  the  mercury  in  the  test-tube,  and  the  former  will  be 
present  in  the  urine.  The  tests  for  sugar  will  either  be  negative  or 
will  be  less  distinct  than  before. 

(2)  Quantitative  Estimation  of  Sugar  in  Urine. — (a)  Volumetrically^ 
the  sugar  can  be  estimated  by  titration  with  Fehling's  solution.  As 
this  does  not  keep  well,  two  solutions  containing  its  ingredients 
should  be  kept  separately  and  mixed  when  required.  Solution  I. : 
Dissolve  34*64  grammes  pure  cupric  sulphate  in  distilled  water,  and 
make  up  the  volume  to  500  c.c.  Solution  II. :  Dissolve  173  grammes 
-  ?5ch§iie_salt  in  400  c.c.  of  water,  add  to  this  51-6  grammes 
sodium  hydrate,  and  make  up  the  volume  with  water  to  500  c.c. 
Keep  in  well-stoppered  bottles  in  the  dark.  For  use,  mix  together 
equal  volumes  of  the  two  solutions.  Ten  c.c.  of  this  mixture  is 
reduced  by  0-05  gramme  dextrose.  To  estimate  the  ssgar  in  urine, 
put  10  c.c.  of  the  mixture  into  a  porcelain  capsule  or  glass  flask,  and 
dilute  it  four  or  five  times  with  distilled  water.  Dilute  some  of  the 
urine,  say  ten  or  twenty  times,  according  to  the  quantity  of  sugar 
indicated  by  a  rough  determination.  Run  the  diluted  urine  from 
a  burette  into  the  Fehling's  solution,  bringing  it  to  the  boil  each 
time  urine  is  added,  until,  on  allowing  the  precipitate  to  settle,  the 
blue  colour  is  seen  to  have  entirely  disappeared  from  the  supernatant 
liquid. 

Suppose  that  10  c.c.  of  Fehling's  solution  is  decolourized  by  20  c.c. 
of  the  ten-times  diluted  urine.  Then  2  c.c.  of  the  original  urine 
contains  0-05  gramme  dextrose.  If  the  urine  of  the  twenty-four 
hours  (from  which  this  sample  is  assumed  to  have  been  taken) 
amounts  to  4,000  c.c.,  the  patient  will  have  passed  0*05  x  2,000=  100 
grammes  sugar,  in  twenty-four  hours. 

(b)  The  polarimeter  affords  a  rapid  and,  with  practice,  a  delicate 
means  of  estimating  the  quantity  of  sugar  in  pure  and  colourless 
solutions,  but  diabetic  urine  must  in  general  be  first  decolourized  by 
adding  lead  acetate  and  filtering  off  the  precipitate.  What  is 


428  A  MANUAL  OF  PHYSIOLOGY 

measured  is  the  amount  by  which  the  plane  of  polarization  of  a  ray 
of  polarized  light  of  given  wave-length  (say  sodium  light)  is  rotated 
when  it  passes  through  a  layer  of  the  urine  or  other  optically  active 
solution  of  known  thickness.  Let  a  be  the  observed  angle  of  rota- 
tion, /  the  length  in  decimetres  of  the  tube  containing  the  solution, 
w  the  number  of  grammes  of  the  optically  active  substance  per  c.c.  of 
solution,  and  (#)D  the  specific  rotation  of  the  substance  for  light  of 
the  wave-length  of  the  part  of  the  spectrum  corresponding  to  the 
D  line  (i.e.,  the  anaount  of  rotation  expressed  in  degrees  which  is 
produced  by  a  layer  of  the  substance  i  decimetre  thick,  when  the 

solution   contains    i    gramme  of  it   per   c.c).     Then    («)D=±  — ' 

In  this  equation  a  and  /  are  known  from  direct  measurement ; 
(a)D  has  been  determined  once  for  all  for  most  of  the  important  active 
substances,  and  therefore  w  is  easily  calculated.  For  dextrose  (a)D  may 
be  taken  as  52*6°.  It  varies  somewhat  with  the  concentration,  but 
for  most  investigations  on  the  urine  these  variations  may  be  neglected. 

It  is  not  possible  to  describe  here  the  numerous  forms  of 
polarimeter  that  are  in  use.  Among  the  best  are  those  constructed 
on  what  is  called  the  '  half-shadow  '  system.  A  half-shadow  polari- 
meter consists,  like  other  polarimeters,  of  a  fixed  Nicol's  prism  (the 
polarizer),  and  a  nicol  capable  of  rotation  (the  analyzer).  In  addition, 
there  is  an  arrangement  which  rotates  by  a  definite  angle  the  plane 
of  polarization  in  one  half  of  the  field,  but  not  in  the  other,  e.g.,  a 
small  nicol  occupying  only  half  of  the  field.  In  the  zero  position  of 
the  analyzer,  both  halves  of  the  field  are  equally  dark.  The  solution 
to  be  investigated  is  placed  in  a  tube  of  known  length,  the  ends  of 
which  are  closed  by  glass  discs  secured  by  brass  screw  caps.  The 
glass  discs  must  be  slid  on,  so  as  to  exclude  all  air.  The  tube 
having  been  introduced  between  the  polarizer  and  analyzer,  the  sharp 
vertical  line  which  indicates  the  division  between  the  two  half-fields 
is  focussed  with  the  eye-piece,  and  then  the  analyzer  is  rotated  till 
the  two  halves  are  again  equally  shadowed.  The  angle  of  rotation, 
0,  is  read  off  on  the  graduated  arc,  which  is  provided  with  a 
vernier. 

Systematic  Examination  of  Urine. — In  examining  urine,  it  is  con- 
venient to  adopt  a  regular  plan,  so  as  to  avoid  the  risk  of  overlooking 
anything  of  importance.  The  following  simple  scheme  may  serve  as 
an  example ;  but  no  routine  should  be  slavishly  followed,  the  object 
being  to  get  at  the  important  facts  with  the  minimum  of  labour  : 

T.  Anything  peculiar  in  colour  or  smell  ?  If  colour  suggests  blood, 
examine  with  spectroscope  j  if  it  suggests  bile,  test  for  bile-pigments. 
(See  pp.  62,  64,  380.) 

2.  Reaction. 

3.  Sediment  or  not  ?     If  the  appearance  of  the  sediment  suggests 
anything  more  than  a  little  mucus,  examine  with  microscope. 

4.  Specific  gravity. 

5.  Quantity  of  urine  in  twenty-four  hours.     If  quantity  abnormally 
large  and  specific  gravity  high,  test  for  sugar. 

6.  Inorganic  constituents  not  generally  of  clinical  importance,  but 


PRACTICAL  EXERCISES  429 

in   special    diseases   they   should   be   examined  —  e.g.,  chlorides   in 
pneumonia. 

7.  Normal  organic  constituents.     Quantitative  estimation  of  urea 
in  fever,  and  often  in  diabetes  and  Bright's  disease. 

8.  Chemical  examination   for  abnormal)  gj3"™1"' 

organic  constituents.  1  ^.-?    '  ,.        ,     . 

[Bile-salts  and  pigments. 

14.  Catheterism.  —  In  many  physiological  experiments  it  is 
necessary  to  obtain  urine  from  the  bladder  by  means  of  a  catheter. 
The  most  suitable  form  for  animals  is  the  flexible  vulcanized  rubber 
tubes,  which  are  also  often  employed  in  man.  It  is  possible  to  pass 
a  fine  catheter  into  the  bladder  of  a  male  dog,  but  it  is  easier  to 
catheterize  a  bitch,  which  is  generally  used  for  such  experiments. 
Even  in  the  bitch  the  opening  of  the  urethra  lies  entirely  concealed 
within  the  vagina,  much  deeper  than  the  cul-de-sac  in  the  mucous 
membrane,  into  which  the  beginner  usually  tries  to  force  the  catheter. 
For  a  first  attempt  the  animal  should  be  etherized  and  fastened  on  a 
holder.  The  little  or  index  finger  of  the  left  hand  is  passed  into  the 
vagina  till  the  symphysis  pubis  can  be  felt.  A  little  below  this  is  the 
opening  of  the  urethra.  With  the  right  hand  the  point  of  a  flexible 
catheter  of  suitable  calibre  is  directed  along  the  finger,  and  after  a 
little  *  guess  and  trial  '  it  slips  into  the  bladder,  its  entrance  being 
announced  by  the  escape  of  urine. 

When  the  animal  is  to  be  used  in  a  long  series  of  experiments  an 
operation  is  sometimes  performed  first  of  all  to  render  the  urethral 
orifice  more  accessible. 


i 


CHAPTER  VII. 
METABOLISM,  NUTRITION  AND  DIETETICS. 

WE  return  now  to  the  products  of  digestion  as  they  are 
absorbed  from  the  alimentary  canal,  and,  still  assuming  a 
typical  diet  containing  proteids,  carbo-hydrates  and  fats,  we 
have  to  ask,  What  is  the  fate  of  each  of  these  classes  of 
proximate  principles  in  the  body  ?  what  does  each  contribute 
to  the  ensemble  of  vital  activity  ?  It  will  be  best,  first  of 
all,  to  give  to  these  questions  what  roughly  qualitative 
answer  is  possible,  then  to  look  at  metabolism  in  its  quanti- 
tative relations,  and  lastly  to  focus  our  information  upon 
some  of  the  practical  problems  of  dietetics. 

i.  Metabolism  of  Proteids. — The  two  chief  proteids  of  the 
blood-plasma,  serum-globulin  and  serum-albumin,  must,  as 
has  been  already  pointed  out,  be  recruited  from  proteids 
absorbed  from  the  intestine  and  for  the  most  part  altered  in 
their  passage  through  the  epithelium  which  lines  it.  What 
at  bottom  the  reason  and  the  mechanism  of  this  alteration 
are,  we  do  not  know ;  but  we  do  know  that  it  is  imperative 
that  peptone  (or  at  least  albumose)  should  not  appear  in 
quantity  in, the  blood,  for  when  injected  it  causes  profound 
changes  in  that  liquid,  one  expression  of  which  is  the  loss 
of  its  power  of  coagulation,  and  is  rapidly  excreted  by 
the  kidneys,  or  separated  out  into  the  lymph.  It  is  not 
definitely  known  whether  the  peptones  formed  in  digestion 
yield,  under  the  influence  of  the  epithelial  cells,  both  the 
chief  proteids  of  the  blood  in  the  proportions  in  which  they 
exist  in  the  plasma,  or  only  one  of  them,  which  is  afterwards 


METABOLISM,  NUTRITION  AND  DIETETICS          431 

and  elsewhere  partially  changed  into  the  other.  But  there 
is  some  evidence  that  serum-albumin  is  more  directly  related 
to  the  proteids  of  the  food  than  serum-globulin.  And  it 
is  said  that  during  starvation  the  albumin  is  relatively 
diminished,  and  the  globulin  relatively  increased.  However 
this  may  be,  it  cannot  be  doubted  that  the  conversion  of 
peptones,  directly  or  indirectly,  into  the  proteids  of  the 
blood-plasma  forms  the  first  recognisable  step  in  the  trans- 
formation of  the  greater  part  of  the  digested  proteids. 

Living  and  Dead  Proteids. — Now  and  again  a  living  proteid 
molecule  in  the  whirl  of  flying  atoms  which  we  call  a  muscle-fibre, 
or  a  gland-cell,  ,or  a  nerve-cell,  falls  to  pieces.  Now  and  again  a 
molecule  of  proteid,  hitherto  dead,  coming  within  the  grasp  of  the 
molecular  forces  of  the  living  substance,  is  caught  up  by  it,  takes  on 
its  peculiar  motions,  acquires  its  special  powers,  and  is,  as  we  phrase 
it,  made  alive.  But  it  is  not  any  difference  in  the  kind  of  proteid 
which  determines  whether  a  given  molecule  shall  become  a  part  of 
one  tissue  rather  than  of  another.  For  it  is  from  the  serum-albumin 
and  serum-globulin  of  the  blood  that  all  the  proteid  material  required 
to  repair  the  waste  of  the  body  must  ultimately  be  derived ;  and  a 
particle  of  serum-albumin  may  chance  to  take  its  place  in  a  liver-cell 
and  help  to  form  bile,  while  an  exactly  similar  particle  may  become 
a  constituent  of  an  endothelial  scale  of  a  capillary  and  assist  in 
forming  lymph,  or  of  a  muscular  fibre  of  the  heart  and  help  to  drive 
on  the  blood,  or  of  a  spermatozoon  and  aid  in  transferring  the 
peculiarities  of  the  father  to  the  offspring.  Indeed,  although  there 
are  differences  of  detail,  the  broad  lines  of  nutrition  are  the  same  for 
all  tissues;  and  just  as  a  tomb  or  a  lighthouse,  a  palace  or  a  church, 
may  be,  and  has  been  built  with  the  same  kind  of  material,  or  even 
in  succession  with  the  very  same  stones,  so  every  organ  builds  up  its 
own  characteristic  structure  from  the  common  quarry  of  the  blood. 

In  the  case  of  the  more  highly  developed  tissues  at  least,  no  mere 
change  of  food  will  radically  alter  structure.  A  cell  may  be  fed  with 
different  kinds  of  food,  it  may  be  over-fed,  it  may  be  ill-fed,  it  may 
be  starved ;  but  its  essential  peculiarities  remain  as  long  as  it  con- 
tinues to  live.  But  in  proportion  as  the  advance  of  physiology  has- 
emphasized  the  dominant  position  of  organization,  it  has  taken  away 
the  hope  of  our  ever  being  able  to  understand  in  what  it  is  that  the 
difference  between  the  living  and  the  dead  cell,  between  living  and 
dead  proteid,  or  protoplasm,  really  consists. 

The  speculation  of  Pfliiger,  that  the  nitrogen  of  living  proteid 
exists  in  the  form  of  cyanogen  radicals,  whilst  in  dead  proteid  it 
is  in  the  form  of  amides,  and  that  the  cause  of  the  characteristic 
instability  of  the  living  substance — its  prodigious  power  of  dissocia- 
tion and  reconstruction — is  the  great  intramolecular  movement  of 
the  atoms  of  the  cyanogen  radicals,  is  very  interesting  and  ingenious, 
but  it  remains,  and  is  likely  to  remain,  a  speculation.  And  the  same 


432  A  MANUAL  OF  PHYSIOLOGY 

is  true  of  the  suggestion  of  Loew  and  Bokorny,  that  the  endowments 
of  living  protoplasm  depend  on  the  presence  of  the  unstable  aldehyde 
group  H-C  =  O.  Nor  do  the  known  differences  of  chemical  com- 
position in  dead  organs  give  any  insight  into  the  peculiarities  of 
organization  and  function  which  mark  off  one  living  tissue  from 
another.  For  so  far  as  they  do  not  depend  upon  differences  in  the 
dead  plasma  which  interpenetrates  the  living  substance,  they  only 
show  that  the  latter  does  not  split  up  quite  in  the  same  way  at  death 
in  all  the  tissues,  while  the  general  similarity  in  the  elementary 
composition  of  excitable  structures  leaves  us  free  to  imagine  as  great 
or  as  small  a  similarity  as  we  please  in  the  grouping  of  the  atoms 
in  the  living  combinations.  Be  this  as  it  may,  the  living  proteid 
molecule,  whatever  function  it  may  have  been  fulfilling  in  the 
organized  elements  of  the  body,  has  certainly  a  much  greater 
tendency  to  fall  to  pieces  than  the  dead  proteid  molecule.  And 
it  falls  to  pieces  in  a  fairly  definite  way,  the  ultimate  products,  under 
the  influence  of  oxygen,  being  carbon  dioxide,  water,  and  compara- 
tively simple  nitrogen- containing  substances,  which  after  further 
changes  appear  in  the  urine  as  urea,  uric  acid,  kreatinin,  and 
ammonia.  We  have  no  definite  information  as  to  the  production 
of  water  from  the  hydrogen  of  the  tissues,  except  what  can  be 
theoretically  deduced  from  the  statistics  of  nutrition  (p.  463).  A 
few  words  will  be  said  a  little  farther  on  about  the  production  of 
carbon  dioxide  from  proteids ;  we  have  now  to  consider  the  seat  and 
manner  of  formation  of  the  nitrogenous  metabolites.  And  since  in 
man  and  the  other  mammals  urea  contains  by  far  the  greater  part  of 
the  excreted  nitrogen,  it  will  be  well  to  take  it  first. 

Formation  of  Urea. — The  starting-point  of  all  inquiries  into 
the  formation  of  urea  is  the  fact  that  it  occurs  in  the  blood, 
although  in  very  small  quantities  (2  to  4  parts  per  10,000). 
Evidently,  then,  some,  at  least,  of  the  urea  excreted  in  the 
urine  may  be  simply  separated  by  the  kidney  from  the 
blood ;  and  analysis  shows  that  this  is  actually  the  case,  for 
the  blood  of  the  renal  vein  is  poorer  in  urea  than  that  of 
the  renal  artery.  If  we  knew  the  exact  quantity  of  blood 
passing  through  the  kidneys  of  an  animal  in  twenty-four 
hours,  and  the  average  difference  in  the  percentage  of  urea 
in  the  blood  coming  to  and  leaving  them,  we  should  at  once 
be  able  to  decide  whether  the  whole  of  the  urea  in  the  urine 
reaches  the  kidneys  ready  made,  or  whether  a  portion  of  it 
is  formed  by  the  renal  tissue.  Although  data  of  this  kind 
are  as  yet  too  inexact  and  too  incomplete  to  enable  us, 
without  other  evidence,  absolutely  to  say  that  all  the  urea 
is  simply  separated  by  the  kidney,  it  is  not  difficult  to  se 


METABOLISM,  NUTRITION  AND  DIETETICS  433 

from  such  rough  measurements  as  have  been  made,  that 
this  is  at  least  possible,  if  not  probable. 

If  we  take  the  weight  of  the  kidneys  of  a  dog  of  35  kilos  at 
1 60  grammes  (^T<yth  of  the  body-weight  is  the  mean  result  of  a  great 
number  of  observations  in  man),  and  the  average  quantity  of  blood 
in  them  at  rather  less  than  one-fourth  of  their  weight,  or  35  grammes, 
and  consider  that  this  quantity  of  blood  passes  through  them  in  the 
average  time  required  to  complete  the  circulation  from  renal  artery 
to  renal  vein,  or,  say,  ten  seconds,  we  get  about  300  kilos  of  blood  as 
the  flow  through  the  kidneys  in  twenty-four  hours.  At  "3  per  1,000, 
the  urea  in  300  kilos  of  blood  would  amount  to  90  grammes.  Now, 
Voit  found  that  a  dog  of  35  kilos  body-weight,  on  the  minimum  proteid 
diet  (450  to  500  grammes  lean  meat  per  day)  which  sufficed  to  main- 
tain its  weight,  excreted  35  to  40  grammes  urea  in  the  twenty-four 
hours.  If,  then,  the  renal  epithelium  separated  somewhat  less  than 
half  of  the  90  grammes  urea  offered  to  it  in  the  circulating  blood,  the 
whole  excretion  in  the  urine  could  be  accounted  for,  and  the  blood 
of  the  renal  vein  would  still  contain  more  than  half  as  much  urea 
as  that  of  the  renal  artery.  So  that  the  whole  of  the  urea  in  the  urine 
may  be  simply  separated  by  the  kidney  from  the  ready-made  urea  of 
the  blood. 

But  it  is  necessary  to  add  that  urea  may  be  formed  to  a 
small  extent  in  the  kidney  itself;  for  when  blood  is  caused 
to  circulate  through  an  excised  '  surviving '  kidney,  urea 
accumulates  in  it  to  a  certain  extent,  and  apparently  in 
greater  amount  than  can  be  accounted  for  on  the  supposi- 
tion that  it  is  merely  washed  out  of  the  secreting  cells. 

Another  line  of  evidence  leads  us  to  the  same  conclusion  : 
that  the  kidney  is,  at  all  events,  not  an  important  seat  of 
urea-formation.  When  both  renal  arteries  are  tied,  or  both 
kidneys  extirpated,  in  a  dog,  urea  accumulates  in  the  blood  '' 
and  tissues;  and,  upon  the  whole,  as  much  urea  seems  to 
be  formed  during  the  first  twenty-four  hours  of  the  short 
period  of  life  which  remains  to  the  animal  as  would  under 
normal  circumstances  have  been  excreted  in  the  urine. 

Where,  then,  is  urea  chiefly  formed?  We  should  naturally 
look  first  to  the  muscles,  which  contain  three-fourths  of  the 
proteids  of  the  body ;  but  we  should  look  there  in  vain  for 
any  great  store  of  urea — none,  or  only  a  trace,  is  normally 
present.  The  liver  contains  a  relatively  large  amount,  and 
there  is  very  strong  evidence  that  it  is  the  manufactory  in 
which  the  greater  part  of  the  nitrogenous  relics  of  broken-j 

28 


d°H 


O  v\  H 


434  A  MANUAL  OF  PHYSIOLOGY 

down  proteids  reach  the  final  stage  of  urea.  This  evidence 
may  be  summed  up  as  follows  : 

An  excised  'surviving'  liver  forms*urea  from  ammonium 
carbonate  mixed  with  the  blood  passed  through  its  vessels, 
while  no  urea  is  formed  when  blood  containing  arnmonium 
*  ^carbonate  i-s  sent  through  the  kidney  or  through  muscles. 
er  salts  of  ammonium,  such  as  the  lactate  and  the  car- 
hamate,  undergo  a  like  transformation  in  the  liver.  It  is 
difficult,  in  the  light  of  this  experiment,  to  resist  the  con- 

n  that  the  increase  in  the  excretion  of  urea  in  man, 
when  salts  of  ammonia  are  taken  by  the  mouth,  is  due  to  a 
similar  action  of  the  hepatic  cells. 

(2)  If  blood  from  a  dog  killed  during  digestion  is  perfused 
through  an  excised  liver,  some  urea  is  formed,  which  cannot 
be  simply  washed  out  of  the  liver-cells,  because  when  the 
blood  of  a  fasting  animal  is  treated  in  the  same  way  there  is 
no  apparent  formation  of  urea  (v.  Schroeder).   This  suggests 
that  during  digestion  certain  substances  which  the  liver  is 
capable    of  changing   into    urea    enter   the   blood   in    such 
amount  that  a  surplus  remains  for  a  time  unaltered.     These 
substances  may  come  directly  from  the  intestine  ;  or  they 
may  be  products  of  general  metabolism,  which  is  increased 
while  digestion  is  going  on  ;  or  they  may  arise  both  in  the 
intestine  and  in  the  tissues.     Leucin  —  which,  as  we  have 
seen,  is  constantly,  or,  at  least,  very  frequently,  present  in 
the  intestine  during  digestion  —  can    certainly  be   changed 
into  urea  in  the  body,  and  there  is  every  reason  to  believe 
that  the  change  takes  place  in  the  liver. 

(3)  Uric  acid  —  which  in  birds  is  the  chief  end-product  of 
proteid  metabolism,  as  urea  is  in  mammals  —  is  formed  in 
the  goose  largely,  and  almost  exclusively,  in  the  liver.     This 
has  been  most  clearly  shown  by  the  experiments  of  Min- 
kowski,  who  took  advantage  of  the  communication  between 
the  portal  and  renal-portal  veins  (p.  328)  to  extirpate  the 
liver  in  geese.     When  the  portal  is  ligatured  the  blood  from 
the  alimentary  canal  can  still  pass  by  the  roundabout  road 
of  the  kidney  to  the  inferior  cava,  and  the  animals  survive 
for  six  to  twenty  hours.     While  in   the   normal  goose  j^o. 
to  jojjer  cent,  of  the  jotal  nitrogen  is  eliminated  as  uric 


METABOLISM,  NUTRITION  AND  DIETETICS          435 

acid  in  the  urine,  and  only  ^_to^  _i §_per  cent,  as  ammonia, 
in  the  operated  goose  uric  acid  represents  only  3  to  6  per 
cent,  of  the  total  nitrogen,  and  ammonia  50  to  60,  per  cent. 
A  quantity  of  lactic  acid  equivalent  to  the  ammonia  appears 
in  the  urine  of  the  operated  animal,  none  at  all  in  the  urine 
of  the  normal  bird.  The  small  amount  of  urea  in  the 
normal  urine  of  the  goose  is  not  affected  by  extirpation  of 
the  liver.  And  while  jurea^  when  injected  into  the  blood,  is 
in  the  normal  goose  excreted  as  uric  acidvit  is  in  the  animal 
that  has  lost  its  liver  eliminated  in  the  urine  unchanged. 

(4)  After  removal  of  the  liver  in  dogs  whose  portal  vein 
has  been  previously  connected  with  the  inferior  vena  cava 
by  an  Eck's  fistula  (p.  328),  the  quantity  of  urea  excreted  is 
markedly  diminished,  and  the  ammonium  salts  in  the  urine 
are  increased. 

(5)  In  acute  yellow  atrophy,  and  in  extensive  fatty  de- 
generation of  the  liver,  urea  may  almost   disappear   from 
the  urine,  and  be  replaced  by  leucin  and  tyrosin. 

If  it  be  granted,  as  in  the  face  of  the  evidence  it  must, 
that  the  liver  plays  an  important  part  in  the  formation  of 
urea,  we  have  still  to  ask  what  the  materials  are  upon  which 
it  works,  and  in  what  organs  they  are  formed  before  being 
brought  to  the  liver.  To  the  latter  question  it  may  be  at 
once  replied  that  proteid  metabolism,  although  its  final 
stages  may  be  worked  out  in  the  hepatic  cells,  must  go  on 
in  all  the  organized  elements  of  every  tissue.  The  living 
substance  everywhere  contains  proteid  ;  proteid  is  every- 
where and  at  all  times  breaking  down.  In  the  muscles 
especially  nitrogenous  substances  on  the  road  to  urea  must 
be  constantly  produced.  Can  we  lay  our  finger  on  any 
such  intermediate  substances  ?  Can  we  with  certainty  state 
that  any  of  the  separate  links  of  the  chain  of  proteid 
metabolism,  except  the  first  and  the  last,  have  actually 
been  discovered,  identified,  and  labelled  ?  The  answer  is 
that  a  whole  series  of  bodies  containing  nitrogen,  simpler 
than  proteids  and  with  a  greater  proportion  of  oxygen,  more 
complex  and  less  oxidized  than  urea,  has  been  found  in 
muscle  and  other  tissues ;  but  we  cannot  say  definitely  that 
any  or  all  of  them,  although  they  are  undoubtedly  stages 

28—2 


^.,  436  A  MANUAL  OF  PHYSIOLOGY 

~nH^co    in  the  downward  course  of  worn-out  proteids,  have  arisen 
'^-,       the  one  from  the  other,  or  must  necessarily  pass  into  the 

~  form  of  urea  before  being  finally  excreted. 
i  Such  substances  are  : 

1  — •  yi  H  * 

'•  =>  •+•' Guanin,  C5H5N5O In   the   pancreas,    liver,    and 

muscles. 


Sarkin,  or  hypoxanthin,  C5H4N4O 


'In  spleen,  liver,  muscles,  and 


0  bone-marrow. 


Xanthin,  C5H4N4O2 


Ei.  nM 


c 


Uric  acid,  C5H5N4O3 


In  spleen,  liver,  muscles, 
brain,  pancreas,  and  in  the 
urine. 

In  liver,  spleen,  lungs,  pan- 
creas, brain,  and  in  urine. 


Kreatin,  C4HN8O2  In  muscles,  blood,  brain. 


Lgm  3V>'2 

increase  in  the  proportion  of  oxygen  from  guanin  to 

~. uric  acid  is  very  striking,  and  particularly  the  regular  series 

formed  by  hypoxanthin,  xanthin  and  uric  acid  ;  and  Bunge 
has  suggested  that  the  first  three  may  be  stages  on  the  way 
to  uric  acid  or  urea.  But  kreatin  is  the  substance  of  this 
,JU  it*.*£~  class  which  exists  in  greatest  amount  in  the  body,  muscle 
\^y  ^containing  from  o'2  to  0*4  per  cent,  of  it;  and  the  total 
quantity  of  nitrogen  present  at  any  given  time  as  kreatin 
is  not  only  greater  than  that  of  the  nitrogen  present  in  urea, 
but  greater  than  the  whole  excretion  of  nitrogen  in  twenty- 
four  hours.  To  kreatin,  then,  we  should  naturally  look  first, 
among  all  these  nitrogenous  metabolites,  in  our  search  for 
a  forerunner  of  urea.  But  there  is  a  difficulty  in  accepting 
it  as  such,  for  although  in  the  laboratory  kreatin  can  be 
changed  into  kreatinin,  and  kreatinin  into  urea,  there  is  no 
proof  that  in  the  body  anything  more  than  the  first  step  in 
this  process  is  accomplished.  When  kreatin  is  introduced 
into  the  intestine,  it  appears  in  the  urine,  not  as  urea,  but 
as  kreatinin ;  injected  into  the  blood,  it  is  excreted  without 
change  by  the  kidneys.  Uric  acid  is,  indeed,  very  closely 
related  to  urea,  and  can  be  made  to  yield  it  by  oxidation 
outside  the  body.  Not  only  so,  but  it  is  excreted  as  urea 
when  given  to  a  mammal  by  the  mouth,  and  it  replaces 
urea  as  the  great  end-product  of  nitrogenous  metabolism 
almost  wholly  in  the  urine  of  birds  and  reptiles,  partially 
in  the  human  subject  in  leukaemia,  and  possibly  to  som 


METABOLISM,  NUTRITION  AND  DIETETICS          437 

extent  in  gout.  But  none  of  these  things  can  be  admitted 
as  evidence  that  in  the  normal  metabolism  of  mammals 
uric  acid  lies  on  the  direct  line  from  proteid  to  urea. 

Then,  again,  the  amido-acids,  leucin,  glycin  and  aspara-  ^^ 
ginic  acid,  when  given  by  the  mouth,  increase  the  output  ^2^ 
of  urea,  so  that  the  leucin  formed  in  the  intestine  during  =Hc^*i 

digestion  is  probably,  in  part  at  least,  a  precursor  of  urea. 

And  since  leucin  and  tyrosin  are  very  widely  spread  in  the  , 


solids  and  liquids  of  the  body,  it  has  been  asserted  that  tht 
amido-acids  are  the  form  in  which  nitrogen  leaves  the  tissues*  VC?OOH 
to  be  converted  into  urea  in  the  liver.  But  it  is  against  this  c  H  ^ 
view  that  there  is  not  enough  carbon  in  proteids  to  convert 
their  nitrogen  into  amido-acids  (Bunge).  Lea  has  suggested 
that  the  amido-acids  and  the  amidated  aromatic  acid,  tyrosin, 
have  quite  another  significance  than  that  of  intermediate 
steps  in  the  downward  metabolism  of  proteids — that  they 
are  destined,  in  fact,  to  take  part  in  synthetic  processes 
within  the  liver — that  they  are  on  the  up,  and  not  on  the 
down,  grade.  And  he  points  out,  in  support  of  this  view, 
that  even  when  the  urea  in  the  urine  is  increased  by  the 
administration  of  these  substances,  the  increase  does  not 
correspond  to  the  whole  of  their  nitrogen :  a  part  of  it  is 
therefore  devoted  to  other  purposes  in  the  body. 

The  conclusion  of  the  whole  matter  is  that,  if  anyone 
chooses  to  assert  that  the  proteids  of  the  tissues  fall  by  a 
single  descent  nearly  to  the  stage  of  urea,  there  is  as  yet  little 
real  evidence  to  contradict  him.  What  is  certain  is  that 
from  most  tissues  the  nitrogen  does  not  pass  out  chiefly  in  the  form 
of  urea,  that  it  appears  in  the  urine  mainly  as  urea,  and  that  the 
change  is  effected  to  a  large  extent,  but  not  exclusively,  in  the 
liver. 

Uric  acid,  like  urea,  is  separated  from  the  blood  by  the 
kidneys,  not  to  any  appreciable  extent  formed  in  them.  In 
birds  it  can  be  detected  in  normal  blood ;  in  man  in  the 
blood  and  transudations  of  gouty  patients,  in  whose  joints 
and  ear -cartilages  it  often  forms  concretions.  '  Chalk- 
stones  '  may  contain  more  than  half  their  weight  of  sodium 
urate.  The  spleen  yields  a  small  quantity  of  uric  acid, 
which  may  be  increased  by  blowing  air  through  a  mixture 


438  A  MANUAL  OF  PHYSIOLOGY 

of  splenic  pulp  and  calf's  blood.  The  fantastic  theory  that 
the  presence  of  uric  acid  in  large  amount  in  the  urine  of 
birds  was  due  to  deficiency  of  oxidation  is  happily  now 
defunct,  and  need  not  detain  us  here. 

acid  can  undoubtedly  be  produced  in  the  kidney. 


no^        If   an    excised    kidney   is   perfused   with   blood   containing 

t«»-  benzoic  acid,  or,  better,  benzoic  acid  and  glycin,  hippuric 

0  acid  is  formed.     In  herbivora  hippuric  acid  cannot  normally 

ew»-Co    '   be  detected  in  the  blood  ;  it  is  present  in  large  quantities  in 

the  urine  ;  it  must  therefore  be  manufactured  in  the  kidney, 

not  merely  separated  by  it.     In  certain  animals,  as  the  dog, 

the  kidney  is  the  sole  seat  of  the  production  of  hippuric 

acid.     But  in  the  rabbit  and  the  frog  some  of  it  may  also 

be   formed    in   other   tissues,   for   after   extirpation    of  the 

kidneys  the  administration  of  benzoic  acid  causes  hippuric 

acid  to  appear  in  the  blood.     It    is  not   known  how  the 

^*v<  ae*^  nitrogenous  glycin,  which  combines  with  the  benzoic  acid 

*V  c      1   derived  from  vegetable  food,  appears  on  the  spot  where  it 

is  wanted  to  form  hippuric  acid,  since  glycin  has  not  been 

found  anywhere  in  the  tissues.    It  is,  however,  a  constituent 

of  glycocholic  acid,  and  may  be  derived  from  that  part  of 

the  bile  which  is  reabsorbed. 

Kreatinin  can  be  so  readily  obtained  from  kreatin  outside 
the  body,  that  it  is  very  tempting  to  suppose  that  the 
kreatinin  of  the  urine  is  manufactured  by  the  kidney  from 
the  kreatin  of  muscle  carried  to  it  by  the  blood.  It  seems, 
however,  more  likely  that  some,  at  any  rate,  of  the  kreatinin 
of  the  urine  is  derived  from  ready-formed  kreatin  in  the  food. 
But  we  have  little  definite  knowledge  on  the  subject. 

Formation  of  Carbon  Dioxide  from  Proteids.  —  We  cannot  say 
whether  carbon  dioxide  is  normally  produced  at  the  moment 
when  the  nitrogenous  portion  of  the  proteid  molecule  splits 
off,  or  whether  a  carbonaceous  residue  may  not  still  hang 
together  and  pass  through  further  stages  before  the  carbon 
is  fully  oxidized.  We  shall  see  that  under  certain  condi- 
tions some  of  the  carbon  of  proteids  may  be  retained  in 
the  body  as  glycogen  or  fat  ;  and  this  suggests  that  in  all 
cases  it  may  run  through  intermediate  products  as  yet 
unknown,  before  being  finally  excreted  as  carbon  dioxide. 


METABOLISM,  NUTRITION  AND  DIETETICS  439 

2.  Metabolism  of  Carbo-hydrates — Glycogen. — The  carbo- 
hydrates of  the  food,  passing  into  the  blood  of  the  portal  vein 
in  the  form  of  dextrose,  are  in  part  arrested  in  the  liver,  and 
stored  up  as  glycogen  in  the  hepatic  cells,  to  be  gradually  given 
out  again  as  sugar  in  the  intervals  of  digestion.  The  proof  of 
this  statement  is  as  follows : 

Sugar  is  arrested  in  the  liver,  for  du-ring  digestion,  espe- 
cially of  a  meal  rich  in  carbo-hydrates,  the  blood  of  the 
portal  contains  more  sugar  than  that  of  the  hepatic  vein. 
In  the  liver  there  exists  a  store  of  sugar-producing  material 
from  which  sugar  is  gradually  given  off  to  the  blood,  for 
in  the  intervals  of  digestion  the  blood  of  the  hepatic  vein! 
contains   more   sugar  (2  parts  per   1,000)  than  the  mixed] 
blood  of  the  body  or  than  that  of  the  portal  vein  (i  to  1*5  | 
part  per  1,000).     When  the  circulation  through  the  liver  is 
cut  off  in  the  goose,  the   blood   rapidly  becomes  free,  or 
nearly  free,  from  sugar  (Minkowski).     And  a  similar  result 
follows  such  interference  with  the  hepatic  circulation  as  is 
caused  by  the  ligation  of  the  three  chief  arteries  of  the 
intestine  in  the  dog,  even  when  the  animal  has  been  pre- 
viously made  diabetic  by  excision  of  the  pancreas  (p.  472). 
The  nature  of  the  sugar-forming  substance  is  made  clear  by 
the  following  experiments :  (i)  A  rabbit  after  a  large  carbo- 
hydrate meal,  of  carrots  for  instance,  is  killed,  and  its  liver 
rapidly  excised,  cut  into  small  pieces,  and  thrown  into  acidu^ 
lated  boiling  water.     After  being  boiled  for  a  few  minutes,, 
the  pieces  of  liver  are  rubbed   up  in  a  mortar  and  again 
boiled  in  the  same  water.    The  opalescent  aqueous  extract  is 
filtered  off  from  the  coagulated  proteids.     No  sugar,  or  only 
traces  of  it,  are  found  in  this  extract ;  but  another  carbo- 
hydrate, glycogen,  an  isomer  of  starch  giving  a  port-wine 
colour  with  iodine  and    capable  of  ready  conversion    into 
sugar  by  amylolytic  ferments,  is  present  in  large  amount. 
(2)  The  liver  after  the  death  of  the  animal  is  left  for  a  time 
in  situ,  or,  if  excised,  is  kept  at  a  temperature  of  30°  to  40°  C., 
or  for  a  longer  period  at  a  low/er  temperature ;    it  is  then 
treated  exactly  as  before,  but  no  glycogen,  or  comparatively 
little,  can  now  be  obtained  from  it,  although  sugar  (dextrose) 
is  abundant.     The  inference  plainly  is  that  after  death  the 


440  A  MANUAL  OF  PHYSIOLOGY 

hepatic  glycogen  is  converted  into  dextrose  by  some  influence 
which  is  restrained  or  destroyed  by  boiling.  This  influence 
may  be  due  to  an  unformed  ferment  or  to  the  direct  action  of 
the  liver-cells,  for  both  unformed  ferments  and  living  tissue 
elements  are  destroyed  at  the  temperature  of  boiling  water. 
And  the  post-mortem  change  is  to  be  regarded  as  an  index 
of  a  similar  action  which  goes  on  during  life :  sugar  in  the 
intact  body  is  changed  into  glycogen  ;  glycogen  is  constantly 
being  changed  into  sugar.  (See  Practical  Exercises,  p.  511.) 

(3)  With  the  microscope,  glycogen,  or  at  least  a  substance 
which  is  very  nearly  akin  to  it,  which  very  readily  yields  it, 
and  which  gives  the  characteristic  port-wine  colour  with 
iodine,  can  be  actually  seen  in  the  liver-cells.  The  liver 
of  a  rabbit  or  dog  which  has  been  fed  on  a  diet  containing 
much  carbo-hydrate  is  large,  soft,  and  very  easily  torn.  Its 
large  size  is  due  to  the  loading  of  the  cells  with  a  hyaline 
material,  which  gives  the  iodine  reaction  of  glycogen,  and  is 
dissolved  out  by  water,  leaving  empty  spaces  in  a  network 
of  cell-substance.  If  the  animal,  after  a  period  of  starvation, 
has  been  fed  on  proteid  alone,  only  a  little  glycogen  is  found 
in  the  shrunken  liver-cells ;  if  the  diet  has  been  wholly  fatty, 
no  glycogen  at  all  may  be  found. 

In  the  liver-cells  of  the  frog  in  winter-time,  a  great  deal 
of  this  hyaline  material — this  glycogen,  or  perhaps  loose 
glycogen  compound — is  present ;  in  summer,  little  or  none. 
The  difference  is  very  remarkable  if  we  consider  that  in 
winter  frogs  have  no  food  for  months,  while  summer  is 
their  feeding-time ;  and  at  first  seems  inconsistent  with 
the  doctrine  that  the  hepatic  glycogen  is  a  store  laid  up 
from  surplus  sugar,  which  might  otherwise  be  swept  into 
the  general  circulation  and  excreted  by  the  kidneys.  But  it 
has  been  found  that  the  *  summer '  condition  of  the  hepatic 
cells  can  be  produced  merely  by  raising  the  temperature 
of  the  air  in  which  a  winter  frog  lives ;  at  20°  or  25°  C. 
glycogen  disappears  from  its  liver.  Conversely,  if  a  summer 
frog  is  artificially  cooled,  a  certain  amount  of  glycogen 
accumulates  in  the  liver.  The  meaning  of  this  seems  to 
be  that  at  a  low  temperature,  when  the  wheels  of  life  are 
clogged  and  metabolism  is  slow,  some  substance,  possibly 


METABOLISM,  NUTRITION  AND  DIETETICS  441 

dextrose,  is  produced  in  the  body  in  greater  amount  than 
can  be  used  up,  and  that  the  surplus  is  stored  as  glycogen ; 
just  as  in  plants  starch  is  put  by  as  a  reserve  which  can  be 
drawn  upon — which  can  be  converted  into  sugar — when  the 
need  arises. 

When  a  fasting  dog  is  made  to  do  severe  muscular  work 
glycogen  soon  disappears  from  its  liver.  When  a  dog  is 
starved,  but  allowed  to  remain  at  rest,  the  glycogen  still 
vanishes,  although  it  takes  a  longer  time ;  and  at  a  period 
when  there  is  still  plenty  of  fat  in  the  body,  there  may  not 
be  a  trace  of  hepatic  glycogen  left.  The  glycogen  which  is 
usually  contained  in  the  muscles  also  disappears  early  during 
hunger.  These  facts  have  been  taken  to  indicate  that 
glycogen  and  the  sugar  formed  from  it  are  the  readiest 
resources  of  the  starving  and  working  organism.  The  fat 
of  the  body  is  a  good  security,  which,  however,  can  only 
be  gradually  realized ;  its  organ-proteids  are  long-date  bills, 
which  will  be  discounted  sparingly  and  almost  with  a 
grudge ;  its  glycogen,  its  carbo-hydrate  reserves,  are  consols, 
which  can  be  turned  into  money  at  an  hour's  warning. 
Glycogen  is  drawn  upon  for  a  sudden  demand,  fat  for  a 
steady  drain,  proteid  for  a  life-and-death  struggle. 

While  the  liver  in  the  adult  may  thus  be  looked  upon 
as  the  main  storehouse  of  surplus  carbo-hydrate,  depots  of 
glycogen  seem  to  be  formed,  both  in 
adult  and  foetal  life,  in  other  situations 
where  the  strain  of  function  or  of  growth 
is  exceptionally  heavy — in  the  muscles 
of  the  adult  (0*3  to  0*5  per  cent,  of  the 
moist  muscle),  in  the  placenta,  in  the 
developing  muscles  of  the  embryo  (as 
much  as  40  per  cent,  of  the  solids).  FlG  ,3I  _  CELLS  OF 

Although  it  cannot  be  doubted  that        PLACENTA    CONTAIN- 

,        r      .        ,  ,  ,  ING  GLYCOGEN. 

much  of   the   hepatic  glycogen  leaves 

the  liver  as  sugar,  there  is  no  proof  that  it  all  does 
so.  It  is  known  that  fat  may  be  formed  from  carbo- 
hydrates (p.  449) :  and  globules  of  oil  are  often  conspicuous 
among  the  contents  of  liver-cells,  side  by  side  with  glycogen. 
It  is  possible,  therefore,  that  some  of  the  glycogen  may 


442  A  MANUAL  OF  PHYSIOLOGY 

represent  a  half-way  house  between  sugar  and  fat,  or,  since 
fat  can  also  be  formed  from  proteid,  and  a  purely  proteid 
diet  produces  some  glycogen,  a  half-way  house  between 
proteid  and  fat.  That  glycogen  may  be  produced  from 
proteids  even  during  starvation  is  shown  by  the  following 
experiment  :  A  fasting  animal  was  put  under  the  influence 
of  strychnia  to  remove  all  glycogen  from  the  liver.  Then 
the  strychnia  spasms  were  cut  short  by  chloral,  and  the 
animal  allowed  to  sleep  for  eighteen  hours.  At  the  end  of 
that  time  a  considerable  amount  of  glycogen  was  found  in 
the  liver  and  muscles,  and  this  must  have  come  from  the 
proteids  of  the  body. 

Pavy  has  put  forward  the  heterodox  view  that  the  glycogen  formed 
in  the  liver  from  the  sugar  of  the  portal  blood  is  never  reconverted 
into  sugar  under  normal  conditions,  but  is  changed  into  some  other 
substance  or  substances,  and  he  denies  that  the  post-mortem  forma- 
tion of  sugar  in  the  hepatic  tissue  is  a  true  picture  of  what  takes 
place  during  life.  But  in  spite  of  the  brilliant  manner  in  which  he 
has  defended  this  thesis  both  by  argument  and  by  experiment,  it 
must  be  said  that  the  older  doctrine  of  Bernard,  which  in  the  main 
we  have  followed  above,  is  attested  by  such  a  cloud  of  modern 
witnesses  that  it  seems  to  be  firmly  and  finally  established. 


of  the  Sugar.  —  What,  now,  is  the  fate  of  the  sugar 
which  either  passes  right  through  the  portal  circulation 
from  the  intestine  without  undergoing  any  change  in  the 
liver,  or  is  gradually  produced  from  the  hepatic  glycogen  ? 
When  the  proportion  of  sugar  in  the  blood  rises  above  a 
certain  low  limit  (about  3  parts  per  1,000),  some  of  it  is 
excreted  by  the  kidneys  (Practical  Exercises,  p.  512). 

A  large  meal  of  carbo-hydrates  is  frequently  followed  by  a 
temporary  glycosuria,  but  something  seems  to  depend  upon  the  form 
in  which  the  sugar-forming  material  is  taken.  Miura,  for  example, 
after  an  enormous  meal  of  rice  (equivalent  to  6-4.  grammes  ash-  and 
water-free  starch  per  kilo  of  body-weight),  which,  as  he  mentions, 
tasked  even  his  Japanese  powers  of  digestion  to  dispose  of,  found  not 
a  trace  of  sugar  in  the  urine.  Glucose,  cane-sugar  and  lactose,  on 
the  other  hand,  when  taken  in  large  amount,  were  in  part  excreted 
by  the  kidneys,  as  was  also  the  case  with  levulose  and  maltose  in  a 
dog  (Practical  Exercises,  p.  513)." 

*  Twenty-four  healthy  students,  whose  urine  had  previously  been 
shown  to  be  free  from  sugar,  ate  quantities  of  cane-sugar  varying  from 
250  grammes  to  750  grammes.  The  urine  was  collected  in  separate 
portions  for  twelve  to  twenty-four  hours  after  the  meal.  In  only  three 


METABOLISM,  NUTRITION  AND  DIETETICS          443 

But,  except  as  an  occasional  phenomenon,  such  an  ex- 
cretion is  inconsistent  with  health  ;  and  therefore  in  the 
normal  body  the  sugar  of  the  blood  must  be  either  destroyed 
or  transformed  into  some  more  or  less  permanent  con- 
stituent of  the  tissues.  The  transformation  of  sugar  into  fat 
we  have  already  mentioned,  and  shall  have  again  to  discuss; 
it  only  takes  place  under  certain  conditions  of  diet,  and  no 
more  than  a  small  proportion  of  the  sugar  which  disappears 
from  the  body  in  twenty-four  hours  can  ever,  in  the  most 
favourable  circumstances,  be  converted  into  fat.  Accordingly, 
it  is  the  destruction  of  sugar  which  concerns  us  here,  and 
there  is  every  reason  to  believe  that  this  takes  place,  not  in 
any  particular  organ,  but  in  all  active  tissues,  especially  in 
the  muscles,  and  to  a  less  extent  in  glands. 

It  has  been  asserted  that  the  blood  which  leaves  even 
a  resting  muscle,  or  an  inactive  salivary  gland,  is  poorer  in 
sugar  than  that  coming  to  it ;  and  the  conclusion  has  been 
drawn  that  in  the  metabolism  of  resting  muscle  and  gland 
sugar  is  oxidized,  the  carbon  passing  off  as  carbon  dioxide 
in  the  venous  blood.  This  is  indeed  extremely  likely,  for 
we  know  that  when  the  skeletal  muscles  of  a  rabbit  or 
guinea-pig  are  cut  off  from  the  central  nervous  system  by 
curara,  the  production  of  carbon  dioxide  falls  much  below 
that  of  an  intact  animal  at  rest ;  and  the  carbon  given  off 
by  such  animal  on  its  ordinary  vegetable  diet  can  be  shown, 
by  a  comparison  of  the  chemical  composition  of  the  food 
and  the  excreta,  to  come  largely  from  carbo-hydrates. 
But,  considering  the  relatively  feeble  metabolism  of  muscles 
and  glands  when  not  functionally  excited,  the  large  volume 
of  blood  which  passes  through  them,  the  difficulty  of  deter- 
mining small  differences  in  the  proportion  of  sugar  in  such 
a  liquid,  the  possibility  that  even  in  the  blood  itself  sugar 
may  be  destroyed,  or  that  it  may  pass  from  the  blood,  with- 

cases  was  reducing  sugar  found  in  the  urine  (by  Fehling's  and  the 
phenylhydrazine  test),  and  then  merely  in  traces.  In  eight  cases  cane- 
sugar  was  found,  and  estimated  by  the  polarimeter,  and,  after  boiling 
with  hydrochloric  acid,  by  Fehling's  solution.  The  greatest  quantity  of 
cane-sugar  recovered  from  the  urine  was  8  grammes  (7*918  grammes  by 
Fehling's  method  and  8'288  grammes  by  the  polarimeter)  ;  the  highest 
proportion  of  the  quantity  taken  which  appeared  in  the  urine  was  2*5  per 
cent.  When  glucose  was  found,  cane-sugar  was  always  present  as  well. 


444  A  MANUAL  OF  PHYSIOLOGY 

out  being  oxidized,  into  the  lymph,  too  much  weight  may 
easily  be  given  to  the  results  of  direct  analysis  of  the 
in-coining  and  out-going  blood.  And  although  the  recent 
results  of  Chauveau  and  Kaufmann,  obtained  in  this  way,  fit 
in  fairly  well  with  what  we  have  already  learnt  by  less 
direct,  but  more  trustworthy,  methods,  they  cannot  be 
accepted  as  yielding  exact  quantitative  information.  They 
found  that  in  one  of  the  muscles  of  the  upper  jaw  of  the 
horse  the  quantity  of  grape-sugar  used  up  during  activity 
(chewing  movements)  was  3*5  times  as  much  as  in  the  same 
muscle  at  rest,  and  this  corresponded  with  the  deficit  of 
oxygen  in  the  blood  entering  the  muscle,  and  with  the  excess 
of  carbon  dioxide  in  the  blood  leaving  it.  More  dextrose 
was  also  destroyed  in  the  active  than  in  the  passive  parotid 
gland  of  the  horse,  but  the  excess  per  unit  of  weight  of  the 
organ  was  far  less  than  in  muscle. 

Diabetes. — In  the  disease  known  as  diabetes  mellitus,  sugar 
accumulates  in  the  blood,  and  is  discharged  by  the  kidneys, 
and  it  has  been  supposed  that  a  derangement  in  the  gly- 
cogenic  function  of  the  liver  is  the  cause  of  this  accumula- 
ic/tu/ue>tion  ancj  of  ^{s  discharge.     An   artificial   and   temporary 
^°      diabetes,  in  which  the  sugar  in  the  urine  undoubtedly  arises 
from  the  hepatic  glycogen,  can,  indeed,  be  caused  by  punc- 
turing   the    medulla  oblongata   in  a  rabbit  at  or  near   the 
region  of  the  vaso-motor  centre  (p.  513).     If  the  animal  h 
been  previously  fed  with  a  diet  rich  in  carbo-hydrates — thai 
is,  if  it  has  been  put  under  conditions  in  which  the  liver  con 
tains  much  glycogen — the  quantity  of  sugar  excreted  by  th 
kidneys  will  be  large.     If,  on  the  other  hand,  the  animal  ha 
been  starved  before  the  operation,  so  that  the  liver  is  fre 
or  almost  free  from  glycogen,  the  puncture  will  cause  littL 
or  no  sugar  to  appear  in  the  urine.    That  nervous  influence 
are    in    some    way  involved    is    shown    by  the    absence  o 
diabetes  if  the  splanchnic  nerves,  or  the  spinal  cord  abov 
the    third    or    fourth   dorsal   vertebra,    be    cut    before 
puncture    is  made.      But    sometimes  these  operations  ar 
themselves  followed  by  temporary  diabetes.     Section  of  thi 
vagi  has  no  effect  either  in  causing  glycosuria  of  itself  or  in 
preventing  the  '  puncture  '  diabetes,  although  stimulation  o; 


METABOLISM,  NUTRITION  AND  DIETETICS          445 

the  central  ends  of  these  and  of  other  afferent  nerves  may 
cause   sugar   to   appear   in    the   urine.      Curara,    morphia, 
phloridzin  (p.  512),  and  other  substances,  also  cause  diabetes.    , 
But  phloridzin  diabetes  differs  from  'puncture'  diabetes  m™~:a'  \£. 
this,  that  it  can  be  produced  in  an  animal  free  from  glycogen, 
and  is  accompanied   by  extensive  destruction  of  proteids. 
Although    several   of    the   operations   which   lead    to   this'  ^  ^ 
temporary  glycosuria  undoubtedly  bring  about  changes  in 
the  hepatic  circulation,  it  is  as  yet  impossible  to  say  whether 
the  whole  phenomenon  is  at  bottom  a  vaso-motor  effect,  or 
is  due  to  direct  nervous  stimulation  of  the  liver-  cells,  or  to 
withdrawal  of  such  stimulation  or  control. 

Recent  experiments  point  to  the  pancreas  as  intimately 
concerned  in  the  metabolism  of  sugar.  Excision  of  this 
organ  in  dogs  causes  permanent  diabetes  (v.  Mering  and 
Minkowski),  which  is  prevented  if  a  portion  of  the  pancreas 
be  left,  or  if  it  be  transplanted  under  the  skin  of  the 
abdomen  (p.  472). 

In  the  natural  diabetes  of  man  it  is  possible  that  in  some  cases 
the  sugar  coming  from  the  alimentary  canal  passes  entirely  or  in  too 
large  amount  through  the  liver,  owing  to  a  deficiency  in  its  power  of 
forming  glycogen.  But  although  in  certain  cases  of  diabetes  speci- 
mens of  the  hepatic  cells,  obtained  by  plunging  a  trocar  into  the 
liver,  have  been  found  free  from  glycogen,  in  others  glycogen  has 
been  present.  And  it  is  remarkable  that  levulose  may  be  entirely 
used  up  in  the  tissues  of  a  diabetic  patient,  or  of  a  dog  rendered 
diabetic  by  extirpation  of  the  pancreas,  while  dextrose,  which  is  so 
closely  allied  to  it,  and  from  which  an  identical  form  of  glycogen  is 
produced,  is  promptly  cast  out  by  the  kidneys.  In  many  cases  even 
when  carbo-hydrates  are  completely,  or  almost  completely,  omitted 
from  the  food,  sugar,  probably  derived  from  the  breaking-down  of 
proteids,  still  continues  to  be  excreted,  although  in  smaller  quantity. 
Other  products  of  the  incomplete  combustion  of  proteids,  such  as 
acetone,  aceto-acetic  acid,  and  oxybutyric  acid,  may  also  appear  in 
the  urine,  or,  accumulating  in  the  blood,  may,  by  uniting  with  its 
alkalies,  seriously  diminish  the  quantity  of  carbon  dioxide  which  that 
liquid  is  capable  of  carrying,  and  thus  lead  to  the  condition  known 
as  diabetic  coma.  The  most  rational  way  of  explaining  many  of  the 
facts  of  diabetes  is  to  suppose  that,  from  some  change  in  the  tissue 
elements,  sugar  has  ceased  to  be  a  food  for  them,  or  is  used  up  in 
smaller  amount  than  in  the  healthy  body,  while  the  actual  production 
of  sugar  is  no  greater  than  in  a  normal  person  with  the  same  diet 
and  the  same  intensity  of  metabolism  of  substances  other  than  carbo- 
hydrates. 

Normal  blood  seems  to  contain  a  ferment  which  has  the  power  of 


446  A  MANUAL  OF  PHYSIOLOGY 

destroying  sugar  and  forming  lactic  acid  ;  and  the  statement  of 
Lupine  and  Barral  that  extirpation  of  the  pancreas,  which  is  followed 
by  diabetes,  causes  a  diminution  in  the  activity  or  in  the  amount  of 
this  ferment,  appeared  to  afford  the  basis  for  a  theory  of  diabetes. 
But  Spitzer  has  asserted  that  the  sugar-destroying  power  of  blood 
taken  from  diabetic  patients,  or  from  animals  in  which  glycosuria 
had  been  caused  by  phloridzin,  is  not  at  all  inferior  to  that  of  healthy 
blood.  And,  indeed,  results  that  depend  upon  the  determination  of 
minute  differences  in  the  quantity  of  sugar  must  be  accepted  with 


3.  Metabolism  of  Fat.  —  The  fat,  passing  along  the  thoracic 
duct  into  the  blood  stream,  is  very  soon  removed  from  the 
circulation,  for  normal  blood  contains  only  traces,  except 
during  digestion.  Where  does  it  go  ?  What  is  its  fate  ? 

The  presence  of  adipose  tissue  in  the  body  might  suggest 
a  ready  answer  to  these  questions.  The  fat  cells  of  adipose 
tissue  are  apparently  ordinary  fixed  connective-tissue  cells 
which  have  become  filled  with  fat,  the  protoplasm  being 
reduced  to  a  narrow  ring,  in  which  the  nucleus  is  set  like  a 
stone.  It  would,  at  first  thought,  seem  natural  to  suppose 
that  the  fat  of  the  food  is  rapidly  separated  by  these  cells 
from  the  blood,  and  slowly  given  up  again  as  the  needs  of 
the  organism  require,  just  as  carbo-hydrate  is  stored  in  the 
liver  for  gradual  use.  And  it  has  been  found  that  a  lean 
dog,  fed  with  a  diet  containing  much  fat  and  little  proteid, 
puts  on  more  fat,  as  estimated  by  direct  analysis,  or  keeps 
back  more  carbon,  as  estimated  by  measurements  of  the 
respiratory  interchange,  than  can  be  accounted  for  on  the 
supposition  that  even  the  whole  of  the  carbon  of  the  broken- 
down  proteid  corresponding  to  the  excreted  nitrogen  has 
been  laid  up  in  the  form  of  fat.  Even  with  a  diet  of  pure 
fat  —  and  with  such  a  diet  digestion  and  absorption  are 
carried  on  under  unfavourable  conditions  —  more  carbon  is 
retained  than  can  have  come  from  the  metabolism  of  the 
proteids  of  the  body,  as  measured  by  the  nitrogen  given  off 
in  the  urine  and  faeces  :  the  fat  passes  rapidly  from  the 
blood  into  the  organs,  and  especially  into  the  liver  (Hofmann, 
Pettenkofer  and  Voit).  It  is  thus  certain  that  some  of  the 
absorbed  fat  may  be  stored  up  as  fat  in  the  body.  The 
observation  of  Radziejewski,  that  a  starved  dog  fed  with 
lean  meat  and  rape-oil  —  which  contains  erucic  acid,  a  fatty 


METABOLISM,  NUTRITION  AND  DIETETICS          447 

acid  not  found  in  animal  fat — put  on  fat  of  normal  com- 
position without  a  trace  of  erucic  acid,  is  not  borne  out  by 
the  careful  experiments  of  Munk,  who  finds  that  when  dogs 
are  fed  with  excess  of  foreign  fat  (linseed-oil,  rape-oil,  mutton- 
fat),  a  fat  is  laid  down  which  is  quite  different  from  dog's 
fat,  and  has  the  greatest  resemblance  to  the  fat  of  the  food. 
But  it  does  not  follow  that  the  cells  of  adipose  tissue  in 
normal  nutrition  simply  separate  the  fats  of  the  food  from 
the  blood  ;  while  there  are  facts  which  show  that  the  fat  of 
the  body  has  other  sources,  and  that  some  of  it  at  all  events 
is  produced  by  more  complex  processes. 

The  fat  of  a  dog  consists  of  a  mixture  of  palmitin,  olein, 
and  stearin.  When  a  starved  dog  was  fed  on  lean  meat  and 
a  fat  containing  palmitin  and  olein,  but  no  stearin,  the  fat 
put  on  contained  all  three,  and  did  not  sensibly  differ  in  it 
composition  from  the  normal  fat  of  the  dog  (Subbotin). 
Stearin  must,  therefore,  have  been  formed  in  some  way  or 
other  in  the  body.  If  it  was  formed  from  the  olein  and 
palmitin  of  the  food,  the  portion  of  these  deposited  in 
the  cells  of  the  adipose  tissue  must  have  undergone  changes 
before  reaching  this  comparatively  fixed  and  final  position. 
But  there  is  conclusive  evidence  that  fat  may  be  derived 
from  proteids  ;  and  it  is  more  likely  that  the  stearin  was 
formed  from  the  proteids  of  the  food  or  tissues  than  directly 
from  fat.  And  if  the  stearin  was  produced  from  proteids, 
it  is  evident  that  the  olein  and  palmitin  might  have  been 
formed  from  proteids  too,  the  portion  of  the  latter  devoted 
to  this  purpose  being  sheltered  from  oxidation  by  the 
combustion  of  the  fats  of  the  food.  It  might  further  be 
asked  whether  the  fat  which  is  normally  excreted  into  the 
intestine  (p.  371),  and  which  is  perhaps  derived  from  broken- 
down  proteids,  might  not  be  reabsorbed,  and  take  its  place 
among  the  fat  '  put  on.'  But  as  yet  there  are  few  ascertained 
facts  to  guide  us  in  such  speculations. 

As  to  the  ultimate  fate  of  the  absorbed  fat,  from  what- 
ever source  it  may  be  derived,  our  knowledge  may  be 
compressed  into  a  single  sentence  :  Some  of  the  fat  may 
be  stored  up  as  fat ;  the  greater  part,  often  the  whole,  is  oxidized 
forthwith  to  carbon  dioxide  and  water,  its  energy  being  converted 


448  A  MANUAL  OF  PHYSIOLOGY 

into  heat  or,  directly  or  indirectly,  into  mechanical  or  chemical 
work. 

Formation  of  Fat  from  other  Sources  than  the  Fat  of  the 
Food.  —  (i)  From  Proteids.  —  Dry  proteid  contains  on  the 
average  15  per  cent,  of  nitrogen  and  50  per  cent,  of  carbon ; 
and  urea  contains  46  per  cent,  of  nitrogen  and  20  per  cent, 
of  carbon.  Urea  is  therefore  rather  more  than  three  times 
as  rich  in  nitrogen  as  the  proteid  from  which  it  is  derived, 
but  two  and  a  half  times  poorer  in  carbon  ;  and  less  than 
one-seventh  of  the  carbon  of  proteid  will  be  eliminated  in 
the  urea,  which  carries  off  all  the  nitrogen.  A  carbonaceous 
residue  is  left,  which  under  certain  circumstances  may  be 
converted  into  fat.  The  proof  of  this  statement  is  very 
complete,  but  only  an  outline  of  it  can  be  given  here. 

A  dog  fed  for  a  time  on  a  liberal  diet  of  lean  meat  may  go 
on  excreting  a  quantity  of  nitrogen  equal  to  that  in  the 
food,  while  there  is  a  deficiency  in  the  carbon  given  off.  Or 
if  the  dog  is  not  in  nitrogenous  equilibrium  (p.  452),  but 
putting  on  nitrogen  in  the  form  of  '  flesh,'  the  deficiency  in 
the  carbon  given  off  may  be  too  great  in  proportion  to  the 
nitrogen  deficit  to  warrant  the  assumption  that  all  the 
retained  carbon  has  been  put  on  in  the  form  of  proteid.  In 
either  case,  carbon  in  large  amount  can  only  come  from  the 
proteids  of  the  food,  and  can  only  be  stored  up  in  the  body 
in  the  form  of  fat ;  for  lean  meat  contains  but  a  trifling 
quantity  of  carbon  in  any  other  proximate  principle  than 
proteid,  and  the  non-proteid  carbon  of  the  animal  body  is 
only  to  a  very  small  extent  contained  in  carbo-hydrates  01 
other  substances  than  fat. 

For  example,  in  an  experiment  of  Pettenkofer  and  Voit  on  a 
in  nitrogenous  equilibrium,  with  a  diet  of  2,000  grammes  of  lear 
meat,  the  animal  on  the  first  day 

Grammes.  Grammes. 

Took  in  in  the  food     -         -                    68'o  N  250*4  C 

'  urine      -         -     66' 5  N  39-9  C 

Gave  out  in  <  faeces     -         -       1*4  9'2 

( respiration     -       o  1 58*3 

67-9  207-4 


Difference        -     +o'i  N  +43'o  C 

Here  the  nitrogen  of  the  body  remained  unaltered,  but  carbor 


METABOLISM,  NUTRITION  AND  DIETETICS          449 

was  put  on  to  the  extent  of  43  grammes,  or   17  per  cent,  of  the 
amount  in  the  food,  representing  about  58  grammes  of  fat. 

This  is  an  exact  quantitative  proof  of  the  conversion  of 
proteids  into  fat.  Qualitative  indications  of  its  possibility 
and  of  its  actual  occurrence  are  numerous.  Such  are  the 
readiness  with  which  fatty  degeneration  occurs  in  the  tissues 
in  pathological  states — for  example,  after  phosphorus  poison- 
ing ;  the  accumulation  of  fat  between  the  hepatic  cells  caused 
by  phloridzin,  which,  as  we  know,  hastens  the  disintegration 
of  proteids  ;  the  formation  of  adipocere  sometimes  seen  in 
dead  bodies  which  have  remained  a  long  time  under  water 
or  in  moist  graveyards  ;  the  formation  of  fat  in  the  cells  of 
the  sebaceous  glands ;  and  the  transformation  of  the  cell- 
substance  of  the  mammary  glands  into  the  fat  of  milk. 
This  last  case  is  of  great  practical  importance,  for  it 
explains  the  rule  which  experience  has  taught,  that  a 
woman  during  lactation  requires  an  excess  of  proteids  in 
her  food  corresponding  not  only  to  the  proteids,  but  also 
to  the  fat  given  off  in  the  milk. 

(2)  From  Carbo-hydrates. — It  has  been  found  that  the 
addition  of  proteid  to  a  diet  of  fat,  and  especially  to  a  diet 
of  carbo-hydrate,  in  larger  amount  than  is  just  necessary 
for  nitrogenous  equilibrium,  leads  to  a  more  rapid  increase 
in  the  carbon  deficit — that  is,  in  the  fat  put  on — than  if  the 
minimum  quantity  of  proteid  required  for  nitrogenous  equi- 
librium had  been  given.  From  this  it  is  inferred  that  the 
carbonaceous  residue  of  the  broken-down  proteid  is  shielded 
from  oxidation  by  the  fat,  and  to  a  still  greater  extent  by 
the  carbo-hydrates,  and  so  retained  in  the  body  as  fat. 
And  it  is  certain  that  the  high  repute  of  carbo-hydrates 
as  fattening  agents  is  in  part  due  to  their  taking  the  place 
of  proteids  and  fats  in  ordinary  '  current '  metabolism,  and 
so  allowing  body-fat  to  be  laid  down  from  these.  Voit, 
indeed,  has  gone  so  far  as  to  assert  that  this  is  the  only 
sense  in  which  carbo-hydrates  can  be  said  to  form  fat,  and 
that,  in  carnivorous  animals  at  least,  a  direct  conversion  never 
occurs.  But  the  experiments  of  Rubner  have  shown  that  in 
a.  dog  fed  with  a  diet  rich  in  car.bo-hydrates,  and  containing 
but  little  fat  and  no  proteids  at  all,  the  carbon  deficit  was 

29 


A  MANUAL  OF  PHYSIOLOGY 

greater  than  could  be  accounted  for  by  the  proteids  broken 
down  in  the  body  and  the  fat  of  the  food.  In  the  pig  and 
goose,  too,  the  direct  formation  of  fat  from  carbo-hydrates 
has  been  demonstrated.  It  is  probable  that  the  carbo- 
hydrates are  first  split  up  to  some  extent,  and  that  the  fats 
are  then  constructed  from  their  decomposition  products, 
oxygen  being  lost  in  the  process,  since  fat  is  poorer  in 
oxygen  than  carbo-hydrate.  The  production  of  wax  by 
bees,  which  used  to  be  given  as  a  proof  of  the  formation 
of  fat  from  sugar,  is  not  decisive,  for  in  raw  honey  proteids 
are  present ;  and  even  when  bees  fed  on  pure  honey  or  sugar 
manufacture  wax,  it  may  be  derived  from  the  broken-down 
proteids  of  their  own  bodies. 

Summary. — At  this  point  let  us  sum  up  what  we  have 
learnt  as  to  the  relation  between  the  proximate  principles 
of  the  tissues  and  the  proximate  principles  of  the  food. 
Inside  the  body  we  recognise  representatives  of  the  three  groups 
of  organic  food -substances  in  a  typical  diet — proteids,  carbo- 
hydrates, and  fats.  But  we  should  greatly  err  if  we  were  to 
imagine  that  the  three  streams  of  food-materials  have  flowed 
from  the  intestines  into  the  tissues  each  in  its  separate 
channel,  neither  giving  to  nor  taking  from  the  others.  The 
fats  of  the  body  may,  indeed,  in  part  be  composed  of  molecules, 
which  were  present  as  fat  in  the  food  ;  but  they  may  also  be  formed 
from  proteids — they  may  also  be  formed  from  carbo-hydrates.  The 
carbo-hydrates  of  the  body — the  glycogen  of  the  liver  and  muscles, 
the  sugar  of  the  blood — may  undoubtedly  be  derived  from  carbo- 
hydrates in  the  food,  but  they  may  also  be  derived  from  proteids ; 
from  fats  they  probably  cannot  come.  The  proteids  of  the  body 
arise  solely  from  the  proteids  of  the  food  ;  neither  fats  nor  carbo- 
hydrates can  form  proteids,  although  both  can  economize  them  and 
shield  them  from  an  over-hasty  metabolism. 

4.  The  Income  and  Expenditure  of  the  Body. — (i)  Income  and 
Expenditure  of  Nitrogen.— 

Preliminary  Data. — The  purpose  of  food  is  to  maintain  the  con- 
stituents of  the  body  upon  the  whole  in  their  normal  proportions. 
A  knowledge  of  the  chemical  composition  of  the  body  is,  therefore, 
an  important  datum  in  the  consideration  of  the  statistics  of  its 
metabolism.  The  body  of  a  man  analyzed  by  Volkmann  had  the 
following  composition : 


METABOLISM,  NUTRITION  AND  DIETETICS          451 


(  Water 
Inorganic  substances  j  Minera, 

(  Carbon 
Organic  substances     < 


matter  - 

18-4  per  cent. 
Hydrogen   27 
Nitrogen      2 '6        „ 
Oxygen        6'o        „ 


65-9  per  cent. 
4'4 

297        „ 


The  muscles,  the  adipose  tissue,  and  the  skeleton  form  nearly 
four-fifths  of  the  total  body-weight  in  the  adult.  The  following  table 
shows  the  percentage  amount  of  each  of  these  tissues  in  a  man,  a 
woman,  and  a  child  (Bischoff): 


Man. 

Woman. 

New-born 
Child. 

Voluntary  muscles 
Adipose  tissue    - 
Skeleton     - 
Rest  of  body 

41-8 
18-2 

15-9 
24'I 

35-8 
28-2 
15-1 

20'9 

23'5 
*3'5 
157 
47-3 

The  nitrogen  is  contained  chiefly  in  the  muscles,  glands,  and 
nervous  system,  and  in  the  constituents  of  the  connective  tissues, 
which  yield  gelatin,  chondrin,  and  elastin.  The  proteids  make  up 
about  9  per  cent,  of  the  weight  of  the  body,  or  22  per  cent,  of  its 
solids ;  the  albuminoids  (gelatin-yielding  material,  etc.)  about  6  per 
cent,  of  the  body-weight.  Nitrogen  exists  in  proteids  to  the  extent 
of  15  per  cent.,  so  that  the  6*5  kilos  of  proteid  of  a  yo-kilo  body 
contain  nearly  i  kilo  of  nitrogen. 

The  carbon  is  contained  chiefly  in  the  fat,  which  forms  a  very 
large  proportion  of  the  water-free  substance  of  the  body,  and  in  the 
bones.  In  the  body  of  a  strong  young  man  weighing  68'6  kilos, 
Voit  found  the  following  quantities  of  dry  fat  in  the  various  tissues : 


Adipose  tissue 

Skeleton 

Muscles   - 

Brain  and  spinal  cord 

Other  organs   - 

Total    - 


-  8809-4  grammes. 

-  2617-2 

-  636-8         „ 

-  226-9 

73*2         „ 

-  12363-5 


equivalent  to  18  per  cent,  of  the  whole  body-weight,  or  44  per  cent, 
of  the  solids.  In  dry  fat  rather  more  than  75  per  cent,  of  carbon 
is  present,  and  in  proteid  about  50  to  55  per  cent. ;  so  that  while  the 
fat  of  the  body  analyzed  by  Voit  contained  more  than  9  kilos  of 
carbon,  only  about  a  third  of  this  amount  would  be  found  in  the 
proteids. 

In  the  fat  there  is,  roughly  speaking,  12  per  cent,  of  hydrogen, 
in  proteids  only  7  per  cent. ;  so  that  from  three  to  four  times  as  much 
hydrogen  is  contained  in  the  fat  of  the  body  as  in  its  proteids. 

Oxygen  forms  about  12  per  cent,  of  fat,  and  20  to  24  per  cent 
of  proteids ;  the  proteid  constituents  of  the  body,  therefore,  contain 
about  as  much  of  its  oxygen  as  the  fat 

29 — 2 


452  A  MANUAL  OF  PHYSIOLOGY 

Nitrogenous  Equilibrium. — It  is  a  matter  of  common  ex- 
perience that  the  weight  of  the  body  of  an  adult  may  remain 
approximately  constant  for  many  months  or  years,  even 
when  the  diet  varies  greatly  in  nature  and  amount.  And 
not  only  may  the  weight  remain  constant,  but  the  relative 
proportions  of  the  various  tissues  of  the  body,  so  far  as 
can  be  judged,  may  remain  constant  too.  Here  it  is  evident 
that  the  expenditure  of  the  body  must  precisely  balance 
its  income :  it  must  lose  as  much  nitrogen  as  it  takes 
in,  otherwise  it  would  put  on  flesh ;  it  must  lose  as  much 


FIG.    132. —DIAGRAM    SHOWING    Loss   OF    WEIGHT   OF   THE   ORGANS    IN 

STARVATION. 

The  numbers  under  I.  are  the  percentages  of  the  total  loss  of  body-weight  borne  by 
the  various  organs  and  tissues.  The  numbers  under  II.  give  the  percentage  loss  of 
weight  of  each  organ  calculated  on  its  original  weight  as  indicated  by  comparison  with 
the  organs  of  a  similar  animal  killed  in  good  condition. 


carbon  as  it  takes  in,  otherwise  it  would  put  on  fat.  Or, 
again,  the  body  may  be  losing  or  gaining  fat,  giving  off 
more  or  less  carbon  than  it  receives,'  while  its  '  flesh '  (its 
proteid  constituents)  remains  constant  in  amount,  the  ex- 
penditure of  nitrogen  being  exactly  equal  to  the  income. 
In  both  cases  we  say  that  the  body  is  in  nitrogenous  equi 
librium. 

A  starving  animal  or  a  fever  patient,  on  the  other  hand,  i 
living  upon  capital,  the  former  entirely,  the  latter  in  part 
the  expenditure  of  nitrogen  is  greater  than  the  income, 
growing  child  is  living  below  its  income,  is  increasing  its 


ii- 

: 


METABOLISM,  NUTRITION  AND  DIETETICS          453 

capital  of  flesh.     In  neither  case  is  nitrogenous  equilibrium 
present. 

The  starving  animal,  as  long  as  life  lasts,  excretes  urea  and 
gives  off  carbon  dioxide ;  but  its  expenditure,  and  especially 
its  expenditure  of  nitrogen,  is  pitched  upon  the  lowest  scale. 
It  lives  penuriously,  it  spins  out  its  resources ;  its  glycogen 
goes,  its  fat  goes,  a  certain  part  of  its  proteid  goes,  and 
when  its  weight  has  fallen  from  25  to  50  per  cent.,  it  dies. 
At  death  the  heart  and  central  nervous  system  are  found  to 
have  scarcely  lost  in  weight;  the  other  organs  have  been 
sacrificed  to  feed  them.  Fig.  132  shows  the  percentage  loss 

A  is  a  curve  representing 
the  quantity  of  urea  excreted 
daily  by  a  fat  dog  in  a  star- 
vation period  of  sixty  days. 
B  is  the  curve  of  urea  ex- 
cretion in  a  lean  young  dog 
in  a  starvation  period  of 
twenty-four  days.  Both  are 
constructed  from  Falck's 
numbers,  but  in  A  only 
every  third  day  is  put  in,  in 
order  to  save  space.  The 
numbers  along  the  vertical 
axis  represent  grammes  of 
urea  ;  those  along  the  hori- 
zontal axis  days  from  the 
beginning  of  starvation. 

FIG.  133. — EXCRETION  OF  UREA  IN  STARVATION. 

of  weight  and  the  proportion  of  the  total  loss  which  falls 
upon  each  of  the  organs  of  a  cat  in  starvation  (Voit). 

For  the  first  day  of  starvation  the  excretion  of  urea  in  a  dog 
or  cat  is  not  diminished ;  it  takes  about  twenty-four  hours 
for  all  the  nitrogen  corresponding  to  the  proteids  of  the  last 
meal  to  be  eliminated.  On  the  second  day  the  quantity  of 
urea  sinks  abruptly ;  then  begins  the  true  starvation  period, 
during  which  the  daily  output  of  urea  diminishes  very  slowly 
until  a  short  time  before  death,  when  it  rapidly  falls  and 
soon  ceases  altogether.  If  the  animal  has  little  fat  in  its 
body  to  begin  with,  the  urea  excretion  rises  somewhat 
after  the  first  few  days,  because  as  soon  as  the  fat  is  all 
consumed  more  proteid  is  used  up.  So  long  as  the  fat 
lasts,  the  rate  at  which  it  is  destroyed — as  estimated  from 
the  amount  of  carbon  given  off  minus  the  carbon  corre- 


454  A  MANUAL  OF  PHYSIOLOGY 

spending  to  the  broken-down  proteids — remains  very  nearly 
constant  after  the  first  day.  The  fat  to  a  certain  extent 
economizes  the  proteids  of  the  starving  body,  but  however 
much  fat  may  be  present,  a  steady  waste  of  the  tissue- 
proteids  goes  on. 

The  results  obtained  on  *  fasting  men '  differ  in  some 
respects  from  those  obtained  on  starving  animals.  The 
excretion  of  nitrogen  has  been  found  to  diminish  con- 
tinuously during  a  fast  extending  over  several  days.  The 
quantity  of  chlorine  and  alkalies  in  the  urine  was  also 
diminished,  while  the  phenol  was  increased.  The  respi- 
ratory quotient  sank  to  0*66  to  o'6g — even  less  than  the 
quotient  corresponding  to  oxidation  of  fats  alone.  The 
meaning  of  this,  in  all  probability,  is  that  some  of  the 
carbon  of  the  broken-down  proteids  was  laid  up  in  the 
body  as  glycogen  (Zuntz).  The  nitrogenous  metabolism  has 
also  been  investigated  during  long-continued  hypnotic  sleep 
(Hoover  and  Sollmann).  The  results  were  very  much  the 
same  as  in  an  ordinary  starvation  experiment. 

It  might  be  supposed  that  if  an  animal  was  given  as  much 
nitrogen  in  the  food  in  the  form  of  proteids  as  corresponded 
to  its  daily  loss  of  nitrogen  during  starvation,  this  loss  would 
be  entirely  prevented  and  nitrogenous  equilibrium  restored. 
The  supposition  would  be  very  far  from  the  reality.  If  a 
dog  of  30  kilos  weight,  which  on  the  tenth  day  of  starva- 
tion excreted  11*4  grammes  urea,  had  then  received  a  daily 
quantity  of  proteid  equivalent  to  this  amount — that  is  to 
say,  about  34  grammes  of  dry  proteid,  or  175  grammes  of 
lean  meat — the  excretion  of  nitrogen  would  at  once  have 
leaped  up  to  nearly  double  its  starvation  value.  If  the 
quantity  of  proteid  in  the  diet  was  progressively  increased, 
the  output  of  urea  would  increase  along  with  it,  but  at  an 
ever-slackening  rate;  and  at  length  a  condition  would  be 
reached  in  which  the  income  of  nitrogen  exactly  balanced  the 
expenditure,  and  the  animal  neither  lost  nor  gained  flesh. 
In  an  experiment  of  Voit's,  for  instance,  the  calculated  loss 
of  flesh  in  a  dog  with  no  food  at  all  was  190  grammes  a  day. 
The  animal  was  now  fed  on  a  gradually  increasing  diet  of 
lean  meat  with  the  following  result : 


METABOLISM,  NUTRITION  AND  DIETETICS 


455 


Flesh  in  the 
Food. 

Flesh  used  up  in 
the  Body. 

Net  Loss  of 
Body-flesh. 

0 

190 

190 

250 

341 

91 

350 

411 

61 

400 

454 

54 

450 

47i 

21 

480 

492 

12 

The  loss  of  nitrogen  in  the  urine  and  faeces  is  what  was  measured. 
Knowing  the  average  composition  of  '  body-flesh '  (muscles,  glands, 
etc.),  it  is  easy  to  translate  results  stated  in  terms  of  nitrogen  into 
results  stated  in  terms  of  'flesh.'  Muscle  contains  approximately 
3-4  per  cent,  nitrogen.  Here,  with  a  diet  of  480  grammes  meat,  the 
dog  was  still  losing  a  little  flesh ;  it  would  probably  have  required 
from  500  to  600  grammes  for  equilibrium.  The  results  are  graphi- 
cally represented  in  Fig.  134. 

The  quantity  of  proteid  food  necessary  for  nitrogenous 
equilibrium  varies  with  the  condition  of  the  organism :  an 
emaciated  body  requires  less  than  a  muscular  and  well- 
nourished  body.  The  least  quantity  which  would  suffice 
to  maintain  in  nitrogenous  equilibrium  the  famous  35  kilo 
dog  of  Voit,  even  in  very  meagre  condition,  was  480  grammes 
of  lean  meat,  corresponding  to  16  grammes  of  nitrogen, 
or  35  grammes  of  urea;  that  is,  about  three  times  the 
daily  loss  during  starvation.  From  this  lower  limit  up  to 
2,500  grammes  of  meat  a  day  nitrogenous  equilibrium 
could  always  be  attained,  the  animal  putting  on  some  flesh 
at  each  increase  of  diet,  until  at  length  the  whole  2,500 
grammes  were  regularly  used  up  in  the  twenty-four  hours. 
A  further  increase  was  only  checked  by  digestive  troubles. 
A  man,  or  at  least  a  civilized  man,  can  consume  a  much 
smaller  amount  both  absolutely  and  in  proportion  to  the 
body-weight.  Rubner,  with  a  body-weight  of  72  kilos,  was 
able  to  digest  and  absorb  over  1,400  grammes  of  lean  meat: 
Ranke,  with  about  the  same  body-weight,  could  only  use  up 
1,300  grammes  on  the  first  day  of  his  experiment,  and  less 
than  1,000  grammes  on  the  third. 

So  much  for  a  purely  proteid  diet.  When  fat  is  given  in 
addition  to  proteid,  nitrogenous  equilibrium  is  attained  with 
a  smaller  quantity  of  the  latter  (7  to  15  per  cent,  less)  A 


456  A  MANUAL  OF  PHYSIOLOGY 

dog  which,  with  proteid  food  alone,  is  putting  on  flesh, 
will  put  on  more  of  it  before  nitrogenous  equilibrium  is 
reached  if  a  considerable  quantity  of  fat  be  added  to  its 

diet.  Fat,  therefore,  economizes 
proteid  to  a  certain  extent,  as  we 
have  already  recognised  in  the  case 
of  the  starving  animal.  On  the 
other  hand,  when  proteid  is  given 
in  large  quantities  to  a  fat  animal, 
the  consumption  of  fat  is  increased  ; 
and  if  the  food  contains  little  or 
none,  the  body-fat  will  diminish, 
while  at  the  same  time  *  flesh  '  may 
be  put  on.  The  Banting  cure  for 
corpulence  consists  in  putting  the 
patient  upon  a  diet  containing  much 
proteid,  but  little  fat  or  carbo- 
hydrate ;  and  the  fact  just  men- 
tioned throws  light  upon  its  action. 

All  that  we  have  here  said  of  fat 
o.  134.  -  CURVES  CON-  is  true  of  carbo-hydrates.  To  a  great 
STRUCTED  TO  ILLUSTRATE  extent  these  two  kinds  of  food  sub- 

NlTROGENOUS          EQUILIB-  .  „       . 

RIUM  (FROM  AN  ExpERi-  stances  are  complementary.     Carbo- 
MENT  OF  VOIT'S).  hydrates  economize  proteids  as  fat 

.does,  but  to  a  greater  extent,  and 
they  also  economize  fat,  so  that  when 


loss  are  laid  off  (in  grammes  of  a   sufficient    quantity   of    starch    or 

'flesh')  along  the  vertical  axis.  .  . 

The  continuous  curve  is  the  sugar  is  given  to  an  otherwise  starv- 

curve    of    income  ;    the    dotted  .  -1111  r  u          r 

curve,  of  expenditure.    With  no  mg  animal,  all  loss  of  carbon  from  I 


the  body,  except  that  which  goes  off 
of  480  grammes  the  expenditure  jn  the  urea  still  excreted,  can  be  pre- 

is  492  and  the  loss  12  grammes.  *''.+**  i  •        i       iJ 

Nitrogenous  equilibrium    is  re-  Vented.       Of  COUrse   the    animal    ultl- 

presen  ted  as  being  reached  with  t       «•         i  ,i_ 

an  income  of  about  530grammes;  mately  dlCS,  because  the   COntmUOUS, 

anShen6  tWO  CUrveS  CUi  One  though  diminished,  loss   of   proteid 

cannot  be  made  good. 

It  is  only  necessary  to  add  that  peptone  can,  while 
gelatin  cannot,  completely  replace  the  natural  proteids  in 
the  food.  Fully  five  -sixths,  however,  of  the  necessary 
nitrogen  may  be  obtained  from  gelatin,  at  least  for  a  few 


METABOLISM,  NUTRITION  AND  DIETETICS          457 

days  (Munk);  so  that  gelatin  economizes  proteid  in  a  much 
greater  degree  than  fat  and  carbo-hydrates  do. 

The  Laws  of  Nitrogenous  Metabolism. — Within  the  limits  of 
nitrogenous  equilibrium,  which  is  the  normal  state  of  the 
healthy  adult,  the  body  lives  up  to  its  income  of  nitrogen ; 
it  lays  by  nothing  for  the  future.  In  the  actual  pinch  of 
starvation  the  organism  becomes  suddenly  economical. 
When  a  plentiful  supply  of  proteid  is  presented  to  the 
starving  tissues,  they  pass  at  once  from  extreme  frugality  to 
luxury ;  some  flesh  may  be  put  on  for  a  short  time,  some 
nitrogen  may  be  stored  up;  but  the  tissues  soon  pitch 
their  wants  to  the  new  scale  of  supply,  and  spend  their 
proteid  income  as  freely  as  they  receive  it.  This  is  the  first 
great  law  of  nitrogenous  metabolism,  and  we  may  formu- 
late it  thus :  Consumption  of  proteid  is  largely  determined  by 
supply  (p.  515). 

Various  hypotheses  have  been  offered  to  explain  this  remarkable 
fact.  It  has  been  suggested  that  a  large  proportion  of  a  heavy 
proteid  meal  may  be  broken  up  into  leucin  and  tyrosin  in  the 
alimentary  canal,  and  may  pass  by  this  short-cut  to  the  stage  of  urea 
without  ever  joining  the  proteid  of  the  blood,  much  less  that  of  the 
organs.  This  would  be  a  form  of  true  luxus-consumption,  of  really, 
and  not  apparently,  wasteful  expenditure.  The  surplus  proteids 
would  be  shunted  out  of  the  main  metabolic  current  at  its  very 
source  ;  and  it  is  conceivable  that  in  this  short-cut  from  proteid  to 
urea  we  have  a  kind  of  physiological  safety-valve  to  protect  the 
tissues  from  the  burden  of  an  excessive  metabolism.  But  it  is 
doubtful  whether  such  a  process  occurs  to  any  great  extent  in  normal 
digestion.  If  it  does  occur,  it  may  bear  a  different  interpretation, 
and  in  any  case  it  probably  plays  only  a  subordinate  part,  and  cannot 
of  itself  explain  all  the  facts  of  nitrogenous  equilibrium. 

Then,  again,  it  has  been  said  that  the  luxus-consumption  takes  the 
form  of  oxidation  of  the  surplus  proteids  in  the  blood  and  lymph. 
Here  the  shunting  would  take  place  farther  down  the  stream,  but 
still  high  enough  up  to  shield  the  tissue  elements  from  excessive 
metabolic  work.  This  theory  of  luxus-consumption  breaks  down, 
however,  under  the  accumulating  evidence  that  the  oxidative  changes 
go  on  chiefly  in  the  living  cells  and  not  in  the  extra-cellular  fluids. 

We  seem  driven  to  locate  the  metabolism  of  actually  absorbed 
proteids,  as  well  as  of  other  food  substances,  within  the  cells  of  the 
body  ;  and  there  are  three  chief  views  as  to  the  manner  of  this 
metabolism : 

(a)  That  the  actual  protoplasmic  substance,  the  living  framework 
of  the  cell,  is  comparatively  stable  ;  that  it  does  not  break  down 


458  A  MANUAL  OF  PHYSIOLOGY 

rapidly ;  and  that  only  a  relatively  small  and  fairly  constant  amount 
of  food-  or  circulating-proteid  is  required  to  supply  the  waste  of  the 
organ-proteid.  It  is  assumed  that  the  greater  part  of  the  former, 
without  being  incorporated  with  the  protoplasm,  is  nevertheless  acted 
upon,  rendered  unstable,  shaken  to  pieces,  as  it  were,  by  the  whirl 
of  life  in  the  organized  framework,  the  interstices  of  which  it  fills. 

(b)  That   we   have  no  right  to  draw  a  distinction  between  the 
consumption  of  organ-  arid  circulating-proteid ;  that  the  whole  of  the 
latter  ultimately  rises  to  the  height  of  organ-proteid,  and  passes  on 
to  the  downward  stage  of  metabolism  only  through  the  topmost  step 
of  organization.     An  increase  in  the  supply  of  nitrogenous  material 
in  the  blood  must,  on  this  view,  be  accompanied  with  an  increased 
tendency  to  the  break-up,  the  dissociation,  as  Pfliiger  puts  it,  of  the 
living   substance.      The   actual   organised   elements,    however,    the 
existing    cells,   are  not   supposed   to   be   destroyed;    the   building 
remains,  for  although  stones  are  constantly  crumbling  in  its  walls, 
others  are  being  constantly  built  in. 

(c)  That  the  tissue  elements  themselves  are  short-lived  ;  that  the 
old  cells  disappear  bodily  and  are  replaced  by  new  cells ;  and  that 
the  whole  of  the  proteids  of  the  food  take  part  in  this  process  of 
total  ruin  and  reconstruction. 

Histological  evidence  is  on  the  whole  strongly  against  (c). 
Although  the  cells  of  certain  glands,  such  as  the  mammary 
sebaceous,  and  perhaps  the  mucous  glands,  are  known  to  break 
down  bodily  as  an  incident  of  functional  activity,  in  most  organs 
there  is  no  proof  of  the  production  of  new  cells  on  the  immense 
scale  which  this  theory  would  require.  There  is  but  little  evidence 
which  would  enable  us  to  decide  with  confidence  between  (a)  and 
(b\  although  the  observation  of  Munk,  that  a  dog  fed  with  proteids 
and  carbo-hydrates  after  a  thirty  days'  fast  used  up  less  proteid  than 
the  minimum  in  starvation,  certainly  suggests  that,  under  those 
conditions  at  least,  the  proteids  of  the  food  were  all  built  up  into 
the  protoplasm  of  the  tissues. 

**A    second    law    of   nitrogenous   metabolism   is   that   within 
"^k^normal  limits  it  is  nearly  independent  of  muscular  work,  that 
is  to  say,  the  quantity  of  nitrogen  excreted  by  a  man  on  a 
given  diet  is  practically  the  same  whether  he  rests  or  works. 
Before  this  was  known  it  was  maintained  by  Liebig  thai 
proteids  alone  could  supply  the  energy  of  muscular  contrac- 
tion— that,   in    fact,   proteids   were    solely   used    up    in    th< 
nutrition  and  functional  activity  of  the  nitrogenous  tissues 
while  the   non-proteid    food  yielded  heat  by  its  oxidation, 
As  exact  experiments  multiplied,  it  was  found  that  musculai 
work,  the  production  of  which  is  the  function  of  by  far  th< 
greatest  mass  of  proteid-containing  tissue,  had  little  or  n< 
effect  upon  the  excretion  of  urea  in  the  urine.     More  th< 


METABOLISM,  NUTRITION  AND  DIETETICS          459 

this,  it  was  shown  that  a  certain  amount  of  work  accom- 
plished (by  Pick  and  Wislicenus  in  climbing  a  mountain)  on 
a  non-nitrogenous  diet  had  double  the  heat  equivalent  of  the 
whole  of  the  proteid  consumed  in  the  body,  as  estimated  by 
the  urea  excreted  during,  and  for  a  given  time  after,  the  work. 
On  the  assumption  that  all  the  urea  corresponding  to  the 
proteid  broken  down  was  eliminated  during  the  time  of  this 
experiment,  a  part  at  least  of  the  work  must  have  been 
derived  from  the  energy  of  non-nitrogenous  material.  And 
the  increase  in  the  carbon  dioxide  given  off,  which  is  as  con- 
spicuous an  accompaniment  of  muscular  work  as  the  con- 
stancy of  the  urea  excretion,  showed  that  during  muscular 
exertion  carbonaceous  substances  other  than  proteids — that 
is  to  say,  fats  and  carbo-hydrates — are  oxidized  in  greater 
amount  than  during  rest. 

So  the  pendulum  of  physiological  orthodoxy  came  full- 
swing  to  the  other  side.  Liebig  and  his  school  had  taught 
that  proteids  alone  were  consumed  in  functional  activity  ; 
the  majority  of  later  physiologists  have  denied  to  the  proteids 
any  share  whatever  in  the  energy  which  appears  as  muscular 
contraction.  The  proteids,  they  say,  '  repair  the  slow  waste 
of  the  framework  of  the  muscular  machine,  replace  a  loose 
rivet,  a  worn-out  belt,  as  occasion  may  require  ;  the  carbo- 
hydrates and  fats  are  the  fuel  which  feeds  the  furnaces  of 
life,  the  material  which,  dead  itself,  is  oxidized  in  the  inter- 
stices of  the  living  substance,  and  yields  the  energy  for  its 
work.' 

Now,  it  is  a  singular  circumstance,  and  full  of  instruction 
for  the  ingenuous  student  of  science,  that  the  facts  which 
have  been  supposed  absolutely  to  disprove  the  older  theory, 
and  absolutely  to  establish  its  modern  rival,  do  neither  the 
one  thing  nor  the  other.  The  fact — and  it  is  a  fact — that 
the  excretion  of  nitrogen  is  but  little  affected  by  muscular 
contraction,  does  not  prove  that  none  of  the  energy  of 
muscular  work  comes  from  proteids;  the  fact  that,  under 
certain  conditions,  some  of  the  muscular  energy  must 
apparently  come  from  non-nitrogenous  materials,  does  not 
prove  that  these  are  the  normal  source  of  it  all.  The  dis- 
tinction has  again  been  made  too  absolute.  The  pendulum 


460  A  MANUAL  OF  PHYSIOLOGY 

must  again  swing  back  a  little ;  and  the  recent  experiments 
of  Pfluger  and  others  have  actually  set  it  moving. 

In  the  first  place,  it  is  not  perfectly  correct  to  say  that 
work  causes  no  increase  in  the  excretion  of  nitrogen  ;  exces- 
sive work  in  man,  and  work,  severe  but  not  excessive,  in  a 
flesh-fed  dog  (Pfluger),  do  cause  somewhat  more  nitrogen  to 
be  given  off.  The  increase  affects  not  only  the  urea  but  ah 
the  ammonia,  kreatinin,  and  if  the  subject  is  in  poor  training, 
the  uric  acid  and  xanthin  bases.  (Paton,  Stockman,  etc.) 

In  the  second  place,  even  if  the  excretion  of  nitrogen  were 
entirely  unaffected  by  work,  this  would  not  prove  that  none 
of  the  energy  of  the  work  comes  from  proteids.  For  the 
animal  body  is  a  beautifully-balanced  mechanism  whicl 
constantly  adapts  itself  to  its  conditions.  If  it  saves 
proteids  by  the  use  of  fat  and  carbo-hydrates  when  its 
nitrogenous  food  is  restricted  or  its  organ-proteid  runs  low, 
it  may  also,  when  called  upon  to  labour,  save  proteids  froi 
lower  uses  to  devote  them  to  muscular  contraction.  In  this 
case  the  excretion  of  nitrogen  would  not  necessarily 
altered  ;  the  proteids  which,  in  the  absence  of  work,  woulc 
have  been  oxidized  within  the  muscular  substance  or  else- 
where, their  energy  appearing  entirely  as  heat,  may,  whei 
the  call  for  proteid  to  take  the  place  of  that  broken  dowi 
in  muscular  contraction  arises,  be  diverted  to  this  purpose. 

Thirdly,  there  is  no  doubt  that  a  dog  fed  on  lean  meat 
may  go  on  for  a  long  time  performing  far  more  work  thai 
can  be  yielded  by  the  energy  of  fat  and  carbo-hydratt 
occurring  in  traces  in  the  food,  or  taken  from  the  stock  ii 
the  animal's  body  at  the  beginning  of  the  period  of  worl 
A  large  portion,  and  perhaps  the  whole,  of  the  work,  must 
in  this  case  be  derived  from  the  energy  of  the  proteids 
(Pfluger). 

Experience  has  shown  that  the  minimum  quantity 
nitrogen  required  in  the  food  of  a  man  whose  daily  worl 
involves  hard  physical  toil  is  higher  than  the  minimum 
required  by  a  person  leading  an  easy  sedentary  life.  This  is 
evidently  in  accordance  with  the  view  that  proteid  is  actually 
used  up  in  muscular  contraction ;  but  it  is  not  inconsistent 
with  the  opposite  view.  For  the  body  of  a  man  fit  for  con- 


METABOLISM,  NUTRITION  AND  DIETETICS          461 

tinuous  hard  labour  has  a  greater  mass  of  muscle  to  feed 
than  the  body  of  a  man  who  is  only  fit  to  handle  a  com- 
posing-stick, or  drive  a  quill,  or  ply  a  needle;  and  the 
greater  the  muscular  mass,  the  greater  the  muscular  waste. 
But  if  an  animal  just  in  nitrogenous  equilibrium  on  a  diet 
of  lean  meat  when  doing  no  work,  is  made  to  labour  day 
after  day,  it  will  lose  flesh  unless  the  diet  be  increased. 
This  must  mean  that  some  of  the  proteid  is  being  diverted 
to  muscular  work,  and  that  the  balance  is  not  sufficient  to 
keep  up  the  original  mass  of  '  flesh  '  (see  p.  468). 

(2)  Income  and  Expenditure  of  Carbon. — This  division  of  the 
subject  has  been  necessarily  referred  to  in  treating  of  the 
nitrogen  balance-sheet,  and  may  now  be  formally  completed. 

Carbon  Equilibrium. — A  body  in  nitrogenous  equilibrium 
may  or  may  not  be  in  carbon  equilibrium.  It  has  been 
repeatedly  pointed  out  that  the  continued  loss  or  gain  of 
carbon  by  an  organism  in  nitrogenous  equilibrium  means 
the  loss  or  gain  of  fat ;  and,  since  the  quantity  of  fat  in 
the  body  may  vary  within  wide  limits  without  harm,  carbon 
equilibrium  is  less  important  than  nitrogen  equilibrium.  It 
is  also  less  easily  attained  when  the  carbon  of  the  food  is 
increased,  for,  although  the  consumption  of  fat  is  to  a  certain 
extent  increased  with  the  supply  of  fat  or  fat-producing  food, 
there  is  by  no  means  the  same  prompt  adjustment  of  ex- 
penditure to  income  in  the  case  of  carbon  as  in  the  case  of 
nitrogen. 

Carbon  equilibrium  can  be  obtained  in  a  flesh-eating 
animal,  like  a  dog,  with  an  exclusively  proteid  diet ;  but 
a  far  higher  minimum  is  required  than  for  nitrogenous 
equilibrium  alone.  Voit's  dog  required  at  least  1,500 
grammes  of  meat  in  the  twenty-four  hours  to  prevent  his 
body  from  losing  carbon.  For  a  man  weighing  70  kilos, 
the  daily  excretion  of  carbon  on  an  ordinary  diet  is  about 
300  grammes.  More  than  2,000  grammes  of  lean  meat 
would  be  required  to  yield  this  quantity  of  carbon ;  and, 
even  if  such  a  mass  could  be  digested  and  absorbed,  more 
than  three  times  the  necessary  nitrogen  would  be  thrown 
upon  the  tissues. 

Not  only  may  carbon  equilibrium   be    maintained    for  a 


462  A  MANUAL  OF  PHYSIOLOGY 


time  in  a  dog  on  a  diet  containing  fat  only,  or  fat  and 
carbo-hydrates,  but  the  expenditure  of  carbon  may  be  less 
than  the  income,  and  fat  may  be  stored  up.  But,  of 
course,  if  this  diet  is  continued,  the  animal  ultimately  dies 
of  nitrogen  starvation. 

So  far  we  have  spoken  only  of  the  income  and  expenditure 
of  carbon  and  nitrogen;  and  from  these  data  alone  it  is 
possible  to  deduce  many  important  facts  in  metabolism, 
since,  knowing  the  elementary  composition  of  proteids,  fats 
and  carbo-hydrates,  we  can,  on  certain  assumptions,  translate 
into  terms  of  proteids  or  fat  the  gain  or  loss  of  an  organism 
in  nitrogen  and  carbon,  or  in  carbon  alone.  But  the 
hydrogen  and  oxygen  contained  in  the  solids  and  water  of 
the  food,  and  the  oxygen  taken  in  by  the  lungs,  are  just  as 
important  as  the  carbon  and  nitrogen;  it  is  just  as  neces- 
sary to  take  account  of  them  in  drawing  up  a  complete  and 
accurate  balance-sheet  of  nutrition.  Fortunately,  however, 
it  is  permissible  to  devote  mu^h  less  time  to  them  here,  for 
when  we  have  determined  the  quantitative  relations  of  th< 
absorption  and  excretion  of  the  carbon  and  nitrogen,  w< 
have  also  to  a  large  extent  determined  those  of  the  oxygei 
and  hydrogen. 

(3)  Income  and  Expenditure  of  Oxygen  and  Hydrogen,  —  Th< 
oxygen  absorbed  as  gas  and  in  the  solids  of  the  food  is 
given  off.  chiefly  as  carbon  dioxide  by  the  lungs  ;  to  a  small 
extent  as  water  by  the  lungs,  kidneys,  and  skin  ;  and 
urea  and  other  substances  in  the  urine  and  faeces.  Th< 
hydrogen  of  the  solids  of  the  food  is  excreted  in  part 
urea,  but  in  far  larger  amount  as  water.  The  hydrogen  am 
oxygen  of  the  ingested  water  pass  off  as  water,  without,  s< 
far  as  we  know,  undergoing  any  chemical  change,  or  existing 
in  any  other  form  within  the  body.  But  it  is  important  t< 
recognise  that  although  none  of  the  water  taken  in  as  such  i< 
broken  up,  some  water  is  manufactured  in  the  tissues  by  the 
oxidation  of  hydrogen.  We  have  already  considered  (p.  225) 
the  gaseous  interchange  in  the  lungs,  and  we  have  seen  that 
all  the  oxygen  taken  in  does  not  reappear  as  carbon  dioxide. 
It  was  stated  there  that  the  missing  oxygen  goes  to  oxidize 
other  elements  than  carbon,  and  especially  to  oxidiz< 


METABOLISM,  NUTRITION  AND  DIETETICS          463 

hydrogen.     We  have  now  to  explain  more  fully  the  cause 
of  this  oxygen  deficit. 

The  Oxygen  Deficit. — The  carbo-hydrates  contain  in  themselves 
enough  oxygen  to  form  water  with  all  their  hydrogen ;  they  account 
for  a  part  of  the  water-formation  in  the  body,  but  for  none  of  the 
oxygen  deficit. 

The  fats  are  very  different ;  their  hydrogen  can  be  nothing  like 
completely  oxidized  by  their  oxygen.  A  gramme  of  hydrogen  is 
contained  in  8-5  grammes  of  dry  fat,  and  needs  8  grammes  of  oxygen 
for  its  complete  combustion.  Only  i  gramme  of  oxygen  is  yielded 
by  the  fat  itself;  so  that  if  a  man  uses  100  grammes  of  fat  in  twenty- 
four  hours,  rather  more  than  80  grammes  of  the  oxygen  taken  in  must 
go  to  oxidize  the  hydrogen  of  the  fat. 

The  proteids  also  contribute  to  the  deficit.  In  100  grammes  of 
dry  proteids  there  are  15  grammes  of  nitrogen,  7  grammes  of 
hydrogen,  and  21  grammes  of  oxygen.  The  carbon  does  not  concern 
us  at  present.  The  33  grammes  of  urea,  corresponding  to  100 
grammes  of  proteid,  contain  15  grammes  of  nitrogen,  a  little  more 
than  2  grammes  of  hydrogen,  and  a  little  less  than  9  grammes  of 
oxygen.  There  remain  5  grammes  of  hydrogen  and  1 2  grammes  of 
oxygen.  But  5  grammes  of  hydrogen  need  for  complete  combustion 
40  grammes  of  oxygen ;  therefore  28  grammes  of  the  oxygen  taken 
in  must  go  to  oxidize  the  hydrogen  of  100  grammes  of  proteid. 
Taking  140  grammes  of  proteid  as  the  amount  in  the  diet  of  a  man, 
we  get  39  grammes  as  the  required  quantity  of  oxygen.  This,  added 
to  the  80  grammes  needed  for  the  hydrogen  of  the  fat,  makes  a  total 
of,  say,  120  grammes,  equivalent  to  about  85  litres  of  oxygen.  A 
small  amount  of  oxygen  also  goes  to  oxidize  the  sulphur  of  proteids. 
With  a  diet  containing  less  fat  and  proteid  and  more  carbo-hydrate, 
the  oxygen  deficit  would  of  course  be  less. 

The  Production  of  Water  in  the  Body. — One  gramme  of  hydrogen 
corresponds  to  9  grammes  of  water.  In  140  grammes  of  proteids 
and  100  grammes  of  fat  there  are,  in  round  numbers,  22  grammes 
of  hydrogen;  in  350  grammes  of  starch,  21-5  grammes.  With  this 
diet,  43*5  grammes  of  hydrogen  are  oxidized  to  water  within  the  body 
in  twenty-four  hours,  corresponding  to  a  water-production  of  391 
grammes,  or  15  to  20  per  cent,  of  the  whole  excretion  of  water.  It 
has  been  observed  that  during  starvation  the  tissues  sometimes 
become  richer  in  water,  even  when  none  is  drunk.  The  only 
explanation  is,  that  the  elimination  of  water  does  not  keep  pace  with 
the  rate  at  which  it  is  produced  from  the  hydrogen  of  the  broken- 
down  tissue-substances,  or  set  free  from  the  solids  with  which  it  is 
(physically  ?)  united. 

Inorganic  Salts.— The  inorganic  salts  of  the  excreta,  like 
the  water,  are  for  the  most  part  derived  from  the  salts  of 
the  food,  which  do  not  in  general  undergo  decomposition 
in  the  body.  A  portion  of  the  chlorides,  however,  is  broken 


464  A  MANUAL  OF  PHYSIOLOGY 

up  to  yield  the  hydrochloric  acid  of  the  gastric  jaice. 
Within  the  body  some  of  the  salts  are  intimately  united  to 
the  proteids  of  the  tissues  and  juices,  some  simply  dissolved 
in  the  latter.  The  chlorides,  phosphates  and  carbonates  are 
the  most  important ;  the  potassium  salts  belong  especially  to 
the  organized  tissue  elements,  the  sodium  salts  to  the  liquids 
of  the  body ;  calcium  phosphate  and  carbonate  predomi- 
nate in  the  bones.  The  amount  and  composition  of  the 
ash  of  each  organ  only  changes  within  narrow  limits.  In 
hunger  the  organism  clings  to  its  inorganic  materials,  as 
it  clings  to  its  proteids;  the  former  are  just  as  essential 
to  life  as  the  latter.  In  a  starving  animal  chlorine  almost 
disappears  from  the  urine  at  a  time  when  there  is  still  much 
chlorine  in  the  body  ;  only  the  inorganic  salts  which  have 
been  united  to  the  used-up  proteids  are  excreted,  so  that  a 
starving  animal  never  dies  for  want  of  salts. 

On  the  other  hand,  when  an  animal  is  fed  with  a  diet  as 
far  as  possible  free  from  salts,  but  otherwise  sufficient,  it 
dies  of  salt-hunger.  The  blood  first  loses  inorganic  material, 
then  the  organs.  The  total  loss  is  very  small  in  proportion 
to  the  quantity  still  retained  in  the  body  ;  but  it  is  sufficient 
to  cause  the  death  of  a  pigeon  in  three  weeks,  and  of  a 
in  six,  with  marked  symptoms  of  muscular  and  nervou; 
weakness.  In  pigeons  on  a  diet  containing  very  littl( 
calcium  the  bones  of  the  skull  and  the  sternum  become 
extremely  thin  and  riddled  with  holes,  while  the  bones 
in  movement  scarcely  suffer  at  all  (E.  Voit). 

(4)  Dietetics. — There  are  two  ways  in  which  we  cai 
arrive  at  a  knowledge  of  the  amount  of  the  various  fc 
substances  necessary  for  an  average  man :  (a)  By  considei 
ing  the  diet  of  large  numbers  of  people  doing  fairly  definite 
work,  and  sufficiently,  but  not  extravagantly,  fed — e.g. 
soldiers,  gangs  of  navvies,  or  plantation  labourers ;  (b)  b] 
making  special  experiments  on  one  or  more  individuals. 

Voit  concluded  that  an  '  average  workman,'  weighing 
to  75  kilos,  and  working  ten  hours  a  day,  required  in  th< 
twenty-four  hours  118  grammes  proteid,  56  grammes  fat 
and  500  grammes  carbo-hydrate,  corresponding  to  about 
18*3  grammes  nitrogen  and  at  least  328  grammes  carbon. 


METABOLISM,  NUTRITION  AND  DIETETICS  465 

0    i  ^ 

Ranke  found  the  following  a  sufficient  diet   for  himself,    ^ 
with  a  body-weight  of  74  kilos  : 

Proteids  -  100  grammes. 

Fat  -        -         -     ioo        „ 

Carbo-hydrates        -        -     240        „ 

This  corresponds  to  only  14  grammes  nitrogen  and,  say, 
230  grammes  carbon. 

A  German  soldier  in  the  field  receives  on  the  average 

Proteids  -         -        -         -     151  grammes. 
Fat  ...      46 

Carbo-hydrates        -        -522        „ 

representing  about  21  grammes  nitrogen  and  340  grammes 
carbon.  But  the  diet  of  certain  miners  (Steinheil)  and 
lumberers  (Liebig)  contained  respectively  133  and  112 
grammes  proteid,  113  and  309  (!)  grammes  fat,  and  634 
and  691  grammes  carbo-hydrates.  The  diet  of  athletes  in 
training  is  richer  in  proteid  than  any  of  these.  So  that  a 
definite  and  typical  diet  for  severe  labour  does  not  exist. 
And  although  perhaps  the  hardest  work  ever  done  in  the 
world  is  to  break  records,  to  cut  and  handle  timber,  to  mine 
coal  and  to  make  war,  the  diet  on  which  these  things  are 
accomplished  is  very  variable. 

Nevertheless,  we  may  conclude  that,  for  a  man  of  70  kilos, 
doing  fairly  hard,  but  not  excessive,  work,  20  grammes  * 
nitrogen  and  300  grammes  carbon  are  a  sufficient,  and 
indeed  a  liberal,  allowance,  while  many  men  are  well  fed 
with  15  grammes  of  nitrogen.  The  20  grammes  nitrogen 
will  be  contained  in  140  grammes  dry  proteid,  which  will 
also  yield  70  grammes  of  the  required  carbon.  The  balance 
of  230  grammes  carbon  could  theoretically  be  supplied  either 
i°  5T7  grammes  starch  or  in  300  grammes  fat.  But  it  has 
been  found  by  experiment  and  by  experience  (which  is 
indeed  a  very  complex  and  proverbially  expensive  form  of 
experiment)  that  for  civilized  man  a  mixture  of  these  is 
necessary  for  health,  although  the  nomads  of  the  Asian 
steppes,  and  the  herdsmen  of  the  Pampas,  are  said  to 
subsist  for  long  periods  on  flesh  alone,  and  a  dog  can  live 
very  well  on  proteids  and  fat.  The  proportion  of  fat  and 
carbo-hydrates  in  a  diet  may,  however,  be  varied  within 

30 


466 


A  MANUAL  OF  PHYSIOLOGY 


ru. 


wide  limits.  Probably  no  '  work  '  diet  should  contain  much 
less  than  50  grammes  of  fat,  but  twice  this  amount  would 
be  better ;  ioo  grammes  fat  give  about  75  grammes  carbon, 
so  that  from  proteids  and  fat  we  have  now  got  145  grammes 
of  the  necessary  300,  leaving  155  grammes  carbon  to  be 
taken  in  350  grammes  starch,  or  an  equivalent  amount  of 
cane-sugar  or  glucose.  Adding  30  grammes  inorganic  salts, 
we  can  put  down  as  the  solid  portion  of  a  good  normal  diet 
for  a  man  of  70  kilos : 

C  ~f  o  %      140  grammes  proteids  =  5^  of  body- weight. 

r<L  74-4:  ,  ioo        „         fat  =  7fo 

(? ,  ISSf,  -  35°        »          carbo-hydrates  =  ^jw  „ 

C         30        „         salts. 

620 

Now,  knowing  the  composition  of  the  various  food  stuffs, 
we  can  easily  construct  a  diet  containing  the  proper  quan- 
tities of  nitrogen  and  carbon,  by  using  a  table  such  as  the 
following : 


Quantity 
required 
to  yield 

Quantity 
required 
to  yield 

N.  in 

IOO 

C.  in 

IOO 

Proteid 
in  ioo 

Fat  in 

IOO 

Carbo- 
hydrate 
in  ioo 

I 
Water 
in  ioo 

20  grms. 

300  crms. 

grms. 

grms. 

grms. 

grms. 

grms. 

grms. 

Cheese 

(Gruyere) 

400 

770 

5 

39 

31 

31 

— 

34 

Peas  (dried) 

570 

840 

3'5 

357 

22 

2 

55 

15 

Lean  meat  - 

590 

2230 

3*4 

13*5 

2  1 

3'5 

74 

Wheat-flour 

870 

750 

2-3 

39'8 

12 

2 

70 

15 

Oatmeal 

760 

740 

2-6 

40-3 

13 

5'5 

65 

15 

Eggs  - 

1040 

2040 

ro 

147 

ri'5 

12 

75 

M  aize 

1080 

730 

1-85 

40-9 

10-5 

7 

65 

15 

Wheat 

bread 

1590 

1340 

1-25 

22-4 

8 

1*5 

49 

40 

Rice   - 

2040 

820 

0-9 

36-6 

5 

83 

10 

Milk  - 

3170 

4250 

0-6 

7 

4 

4 

5 

85 

Potatoes     - 

5000 

2860 

0-4 

10-5 

2 

0-15 

21 

75 

Good  butter 

13000 

43° 

0-15 

69 

I 

90 

— 

Economic  and  social  influences — prices  and  habits — and  not  purely 
physiological  rules,  fix  the  diet  of  populations.  The  Chinese  labourer, 
for  example,  lives  on  a  diet  which  no  physiologist  would  commend. 
In  order  to  obtain  20  grammes  nitrogen  or  140  grammes  proteid, 
he  must  consume  nearly  2,000  grammes  rice,  which  will  yield  700 
grammes  carbon,  or  twice  as  much  as  is  required ;  but  if  the  Chinese 
labourer  could  not  live  on  rice,  he  could  not  live  at  all.  The  Irish 
peasant  is  even  in  worse  case ;  he  must  consume  5  kilos  of  potatoes 


METABOLISM,  NUTRITION  AND  DIETETICS          467 


to  obtain  his  20  grammes  nitrogen,  while  little  more  than  half  this 
amount  would  furnish  the  necessary  300  grammes  carbon.*  A  man 
attempting  to  live  on  flesh  alone  would  be  well  fed  as  regards 
nitrogen  with  600  grammes  of  meat,  but  nearly  four  times  as  much 
would  be  required  to  yield  300  grammes  carbon.  Oatmeal  and 
wheat-flour  contain  nitrogen  and  carbon  in  nearly  the  right  propor- 
tions (i  N  •  15  C),  oatmeal  being  rather  the  better  of  the  two  in  this 
respect ;  and  the  best-fed  labouring  populations  of  Europe  still  live 
largely  on  wheaten  bread,  while,  one  hundred  years  ago,  the  Scotch 
peasant  still  cultivated  the  soil,  as  the  Scotch  Reviewer  the  Muses, 
*  on  a  little  oatmeal.'  But  although  bread  may,  and  does,  as  a  rule, 
form  the  great  staple  of  diet,  it  is  not  of  itself  sufficient. 

We  may  take  500  grammes  of  bread  and  250  grammes  of  lean 
meat  as  a  fair  quantity  for  a  man  fit  for  hard  work.  Adding  500 
grammes  milk,  75  grammes  oatmeal  (as  porridge),  30  grammes  butter, 
30  grammes  fat  (with  the  meat,  or  in  other  ways),  and  450  grammes 
potatoes,  we  get  approximately  20  grammes  nitrogen  and  300  grammes 
carbon  contained  in  135  grammes  proteid,  rather  less  than  100 
grammes  fat,  and  somewhat  over  400  grammes  carbo-hydrates. 
Thus  : 


Carbo 

N. 

C. 

Proteids. 

Fat. 

hydrates. 

Salts. 

(9  02.)  250  grms.  lean  meat 

8 

33 

55 

8-5 

— 

4 

(18  oz.)  500  grms.  bread 

6 

112 

40 

7'5 

245 

6-5 

(f  pint)  500  grms.  milk 

3 

35 

20 

20 

25 

3'5 

(i  oz.)  30  grms.  butter 

20 



27 

0-5 

(  i  oz.)  30  grms.  fat 

— 

22 

— 

30 

— 

(16  oz.)  450  grms.  potatoes 

i'5 

47 

10 

95 

4'5 

(3  oz.)  75  grms.  oatmeal 

17 

30 

10 

4 

48 

2 

20'2 

299  1    135 

97 

413 

21 

This  would  be  a  fair  '  hard  work  '  diet  for  a  well-nourished  labourer. 
But  the  great  elasticity  of  dietetic  formulae  is  shown  by  comparing 
the  ration  of  the  English  and  German  soldier  as  given  in  the  follow- 
ing tables : 

Ration  oj  the  English  Soldier. 
Bread       ....     680  grammes. 
Meat        -  340 

Vegetables       -        -        -     226 
Potatoes  -        -        -        -453 
Milk         ....      93 
Sugar       -         -         -        -       377 
Coffee      ....        9-4 
Tea          ....        4-6 
Salt          ....         7 

*  Of  course  a  diet  consisting,  week  in  week  out,  entirely  of  potatoes  or 
rice,  would  represent  an  extreme  case.  A  certain  amount  of  the  necessary 
nitrogen  is  often  obtained  even  by  the  poorest  populations,  in  the  form  of 
fish,  milk,  eggs  or  bacon. 

30 — 2 


468  A  MANUAL  OF  PHYSIOLOGY 


Ration  of  the  German  Soldier. 
Peace.  War. 

Bread   -         -        -     750  grammes.       Bread  750  grammes, 

Meat     -  -     150  Biscuit  -         -         -     500 


Rice      -         -  -  50 

or  barley  groats  -  120 

Legumes       -  -  230 

Potatoes        -  -  1500 


Meat  -  -375 

Smoked  meat  -  250 

or  fat  -  -  -  170 

Rice  -  -  125 

or  barley  groats  -  125 

Legumes  -  -  250 


In  prisons  the  object  is  to  give  the  minimum  amount  of  the 
plainest  food  which  will  suffice  to  maintain  the  prisoners  in  health. 
A  'hard  work'  prison  diet  in  Munich  was  found  to  contain  104 
grammes  proteids,  38  grammes  fat,  and  521  grammes  carbo-hydrates  ; 
a  'no  work'  diet,  only  87  grammes  proteids,  22  grammes  fat,  and 
305  grammes  carbo-hydrates.  Here  we  recognise  the  influence  of 
price ;  carbon  can  be  much  more  cheaply  obtained  in  vegetable 
carbo-hydrates  than  in  animal  fats ;  the  cheapest  possible  diet  contains 
a  minimum  of  fat  and  proteids. 

Many  poor  persons  live  on  a  diet  which  would  not  maintain  a 
strong  man,  for  an  emaciated  body  has  a  smaller  mass  of  flesh  to- 
keep  up,  and  therefore  needs  less  proteid ;  it  can  do  little  work,  and 
therefore  needs  less  food  of  all  kinds.  A  London  needlewoman, 
according  to  Playfair,  subsists,  or  did  subsist,  thirty  years  ago,  on 
54  grammes  proteid,  29  grammes  fat,  and  292  grammes  carbo- 
hydrates. But  this  is  the  irreducible  minimum  of  the  deepest 
poverty ;  and  a  woman,  with  a  smaller  mass  of  flesh  and  leading 
a  less  active  life  than  a  man,  requires  less  food  of  all  sorts.  Even 
the  Trappist  monk,  who  has  reduced  asceticism  to  a  science,  and, 
instead  of  eating  in  order  to  live,  lives  in  order  not  to  eat,  consumes, 
according  to  Voit,  68  grammes  proteid,  n  grammes  fat,  and  469! 
grammes  carbo-hydrates;  but  manual  labour  is  a  part  of  the  dis- 
cipline of  the  brotherhood,  and  this  must  be  still  above  the  lowest 
subsistence  diet. 

A  growing  child  needs  far  more  food  than  its  weight  alone  would 
indicate ;  for,  in  the  first  place,  its  income  must  exceed  its  expendi- 
ture so  that  it  may  grow ;  and,  in  the  second  place,  the  expenditure 
of  an  organism  is  pretty  nearly  proportional,  not  to  its  mass,  but  to 
its  surface.  Now,  speaking  roughly,  the  cube  of  the  surface  of  an 
animal  varies  as  the  square  of  the  mass ;  when  the  weight  is  doubled, 
the  surface  only  becomes  3v/~~,  or  one  and  a  half  times  as  great. 
The  surface  of  a  boy  of  six  to  nine  years,  with  a  body-weight  of 
18  to  24  kilos,  is  two-fifths  to  one-half  that  of  a  man  of  70  kilos; 
and  he  should  have  about  half  as  much  food  as  the  man — say,  70 
grammes  proteids,  40  grammes  fat,  and  200  grammes  carbo-hydrates. 
A  child  of  four  months,  weighing  5  '3  kilos,  consumed  per  diem  food 
containing  '6  gramme  nitrogen  per  kilo  of  body-weight,  or  3'i8 
grammes  nitrogen  altogether,  as  against  a  daily  consumption  of  only 
•275  gramme  nitrogen  per  kilo  in  a  man  of  71  kilos  (Voit)  (p.  497). 

An  infant  for  the  first  seven  months  should  have  nothing  exce 


• 


METABOLISM,  NUTRITION  AND  DIETETICS  469 

milk.  Up  to  this  age  vegetable  food  is  unsuited  to  it ;  it  is  a  purely 
carnivorous  animal.  Human  milk  contains  about  4  per  cent,  of 
proteids  (casein),  2*6  per  cent,  of  fat,  4*3  per  cent,  of  carbo-hydrates 
(milk-sugar).  Of  the  solids  the  proteids  make  up  36  per  cent.,  the 
fats  24  per  cent.,  the  carbo-hydrates  39  per  cent.  In  the  typical  diet 
for  an  adult,  which  we  have  given  above,  the  proteids  amount  to 
20  per  cent,  of  the  solids,  the  fats  to  15  per  cent,  the  carbo-hydrates 
to  more  than  60  per  cent.  The  diet  of  the  infant  is  therefore  nearly 
twice  as  rich  in  proteids,  half  as  rich  again  in  fats,  and  little  more 
than  half  as  rich  in  carbo-hydrates,  as  that  of  the  adult.  It  is  in 
a  physiological  sense  a  generous  and  even  a  luxurious  diet.  '  The 
poorest  mother  in  London  or  New  York  feeds  her  child  as  if  he  were 
a  prince.  Perhaps  not  once  in  a  hundred  times  is  the  man  as  richly 
fed  as  the  young  child,  unless  accident  has  made  him  a  Gaucho  or 
study  and  reflection  a  gourmand.'  And  the  reason  is  that  the  strain 
of  growth  falls  heavier  upon  the  more  precious  proteids  than  upon 
the  more  cheap  and  common  carbo-hydrates. 

As  to  the  place  of  water  and  inorganic  salts  in  diet,  it  is 
neither  necessary  nor  practicable  to  lay  down  precise  rules. 
In  most  well-settled  countries  they  cost  little  or  nothing ; 
very  different  quantities  can  be  taken  and  excreted  without 
harm ;  and  both  economics  and  physiology  may  well  leave 
every  man  to  his  taste  in  the  matter.  Salt  is  indeed  for 
the  most  part  used,  not  as  a  special  article  of  diet,  but  as  a 
condiment  to  give  a  relish  to  the  food,  just  as  a  great  deal 
more  water  than  is  actually  needed  is  often  drunk  in  the 
form  of  beverages.  It  is  certain  that  the  quantity  of  salt 
required,  in  addition  to  the  salts  of  the  food,  to  keep  the 
inorganic  constituents  of  the  body  at  their  normal  amount, 
is  very  small.  A  3O-kilo  dog  obtains  in  his  diet  of  500 
grammes  of  lean  meat  only  o'6  gramme  sodium  chloride, 
and  needs  no  more.  An  infant  in  a  litre  of  its  mother's 
milk,  which  is  a  sufficient  diet  for  it,  gets  only  0*8  gramme 
sodium  chloride.  Bunge,  however,  has  shown  that  the  pro- 
portion of  potassium  and  sodium  salts  in  the  food  is  a  factor 
in  determining  the  quantity  of  sodium  chloride  required. 
A  double  decomposition  takes  place  in  the  body  between 
potassium  phosphate  and  sodium  chloride,  potassium  chloride 
and  sodium  phosphate  being  formed  and  excreted ;  and  the 
loss  of  sodium  and  chlorine  in  this  way  depends  on  the 
relative  proportions  of  potassium  and  sodium  in  the  food. 
In  most  vegetables  the  proportion  of  potassium  to  sodium 


470  A  MANUAL  OF  PHYSIOLOGY 

is  much  greater  than  in  animal  food,  so  that  vegetable- 
feeding  animals  and  men  as  a  rule  desire  and  need  relatively 
great  quantities  of  sodium  chloride.  But  it  is  stated  that 
the  inhabitants  of  a  portion  of  the  Soudan  use  potassium 
chloride  instead  of  sodium  chloride,  obtaining  the  potassium 
salt  by  burning  certain  plants  which  leave  an  ash  poor  in 
carbonates,  and  then  extracting  the  residue  with  water  and 
evaporating  (Dybowski).  A  beef-eating  English  soldier 
consumes  about  7  grammes  (J  oz.),  a  rice-eating  Sepoy 
about  18  grammes  (f  oz.),  of  common  salt  per  day. 

Wine,  beer,  tea,  coffee,  cocoa,  etc.,  belong  to  the  im- 
portant class  of  stimulants.  Some  of  them  contain  small 
quantities  of  food  substances,  but  these  are  of  secondary 
interest.  In  beer,  for  example,  there  are  traces  of  proteids, 
dextrin,  and  sugar.  But  18  litres  of  beer  would  be  required 
to  yield  20  grammes  nitrogen,  and  12  litres  to  give  300 
grammes  carbon ;  and  nobody,  except  a  German  corps 
student,  could  consume  such  quantities. 

In  some  cocoas  there  is  as  much  as  50  per  cent,  of  fat, 
4  per  cent,  of  starch,  and  13  per  cent-  of  proteids ;  and  in 
the  cheaper  cocoas  much  starch  is  added.  Still,  a  large 
quantity  of  the  ordinary  infusion  would  be  needed  for  a 
satisfying  meal.  Frederick  the  Great,  indeed,  in  some  of 
his  famous  marches  dined  off  a  cup  of  chocolate,  and  beat 
combined  Europe  on  it ;  but  his  ordinary  menu  was  much 
more  varied  and  substantial. 

The  great  social  and  hygienic  evils  connected  with  the  abuse  of 
alcohol,  as  well  as  its  applications  in  therapeutics,  render  it  necessary, 
or  at  least  permissible,  to  state  a  little  more  fully,  though  only  in  the 
form  of  summary,  some  of  the  chief  conclusions  that  may  be  drawn 
as  to  its  action  and  uses. 

(1)  In  small  quantities  alcohol  is  oxidized  in  the  body,  a  little  of 
it,  however,  being  excreted  unchanged  in  the  breath  and  urine.     It 
is  therefore  to  some  extent  a  food  substance,  although  it  is  never 
taken  for  the  sake  of  the  energy  its  oxidation  can  supply,  but  always 
as  a  stimulant, 

(2)  There  is  no  reason  to  suppose  that  this  energy  cannot  be 
utilized  as  a  source  of  work  in  the  body.     Heat  can  certainly  be 
produced  from  it,  but  this  is  far  more  than  counterbalanced  by  the 
increase  in  the  heat  loss  which  the  dilatation  of  the  cutaneous  vessels 
caused  by  alcohol  brings  about. 

(3)  It  is  a  very  valuable  drug,  when  judiciously  employed,  as  a 
cardiac  and  general  stimulant  in  certain  diseases,  e.g.,  pneumonia. 


METABOLISM,  NUTRITION  AND  DIETETICS  471 

(4)  Alcohol  is  occasionally  of  use  in  disorders  not  amounting  to 
serious  disease,  e.g.,  in  some  cases  of  slow  and  difficult  digestion. 

(5)  Alcohol  is  of  no  use  for  healthy  men. 

(6)  Alcohol  in  strictly  moderate  doses  is  not  harmful  to  healthy 
men,  living  and  working  under  ordinary  conditions. 

(7)  Recent  experience  goes  to  show  that  in  severe  and  continuous 
exertion,  coupled  with  exposure  to  all  weathers,  as  in  war  and  in 
exploring  expeditions,  alcohol  is  injurious,  and  it  is  well  known  that 
it  must  be  avoided  in  mountain  climbing. 

Tea,  coffee,  and  cocoa  are  more  suitable  stimulants  for  healthy 
persons,  because  they  are  less  dangerous  than  alcohol,  and  they  leave 
no  unpleasant  effects  behind  them.  But  it  should  be  remembered 
that  there  is  no  stimulant  which  is  not  liable  to  be  abused. 

Certain  organic  acids  contained  in  fresh  vegetables,  although 
neither  in  the  ordinary  sense  foods  nor  condiments,  seem  to  be 
necessary  for  the  maintenance  of  health,  for  in  circumstances  in 
which  these  cannot  be  obtained  for  long  periods,  scurvy  is  liable  to 
break  out.  It  is  prevented  by  the  use  of  lime  or  lemon-juice,  in 
which  citric,  and  a  trace  of  malic  acid  are  contained. 


INTERNAL  SECRETION. 

It  is  long  since  Caspar  Friedrich  Wolff  expressed  the  idea 
that  'each  single  part  of  the  body,  in  respect  of  its 
nutrition,  stands  to  the  whole  body  in  the  relation  of  an 
excreting  organ,'  and  thus  emphasized  the  importance 
of  substances  produced  by  the  activity  of  one  kind  of 
cell  for  the  normal  metabolism  of  another.  But  it  is  only  in 
recent  years  that  it  has  become  possible  to  illustrate  this 
mutual  relation  by  any  large  number  of  experimental  facts. 

Certain  of  the  substances  taken  in  from  the  blood  by  the 
liver  find  their  way,  after  undergoing  various  changes,  into 
the  biliary  capillaries,  and  are  excreted  as  bile  ;  certain  other 
substances,  such  as  sugar  and  the  precursors  of  urea,  are 
taken  up  by  the  hepatic  cells,  transformed  and  sometimes 
stored  for  a  time  within  them,  and  then  given  out  again  to 
the  blood.  Bile  we  may  call  the  external  secretion  of  the  liver, 
glycogen  and  urea  constituents  of  its  internal  secretion.  In 
one  sense  it  is  evident  that  all  tissues,  whether  glands  in  the 
morphological  sense  or  not,  may  be  considered  as  manu- 
facturing an  internal  secretion.  For  everything  that  an 
organ  absorbs  from  the  blood  and  lymph  it  gives  out  to 
them  again  in  some  form  or  other  except  in  so  far  as  it 


472  A  MANUAL  OF  PHYSIOLOGY 

forms  or  separates  a  secretion  that  passes  away  by  special 
ducts.  But  it  is  usual  to  employ  the  term  only  in  relation  to 
organs  of  glandular  build,  whether  provided  with  ducts 
or  not. 

It    is  known  that  in  the  case  of  the  liver  the  internal 
secretion  is  more  important  than  the  external,  for  an  animal 
cannot  live  without  its  liver,  while  it  is  but  little  affected  by 
the  continuous  escape  of  the  bile  through  a  fistulous  open- 
ing.    The  internal  secretions  of  the  pancreas  and  the  kidney 
are  also  indispensable.     For  when  the  pancreas  is  excised 
death  follows  in  many  species  of  animals  ;  and  in  man  severe 
and  ultimately  fatal  diabetes  is  often  associated  with  pan- 
creatic disease,  while  the  mere  loss  of  the  pancreatic  juice 
through  a  fistula  does  not  necessarily  shorten  life,  although 
the  absorption  of  fat  is  seriously  interfered  with.     And  when 
the  half  or  two-thirds  of  one  kidney  and  the  whole  of  the  other 
have  been  removed  from  a  dog  by  successive  operations, 
death  also  ensues,  although  the  quantity  both  of  water  and 
urea  excreted  by  the  fragment  of  renal  substance  that  remains 
is  far  above  the  normal  (polyuria).     The  cause  of  death  in 
both    these   cases  seems  to  be  a  profound   disturbance  of 
metabolism,    of    which   the    most    significant    token    after 
extirpation  of  the  pancreas  is  the  increased  production  of 
sugar  and  its  appearance  in  the  urine,  and  after  interference 
with  the  kidneys  the  increased  production  of  urea.     Both 
in    pancreatic   diabetes   and    in   experimental    polyuria  the 
destruction  of  proteids  is  increased.     When  only  one  kidney 
is  excised  the  other  hypertrophies  and  no  ill  effects  ensue  ; 
nor    does    diabetes    appear    after   partial    removal    of    the 
pancreas,  so  long  as  a  comparatively  small  fraction   (one 
quarter  or  one-fifth)  of  it  is  left,  even  when  this  remnant  is 
transplanted  from   its  original  position  and  grafted  in  the 
peritoneal  cavity  or  indeed  under  the  skin.     Although  as  yet 
we  are  entirely  ignorant  of  the  manner  in  which  the  kidney 
and  the  pancreas  influence  the  metabolism  of  the  body,  it 
'We/U'GJis  impossible  to  doubt,  in  view  of  the  facts  we  have  men- 
Itioned,    that   both    of  these  organs,  like  the  liver,   are,   in 
addition   to   the  preparation  of  their  ordinary  or   external 
secretions,  engaged  in  an  active  and  all-important  commerce 


METABOLISM,  NUTRITION  AND  DIETETICS  473 

with  the  circulating  fluids,  giving  to  them  or  taking  from 
them  substances  on  the  manufacture  or  destruction  of  which 
the  normal  metabolic  processes  depend.  Schafer  has  sug- 
gested that  the  seat  of  the  internal  secretion  of  the  pancreas 
is  the  very  vascular  epithelioid  tissue  which  is  peculiar  to 
this  gland,  and  occurs  in  islands  between  the  alveoli.  For 
animals  survive  the  complete  atrophy  of  the  ordinary  secret- 
ing epithelium  caused  by  the  injection  of  paraffin  into  the 
ducts ;  no  sugar  appears  in  the  urine,  and  the  grafting  of 
such  an  atrophied  organ  prevents  pancreatic  diabetes. 

The  influence  of  castration  in  preventing  the  physical 
and  psychical  changes  that  normally  occur  at  puberty,  is  no 
doubt  also,  in  part  at  least,  due  to  the  loss  of  the  internal 
secretion  of  the  testes.  And  the  efficacy  of  orchitic  extract 
in  increasing  the  capacity  for  muscular  work,  as  tested  by 
the  ergograph  (p.  597),  is  sufficient  to  encourage  the  hope 
that  it  may  possess  a  certain  therapeutic  value. 

But  the  capacity  of  manufacturing  internal  secretions  of 
high  importance  can  neither  be  attributed  to  all  glands  with 
ducts  nor  denied  to  all  other  organs.  For  the  salivary, 
mammary  and  gastric  glands  may  be  completely  removed 
without  causing  any  serious  effects,  while  death  follows 
excision  of  the,  so  far  as  mere  bulk  is  concerned,  apparently 
insignificant  masses  of  tissue  in  the  ductless  thyroid, 
suprarenal  and  pituitary  bodies. 

When  the  thyroid  is  completely  removed,  symptoms  and 
pathological  changes  ensue  which  differ  in  different  species 
of  animals,  but  in  monkeys  (and  in  man  when  the  thyroid 
has  been  excised  for  goitre)  resemble  those  of  the  disease 
known  as  myxoedema,  in  which  the  characteristic  change  is 
an  increase  (a  hyperplasia)  of  the  connective  tissue  in  and 
under  the  true  skin.  The  newly-formed  connective  tissue  is 
of  embryonic  type,  and  for  this  reason  contains  more  than 
the  usual  amount  of  mucin.  Carnivorous  animals  do  not, 
as  a  rule,  survive  the  operation  long  enough  for  these 
changes  to  be  developed  (p.  515).  Muscular  weakness  soon 
becomes  marked ;  tremors  of  central  origin  appear,  and 
increase  in  severity  until  at  length  they  culminate  in  general 
spasmodic  attacks.  The  tissues  waste,  the  temperature 


474  A  MANUAL  OF  PHYSIOLOGY 

becomes  subnormal,  and  this  is  associated  with  changes  in 
the  heat  regulation  (p.  498).  Dogs  and  cats  often  die  in  a 
few  days  after  the  operation  ;  occasionally  they  survive  some 
months,  and  in  rare  cases  a  year.  If  a  portion  of  the 
thyroid  be  left,  or  a  graft  be  made,  these  effects  are  entirely 
obviated.  Not  only  so,  but  the  administration  of  extracts 
of  the  thyroid  glands  by  subcutaneous  injection,  or  the 
glands  themselves  by  the  mouth,  brings  about  a  cure  in 
cases  of  myxcedema  in  man,  and  sometimes,  but  with  far 
less  certainty,  prevents  the  development  of  the  symptoms  in 
animals  or  removes  them  when  they  have  appeared.  The 
same  is  true,  although  in  a  minor  degree,  of  certain  com- 
pounds rich  in  iodine,  for  instance  the  so-called  thyro-iodine, 
which  have  been  extracted  from  the  organ.  While  the 
precise  role  played  by  the  thyroid  in  the  economy  remains 
obscure,  it  is  very  evident  that  its  secretion  is  of  the  utmost 
importance,  whether  it  be  solely  the  quasi-external  secretion 
of  '  colloid  '  that  collects  in  its  alveoli  and  slowly  passes  out 
of  them  by  the  lymphatics,  or  some  other  substance,  which, 
like  the  glycogen  of  the  liver,  never  finds  its  way  into  the 
lumen  of  the  gland  tubes  at  all.  And  it  seems  certain  that 
the  main  function  of  the  organ  is  not  to  destroy  toxic  bodies 
produced  elsewhere,  but  to  form  substances  indispensable  to 
the  organism.  It  is  a  remarkable,  and  as  yet  inexplicable, 
fact  that  in  birds  thyroidectomy  appears  to  be  harmless. 
The  apparent  immunity  of  rodents  to  this  operation  is  due, 
it  has  been  suggested,  to  the  presence  of  sporadic  masses  of 
thyroid  tissue  (accessory  thyroid  glands),  or  to  the  presence 
of  small  bodies  in  the  neighbourhood  of  the  thyroid  but  of 
a  different  structure  (parathyroids).  Some  have  even  gone 
so  far  as  to  assert  that,  in  animals  which  possess  them,  it  is 
the  parathyroids  and  not  the  thyroids  which  are  important, 
and  that  the  extirpation  of  the  latter  is  harmless  unless  the 
former  be  also  removed.  But  the  matter  is  not  yet  beyond 
the  pale  of  controversy. 

Suprarenal  Capsules. — It  had  been  observed  by  Addison  that 
the  malady  which  now  bears  his  name,  and  in  which  certain 
vascular  changes,  with  muscular  weakness  and  pigmentation 
or  '  bronzing '  of  the  skin,  are  prominent  symptoms,  was 


METABOLISM,  NUTRITION  AND  DIETETICS          475 

associated  with  disease  of  the  suprarenals.  This  clinical 
result  was  soon  supplemented  by  the  discovery  that  extirpa- 
tion of  the  capsules  in  animals  is  incompatible  with  life 
(Brown  -  Sequard).  Our  knowledge  of  the  functions  of 
these  hitherto  enigmatic  organs  has  been  greatly  extended 
by  the  experiments  of  Oliver  and  Schafer,  who  have  in- 
vestigated the  action  of  extracts  of  the  suprarenals  (of  calf, 
sheep,  dog,  guinea-pig  and  man)  when  injected  into  the 
veins  of  animals.  The  arteries  are  greatly  contracted,  and  i 
this  independently  of  the  vaso-motor  centre.  The  blood- 
pressure  rises  rapidly,  although  the  heart  is  strongly 
inhibited  through  the  vagus  centre.  When  the  vagi  are  cut 
the  action  of  the  heart  is  markedly  augmented,  and  the 
arterial  pressure  rises  enormously  (to  four  or  five  times  its 
original  amount).  Stimulation  of  the  depressor  is  of  no 
avail  in  combating  this  increase  of  blood-pressure.  The 
curve  of  contraction  of  the  skeletal  muscles  is  lengthened 
as  in  veratria  poisoning  (p.  551),  though  to  a  less  extent. 
The  active  principle  that  produces  these  effects  is  solely 
contained  in  the  medulla  of  the  gland,  and  such  is  its 
extraordinary  power  that  a  dose  of  one-millionth  of  a  gramme 
per  kilo  of  body-weight  is  sufficient  to  cause  a  distinct 
effect  upon  the  heart  and  bloodvessels.  It  was  entirely 
absent  from  the  suprarenals  of  a  person  who  had  died  of 
Addison's  disease.  Oliver  and  Schafer  conclude  that  the 
function  of  the  capsules  is  to  secrete  a  substance,  probably 
of  great  physiological  importance  for  maintaining  the 
tonicity  of  the  muscular  tissues  in  general,  and  especially  of 
the  heart  and  arteries. 

When  the  pituitary  body  is  removed  (in  cats),  death 
generally  occurs  within  a  fortnight,  with  symptoms  not 
unlike  those  that  follow  excision  of  the  thyroid.  It  has  been 
stated,  too,  that  the  pituitary  undergoes  (compensatory?) 
hypertrophy  after  thyroidectomy,  and  many  observers  have 
accordingly  assumed  a  similarity  of  function  for  these 
organs.  But,  according  to  Schafer,  there  is  no  basis  for 
this  assumption.  For  in  man  pathological  changes  in  the 
pituitary  body  are  associated,  not  with  myxcedema,  as 
disease  of  the  thyroid  is,  but  with  another  condition,  called 


476  A  MANUAL  OF  PHYSIOLOGY 

acromegaly,  in  which  the  bones  of  the  limbs  and  face 
become  hypertrophied.  And  the  effects  on  the  vascular 
system  of  intravenous  injection  of  extracts  of  the  gland  are 
just  the  reverse  of  those  caused  by  thyroid  extract ;  while 
thyroid  extract  brings  about  a  fall  of  blood-pressure  without 
affecting  the  heart-beat,  pituitary  extract  causes  a  rise  of 
pressure,  due  partly  to  increase  in  the  force  of  the  heart 
(without  any  change  in  rate)  and  partly  to  constriction  of 
the  arterioles  (Oliver  and  Schafer). 

The  removal  of  the.  thymus  in  the  frog,  in  which  animal  the  organ 
persists  throughout  life,  is  said  to  cause  death.  The  chief  symptoms 
are  muscular  weakness  going  on  to  paralysis,  trophic  disturbances, 
including  discolouration  of  the  skin  and  certain  alterations  in  the 
blood. 

The  spleen  does  not  appear  to  produce  an  internal  secretion,  or  at 
least  an  internal  secretion  of  any  great  importance,  for  it  can  be 
removed  both  in  animals  and  in  man,  not  only  without  endangering 
life,  but  often  without  the  development  of  any  symptoms.  It  is 
possible  that  its  blood-forming  and  blood-destroying  functions 
(p.  32)  are  taken  on  by  other  structures  (the  red  bone-marrow  and 
the  lymphatic  glands). 

The  salivary  glands  may  also  be  extirpated  without  the  slightest 
change  being  produced  in  the  normal  metabolism. 


CHAPTER    VIII. 
ANIMAL  HEAT. 

FROM  the  earliest  ages  it  must  have  been  noticed  that  the 
bodies  of  many  animals,  and  particularly  of  men,  are  warmer 
than  the  air  and  than  most  objects  around  them.  The 
'  vulgar  opinion  '  of  Bacon's  time,  '  that  fishes  are  the  least 
warm  internally,  and  birds  the  most,'  if  it  does  not  imply 
a  very  extensive  knowledge  of  animal  temperature,  at  least 
shows  that  the  fundamental  distinction  of  warm  and  cold- 
blooded animals,  which  is  to-day  more  accurately  expressed 
as  the  distinction  between  animals  of  constant  temperature 
(homoiothermal)  and  animals  of  variable  temperature 
(poikilothermal),  had  been  grasped,  and  was  even  popularly 
known.  Since  that  time  the  accumulation  of  accurate 
numerical  results,  and  the  advance  of  physical  and  physio- 
logical doctrine,  have  given  us  definite  ideas  as  to  the  rela- 
tion of  animal  heat  to  the  metabolic  processes  of  the  body. 
It  is  impossible  to  understand  the  present  position  of  the 
subject  without  an  elementary  knowledge  of  the  science  of 
heat.  For  this  the  student  is  referred  to  a  text-book  of 
physics.  All  that  can  be  done  here  is  to  preface  the  physio- 
logical portion  of  the  subject  by  a  few  remarks  on  the 
physical  methods  and  instruments  employed  : 

Temperature. — Two  bodies  are  at  the  same  temperature  if,  when 
piaced  in  contact,  no  exchange  of  heat  takes  place  between  them. 
They  are  at  different  temperatures  if,  on  the  whole,  heat  passes  from 
one  to  the  other,  and  that  body  from  which  the  heat  passes  is  at  the 
higher  temperature  It  is  known  by  experiment  that  if  two  bodies  of 
different  temperature  are  placed  in  contact,  heat  will  pass  from  one 
to  the  other  till  they  come  to  have  the  same  temperature.  If,  then, 


478  A  MANUAL  OF  PHYSIOLOGY 

we  have  the  means  of  finding  out  the  temperature  of  any  one  body, 
we  can  arrive  at  the  temperature  of  any  other  by  placing  the  two 
in  contact  for  a  sufficiently  long  time,  under  the  proviso  that  the 
quantity  of  heat  necessary  to  bring  the  temperature  of  the  first  body, 
which  may  be  called  the  *  measuring '  body,  to  equality  with  that  of 
the  second,  is  so  small  as  not  to  make  a  sensible  difference  in  the 
latter.  This  is  the  principle  on  which  thermometric  measurements 
depend.  A  mercurial  thermometer  consists  of  a  quantity  of  mercury 
ordinarily  contained  in  a  thin  glass  bulb,  the  cavity  of  which  is  con- 
tinued into  a  tube  of  very  fine  bore  in  the  stem.  Like  most  other 
substances,  mercury  expands  when  the  temperature  rises,  and  con- 
tracts when  it  sinks,  and  the  amount  of  expansion  or  contraction  is 
shown  by  the  rise  or  fall  of  the  mercurial  column  in  the  stem  of  the 
thermometer.  The  point  at  which  the  meniscus  stands  when  the 
bulb  is  immersed  in  melting  ice  or  ice-cold  water  is,  on  the  centi- 
grade scale,  taken  as  zero ,  the  point  at  which  it  stands  when  the 
thermometer  is  surrounded  by  the  steam  rising  from  a  vessel  of 
boiling  water  is  taken  as  100  degrees.  The  intermediate  portion  of 
the  stem  is  divided  into  degrees  and  fractions  of  degrees.  When, 
now,  we  measure  the  temperature  of  any  part  of  an  animal  with  such 
a  thermometer,  we  place  the  bulb  in  contact  with  the  part  until  the 
mercury  has  ceased  to  rise  or  fall.  We  know  then  that  the  mercury 
has  ceased  to  expand  or  contract,  and  therefore  that  its  temperature 
is  stationary,  and  presumably  the  same  as  that  of  the  part.  It  is  to  be 
noted  that  we  have  gained  no  information  whatever  as  to  the  amount 
of  heat  in  the  body  of  the  animal.  We  have  only  observed  that  the 
mercury  of  the  thermometer  when  its  temperature  is  the  same  as  that 
of  the  given  part  expands  to  an  extent  marked  by  the  division  of  the 
scale  at  which  the  column  is  stationary.  And  we  know  that  if  the 
mercury  rises  to  the  same  point  when  the  thermometer  is  applied  to 
another  part,  the  temperature  of  the  latter  is  the  same  as  that  of  the 
first  part;  if  the  mercury  rises  higher,  the  temperature  is  greater; 
if  not  so  high,  it  is  less.  The  thermometer,  then,  only  informs  us 
whether  heat  would  flow  from  or  into  the  part  with  which  it  is  in 
contact  if  the  part  were  placed  in  thermal  connection  with  any  other 
body  of  which  the  temperature  is  known.  In  other  words,  the 
temperature  is  a  measure  of  the  heat  '  tension,'  so  to  speak  ;  and 
difference  of  temperature  between  two  bodies  is  analogous  to  differ- 
ence of  potential  between  the  poles  of  a  voltaic  cell  (p.  518),  or  to 
difference  of  level  between  the  surface  of  a  mill-pond  and  the  race 
below  the  wheel. 

The  temperature  of  an  animal  is  measured  in  one  of  the  natural 
cavities,  as  the  rectum,  vagina,  mouth,  or  external  ear,  or  in  the  axilla, 
or  at  any  part  of  the  skin.  For  the  cavities  a  mercury  thermometer 
is  nearly  always  used ;  the  ordinary  little  maximum  thermometer  is 
most  convenient  for  clinical  purposes.  The  temperature  of  the  skin 
may  be  measured  by  an  ordinary  mercury  thermometer,  the  outer 
portion  of  the  bulb  of  which  is  covered  by  some  badly  conducting 
material.  An  uncovered  thermometer,  heated  nearly  to  the  tem- 
perature expected,  will  also  give  approximate  results,  especially  if  the 


ANIMAL  HEAT  479 

bulb  is  in  the  form  of  a  flat  spiral,  which  can  be  easily  applied  to  the 
surface.  But  a  certain  error  is  always  introduced  by  the  interference 
with  the  normal  heat  loss  from  the  portion  of  skin  covered  by  the 
thermometer.  A  better  method  is  the  use  of  a  thermo-electric 
junction,  or  a  resistance  thermometer  formed  of  a  grating  cut  out 
of  thin  lead-paper  or  tinfoil  (Fig.  135).  This  is  especially  useful  for 
comparing  the  temperature  of  two  portions  of  skin.  The  tempera- 
ture of  the  solid  tissues  and  liquids  of  the  body  may  also  be  measured 
or  compared  by  the  insertion  of  mercurial  or  resistance  thermometers 
or  thermo-electric  junctions  (p.  560). 

Calorimetry. — The  quantity  of  heat  given  off  by  an  animal  is 
generally  measured  by  the  rise  of  tem- 
perature which  it  produces  in  a  known 
mass    of     some    standard    substance. 
Sometimes,    however,    as   in   the    ice- 
calorimeter  of  Lavoisier  and   Laplace 
and  the  ether  calorimeter  of  Rosenthal, 
a  physical  change  of  state — in  the  one 
case  liquefaction  of  ice,  in   the  other 
evaporation  of  ether — is  taken  as  token 
and  measure  of  heat  received  by  the 
measuring   substance,   the   number   of 
units  of  heat  corresponding  to  liquefac- 
tion of  unit  mass  of  ice  or  evaporation 
of   unit  mass  of   ether  being  known.   FJG    I35._RES1STANCE  THER. 
The    unit    generally    adopted    in    the       MOMETER     FOR    MEASURING 
measurement  of  heat  is  the  quantity      TEMPERATURE  OF  SKIN. 
required  to  raise  the  temperature  of  a      G,  grating  of  lead-paper,  attached 

kilogramme  Of  water  I°  C,  which  is  to  a  cover-slip,  and  mounted  on  a 
called  a  calorie,  or  kilocalorie,  Or  large  Whetstone's  bridge .W>  An  increase 
calorie.  The  thousandth  part  of  this,  of  temperature  causes  an  increase 

the  quantity  needed  to  raise  the  tern-  in  the  resistance  of  the  lead.    The 

/  -  ,          o     balance  of  the  bridge  is  thus  dis- 

perature   of  a  gramme  Of  water  by   I   ,    turbed.     By   experimental   gradua- 

is  termed  a  small  calorie  or  millicalorie.  tion  the  temperature  value  of  the 

In  the  calorimeters  which  have  been 
chiefly  used  in  physiology  either  water  (£"519)^ 
or  air  has  been  taken  as  the  measuring 
substance.  The  most  convenient  form  of  water  calorimeter  is  a  box  with 
double  walls,  the  space  between  which  is  filled  with  a  weighed  quantity 
of  water.  The  animal  is  placed  inside  the  vessel,  and  the  temperature 
of  the  water  noted  at  the  beginning  and  end  of  the  experiment. 
Suppose  that  the  quantity  of  water  is  10  kilos,  and  that  the  temperature 
rises  one  degree  in  thirty  minutes,  then  the  amount  of  heat  lost  by 
the  animal  is  10,000  small  calories  in  the  half-hour,  or  480,000  in 
the  twenty-four  hours ;  and  if  the  rectal  temperature  is  unchanged, 
this  will  also  be  the  amount  of  heat  produced.  Here  we  assume 
(i)  that  all  the  heat  lost  by  the  animal  has  gone  to  heat  the  water, 
and  none  to  heat  the  metal  of  tbe  calorimeter ;  (2)  that  none  has  been 
radiated  away  from  the  outer  surface  of  the  latter.  The  first  assump- 
tion will  seldom  introduce,  any  sensible  error  in  a  prolonged  physio- 


480  A  MANUAL  OF  PHYSIOLOGY 

logical  experiment ;  but  it  is  very  easy  to  determine  by  a  separate 
observation  the  water-equivalent  of  the  calorimeter — that  is,  the 
quantity  of  water  whose  temperature  will  be  raised  i°  by  a  quantity 
of  heat  which  just  suffices  to  raise  the  temperature  of  the  metal  by 
i°  (p.  514).  Then  the  water-equivalent  is  added  to  the  quantity  of 
water  actually  present,  and  the  sum  is  multiplied  by  the  rise  of 
temperature.  If  the  temperature  of  the  room  is  constant,  as  will  be 
approximately  the  case  in  a  cellar,  any  error  due  to  interchange  of 
heat  between  the  calorimeter  and  its  surroundings  may  be  eliminated 
by  making  the  initial  temperature  of  the  water  as  much  less  than  that 
of  the  air  as  the  final  temperature  exceeds  it.  Then  if  the  loss  of 
heat  by  the  animal  is  uniform,  as  much  heat  is  gained  during  the  first 
half  of  the  experiment  by  the  calorimeter  from  the  air  as  is  lost  by  it 
to  the  air  during  the  last  half.  Or,  without  lowering  the  temperature 
of  the  water,  the  amount  of  heat  lost  by  the  calorimeter  during  an  ex- 
periment may  be  previously  determined  by  a  special  observation, 
and  added  to  the  quantity  calculated  from  the  observed  rise  of 
temperature.  Or,  finally,  two  similar  calorimeters  may  be  used,  one 
containing  the  animal  and  the  other  a  hydrogen  flame,  or  a  coil  of 
wire  traversed  by  a  voltaic  current,  which  is  regulated  so  as  to  keep 
the  temperature  the  same  in  the  two  calorimeters.  From  the  quantity 
of  hydrogen  burnt,  or  electricity  passed,  the  heat-production  of  the 
animal  can  be  calculated. 

Of  late  years  air  calorimeters  have  come  into  vogue  for  physio- 
logical purposes.  A  diagram  of  one  is  shown  in  Fig.  136.  Such 
calorimeters  are  really  thermometers  with  an  immense  radiating 
surface,  for  only  a  small  proportion  of  the  heat  given  off  by  the 
animal  goes  to  heat  the  measuring  substance.  The  specific  heat  of 
air,  or  the  quantity  of  heat  required  to  raise  the  temperature  of  unit 
mass  of  air  by  one  degree,  is  very  small  in  comparison  with  that  of 
water.  A  given  quantity  of  heat  raises  the  temperature  of  an  air 
calorimeter  much  more  than  that  of  a  water  calorimeter  of  the  same 
dimensions ;  and  the  loss  of  heat  to  the  surroundings  being  propor- 
tional to  the  elevation  of  temperature,  in  the  water  calorimeter  the 
chief  part  of  the  heat  is  actually  retained  in  the  water,  while  in  an  air 
calorimeter  the  greater  portion  passes  through  the  air  space,  and  is 
radiated  away.  When  the  amount  of  heat  lost  by  the  calorimeter 
becomes  equal  to  that  gained  from  the  animal,  the  '  steady '  reading 
of  the  instrument  is  taken,  and  from  this  the  heat  production  can  be 
deduced  by  an  experimental  graduation  of  the  apparatus.  One  advan- 
tage of  an  air  calorimeter  is  that  it  follows  more  closely  rapid  variations 
in  the  heat  production  of  the  animal,  or,  to  speak  more  correctly,  in 
the  heat  loss.  It  should  be  carefully  noted  that  in  calorimetry  what 
is  directly  measured  is  the  quantity  of  heat  given  out  by  the  animal, 
not  the  quantity  produced.  The  two  quantities  are  identical  only 
when  the  temperature  of  the  animal  has  remained  unchanged  through- 
out the  experiment.  If  the  temperature  has  fallen,  the  quantity  of 
heat  produced  is  equal  to  the  quantity  measured  by  the  calorimeter 
minus  the  difference  between  the  quantity  in  the  animal  at  the  begin- 
ning and  at  the  end  of  the  observation.  This  difference  is  equal  to 


ANIMAL  HEAT 


481 


the  average  specific  heat  of  the  animal  multiplied  by  its  weight  and 
by  the  fall  of  temperature.  It  can  be  approximately  found  by 
multiplying  the  weight  (in  kilogrammes  or  grammes)  by  the  fall  of 
rectal  temperature  (in  degrees),  since  the  average  specific  heat  of  the 
body  of  a  mammal  at  least  is  not  very  different  from  that  of  water, 
and  the  specific  heat  of  water  is  taken  as  unity. 

All  the  higher  animals  (mammals  and  birds)  have  a  prac- 
tically constant  internal  temperature  (swallow  44°,  mouse  41°, 
dog  39°,  man  38°  in  the  rectum),  but  a  few  hibernating 
mammals,  such  as  the  marmot,  are  homoiothermal  in  summer, 


FIG.  136. — AIR  CALORIMETER. 

(/.),  cross-section  ;  (//.),  longitudinal  section  ;  A,  cavity  of  calori- 
meter for  animal  ;  B,  copper  cylinder  corrugated  so  as  to  increase 
the  radiating  surface  ;  C,  air  space  enclosed  between  B  and  a  con- 
centric copper  cylinder  F  ;  C  is  air-tight,  and  is  connected  by  the  tube  2  with  the  mano- 
meter M.  The  other  end  of  the  manometer  is  connected  with  an  exactly  similar 
calorimeter,  in  which  a  hydrogen  flame  is  burnt  in  the  space  corresponding  to  A,  or  in 
which  the  air  in  A  is  heated  by  a  coil  of  wire  traversed  by  an  electrical  current.  _  The 
flame  or  current  is  regulated  so  as  to  keep  the  coloured  petroleum  or  mercury  in  the 
manometer  M  at  the  same  level  in  both  limbs  ;  the  amount  of  heat  given  off  to  the  one 
calorimeter  by  the  flame  or  current  is  then  equal  to  that  given  off  by  the  animal  to  the 
other.  D  is  an  external  cylinder  of  copper  or  tin  perforated  by  holes  (6,  7)  at  intervals. 
The  purpose  of  it  is  to  prevent  draughts  from  affecting  the  loss  of  heat  from  F  ;  4,  5, 
are  tubes  through  which  thermometers  can  be  introduced  into  C  ;  I  is  the  terminal  ot  a 
spiral  tube,  which  is  coiled  in  the  end  portion  of  the  air  space  C.  The  sections  of  the 
coils  are  indicated  by  small  circles.  The  other  end  of  the  spiral  tube  is  3  ;  through 
this  tube  air  is  sucked  out,  and  so  the  proper  ventilation  of  the  animal  is  kept  up.  The 
object  of  the  spiral  arrangement  is  that  the  air  aspirated  out  of  A  may  give  up  its  heat 
to  the  air  in  C  before  passing  out.  E  is  a  door  with  double  glass  walls. 

poikilothermal  during  their  winter  sleep.  In  the  lower  forms 
the  body  temperature  follows  closely  the  temperature  of  the 
environment,  and  is  never  very  much  above  it  (frog  0*5°  to 
3°  above  external  temperature).  Both  in  a  frog  and  in  a 
pigeon  heat  is  evolved  as  long  as  life  lasts ;  but  per  unit  of 
weight  the  amphibian  produces  far  less  than  the  bird,  and 
loses  far  more  readily  what  it  does  produce.  The  tempera- 
ture of  the  frog  may  be  30°  in  June  and  5°  in  January.  The 
structure  of  its  tissues  is  unaltered  and  their  vitality  un- 


482  A  MANUAL  OF  PHYSIOLOGY 

impaired  by  such  violent  fluctuations.  But  it  is  necessary, 
not  only  for  health,  but  even  for  life,  that  the  internal 
temperature  (the  temperature  of  the  blood)  of  a  man  should 
vary  only  within  relatively  narrow  limits  around  the  mean 
of  37°  to  38°  C. 

Why  it  is  that  a  comparatively  high  temperature  should 
be  needed  for  the  full  physiological  activity  of  the  tissues 
of  a  mammal,  while  the  in  many  respects  similar  tissues 
of  a  fish  work  perfectly,  although  perhaps  more  sluggishly, 
at  a  much  lower  temperature,  is  not  quite  clear ;  nor  do 
we  know  the  precise  significance  of  that  constancy  of 
temperature  in  the  warm-blooded  animal,  which  is  as  im- 
portant and  peculiar  as  its  absolute  height.  The  higher 
animals  must  possess  a  superior  delicacy  of  organization, 
hardly  revealed  by  structure,  which  makes  it  necessary  that 
they  should  be  shielded  from  the  shocks  and  jars  of  varying 
temperature  that  less  highly-endowed  organisms  endure  with 
impunity.  Leaving  the  discussion  of  the  local  differences 
and  periodic  variations  of  the  temperature  of  warm-blooded 
animals  to  a  future  page,  let  us  consider  now  the  mechanism 
by  which  the  loss  of  heat  is  adjusted  to  its  production,  so 
that  upon  the  whole  the  one  balances  the  other. 

Heat  Loss. — Heat  is  lost  (i)  from  the  surfaces  of  the  body 
by  radiation,  conduction,  and  convection ;  (2)  as  latent  heat 
in  the  watery  vapour  given  off  by  the  skin  and  lungs ;  and 
(3)  in  the  excreta.  Even  in  the  bulky  excrement  of  herbivora 
a  comparatively  trifling  part  of  the  total  heat  is  lost.  The 
second  channel  of  elimination  is  much  more  important ;  the 
first  is  in  general  the  most  important  of  all. 

The  loss  of  heat  by  direct  radiation  from  a  portion  of  the  skin 
or  clothes,  or  from  hair,  fur,  or  feathers  covering  the  skin,  may 
be  measured  by  means  of  a  thermopile  or  a  resistance  radiometer 
(bolometer).  The  latter  instrument  is  similar  in  principle  and  allied 
in  construction  to  the  resistance  thermometer  used  in  measuring 
superficial  temperatures,  and  already  described  (Fig.  135,  p.  479). 
It  may  consist  of  a  grating  of  lead-paper  or  tinfoil  fixed  vertically 
in  a  small  box  which  protects  it  from  draughts.  The  box  has  a 
sliding  lid,  which  is  kept  closed  till  the  moment  of  the  observation, 
when  it  is  withdrawn  and  the  portion  of  skin  applied  to  the  opening 
at  a  fixed  distance  (5  to  10  cm.)  from  the  grating.  The  intensity 
of  radiation  depends  on  the  excess  of  temperature  of  the  radiating 
surface  over  that  of  the  surroundings,  as  well  as  on  the  nature  of  the 


ANIMAL  HEAT  483 

surface.  The  uncovered  parts  of  the  skin  (face  and  hands  in  man) 
radiate  more  per  unit  of  area  than  the  clothes  or  hair;  and  the  warm 
forehead  more  than  the  comparatively  cool  lobe  of  the  ear  or  tip  of 
the  nose.  When  a  man  is  sitting  at  rest  in  a  still  atmosphere,  pure 
radiation  plays  a  greater,  and  conduction  and  convection  play  a 
smaller,  part  in  the  total  loss  of  heat  from  the  skin  than  when  he  is 
walking  about  or  sitting  in  a  draught.  The  more  rapidly  the  air  in 
contact  with  the  skin  and  clothes  is  renewed,  the  lower,  other  things 
being  equal,  is  the  temperature  of  the  radiating  surfaces  kept,  the 
greater  is  the  loss  of  heat  by  conduction  to  the  adjacent  portions  of 
air,  and  the  smaller  the  loss  by  radiation  to  the  walls  of  the  room, 
the  furniture,  and  other  surrounding  objects.  It  is  probable  that, 
under  the  most  favourable  conditions,  the  amount  of  heat  lost  from 
the  surface  by  true  radiation  does  not  exceed  the  amount  lost  by 
conduction  and  conveciion. 

The  loss  of  heat  by  evaporation  of  water  from  the  skin  can  be 
calculated  if  we  know  the  quantity  of  water  so  given  off.  For  a 
gramme  of  water  at  the  ordinary  temperature  (say,  15°  C.)  needs 
555  millicalories  to  convert  it  into  aqueous  vapour  at  the  average 
temperature  of  the  skin.  If  we  take  the  average  quantity  of  water 
excreted  as  sweat  in  twenty-four  hours  as  750  c.c.,  this  will  be 
equivalent  to  a  heat  loss  of  416,250 — say,  in  round  numbers,  400,000 
millicalories. 

The  quantity  of  heat  given  off  by  the  lungs  may  be  also  deduced 
from  calculation,  the  data  being  (i)  the  weight,  temperature,  and 
specific  heat  of  the  expired  air,  and  (2)  the  excess  of  water  it  contains 
in  the  form  of  aqueous  vapour  over  that  contained  in  the  inspired 
air.  Helmholtz  calculated  the  quantity  of  heat  needed  to  warm  the 
air  expired  by  a  man  in  twenty-four  hours  from  an  initial  temperature 
of  20°  to  body  temperature,  at  70,000  small  calories,  and  that  required 
to  evaporate  the  water  given  off  by  the  lungs  at  397,000,  making  the 
total  heat-loss  by  the  lungs  from  400,000  to  500,000  small  calories. 
By  direct  calorimetric  observations  it  was  found  that  a  man  of  70 
kilos  weight  gave  off  in  normal  breathing,  with  an  air  temperature 
of  12°  to  15°  C.,  from  350,000  to  450,000  small  calories.  Forced 
respiration,  as  might  be  expected,  increased  the  amount  often  to 
double  or  even  treble.  A  diagram  of  a  respiration  calorimeter  is 
shown  in  Fig.  137.  (See  Practical  Exercises,  p.  515.) 

The  following  table  gives  an  analysis  of  the  heat-loss  of 
an  average  man.  It  must  be  understood  that  the  figures  are 
only  approximate. 

Per  cent.  Millicalories. 

[Evaporation  of  water     -         -  15     \  400,000 

Skin   4  Radiation      -  30      -  80          750,000 

[Conduction  (and  convection)  -  35      j  900,000 

f  Evaporation  of  water     -  15     \  .      (400,000 

'\Heatingtheexpiredair-        -  2-5)  I^§.-|  70,000 

Heating  the  excreta       -  2-5         70,000 

100     2,590,000 

31 2 


484 


A  MANUAL  OF  PHYSIOLOGY 


In  the  rabbit,  according  to  Nebelthau,  the  heat  lost  by  evaporation 
of  water  is  about  16  per  cent,  of  the  whole,  or  about  half  the  pro- 
portion in  man,  according  to  the  above  calculation.  This  is  not 
surprising  when  we  reflect  that  the  rabbit  does  not  sweat,  and  drinks 
comparatively  little  water. 

Sources  of  the  Heat  of  the  Body.— Heat-production. — Some 
heat  enters  the  body  as  such  from  without — in  the  food, 
and  by  radiation  from  the  sun  and  from  fires.  The  ultimate 
source  of  all  the  heat  produced  in  the  body  is  the  chemical 
energy  of  the  food  substances.  Whatever  intermediate 
forms  this  energy  may  assume — whether  the  mechanical 
energy  of  muscular  contraction ;  the  energy  of  electrical 
separation  by  which  the  currents  of  the  tissues  are  pro- 
duced ;  the  energy  of  the  nerve  impulse ;  or  the  energy,  be 

it  what  it  may,  which  enables 
the  living  cells  to  perform  their 
chemical  labours — it  all  ultimately, 
except  so  far  as  external  mechani- 
cal work  may  be  done,  appears  in 
the  form  of  heat.  We  do  not 
know  at  what  precise  stage  of 
metabolism  the  chief  outburst  of 
heat  takes  place,  but  we  may  be 
sure  that  the  food,  whether  it  is 
burned  in  a  calorimeter  to  simple 
end-products  like  carbon  dioxide 
and  water,  or  more  slowly  oxidized 
in  the  body,  yields  the  same 

sule  4  ;  4  is  connected  with  a  similar  r    i  •  j    j       i 

capsule  3  by  a  short  tube,  which  amount  of  heat,  provided  always 

passes   out    from   it   at   the    side  tilat   :n    Koth    rases    it    k    entirelv 

opposite  to  that  at  which  B  enters  ;  Inai    1 

2  and  i  are  similar  capsules.     From  consumed,    and     that     HO    Work 

i  an  outlet  tube  C  passes  off.     The  . 

whole  is  set  in  a  copper  cylinder  A  transferred  to  the  OUtSlde.       In  th< 

filled  with  water.     A  piece  is  sup-  i_     j        .1  u    _«.•  r  i_ 

posed  to  be  cut  out  of  A  in  order  to  body   the    combustion    of    carbo- 

m  hydrates  and  fats  is  complete  ;  but 
the  nitrogenous  residues  of  th< 
proteids — urea,  uric  acid,  etc. — can  be  further  oxidized,  an< 
the  remnant  of  energy  which  they  yield  must  be  taken  int< 
account  in  any  calculation  of  the  total  heat-productioi 
founded  on  the  heat  of  combustion  of  the  food  substances 


FIG.  137.— RESPIRATION 
CALORIMETER. 

B,  copper  tube  with  mouthpiece, 
connected  with  the  thin  brass  cap- 


ANIMAL  HEAT  485 

From  careful  experiments,  it  has  been  found  that  a  gramme  of 
dry  proteid  (egg-albumin),  when  burned  in  a  calorimeter, yields 
5,735  millicalories  of  heat,  a  gramme  of  grape-sugar  3,742, 
and  a  gramme  of  animal  fat  9,500  millicalories  (Stohmann). 

Calories. 

Heat  equivalent  of  i  gramme  of  albumin  -  -  5,735 
Albumin  (minus  urea  produced  from  it)  •  4,949 
Cane-sugar  -  -  3,955 

Kreatin  (water-free)       -  -       4,275 

Starch  -       4,182 

In  applying  such  results  to  the  calculation  of  the  heat-production 
of  the  body,  it  is  not  sufficient  to  deduct  from  the  heat  of  combustion 
of  the  proteids  the  heat  which  the  residual  urea  would  yield  if  fully 
oxidized.  For  other  incompletely  oxidized  products  arise  from 
proteids  when  consumed  in  the  body,  and  Rubner  has  shown,  by 
actually  determining  the  heat  of  combustion  of  the  urine  and  faeces, 
that  the  real  equivalent  of  a  gramme  of  albumin  is  at  most  only 
4,420  millicalories.  The  heat-equivalent  of  our  specimen  diet  (p.  467) 
will  be  approximately : 

Millicalories. 

t          Proteid,  say,  130  grammes          X         4,420       =       574,600 
Fat,  100  grammes  X         9, 500       =       950,000 

Carbo  -  hydrate     (reckoned     as 
glucose),  400  grammes         X         3,742       =     1,496,800 

3,021,400 

But  this  is  the  diet  of  a  man  doing  a  fair  day's  work ;  and  to 
get  the  quantity  of  energy  which  actually  appears  as  heat,  the  heat- 
equivalent  of  the  mechanical  work  performed  must  be  deducted. 
A  fair  day's  work  is  about  150,000  kilogramme-metres — that  is,  an 
amount  equal  to  the  raising  of  150,000  kilogrammes  to  the  height 
of  a  metre.  Now,  a  kilogramme-degree  or  calorie  of  heat  is  equiva- 
lent to  (say)  427  kilogramme-metres  of  work,  and  a  kilogramme- 
metre  to  -  —  millicalories.  The  heat-equivalent  of  the  day's  work 

is,  therefore,  150,000  x  —  —  =  351,000  millicalories.     Deducting  this 

427 

from  the  heat-equivalent  of  the  food,  we  get  in  round  numbers 
2,670,000  millicalories  as  the  quantity  of  heat  given  off.  This  cor- 
responds fairly  well  with  the  calculated  heat-loss  (p.  483).  Calori- 
metric  observations  have  given  results  in  some  cases  not  widely 
different,  in  others  considerably  higher.  Thus,  Him  found  that  a 
man  of  73  kilos  weight  produced  140,000  millicalories  per  hour 
during  rest,  and  229,000  during  an  hour's  work  of  32,550  kilogramme- 
metres.  At  the  same  rate  for  the  twenty-four  hours  these  numbers 
would  correspond  respectively  to  3,360,000  and  5,496,000  small 
calories.  But  it  is  not  legitimate  to  apply  the  results  of  compara- 
tively short  observations  in  this  way ;  for,  on  the  one  hand,  the  heat- 


486  A  MANUAL  OF  PHYSIOLOGY 

production  during  sleep  is  much  less  than  in  the  '  rest '  of  ordinary 
waking  life;  and,  on  the  other,  continuous  labour  for  twenty-four 
hours  at  the  rate  of  more  than  30,000  kilogramme-metres  per  hour 
would  either  be  impossible,  or  would  be  associated  with  a  greater 
consumption  of  food  or  of  tissue  than  corresponds  to  the  diet  on 
which  our  calculation  was  based.  During  the  normal  eight  hours 
of  sleep  the  heat-production  of  a  73  kilo  man  is  only  about  45,000 
millicalories  per  hour  (Helmholtz),  or  360,000.  Adding  to  this 
2,240,000  (i6x  140,000),  for  the  sixteen  resting  but  waking  hours, 
we  get  2,600,000  as  the  total  heat-production  of  the  'resting'  man. 
Dividing  the  day  into  eight  hours  of  work  at  the  rate  of  32,550 
kilogramme-metres  per  hour  (a  hard  day's  labour),  eight  hours' 
waking  rest,  and  eight  hours'  sleep,  we  get  a  heat-production  of 
3,312,000  small  calories  in  twenty-four  hours,  made  up  thus : 

Eight  hours'  work  x          229,000     =      1,832,000 

Eight  hours' '  rest '  x          140,000     =      1,120,000 

Eight  hours'  sleep  x  45,000     =        360,000 

3,312,000 

Observations  have  also  been  made  on  man  by  Ott  witJ 
a  water,  and  by  D'Arsonval  with  an  air,  calorimeter.  Sucl 
experiments  are  still  open  to  considerable  errors,  and  th< 
heat-production  necessarily  varies  widely  with  the  diet.  Bu 
from  the  general  agreement  of  calculated  results  with  actua 
measurements  we  can  safely  conclude  that  most  healthy  adult, 
produce  between  2,000,000  and  3,000,000  small  calories  on 
*  rest '  day,  or  a  day  of  light  labour,  and  between  3,000,000  anc> 
4,000,000  on  a  day  of  hard  manual  work. 

Rubner  has  calculated  from  the  diet  the  heat-productior 
of  various  classes  of  men,  reducing  everything  to  the  standarc 
of  a  body-weight  of  67  kilos.  The  fasting  man,  of  67  kilos 
body-weight,  produces  2,303,000  calories  in  the  twenty-foui 
hours.  The  class  of  brain-workers,  represented  by  physicians 
and  officials,  produce  only  a  little  more  heat  than  the  fasting 
man,  viz.,  2,445,000  calories.  The  second  class,  representec 
by  soldiers  (presumably  in  time  of  peace)  and  day-labourers 
(probably  of  a  cautious  and  conservative  type),  work  up  tc 
2,868,000  calories.  The  third  class,  composed  of  men  whc 
work  with  machines  and  other  skilled  labourers,  attain 
heat-production  of  3,362,000  calories.  The  fourth  class 
typified  by  miners  (who  are  engaged,  usually  by  the  piece 
and  not  by  the  day,  in  severe  and  exhausting  toil),  produce 
as  much  as  4,790,000  calories.  In  the  fifth  and  last  class, 


ANIMAL  HEAT  487 

represented  by  lumberers  and  other  out-of-door  labourers 
(who,  in  addition  to  excessive  exertion,  have  often  to  face 
intense  cold),  the  heat-production  rises  to  5,360,000  calories. 
The  Seats  of  Heat-production. — We  have  already  recognised 
the  skeletal  muscles  as  important  seats  of  heat-production. 
A  frog's  muscle,  contracting  under  the  most  favourable  con- 


FIG.  138.— DIAGRAM  SHOWING  THE  HEAT   EQUIVALENT  OF  VARIOUS 

DIETARIES. 
A,  proteids ;  B,  fats  ;  C,  carbo-hydrates  ;  D,  heat  equivalent. 

ditions,  does  not  convert  at  most  more  than  one-fourth  or 
one-fifth  of  the  energy  it  expends  into  mechanical  work ;  at 
least  three-fourths  or  four-fifths  of  the  energy  appears  as 
heat.  If  we  assume  that  the  muscles  of  the  human  body 
do  not,  upon  the  whole,  work  more  economically  than 
the  frog's  muscles  at  their  maximum  efficiency  —  an 
assumption  in  favour  of  which  a  good  deal  of  evidence  can 
be  brought  forward,  and  which,  at  any  rate,  does  not  seem 
to  be  very  wide  of  the  truth — then  it  is  easy  to  show  that 


488  A  MANUAL  OF  PHYSIOLOGY 

the  greater  part  of  the  heat-production  of  the  body  of  a 
man  doing  ordinary  work  is  accounted  for  by  the  contraction 
involuntary  and  voluntary  muscles. 

j  If  the  work  of  the  heart  is  taken  as  27,000  kilogramme- metres  in 
twenty-four  hours  (p.  126),  the  total  heat  produced  by  this  organ 
will  be  equivalent  (on  the  above  assumption)  at  least  to  108,000 
kilogramme-metres,  or  252,000  small  calories,  since,  practically,  the 
whole  work  is  expended  in  overcoming  the  friction  of  the  vessels, 
and  finally  appears  as  heat.  Enough  energy  is  transformed  in 
twenty-four  hours  in  the  heart  of  the  colonel  of  a  regiment  of  1,000 
men  to  lift  the  whole  regiment  to  a  height  of  nearly  2  metres,  if  it 
could  be  all  changed  into  mechanical  work.  The  work  of  the 
inspiratory  muscles  may  be  reckoned  at  13,000  kilogramme-metres, 
equal  to  30^00  small  calories,  and  the  heat  produced  by  them  at, 
say,  four  times  the  equivalent  of  this,  or  122,000  small  calories.  In 
sum,  the  muscular  work  of  the  circulation  and  respiration  is 
responsible  for  the  production  of  at  least  374,000  small  calories 
(without  including  the  heat  produced  by  the  smooth  muscle  of  the 
bronchi  and  bloodvessels),  or  nearly  one-sixth  of  the  total  pro- 
duction of  a  man  doing  ordinary  labour.  During  eight  hours  of 
sleep  a  man  produces  altogether  about  320,000  small  calories.  Of 
this  the  share  due  to  the  heart  and  respiratory  muscles  may  be  taken 

374,000 
as  -         —  =  124,000;    or,  since  the  work  of  the  circulation  and 

respiratory  system  is  less  during  sleep,  say,  120,000  small  calories. 
Taking  into  account  the  production  of  heat  in  the  smooth  muscle  of 
the  alimentary  canal,  etc.,  we  see  that  muscular  contraction  may  be 
the  source  of  the  greater  part  of  the  heat  formed  during  sleep. 

Again,  it  follows  from  Hirn's  mean  results  that  a  70  kilo  man 
doing  27,700  kilogramme-metres  of  work  in  an  hour  gives  off 
283,000  small  calories  of  heat.  Now,  27,700  kilogramme-metres  = 
say,  65,000  small  calories  ;  and  on  the  assumption  that  the  skeletal 
muscles  produce  four  or  even  three  times  as  much  heat  as  work,  the 
contraction  of  these  alone,  without  reckoning  the  heat  produced  by 
the  heart,  would  account  for  by  far  the  greatest  part  of  the  total  heat- 
production.  But  even  in  muscles  completely  at  rest  a  certain 
amount  of  metabolism  goes  on,  a  certain  amount  of  heat  is  pro 
duced.  The  muscles  of  a  dog's  legs,  through  which  an  artificial 
circulation  of  defibrinated  blood  is  kept  up,  consume  at  body 
temperature  on  the  average  about  150  c.c.  of  oxygen  per  kilo  per 
hour.  This  is  about  one-fifth  the  rate  of  consumption  per  kilo  of  a 
normal  rabbit  in  a  bath  at  39°  C.,  reckoned  on  the  net  weight  of  the 
animal  after  deduction  of  the  contents  of  the  alimentary  canal 
(770  c.c.  per  kilo  per  hour).  Taking  the  muscles  as  45  per  cent,  of 
the  body-weight,  and  assuming  (i)  that  oxygen  consumption  an 
heat-production  are  under  the  given  conditions  approximately  pro 
portiona!,  and  (2)  that  the  oxygen  consumption  of  isolated  muscle 

150      45        3 
of  dog  and  rabbit  is  not  very  different,  we  get x  —  =  —  or 

770      100     32 


ANIMAL  HEAT  489 

say,  i  :  10,  as  the  ratio  of  the  heat-production  of  muscles  absolutely 
at  rest,  and  removed  from  the  influence  of  the  nervous  system,  to 
the  total  heat-production.  And  in  man  the  gaseous  metabolism 
easily  rises  to  five  times,  in  severe  work  to  nine  times,  its  resting 
value;  although  persons  inured  to  labour  work  more  economically 
than  amateurs. 

It  is  probable  that  in  the  skeletal  muscles  of  curarized  animals 
the  heat-production  is  not  far  different  from  that  in  isolated  muscles 
at  body  temperature,  and  subjected  to  a  good  artificial  circulation. 
Now,  curara  reduces  the  oxygen  consumption  of  a  rabbit  from 
770  c.c.  to  500  c.c.  per  kilo  per  hour;  270  c.c.  per  kilo  of  body- 
weight,  or  600  c.c.  per  kilo  of  muscle,  may  therefore  be  taken  as  the 
portion  of  the  oxygen  consumption  of  skeletal  muscle  which  is 
under  the  control  of  the  nervous  system.  Adding  150  c.c.,  the 
hourly  oxygen  consumption  of  a  kilo  of  isolated  muscles,  we  get 
750  c.c.  per  kilo  per  hour  as  the  total  consumption  of  skeletal 
muscles  connected  with  the  nervous  system,  though  not  in  active 
contraction.  Separation  from  the  nervous  system  therefore  cuts  away 
four-fifths  of  the  muscular  metabolism,  and  leaves  one-fifth  intact. 

In  a  curarized  dog  or  rabbit  the  heat-production  or  respiratory 
exchange  are  diminished  by  about  35  per  cent.  The  remaining 
65  per  cent,  may  perhaps  be  apportioned  as  follows:  heart  15, 
skeletal  muscles  10,  smooth  muscle,  glands  and  other  tissues  40.  So 
that  the  heat-production  of  the  heart  may  be  nearly  one-fourth  of 
the  total  production  in  a  curarized  animal,  that  of  the  skeletal  muscles 
one-sixth. 

The  glands,  and  then  the  central  nervous  system,  rank 
after  the  muscles,  though  at  a  great  distance,  as  seats  of  heat- 
production.  The  liver  and  brain  (?)  are  the  hottest  organs 
in  the  body ;  and  that  this  is  not  altogether  due  to  their 
being  well  protected  against  loss  of  heat  is  shown,  in  the 
case  of  the  liver,  by  the  excess  of  temperature  of  the  blood 
of  the  hepatic  over  that  of  the  portal  vein.  In  view, 
however,  of  the  exaggerated  importance  which  some  have 
given  to  these  organs,  as  foci  of  heat-production,  it  may 
be  well  to  point  out  that  although  many  of  the  chemical 
changes  in  the  animal  body  are  undoubtedly  associated  with 
the  setting  free  of  heat,  other,  and  not  less  weighty  and 
characteristic,  reactions  may  cause  the  absorption  of  heat ; 
and  it  is  possible  that  some  of  the  syntheses  which  the 
hepatic  and  other  glandular  tissues  seem  to  be  capable  of 
performing  may  be  included  in  this  latter  category.  For 
example,  when  urea  is  decomposed  so  as  to  yield  ammonium 
carbonate  (p.  387),  heat  is  set  free.  We  must  assume, 


T 


490  A  MANUAL  OF  PHYSIOLOGY 

therefore,  that  if  ammonium  carbonate  were  transformed  into 
urea  in  the  liver,  an  equal  amount  of  heat  would  be,  on  the 
whole,  absorbed.  So  that  the  heat-production  of  an  organ 
may  depend,  not  only  on  the  quantity,  but  also  on  the 
quality,  of  its  chemical  activity.  When  we  consider  the 
enormous  tide  of  blood  which  during  digestion  sets  through 
the  portal  system,  we  shall  look  with  suspicion  upon  results 
that  announce  a  difference  of  more  than  a  small  fraction  of 
a  degree  in  the  temperature  of  the  incoming  and  outgoing 
blood  of  the  liver.  Probably  not  less  than  200  litres  of 
blood  pass  in  twenty-four  hours  through  the  liver  of  a  2  kilo 
rabbit.  If  the  temperature  of  this  blood  is  raised  even 
one-tenth  of  a  degree  in  its  passage  through  the  hepatic 
capillaries,  this  would  correspond  to  a  heat-production  of 
20,000  small  calories,  or  one-tenth  of  the  whole  heat  pro- 
duced in  the  animal. 

In  the  case  of  the  brain  ic  has  been  shown  by  comparison  of  the 
gases  of  blood  taken  from  the  carotid  and  from  the  venous  sinuses 
(torcula  Herophili)  that  the  metabolism  is  feeble  as  compared  even 
with  that  of  resting  muscles  (Hill).  Nor  is  it  possible  to  demon- 
strate any  marked  or  constant  increase  when  the  cerebral  cortex  is 
roused  to  such  an  active  discharge  of  impulses  as  leads  to  general 
epileptiform  convulsions.  The  rise  of  temperature  of  certain  regions 
of  the  scalp  observed  by  Lombard  during  mental  activity  cannot, 
therefore,  be  supposed  due  to  conduction  of  heat  from  the  brain 
through  the  skull.  It  is  perhaps  caused  by  vaso-motor  changes  in 
the  scalp,  associated,  it  may  be,  with  corresponding  changes  in  related 
areas  of  the  cortex.  And,  indeed,  if  we  remember  how  large  a  pro- 
portion of  the  central  nervous  system  is  made  up  of  nerve-fibres,  in 
which,  or  at  any  rate  in  the  fibres  of  peripheral  nerves,  no  sensible 
production  of  heat  has  ever  been  demonstrated,  it  will  not  appear 
surprising  if  even  a  considerable  increase  in  the  metabolism  of  the 
really  active  elements  should  fail  to  make  itself  felt. 

With  regard  to  the  muscles,  we  are  as  yet  in  the  dark  as 
to  the  precise  relation  of  the  energy  which  appears  as  heat 
and  of  that  which  is  converted  into  work.  The  original 
source  of  both  is,  of  course,  the  oxidation  of  the  food  sub- 
stances ;  but  we  do  not  know  whether  in  a  muscle,  as  in  a 
heat-engine,  the  chemical  energy  is  first  converted  into  heat, 
and  part  of  the  heat  then  transformed  into  work,  or  whether 
the  chemical  energy  is  immediately  changed  into  work,  or 
whether  there  is  an  intermediate  form  of  energy  other  than 


ANIMAL  HEAT  4qi 

heat.  Some  have  supposed  that  the  chemical  energy  is  first 
converted  into  electrical  energy,  and  that  the  latter  in  giving 
rise  to  the  work  of  the  contracting  muscle  is  partly  wasted 
as  heat.  It  has  been  stated  that  under  certain  conditions 
a  muscle,  instead  of  becoming  warmer,  may  become  colder 
during  contraction.  If  this  were  established,  it  would  be 
in  favour  of  the  view  that  heat  is  directly  transformed  into 
muscular  work.  But  it  would  not  be  an  unequivocal  proof; 
for  the  cooling  might  be  due  merely  to  chemical  or  physical 
reactions  between  the  products  formed  in  the  active  muscle 
and  other  muscular  constituents. 

It  has  been  very  generally  admitted  that  the  chief  seat  of  . 
excessive  metabolism  in  fever  is  the  muscles ;  but  U.  Mosso 
has  stated  that  cocaine  fever — the  marked  rise  of  tempera- 
ture produced  by  injection  of  cocaine — can  be  obtained  in 
animals  paralyzed  by  curara.  This,  even  if  true,  would  not 
support  the  conclusion  that  a  '  nervous  fever ' — that  is  to 
say,  a  fever  due  solely  to  increased  metabolism  in  the  nervous 
system — exists ;  for  in  a  curarized  animal  a  large  amount  of 
'  active '  tissue  (glands,  heart,  smooth  muscle)  still  remains 
in  physiological  connection  with  the  brain  and  cord.  But, 
as  a  matter  of  fact,  in  an  animal  under  a  dose  of  curara 
sufficient  to  completely  paralyze  the  skeletal  muscles  cocaine 
causes  no  rise  of  rectal  temperature ;  and  this  is  strongly 
in  favour  of  the  view  that,  the  fever  produced  in  the  non- 
curarized  animal  is  connected  with  excessive  muscular 
metabolism. 

Thermotaxis. — What,  now,  is  the  mechanism  by  which  the  ~j~~ 
balance  is  maintained  in  the  homoiothermal  animal  between 
heat-production  and  heat-loss  ?  In  answering  this  question 
we  have  to  recognise  that  both  of  these  quantities  are 
variable,  that  a  fall  in  the  production  of  heat  may  be  com- 
pensated by  a  diminution  of  heat-loss,  and  an  increase  in 
the  loss  of  heat  balanced  by  a  greater  heat-production. 

The  loss  of  heat  from  the  surfaces  of  the  body  may  be 
regulated  both  by  involuntary  and  by  voluntary  means.  It 
is  greatly  affected  by  the  state  of  the  cutaneous  vessels,  and 
these  vessels  are  under  the  influence  of  nerves.  A  cold  skin 
is  pale,  and  its  vessels  are  contracted.  In  a  warm  atmo- 


492  A  MANUAL  OF  PHYSIOLOGY 

sphere  the  skin  is  flushed  with  blood,  its  vessels  are  dilated, 
its  temperature  is  increased ;  an  effort,  so  to  speak,  is  being 
made  by  the  organism  to  maintain  the  difference  of  tempera- 
ture between  its  surface  and  its  surroundings  on  which  the 
rate  of  heat-loss  by  radiation  and  conduction  depends.  A 
still  more  important  factor  in  man,  and  in  animals  like  the 
horse,  which  sweat  over  their  whole  surface,  is  the  increase 
and  decrease  in  the  quantity  of  water  evaporated  and  of 
heat  rendered  latent.  It  is  owing  to  the  wonderful  elasticity 
of  the  sweat-secreting  mechanism,  and  to  the  increase  of 
respiratory  activity,  and  the  consequent  increase  in  the 
amount  of  watery  vapour  given  off  by  the  lungs,  that  men 
are  able  to  endure  for  days  an  atmosphere  hotter  than  the 
blood,  and  even  for  a  short  time  a  temperature  above  that 
of  boiling  water.  The  temperature  of  a  Turkish  bath  may 
be  as  high  as  65°  to  80°  C.  Blagden  and  Fordyce  exposed 
themselves  for  a  few  minutes  to  a  temperature  of  nearly 
127°  C.  Although  meat  was  being  cooked  in  the  same 
chamber  by  the  heat  of  the  air,  they  experienced  no  ill 
effects,  nor  was  their  body  temperature  even  increased. 
But  a  far  lower  temperature  than  this,  if  long  continued, 
is  dangerous  to  life.  In  the  summers  of  1892  and  1896 
hundreds  of  persons  died  in  the  United  States  within  a  few 
days  from  the  excessive  heat.  During  the  unusually  hot 
summer  of  1819  the  temperature  at  Bagdad  ranged  for  a 
considerable  time  between  108°  and  120°  F.  (42°  to  49°  C.), 
and  there  was  great  mortality.  A  much  higher  temperature 
may  be  borne  in  dry  air  than  in  air  saturated  with  watery 
vapour.  A  shade  temperature  of  100°  F.  (37*7°  C.)  in  the 
dry  air  of  the  South  African  plateaux  is  quite  tolerable, 
while  a  temperature  of  85°  F.  (29*4°  C.)  in  the  moisture- 
laden  atmosphere  of  Bombay  may  be  oppressive.  The 
reason  is  that  in  dry  air  the  sweat  evaporates  freely  and 
cools  the  skin.  In  saturated  air  at  the  body  temperatur 
no  loss  of  heat  by  perspiration  or  by  evaporation  from  the 
pulmonary  surface  is  possible  ;  the  temperature  of  an  animal 
in  a  saturated  atmosphere  at  35°  to  40°  C.  soon  rises,  and 
the  animal  dies.  In  animals  like  the  dog,  which  sweat  little 
or  not  at  all  on  the  general  surface,  the  regulation  of  th 


ANIMAL  HEAT  493 

heat-loss  by  respiration  is  relatively  more  important  than  in 
man. 

The  winter  fur  of  Arctic  animals  is  a  special  device  of 
Nature  to  meet  the  demands  of  a  rigorous  climate,  and 
combat  a  tendency  to  excessive  loss  of  heat.  The  experi- 
ments of  Hosslin  and  the  experience  of  squatters  in  Australia 
go  to  show  that  even  domesticated  animals  have  a  certain 
power  of  responding  to  long-continued  changes  in  external 
temperature  by  changes  in  the  radiating  surfaces  which 
affect  the  loss  of  heat.  It  is  said  that  in  the  hot  plains  of 
Queensland  and  New  South  Wales  the  fleeces  of  the  sheep 
show  a  tendency  to  a  progressive  decrease  in  weight.  And 
Hosslin  found  that  a  young  dog  exposed  for  eighty-eight  days  ^ 
to  a  temperature  of  5°  C.  developed  a  thick  coat  of  fine  woolly  t 
hairs.  Another  dog  of  the  same  litter,  exposed  for  the  same 
length  of  time  to  a  temperature  of  3i'5°  to  32°  C.,  had  a 
much  scantier  covering.  The  increased  protection  against 
heat-loss  in  the  case  of  the  '  cooled '  dog  was  not  sufficient 
fully  to  compensate  for  the  lowered  external  temperature. 
The  metabolism — that  is  to  say,  the  heat-production — was 
also  increased.  And  although  the  food  was  exactly  the  same 
for  both  animals  in  quantity  and  quality,  the  dog  at  5°  C. 
put  on  less  than  half  as  much  fat  in  the  period  of  the 
experiment  as  the  '  heated '  dog,  but  the  same  amount  of 
'  flesh.' 

The  voluntary  factor  in  the  regulation  of  the  heat-loss  is  of 
great  importance  in  man.  Clothes,  like  hair  and  other 
natural  coverings,  retard  the  loss  of  heat  from  the  skin 
chiefly  by  maintaining  a  zone  of  still  air  in  contact  with  it, 
for  air  at  rest  is  an  exceedingly  bad  conductor  of  heat.  A 
man  clothed  in  the  ordinary  way  has  two  or  three  concentric 
air-jackets  around  him.  The  air  in  the  intervals  between 
the  inner  and  outer  garments  is  of  importance  as  well  as 
that  in  the  pores  of  the  clothes  themselves ;  and  it  is  for 
this  reason  that  two  thin  shirts  put  on  one  above  the  other 
are  warmer  than  the  same  amount  of  material  in  the  form 
of  a  single  shirt  of  double  thickness.  When  a  man  feels 
himself  too  hot,  and  throws  off  his  coat,  he  really  removes 
one  of  the  badly  conducting  layers  of  air,  and  increases 


494  A  MANUAL  OF  PHYSIOLOGY 

the  rate  of  heat -loss  by  radiation  and  conduction.  At 
the  same  time  the  water-vapour,  which  practically  saturates 
the  layer  of  air  next  the  skin,  is  allowed  a  freer  access  to 
the  surface,  and  the  loss  of  heat  by  the  evaporation  of  the 
sweat  becomes  greater.  The  power  of  voluntarily  influencing 
the  heat-loss  must  be  looked  upon  in  man  as  one  of  the  most 
important  means  by  which  the  equilibrium  of  temperature 
is  maintained.  In  the  lower  animals  this  power  also  exists, 
but  to  a  much  smaller  extent.  A  dog  on  a  hot  day  puts  out 
its  tongue  and  stretches  its  limbs  so  as  to  increase  the 
surface  from  which  heat  is  radiated  and  conducted.  The 
mere  placing  of  a  rabbit  on  its  back,  with  its  legs  apart, 
may  cause  in  an  hour  or  two  a  fall  of  i°  to  2°  C.  in  the  rectal 
temperature.  The  power  of  covering  themselves  with  straw 
or  leaves,  of  burrowing  and  of  forming  nests,  may  be  in- 
cluded among  the  voluntary  means  of  regulation  of  the  heat- 
loss  possessed  by  animals.  A  man  opens  the  window  when 
he  is  too  hot,  and  pokes  the  fire  when  he  feels  cold.  Both 
actions  are  a  tribute  to  his  status  as  a  homoiothermal  animal, 
and  illustrate  the  importance  of  the  voluntary  element  in  the 
mechanism  by  which  his  temperature  is  controlled. 

The  production  of  heat,  like  the  loss,  is  to  a  certain 
extent  under  voluntary  control.  Rest,  and  especially  sleep, 
lessen  the  production  ;  work  increases  it.  The  inhabitants 
of  the  tropics,  human  and  brute,  often  tide  over  the  hottest 
part  of  the  day  by  a  siesta  ;  and  it  is  as  natural,  and  as 
much  in  accordance  with  physiological  laws,  that  a  man 
overpowered  by  the  heat  should  lie  down,  as  it  is  that  he 
should  walk  about  and  stamp  his  feet  or  clap  his  hands  on 
a  cold  winter  morning.  In  the  one  case  a  diminution,  in  the 
other  an  increase,  in  the  heat-production  is  aimed  at  by  a 
corresponding  change  in  the  amount  of  muscular  contrac- 
tion. The  quantity  and  quality  of  the  food  also  influence 
the  production  of  heat.  The  Eskimo,  who  revels  in  train-oil 
and  tallow-candles,  unconsciously  illustrates  the  experimental 
fact  that  the  heat  of  combustion  of  fat  is  high  ;  the  ric< 
diet  of  the  ryot  of  the  Carnatic,  with  its  low  heat  equivalent, 
seems  peculiarly  adapted  to  the  dweller  in  tropical  lands. 
But  it  would  be  easy  to  attach  too  much  weight  to  con- 


ANIMAL  HEAT  495 

siderations  such  as  these.  The  Arctic  hunter  eats  animal 
fat,  and  the  Indian  peasant  vegetable  carbo-hydrate,  not 
only  because  fat  has  a  high  and  carbo-hydrate  a  low  heat- 
equivalent,  but  because  in  the  climate  of  the  far  North 
animals  with  a  thick  coating  of  badly-conducting  fat  are 
plentiful,  and  vegetable  food  scarce;  whereas  in  the  river- 
valleys  of  India  nature  favours  the  growth  of  rice,  and 
religion  forbids  the  killing  of  the  sacred  cow. 

The  production  of  heat  is  also  controlled  by  an  involuntary 
nervous  mechanism,  upon  which  much  light  has  been  thrown 
by  the  researches  of  the  last  twenty  years,  and  especially 
by  those  of  Pfliiger  and  his  school  (p.  228).  It  is  a  matter 
of  everyday  experience  that  cold  causes  involuntary  shiver- 
ing— involuntary  muscular  contractions — the  object  of  which 
seems  a  direct  increase  in  the  heat-production.  But  besides 
this  visible  mechanical  effect,  the  application  of  cold  to  a 
warm-blooded  animal,  when  not  carried  so  far  as  to  greatly 
reduce  the  rectal  temperature,  is  accompanied  by  a  marked 
increase  in  the  metabolism,  as  shown  by  an  increased  pro- 
duction of  carbon  dioxide  and  consumption  of  oxygen.  In 
cold-blooded  animals  like  the  frog  the  metabolism,  on  the 
other  hand,  rises  and  falls  with  the  external  temperature ; 
there  is  no  automatic  mechanism  which  answers  an  in- 
creased drain  upon  the  stock  of  heat  in  the  body  by  an 
increased  supply.  Or,  perhaps,  in  the  light  of  recent  experi- 
ments, we  ought  rather  to  say  that,  although  the  rudiments 
of  a  heat-regulating  mechanism  may  exist  in  such  animals 
as  the  frog,  the  newt,  and  even  the  earthworm  (Vernon),  it  is 
only  able  to  modify  to  a  certain  extent  the  effects  of  changes 
of  external  temperature,  not  to  balance  or  even  override 
them,  as  in  the  homoiothermal  animal.  The  warm-blooded 
animal  loses  its  heat-regulating  power  when  a  dose  of  curara 
sufficient  to  paralyze  the  voluntary  muscles  is  given.  A 
curarized  rabbit,  kept  alive  by  artificial  respiration,  reacts 
to  changes  of  external  temperature  like  the  cold-blooded 
frog.  Now,  the  only  action  of  curara  adequate  to  account 
for  this  effect  is  its  power  of  paralyzing  the  motor  nerve- 
endings,  and  so  cutting  off  from  the  skeletal  muscles  impulses 
which  in  the  intact  animal  would  have  reached  them.  The 


496  A  MANUAL  OF  PHYSIOLOGY 

excitation  by  cold  of  the  cutaneous  nerves,  or  some  of  them, 
which  in  the  unpoisoned  animal  is  reflected  along  the  motor 
nerves  to  the  muscles,  and  causes  the  increase  of  meta- 
bolism, is  now  blocked  at  the  end  of  the  motor  path ;  and 
the  muscles,  the  great  heat-producing  tissues,  are  abandoned 
to  the  direct  influence  of  the  external  temperature. 

How  is  it,  then,  that   nervous   impulses   from   the   skin 
produce  in  the  intact  animal  their  effect  upon  the  chemical 
processes  in  the  muscles  ?     We  know  that  the  heat-produc- 
tion of  a  muscle  is  greatly  increased  when  it  is  caused  to 
contract ;  but  it  has  not  hitherto  been  possible  by  artificial 
stimulation  to  demonstrate  that    any  chemical  or  physical 
effect  is  produced   in  a  muscle  by  excitation  of  its  motor 
nerve  unless  as  the  accompaniment  of  a  mechanical  change. 
When  the  gastrocnemius  of  a  frog  poisoned  with  not  too 
large  a  dose  of  curara  is  laid  on  a  resistance  thermometer 
(p.  479),  and  its  nerve  stimulated  from  time  to  time  as  the 
curara  paralysis  deepens,  heating  of  the  muscle  is  observed  as 
long  as,  and  only  as  long  as,  there  is  any  visible  contraction. 
The  gaseous  metabolism  of  a  rabbit  immersed  in  a  bath  of 
constant  temperature  may  sink  by  as  much  as  30  to  40  per 
cent,  when  curara  is  given.     One  obvious  cause  of  this  is  the 
complete  muscular  relaxation.     And  the  whole  secret  of  the 
regulation  of  the  heat-production  might  be  plausibly  sup- 
posed to  lie  in  the  bracing  effect  of  cold  upon  the  skeletal 
muscles  and  the  relaxing  effect  of  heat.     And,  indeed,  in 
man  it  has  been   observed  that  cold   causes  no  metabolic 
increase  when  shivering  is  prevented  by  a  strong  effort  of  th 
will  (Loewy).     Nevertheless,  the  explanation  is  inadequat 
in  the  case  of  small  animals,  such  as  guinea-pigs,  rabbits, 
and  cats ;  for  very  great  changes  in  the  metabolism  may  be 
brought  about  by  external  cold  without  any  outward  token 
of  increased  muscular  activity. 

It  must  be  admitted,  then,  that — at  least  in  the  smaller 
homoiothermal  animals — the  metabolic  changes  normally 
going  on  in  the  resting  muscles  may  be  reflexly  increased 
without  the  usual  accompaniment  of  mechanical  contrac- 
tion, and  that  such  an  increase  of  '  chemical  tone '  may  be 
an  important  means  by  which  the  temperature  is  regulated. 


: 


ANIMAL  HEAT 


49? 


It  is  possible  that  other  organs  besides  the  muscles  may  be 
concerned,  though  not  to  a  sufficient  extent  to  secure  the 
due  regulation  of  temperature  during  curara  paralysis.     It  is 
obvious  that  in  man,  whose  environment  is  so  much  under 
his  own  control,  a  mere  automatic  regulation  is  less  required 
than  in  the  inferior  animals,  and  that  a  regulative  power,  if 
present  in  rudiment,  would  tend  to  '  atrophy  '  by  disuse.     In 
the  larger  animals,  again,  mere  bulk  is  an  important  safe- 
guard against  any  sudden  change  of  internal  temperature. 
To  reduce  the  temperature  of  a   horse  or  an  elephant  by 
i°,  a  considerable  quantity  of  heat  must  be  lost,  while  a  very 
slight  loss  would  suffice  to  cool  a  mouse  by  that  amount. 
Not  only  so,  but  the  surface  by  which  heat  is  lost  is  greater 
in  proportion   to  the   mass   of  the   body  in  small  than  in 
large  animals.     The  power  of  rapidly  increasing  the  heat- 
production  to  meet  a  sudden  demand  is,  therefore,  far  more 
important  to  the  mouse  than   to  the  horse ;    and  the  fact 
(p.  468)  that  the  metabolism  of  an  animal  varies  approxi- 
mately as  its  surface,  and  not  as  its  mass,*  is  an  illustration 
of  the  nice  adjustment  by  which  heat-equilibrium  is  main- 
tained. 

The  following  table,  calculated  by  Rubner  from  the 
quantity  of  tissue-proteid  and  fat  consumed,  shows  the  rela- 
tive intensity  of  heat-production  in  fasting  dogs  of  different 
sizes : 


Body-weight. 
& 

Small  calories  per 
kilo  per  hour. 
oJl 

31  K 

^1,1*0  1,580 

24 

*s-o  $06  i,7°° 

20 

37,^00  1,870 

18 

J¥,S10  1,920 

10 

2-X  S~D  O  2,550 

6 

n,o*fo  2,840 

3 

11.3*0  3,780 

The  relation  between  mass  and  surface  in  man  is  approximately 


expressed  by  the  equation 


SC/M 
M 


K,  where  S  is  the  surface  expressed  in 


square  centimetres,  M  the  mass  expressed  in  grammes,  and  K  a  constant 

K' 


* 
whose  mean  value  is   12-3  (Meeh).      The  equation  'ZZ—1 


I?   C2 


M.  J-.  C_/ 
32 


498  A  MANUAL  OF  PHYSIOLOGY 

Rubner  has  found  that  animals  abundantly  fed  do  not 
show  so  much  change  in  the  production  of  heat  when  the 
external  temperature  is  varied  as  starving  animals,  perhaps 
because  the  thicker  coat  of  subcutaneous  fat  so  steadies  the 
rate  at  which  heat  is  lost  that  it  becomes  easy  for  the 
vaso-motor  mechanism  alone  to  hold  the  balance  between 
loss  and  production.  In  well-fed  animals  it  is  the  heat-loss 
which  is  chiefly  affected,  and  it  may  be  that  this  has  some- 
thing to  do  with  the  explanation  of  Loewy's  results  on  man. 

Lorrain  Smith  has  discovered  the  curious  and  interesting 
fact  that  after  removal  of  the  thyroid  glands  (in  cats),  the 
heat-production,  as  measured  by  the  amount  of  carbon 
dioxide  given  off,  is  more  sensitive  to  changes  of  external 
temperature  than  in  the  normal  animal. 

But  it  must  not  be  imagined  that  the  production  of  heat 
can  be  increased  indefinitely  to  meet  an  increased  heat-loss. 
The  organism  can  make  considerable  efforts  to  protect  itself, 
but  the  loss  of  heat  may  easily  become  so  great  that  the 
increase  of  metabolism   fails  to  keep  pace   with   it.     The 
internal   temperature    then    falls,    and    if   the    fall   be    not 
checked,  the  animal  dies.     A  mammal,  when  cooled  arti- 
ficially  to   the   temperature   of  an   ordinary   room    (15°  to 
20°  C.),  does  not  recover  of  itself,  but  may  be  revived  by  the 
employment  of  artificial  respiration  and  hot  baths,  even  when 
the  rectal  temperature  has  sunk  to  5°  to  10°  C.     If  the  skin 
of  a  rabbit  be  varnished,  and  the  air  which  it  is  the  function 
of  the  fur  to  maintain  at  rest  around  it  be  thus  expelled,  th< 
animal  dies   of  cold,  unless  the  loss  of  heat  is  artificially 
prevented.    If,  without  varnishing  at  all,  the  greater  portioi 
of  the  skin  of  a  rabbit  or  guinea-pig  be  closely  clipped  01 
shaved,  similar  phenomena  are  observed.     Prevented  froi 
covering  itself  with  straw,  the  animal    dies,  sometimes  ii 
twenty  -  four    hours.      The    radiation   from    the    skin,    as 
measured  by  the  resistance-radiometer  (p.  482),  is  greatl; 
increased ;    the   animal    shivers   constantly,  and   the  rect< 

expresses  the  relation  between  surface  (S),  mass  (M),  length  of  body  (L)r 
and  circumference  of  chest  (C)  just  above  the  nipples  in  the  '  mean ' 
position  of  respiration.  K'  is  a  constant  whose  mean  value  is  4'5-  S  is 
expressed  in  square  centimetres,  M  in  grammes,  L  and  V  in  centimetres. 


ANIMAL  HEAT  499 

temperature  falls.  Placed  in  a  warm  chamber  before  the 
temperature  in  the  rectum  has  fallen  below  25°,  the  animal 
recovers  perfectly.  If  the  fall  is  allowed  to  go  on,  it  dies. 
If  it  is  kept  from  the  first  in  the  warm  chamber,  no  fall  of 
temperature  occurs.  When  the  increased  loss  of  heat  is  less 
perfectly  compensated — when,  for  example,  the  animal  is  left 
at  the  ordinary  temperature,  but  supplied  with  sufficient 
straw  to  cover  itself,  or  allowed  to  crouch  among  other 
animals — a  curious  phenomenon  may  sometimes  be  seen. 
The  rectal  temperature,  which  has  fallen  sharply  during  the 
operation,  remains  subnormal  (as  much  as  2°  to  3°  below  the 
ordinary  temperature)  for  a  time  (a  week  or  more),  and 
then  gradually  rises  as  the  coat  again  begins  to  grow.  The 
meaning  of  this  seems  to  be  that  the  power  of  regulating 
the  temperature  by  increasing  the  metabolism  is  overtasked 
by  the  removal  of  the  natural  protective  covering,  unless 
the  escape  of  heat  is  artificially  diminished.  When  the  loss 
of  the  fur  is  entirely  compensated,  no  fall  of  temperature 
occurs ;  when  it  is  not  compensated  at  all,  the  animal  cools 
till  it  dies ;  when  it  is  partially  compensated,  the  increased 
metabolism  may  only  suffice  to  maintain  a  temperature 
lower  than  the  normal,  although  constant  muscular  con- 
tractions (shivering)  are  brought  in  to  supplement  the  efforts 
of  the  regulative  chemical  processes. 

Hitherto  we  have  only  spoken  of  a  reflex  regulation  of 
the  heat-production  called  into  play  by  external  cold.  It 
might  be  supposed — and,  indeed,  has  often  been  assumed — 
that  heat  would  lessen  the  metabolism,  as  cold  increases  it ; 
and  there  are  indications  that  in  the  smaller  animals  this  is 
the  case,  although  the  influence  of  heat  seems  to  be  much 
smaller  than  the  influence  of  cold.  But  neither  experi- 
mental results  nor  general  reasoning  have  as  yet  shown 
that  in  man,  either  in  the  tropics  (Eykman)  or  in  the  north 
temperate  zone  (Loewy),  the  chemical  tone  is  diminished 
by  a  rise  of  external  temperature  much  above  the  mean  of 
an  ordinary  English  summer,  apart  from  the  effect  of  the 
muscular  relaxation  which  heat  induces.  In  a  man,  indeed, 
at  rest  in  a  hot  atmosphere,  the  production  of  carbon  dioxide 
and  consumption  of  oxygen  are,  if  anything,  greater  than 

32—2 


500  A  MANUAL  OF  PHYSIOLOGY 

at  the  ordinary  temperature.  The  regulation  of  tempera- 
ture in  an  environment  warmer  than  the  normal  seems,  in 
fact,  to  be  brought  about  more  by  an  increase  in  the  loss 
than  a  decrease  in  the  production  of  heat.  Evaporation 
from  the  skin  and  lungs  is  an  automatic  check  upon  over- 
heating as  important  as  the  involuntary  increase  of  meta- 
bolism upon  excessive  cooling. 

While  it  is  known  that  the  skeletal  muscles,  and  perhaps 
the  glands  and  other  tissues,  are  at  one  end  of  the  reflex  arc 
by  which  the  impulses  pass  that  regulate  the  temperature 
through  the  metabolism,  we  are  as  yet  ignorant  of  the 
precise  paths  by  which  the  afferent  impulses  travel,  of  the 
nerve-centres  to  which  they  go,  and  even  of  the  end-organs 
in  which  they  arise.  There  are  nerves  in  the  skin  which 
minister  to  the  sensation  of  temperature  (Chap.  XIII.).  A 
change  of  temperature  is  their  '  adequate  '  and  sufficient 
stimulus  ;  and  it  is.  a  tempting  hypothesis,  though  nothing 
more,  that  these  are  the  afferent  nerves  concerned  in  the 
reflex  regulation  of  temperature — that  impulses  carried  up 
by  them  to  some  centre  or  centres  in  the  brain  or  cord  are 
reflected  down  the  motor  nerves  to  control  the  metabolism 
of  the  skeletal  muscles,  and  down  the  vaso-motor  nerves  to 
control  the  loss  of  heat  from  the  skin. 

Heat   Centres. — It   is  known  that  certain   injuries  of  the 
central  nervous  system   are  related  to   disturbance  of  the 
heat-regulating  mechanism.    Puncture  of  the  median  portion 
of  the  corpus  striatum   in  the  rabbit  by   a   needle  thrust 
through  a  trephine  hole  in  the  skull  is  followed  by  a  rise  of 
rectal  temperature  (i°  to  2°),  heat-production  and  respira- 
tory exchange,  which  may  last  for  several  days  (Ott,  Richet, 
Aronsohn   and  Sachs).     This  is  due  to  stimulation  of  th< 
portions  of  the  brain  in    the  immediate  neighbourhood   of 
the  injury,  and  electrical  stimulation  of  this  region  has 
similar    effect.      When   the  temperature   has   returned   t< 
normal,  a  fresh  puncture  may  again  cause  a  rise.     Inju: 
to  various  portions  of  the  cortex  cerebri  in  the   dog  an< 
other  animals,  and  lesions  of  the  pons,  medulla  oblongat; 
and    cord  in    man    may   also    be  followed   by   increase   oi 
temperature.     When  the  spinal  cord  is  cut  below  the  lev< 


ANIMAL  HEAT  501 

of  the  vaso-motor  centre  the  increased  loss  of  heat  from  the 
skin  due  to  dilatation  of  the  cutaneous  vessels  masks  any 
increase  of  the  heat-production  which  may  possibly  have 
taken  place,  and  the  internal  temperature  falls ;  but  if  the 
loss  of  heat  is  diminished  by  wrapping  the  animal  in  cotton- 
wool the  temperature  may  rise.  From  such  phenomena  it 
has  been  surmised  that  certain  '  centres  '  in  the  brain  have 
to  do  with  the  regulation  of  temperature  by  controlling  the 
metabolism  of  the  tissues  ;  that  they  cause  increased  meta- 
bolism when  the  internal  temperature  threatens  to  sink, 
diminished  metabolism  when  it  tends  to  rise.  The  cutting 
off,  it  is  said,  of  the  influence  of  the  '  heat  centres '  by 
section  of  the  paths  leading  from  them  allows  the  meta- 
bolism of  the  tissues  to  run  riot,  and  the  temperature  to 
increase. 

Fever  is  a  pathological  process  generally  caused  by  the 
poisonous  products  of  bacteria,  and  characterized  by  a  rise 
of  temperature  above  the  limit  of  the  daily  variation  (p.  509). 
It  is  further  associated  with  an  increase  in  the  rate  of  the 
heart  and  the  respiratory  movements,  often  with  an  increase 
in  the  excretion  of  urea  and  ammonia  in  the  urine,  and  a 
diminution  in  the  alkalies  and  carbon  dioxide  of  the  blood. 
It  has  been  suggested  that  the  proximate  cause  of  fever  is 
the  action  of  bacterial  poisons  or  of  other  substances  on  the 
'  heat  centres,'  and  that  antipyretics,  or  drugs  which  reduce 
the  temperature  in  fever,  do  so  by  restoring  the  centres  to 
their  normal  state,  by  preventing  the  development  of  the 
poisons,  aiding  their  elimination,  or  antagonizing  their  action. 
In  favour  of  this  view,  it  has  been  stated  that  when  the 
basal  ganglia  are  cut  off,  by  section  of  the  pons,  from  their 
lower  nervous  connections,  fever  is  no  longer  produced  by 
injection  of  cultures  of  bacteria  which  readily  cause  it  in 
an  intact  animal,  while  antipyrin  has  no  influence  upon  the 
temperature  (Sawadowski).  But  some  observers  have  been 
unable  to  find  any  clear  evidence  of  the  existence  of  '  heat 
centres  ' — that  is,  of  localized  portions  of  the  central  nervous 
system  specially  concerned  in  the  regulation  of  the  body 
temperature.  And  while  it  is  almost  certain  that  some 
pyrogenic  or  fever-producing  agents — cocaine,  e.g. — act  in- 


502 


A  MANUAL  OF  PHYSIOLOGY 


Normal 


Temperature 
aboire  normal  s 


directly,  through  the  brain  or  cord,  it  is  quite  possible  that 
others  affect  directly  the  activity  of  the  tissues  in  general, 
just  as  some  antipyretics  or  fever-reducing  agents,  such  as 
quinine,  seem  to  act  immediately  upon  the  heat-forming 
tissues,  while  others,  like  antipyrin,  affect  them  through  the 
nervous  system. 

Fever  is  a  condition  so  interesting  from  a  physiological 

point  of  view,  and  of 
such  importance  in 
practical  medicine,  that 
it  will  be  well  to  con- 
sider a  little  more 
closely  the  possible  ways 
in  which  a  rise  of  tem- 
perature may  occur.  It 
must  not  be  forgotten 
that  the  febrile  increase 
of  temperature  is  always 
accompanied  by  other 
departures  from  the 
normal,  and  that  all 
the  fundamental  febrile 
changes  may  even,  in 
certain  cases,  be  present 
without  elevation,  and 
even  with  diminution  of 
temperature.  But  here 
we  have  only  to  do  with 
the  disturbance  of  the 

normal  equilibrium  between  the  loss  and  the  production 
of  heat ;  and  it  is  evident  that  any  of  the  five  conditions 
illustrated  in  the  diagram  may  give  rise  to  an  increase 
of  temperature.  It  is  not  necessary  to  discuss  whether 
cases  of  fever  can  actually  be  found  to  illustrate  every 
one  of  these  possibilities.  It  is  probable  that  not  infre- 
quently diminished  loss  and  increased  production  may 
be  both  involved;  and  it  ought  to  be  remembered  that 
the  healthy  standard  with  which  the  heat-production  of  a 
fever  patient  should  be  compared  is  not  that  of  a  man 


He.  at  Production 


FIG.  139.— DIAGRAM  TO  SHOW  THE  POSSIBLE 
RELATIONS  BETWEEN  HEAT-PRODUCTION 
AND  HEAT-LOSS  IN  FEVER. 


ANIMAL  HEAT  503 

doing  hard  work  on  a  full  diet,  but  that  of  a  healthy  person 
in  bed,  and  on  the  meagre  fare  of  the  sick-room.  When 
this  is  kept  in  view,  the  comparatively  low  heat-production 
and  respiratory  exchange  which  have  sometimes  been  found 
in  fever  cease  to  excite  surprise.  But,  in  any  case,  no  mere 
change  in  the  relative  proportions  of  heat  formed  and  lost 
is  sufficient  to  explain  the  febrile  rise  of  temperature. 
That  an  increase  in  heat-production  is  not  of  itself  enough 
to  produce  fever  is  proved  by  the  fact  that  severe  muscular 
work,  which  increases  the  metabolism  more  than  high  fever, 
only  causes  a  slight  and  transient  rise  of  temperature  in  a 
healthy  man.  The  essence  of  the  change  is  a  derangement 
of  the  mechanism  by  which  in  the  healthy  body  excess  or 
defect  of  average  metabolism,  or  of  average  heat-loss,  is  at 
once  compensated  and  the  equilibrium  of  temperature  main- 
tained. 

This  derangement  only  lasts  as  long  as  the  temperature  is 
rising.  When  it  becomes  stationary  at  its  maximum  we 
have  again  adjustment,  again  equality  of  production  and 
escape  of  heat ;  but  the  adjustment  is  now  pitched  for  a 
higher  scale  of  temperature.  A  rough  analogy,  so  far  as 
one  part  of  the  process  is  concerned,  may  be  found  in  the 
behaviour  of  the  ordinary  gas-regulator  of  a  water-bath.  It 
can  be  '  set '  for  any  temperature.  That  temperature,  once 
reached,  remains  constant  within  narrow  limits  of  oscilla- 
tion ;  but  the  regulator  can  be  equally  well  adjusted  for  a 
higher  or  a  lower  temperature. 

Rosenthal  has  concluded  from  calorimetric  observations 
that,  in  the  first  stage  of  fever,  while  the  temperature  is 
rising,  there  is  always  increased  retention  of  heat.  Marag- 
liano  actually  found  evidence,  by  means  of  the  plethysmo- 
graph,  that  the  cutaneous  vessels  are  at  this  stage  con- 
stricted, and  that  the  constriction  may  even  precede  the 
rise  of  temperature.  Both  observations  lend  support  to  the 
famous  '  retention  '  theory  of  Traube.  At  the  height  of 
the  fever  there  is  often,  though  apparently  not  always,  an 
increase  in  the  heat-production.  After  the  crisis,  while  the 
fever  is  subsiding,  the  rate  at  which  heat  is  being  lost  rises 
sharply.  As  to  the  explanation  of  the  increase  of  metabolism 


504  A  MANUAL  OF  PHYSIOLOGY 

in  fever,  various  views  have  been  held.     Some  have  gone  so 
far  as  to  say  that  the  increase  is  merely  the  consequence, 
not  the  cause,  of  the  rise  of  temperature.    But  the  rebutting 
evidence  which  has  been  brought  against  this  view  is  strong 
anc^'    indeed,    overwhelming.      The    increase    of    urea,    for 
example,  is  often  much  greater  in  fever  than  any  increase 
I  which  can  be  brought  about  by  artificially  raising  the  tem- 
'  perature  of  a  healthy  individual  by   means  of  hot  baths. 
Further,  this  excessive  excretion  of  urea  does  not  run  parallel 
with  the  rise  of  temperature  in  fever,  but  is  generally  most 
marked  after  the  crisis.    During  the  stage  of  defervescence  an 
enormous  amount  of  urea  is  sometimes  given  off.     In  a  case 
of  typhus,  in  the  mixed  urine  of  the  third  and  fourth  days 
after  the  crisis,  no  less  than  160  grammes  urea  was  found 
(Naunyn),  or  nearly  three  times  the  normal  amount  for  a 
man  on  full  diet.     Again,  when  fever  is  caused  by  the  in- 
jection  of  bacteria  or  their  products,  the  increase  in  the 
carbon  dioxide  eliminated  and  oxygen  consumed  occurs  even 
when  the  temperature  is  prevented  from  rising  by  cold  baths. 
It  seems  perfectly  clear,  then,  that  the  increase  of  metabolism 
is,  in  many  cases  at  least,  a  primary  phenomenon  of  fever, 
and  it  remains  to  ask  whether  the  rise  of  temperature  is 
anything   more   than    a    superficial,   and,   so   to    speak,   an 
accidental,   circumstance.      The    orthodox  view   for    many 
ages  has  undoubtedly  been  that  the  increase  of  temperature 
is  in  itself  a   serious   part   of  the  pathological  process,  a 
symptom  to  be  fought  with,  and,  if  possible,  removed.     And, 
indeed,  it  is  not  denied  by  anyone  that  the  excessive  rise  of 
temperature  seen  in  some  cases  of  febrile  disease  (to  43°  C., 
and,  it  is  said,  even  to  44°  in  influenza,  e.g.),  is,  apart  from 
all  other  changes,  a  most  imminent  danger  to  life.     But 
some  evidence  has  of  late  been  brought  forward,   mostly 
from    the  field    of  bacteriology,   to   support  the    idea    that 
the   rise  of  temperature  is  of  the  nature   of  a   protective 
mechanism,   that  fever  is,   indeed,  a  consuming  fire,  but  a 
fire  that  wastes  the  body,  to  destroy  the    bacteria.     The 
streptococcus  of  erysipelas,  for  example,  does  not  develop 
at  39°  to  40°  C.,  and  is  killed  at  39*5°  to  41°  C.     Anthrax 
bacilli,  kept  at  42°  to  43°  C.  for  some  time,  are  *  attenu- 


ANIMAL  HEAT  505 

ated,'  and  when  injected  into  animals  confer  immunity  to 
the  disease.  Heated  for  several  days  to  41°  to  42°  C., 
pneumococci  render  rabbits  immune  to  pneumonia.  These 
bacteriological  results  are  supported  to  a  certain  extent  by 
clinical  experience.  For  it  has  been  observed  that  a  cholera 
patient  with  distinct  fever  has  a  better  chance  of  recovery 
than  a  case  which  shows  no  fever.  But  too  much  weight 
ought  not  to  be  given  to  isolated  facts  of  this  sort,  and 
adverse  evidence  can  be  produced  both  from  the  laboratory 
and  the  hospital.  For  although  hens  are  immune  to  anthrax 
under  ordinary  conditions,  but  can  be  infected  by  inocula- 
tion when  artificially  cooled,  frogs,  equally  immune  at  the 
temperature  of  the  air,  become  susceptible  when  artificially 
heated.  And  it  is  impossible  to  deny  that  the  use  of 
cold  baths  in  typhoid  fever  is  sometimes  of  remarkable 
benefit. 

Distribution  of  Heat. — The  great  foci  of  heat-formation — the 
muscles  and  glands — would,  if  heat  were  not  constantly  leaving 
them,  in  a  short  time  become  much  warmer  than  the  rest  of  the 
body  ;  while  structures  like  the  bones,  skin,  and  adipose  tissue,  in 
which  chemical  change  and  heat-production  are  slow,  would  soon 
cool  down  to  a  temperature  not  much  exceeding  that  of  the  air. 
The  circulation  of  the  blood  ensures  that  heat  produced  in  any 
organ  shall  be  carried  away  and  speedily  distributed  over  the  whole 
body;  while  direct  conduction  also  plays  a  considerable  part  in 
maintaining  an  approximately  uniform  temperature.  The  uniformity, 
however,  is  only  approximate.  The  temperature  of  the  liver  is 
several  degrees  higher  than  that  of  the  skin,  and  the  temperature  of 
the  brain  several  degrees  higher  than  that  of  the  cornea.  The  blood 
of  the  superficial  veins  is  colder  than  that  of  the  corresponding 
arteries.  The  crural  vein,  for  example,  carries  colder  blood  than  the 
crural  artery,  and  the  external  jugular  than  the  carotid.  The  heat 
produced  in  the  deeper  parts  of  the  regions  which  they  drain  is 
more  than  counterbalanced  by  the  heat  lost  in  the  more  superficial 
parts.  When  loss  of  heat  from  the  surface  is  sufficiently  diminished 
by  an  artificial  covering,  or  prevented  by  the  protected  situation  of 
any  organ  with  an  active  metabolism,  the  venous  blood  leaving  it  is 
warmer  than  the  arterial  blood  coming  to  it.  The  temperature  of 
the  blood  passing  from  the  levator  labii  superioris  muscle  of  the 
horse  during  mastication  may  be  sensibly  higher  than  that  of  the 
blood  which  feeds  it ;  the  blood  in  the  vena  profunda  femoris,  and 
in  the  crural  vein  of  a  dog  with  the  leg  wrapped  in  cotton-wool,  is 
warmer  by  'i°  to  -3°  than  the  blood  of  the  crural  artery.  This 
difference  of  temperature  is  due  to  the  heat  produced  in  the  muscles. 


5o6  A  MANUAL  OF  PHYSIOLOGY 

and  it  is  not  difficult  to  show  that  the  difference  ought  to  be  of  this 
order  of  magnitude.  The  quantity  of  blood  in  a  7  kilo  dog  is  about 
J  kilo ;  J  of  this,  or  J  kilo,  is  in  the  skeletal  muscles,  and  the 
average  circulation-time  through  them  may  be  taken  as  ten  seconds. 
Six  times  in  the  minute,  or  360  times  in  the  hour,  J  kilo  of  blood 
passes  through  the  muscles,  and  is  heated  on  the  average  by  '2°.  If 
we  take  the  specific  heat  of  blood  as  about  equal  to  that  of  water, 

this  represents  a  heat-production  of  ^—  x  --  x  1,000,  or  9,000  small 

o         i  o 

calories  per  hour.  Now,  the  total  heat-production  of  a  7  kilo  dog 
is  about  19,000  small  calories  per  hour,  of  which  somewhat  less  than 
one-half  is  probably  formed  in  the  skeletal  muscles. 

The  blood  of  the  inferior  vena  cava  at  the  level  of  the  kidneys 
may  be  *i°  colder  than  that  of  the  abdominal  aorta,  but  is 
warmer  than  the  blood  of  the  superior  cava.  The  right  heart, 
therefore,  receives  two  streams  of  blood  at  different  temperatures, 
which  mingle  in  its  cavities.  A  controversy  was  long  carried  on  as 
to  the  relative  temperature  of  the  blood  of  the  two  sides  of  the 
heart ;  but  the  researches  of  Heidenhain  and  Korner  have  shown 
that  a  thermometer  passed  into  the  right  ventricle  through  the  jugular 
vein  stands,  as  a  rule,  slightly  higher  than  a  thermometer  introduced 
through  the  carotid  into  the  left  ventricle.  They  consider  that  the 
method  gives  not  so  much  the  temperature  of  the  blood  in  the  two 
cavities  as  that  of  their  walls.  The  thin-walled  right  ventricle, 
according  to  them,  is  heated  by  conduction  from  the  warm  liver, 
from  which  it  is  only  separated  by  the  diaphragm,  while  the  left 
ventricle  loses  heat  to  the  cooler  lungs.  They  deny  that  the 
difference  of  temperature  is  caused  by  cooling  of  the  blood  in  its 
passage  through  the  pulmonary  capillaries.  Under  ordinary  circum- 
stances, they  say,  the  inspired  air  is  already  heated  almost  to  body 
temperature  before  it  reaches  the  alveoli ;  but,  while  this  is  the  case, 
it  is  possible  that  much  of  the  water-vapour  required  to  saturate  it  is 
evaporated  from  the  alveolar  walls.  Even  when  respiration  is 
suspended,  they  find  a  difference  of  temperature  between  the  two 
sides  of  the  heart.  A  slight  difference,  however,  might  be  caused  in 
the  blood  of  the  two  ventricles,  even  in  the  absence  of  respiration, 
by  the  heat  developed  in  the  cardiac  muscle  itself  during  con- 
traction. A  large  proportion  of  this  heat  must  be  conveyed  by  the 
blood  of  the  coronary  veins  into  the  right  side  of  the  heart.  But 
the  whole  of  it  would  only  suffice  to  raise  the  temperature  of  the 
blood  in  the  right  ventricle  by  <>V  to  iV ;  while  a  fall  of  TV  in  the 
temperature  of  the  blood  passing  through  the  lungs  would  account  for 
all  the  heat  lost  by  the  expired  air,  and  if  half  of  the  loss  took  place 
in  the  upper  air-passages,  sV  would  be  sufficient. 

The  surface  temperature  varies  between  rather  wide  limits  with 
the  temperature  of  the  environment.  The  temperature  of  cavities 
like  the  rectum,  vagina,  and  mouth  approximates  to  that  of  the 
blood  in  the  great  vessels  or  the  heart,  and  undergoes  only  slight 
changes.  An  increase  in  the  velocity  of  the  blood  causes  the 


ANIMAL  HEAT  507 

internal  and  surface  temperatures  to  come  nearer  to  each  other,  the 
former  falling  and  the  latter  rising.  When  the  loss  of  heat  from  a 
portion  of  the  surface  is  prevented,  the  temperature  of  this  portitin 
approaches  the  internal  temperature.  For  this  reason  a  thermometer 
placed  in  the  axilla  approximately  measures  the  internal  temperature, 
and  not  that  of  the  skin ;  and  a  thermometer  in  the  groin  of  a  rabbit, 
and  completely  covered  by  the  flexed  thigh,  may  stand  as  high  as, 
or,  it  is  said,  even  higher  than,  a  thermometer  in  the  rectum  (Hale 
White). 

The  surface  temperature  is  a  rough  index  of  the  rate  of  heat-loss ; 
the  internal  temperature,  of  the  rate  of  heat-production.  A  normal 
skin  temperature  and  a  rising  rectal  temperature  would  probably  indi- 
cate increased  production  of  heat;  an  increased  rectal  temperature,  in 
conjunction  with  a  diminished  surface  temperature,  as  in  the  cold 
stage  of  ague,  might  be  due  either  to  diminished  heat-loss  while  the 
heat-production  remained  normal,  or  to  diminished  heat-loss  plus 
increased  heat-production. 

The  following  tables  illustrate  the  differences  of  tempera- 
ture found  in  the  body.  It  should  be  remembered  that  the 
numbers  are  not  strictly  comparable  with  each  other ;  there 
is  no  constant  ratio  between  the  temperature  of  the  blood 
in  two  vessels  or  of  the  skin  at  two  points.  Even  in  the 
same  vessel  the  temperature  may  vary  with  many  circum- 
stances, such  as  the  velocity  of  the  stream,  and  the  state 
of  activity  of  the  organ  from  which  it  comes.  Apart  from 
physiological  variations,  experimental  fallacies  sometimes 
cause  a  want  of  constancy,  especially  in  measurements  of 
blood  temperature.  The  insertion  of  a  mercurial  ther- 
mometer into  a  vessel  is  very  likely  to  obstruct  the  passage 
of  the  blood ;  and  if  the  blood  lingers  in  a  warm  organ,  it 
will  be  heated  beyond  the  normal. 

Blood.     (Dog.) 

Right  heart  -     38 '8°  C. 

Left      „  38-6 

Aorta  -     387 

Superior  vena  cava       -  -     36  8 

Inferior          „  -     38*1 

Crural  vein  -     37-2 

Crural  artery        -  -         -     38* 

Profunda  femoris  vein  -     38*2 

Portal  vein  38-39    Waries  with  activity 

Hepatic  vein       -  -      38*4-39*7 /of  digestive  organs. 


508 


A  MANUAL  OF  PHYSIOLOGY 


Leg  of  dog  lightly  wrapped  in  wool. 
Crural  artery  -     34'95 

„      vein  3476 


Crural  artery 
vein 


Leg  more  carefully  wrapped  up. 


3470 
34-82 


Rectum,  36-2. 
" 


Air, 


i6*3. 


Tissues. 


Brain  -  -     40 

Liver  -     40-6-40*9 

Subcutaneous    tissue    2*1     lower 

than  that  of  subjacent  muscles 

(man). 

Anterior  chamber  of  eye  31 

Vitreous  humour  36 

Cavities.     (Man.) 

Axilla          •  36-3-37-5°  C.(97'3-99'5°  F.) 

Rectum       -  -                  -  37-5-38 

Mouth  -                  -  37*25 

Vagina  -  37'5-38 

Uterus  -  377-38-3 

External  auditory  meatus     -  3 7 '3-3 7 '8 

(Bladder,  urine)  -                 -  37*03 

Natural  Surfaces. 

Cheek  (boy,  immediately  after  running)  -  36*25 

Anterior  surface  of  forearm  -  33'5-34'4 

Posterior         „  „  -  34- 

Skin  over  biceps    -  -  35* 

„       ,,     head  of  tibia  -  31*9 

„     immediately  below  xiphoid  cartilage  34*7 


(Man) 
Room 

temperature. 


„     over  sternum  - 
On  hair  (boy) 

Under  hair  over  sagittal  suture  (boy) 
Shaved  skin  of  neck  (rabbit)  - 
On  hair     „          „          ,, 
„       between  eyes     ,, 

Artificial  Surfaces. 
Room        [Surface  of  trousers  over  thigh 


temperature,  j 


coat  over  arm 
waistcoat 


33*2 

30* 

337-34* 
36  5 
31*5 
30*7 


237-287 

26-8 

26- 


-j-       Normal  Variations  in  the  Temperature. — The  internal  tem- 
perature, as  has  been  already  said,  is  not  strictly  constant. 


ANIMAL  HEAT  509 

It  varies  with  the  time  of  day ;  with  the  taking  of  food ; 
with  age;  to  a  slight  extent  with  violent  changes  in  the 
external  temperature,  such  as  those  produced  by  hot  or  cold 
baths  ;  and  possibly  with  sex. 

The  daily  curve  of  temperature  shows  a  minimum  in  the 
early  morning  (two  to  six  o'clock),  and  a  maximum  in  the 
evening  (five  to  eight  o'clock)  (Fig.  140).  The  extreme  daily 
range  in  health  may  be  taken  as  a  little  over  i°  C.  In  fever 
it  is  generally  greater,  but  the  maximum  and  minimum  fall 
at  the  same  periods;  and  it  is  of  scientific,  and  perhaps  of 
practical,  interest  that 
the  early  morning,  when 
the  temperature  and 
pulse-rate  are  at  their 
minimum,  is  often  the 
time  at  which  the 
flagging  powers  of  the 
sick  give  way.  From 
two  to  six  o'clock  in  the 
morning  the  daily  tide 
of  life  may  be  said  to 
reach  low-water  mark. 

Fvpn    in    a     faQtincr    man     FlG.      140.  — CURVE     SHOWING     THE     DAILY 

tvei  m  a  lasting  man  VARIATION  OF  BODY  TEMPERATURE. 
the  diurnal  tempera- 
ture curve  runs  its  course,  but  the  variations  are  not  so 
great.  The  taking  of  food  of  itself  causes  an  increase  of 
temperature,  although  in  a  healthy  man  this  rarely  amounts 
to  more  than  half  a  degree.  The  rise  of  temperature  is 
certainly  due  in  part  to  the  increased  work  of  the  alimentary 
canal,  but  may  also  be  connected  with  the  increase  of 
metabolic  activity  which  the  entrance  of  the  products  of 
digestion  into  the  blood  brings  about.  The  solution  of  the 
solids  of  the  food  by  the  digestive  juices  is  associated 
with  absorption  of  heat,  as  has  been  observed  in  artificial 
digestion,  and  even  in  a  case  of  gastric  fistula.  The 
increased  heat-production,  however,  is  more  than  suffi- 
cient to  prevent  any  fall  of  body  temperature  from  this 
cause. 

As  to  the  relation  of  age  and  sex  to  temperature,  it  is 


5io  A  MANUAL  OF  PHYSIOLOGY 

only  necessary  to  remark  that  the  mean  temperature  of  the 
young  child  is  somewhat  higher,  and  that  of  the  old  man 
somewhat  lower,  than  that  of  the  vigorous  adult  ;  but  a 
point  of  more  importance  is  the  relative  imperfection  of  the 
heat-regulation  in  infancy  and  age,  and  the  greater  effect  of 
accidental  circumstances  on  the  mean  temperature.  Thus,  old 
people  and  young  children  are  specially  liable  to  chills,  and 
a  fit  of  crying  may  be  sufficient  to  send  up  the  temperature 

of  a  baby.  The  tem- 
perature of  women  is 
generally  a  little  higher 
than  that  of  men,  and 
is  also,  perhaps,  some- 
what more  variable. 

After  death  the  body 
cools  at  first  rapidly, 
then  more  slowly  (Fig. 
141).  But  occasionally 
a  post-mortem  rise  of 
temperature  may  take 
place.  In  certain  acute 
diseases  (like  tetanus) 

F.C..4..-CURVE  OF  COOL.NC  AFTER  DEATH  aSSOciated    ™th    exces- 
(GUINEA-PIG).  sive   muscular  contrac- 

Time  marked  along  horizontal,  and  temperature  tion  this  has   been  eSDC- 
along  vertical  axis.     At  a  ether  and   chloroform  .  .  . 

given  to  kill  animal  ;  death,  as  indicated  by  stoppage  daily  noticed  J  in  bodies 
of  the  heart,  took  place  at  b.  The  dotted  line  j  u  i  j 

shows  the  course  the  curve  would  have  taken  if  Wasted       by      prolonged 

the  anDesthetics  illness  u  does  not  occur- 


Nearly  an  hour  after 
death,  in  a  case  of  tetanus,  the  temperature  was  found  to  be 
45*3°  (Wunderlich).  In  dogs  a  slight  post-mortem  rise  may 
be  demonstrated,  especially  when  the  body  is  wrapped  up  ; 
but  when  an  animal  has  been  long  under  the  influence  oi 
anaesthetics,  no  indication  whatever  of  the  phenomenoi 
may  be  obtained.  The  explanation  of  post-mortem  rise  ol 
temperature  is  to  be  found  :  (i)  In  the  continued  meta- 
bolism of  the  tissues  for  some  time  after  the  heart  has 
ceased  to  beat,  for  the  cell  dies  harder  than  the  body. 
(2)  In  the  diminished  loss  of  heat,  due  to  the  stoppage  oi 


PRACTICAL  EXERCISES  511 

the  circulation.  (3)  Possibly  to  a  small  extent  in  physical 
changes  (rigor  mortis,  coagulation  of  blood)  in  which  heat 
is  set  free. 


PRACTICAL  EXERCISES  ON  CHAPTERS  VII.  AND  VIII. 

i.  Glycogen — (i)  Preparation. — (a)  Place  in  a  mortar  some  fine 
sand  and  a  mixture  of  equal  volumes  of  saturated  solution  of 
mercuric  chloride  and  Esbach's  reagent."*  Put  one  or  two  oysters 
in  the  mortar,  rub  up  thoroughly,  and  let  the  mass  stand  till  (b}  and 
(c)  have  been  done,  stirring  it  occasionally.  Then  filter  and  pre- 
cipitate the  glycogen  from  the  filtrate  with  alcohol.  Filter  again, 
wash  the  precipitate  on  the  filter  with  a  little  alcohol,  dissolve  it  in 
i  or  2  c.c.  of  water,  and  test  for  glycogen  as  in  (b).  The  mercuric 
chloride  and  Esbach's  reagent  are  added  to  precipitate  the  proteids, 
which  are  more  completely  thrown  down  in  this  way  than  by  the 
methods  used  in  (b)  and  (c)  (Huizinga). 

(b)  Cut  an  oyster  into  two  or  three  pieces,  throw  it  into  boiling 
water,  and  boil  for  a  minute  or  two.     Rub  up  in  a  mortar  with  clean 
sand,  and  again  boil.     Filter.     Precipitate  any  proteids  which  have 
not  been  coagulated,  by  adding  alternately  a  drop  or  two  of  hydro- 
chloric acid  and  a  few  drops  of  potassio-mercuric  iodide  so  long  as 
a  precipitate  is  produced.     Only  a  small  quantity  of  these  reagents 
will  be  required,  as  the  greater  part  of  the  proteids  has  been  already 
coagulated  by  boiling.     Filter  if  any  precipitate  has  formed.     The 
filtrate  is  opalescent.    Precipitate  the  glycogen  from  the  filtrate  (after 
concentration  on  the  water-bath  if  it  exceeds  a  few  c.c.  in  bulk)  by 
the  addition  of  four  or  five  times  its  volume  of  alcohol.     Filter  off 
the  precipitate,  wash  it  on  the  filter  with  alcohol,  and  dissolve  it  in  a 
little  water.     To  some  of  the  solution  add  a  drop  or  two  of  iodine ; 
a  reddish-brown  (port  wine)  colour  is  produced,  which  disappears  on 
heating,  returns  on  cooling,  is  removed  by  an  alkali,  restored  by  an 
acid.     Add  saliva  to  some  of  the  glycogen  solution,  and  put  in  a 
bath  at  40°  C.     In  a  few  minutes  reducing  sugar  (maltose)  will  be 
found  in  it  by  Trommer's  test  (p.  23). 

Note  that  dextrin  (erythrodextrin)  gives  the  same  colour  with 
iodine  as  glycogen  does.  Dextrin  is  also  precipitated  by  alcohol, 
but  a  greater  proportion  must  be  added  to  cause  complete  precipita- 
tion. Glycogen  is  completely  precipitated  by  saturation  with  mag- 
nesium sulphate  or  ammonium  sulphate,  while  a  pure  solution  of 
eiythrodextrin  is  not  precipitated.  Digest  a  solution  of  sugar-free 
dextrin  with  saliva  at  40°  C.  Reducing  sugar  is  formed,  but  the 
digestion  is  neither  so  rapid  nor  so  complete  as  in  the  case  of 
glycogen. 

(c)  Cut   another  oyster  into  pieces,  throw  it  into  boiling  water 
acidulated  with  dilute  acetic  acid,  and  boil  for  a  few  minutes.     Rub 
up  in  a  mortar  with  sand,  boil  again,  and  filter.     Test  a  portion  of 

*  Esbach's  reagent  is  a  solution  of  10  grm.  picric  acid  and  20  grm. 
citric  acid  in  a  litre  of  water. 


512  A  MANUAL  OF  PHYSIOLOGY 

the  filtrate  with  iodine  for  glycogen.     Precipitate  the  rest  with  alcohol, 
filter,  dissolve  the  precipitate  in  water,  and  test  again  for  glycogen. 

(2)  Deeply  etherize  a  dog  or  rabbit  five  hours  after  a  meal  rich  in 
carbo-hydrates  (e.g.,  rice  and  potatoes).  Fasten  it  on  a  holder.  Clip 
off  the  hair  over  the  abdomen  in  the  middle  line.  Make  a  mesial 
incision  through  the  skin  and  abdominal  wall  from  the  ensiform  car- 
tilage to  the  pubis.  The  liver  will  now  be  rapidly  cut  out  [by  the 
demonstrator]  and  divided  into  two  portions,  one  of  which  will  be 
[distributed  among  the  class  and]  treated  as  in  (a)  or  (b) ;  the  other 
will  be  kept  for  an  hour  at  a  temperature  of  40°  C,  and  then  sub- 
jected to  processes  (a)  or  (£).  Little,  if  any,  sugar  and  much 
glycogen  will  be  found  in  the  portion  which  was  boiled  imme- 
diately after  excision.  Abundance  of  sugar  will  be  found  in  the 
portion  kept  at  40°  C. ;  it  may  or  may  not  contain  glycogen. 

2.  Glycosuria. — (i)  Weigh  a  dog  (female  by  preference)  or  rabbit. 
Give  morphia  to  the  dog  or  chloral  to  the  rabbit,  as  described  on 
pp.  176,  189.  Fasten  on  a  holder,  and  etherize.  Insert  a  glass  cannula 
into  the  femoral  or  saphena  vein  of  the  dog,  or  into  the  jugular  of 
the  rabbit  (p.  177).  Fill  a  large  syringe  with  a  2  per  cent,  solution 
of  dextrose  (glucose)  in  normal  saline,  connect  it  with  the  cannula 
by  means  of  an  indiarubber  tube,  taking  care  that  there  are  no  air- 
bubbles  in  the  tube,  and  slowly  inject  as  much  of  the  solution  as 
will  amount  to  J  to  f  grm.  sugar  per  kilo  of  body-weight.  Tie  the 
vein,  remove  the  cannula,  and  in  half  an  hour  evacuate  the  bladder 
by  passing  a  catheter  (p.  429),  by  pressure  on  the  abdomen,  or,  if 
both  of  these  methods  fail,  by  tapping  the  bladder  with  a  trocar 
pushed  through  the  linea  alba  (supra-pubic  puncture).  In  an  hour 
again  draw  off  the  urine.  Test  both  specimens  for  sugar. 

In  this  experiment,  the  opportunity  may  also  be  taken  to  demon 
strate  that  egg-albumin,  when  injected  into  the  blood,  is  excreted  by 
the  kidneys,  a  filtered  solution  containing  the  albumin  of  one  egg  and 
sugar  in  the  quantity  mentioned  being  injected. 

The  catheter  may  be  inserted  before  the  injection  is  begun,  and 
the  bladder  evacuated.  After  the  injection  the  urine  that  drops 
from  the  catheter  may  be  collected  in  test-tubes,  first  every  minute, 
and  then,  as  soon  as  sugar  is  found,  every  ten  minutes.  Determine 
the  interval  between  injection  and  the  appearance  of  the  first  trace 
of  sugar  and  albumin.  If  a  sufficient  amount  of  urine  is  obtained, 
the  quantity  of  sugar  in  successive  specimens  may  be  estimated  and 
compared.  The  rate  of  flow  of  the  urine  as  measured  by  the  number 
of  drops  falling  from  the  catheter  may  also  be  estimated  from  time  to 
time,  in  order  to  determine  whether  diuresis  is  taking  place. 

(2)  Phloridzin  Diabetes. — Dissolve  J  grm.  of  phloridzin  in  warm 
water,  and  inject  it  subcutaneously  into  a  rabbit.  Obtain  a  sample 
of  the  urine  at  the  end  of  two  hours,  by  pressure  on  the  abdomen, 
and  test  for  sugar.  If  none  is  present,  wait  for  another  interval,  and 
again  test  the  urine. 

This  experiment  can  also  be  performed  without  risk  on  man. 
One  grm.  of  phloridzin  has  been  injected  twice  a  day  without  dis- 
turbing the  individual.  Much  sugar  is  found  in  the  urine,  but  it 


PRACTICAL  EXERCISES  513 

disappears  the  day  after  the  administration  of  phloridzin  is  stopped. 
The  phloridzin  may  also  be  given  by  the  mouth,  but  more  is  required, 
and  it  is  not  very  easily  absorbed,  and  often  causes  diarrhoea 
(v.  Mering). 

(3)  Puncture    Diabetes* — Anaesthetize  a  rabbit  with   ether,  and 
fasten  it  (belly  down)  on  a  holder.     Put  a  pad  or  a  rolled-up  towel 
under  the  neck  so  as  to  raise  the  back  of  the  head.     Divide  the  skin 
over  the  occipital  protuberance  down  to  the  bone.     Make  a  small 
trephine  hole  just  behind  the  protuberance.     Push  in  through  the 
cerebellum  a  thin  glass  rod  drawn  out  to  not  too  sharp  a  point  in  the 
blowpipe  flame.     Hold  the  rod  so  that  it  will  bisect  the  line  joining 
the  external  openings  of  the  two  ears,  and  send  it  in  till  it  is  felt  to 
have  met  the  basilar  bone.     Empty  the  bladder  in  an  hour,  and  test  for 
sugar  by  Trommer's  (p.  23)  and  the  phenyl  hydrazine  test  (p.  426). 

(4)  Alimentary  G/ycosuria. — The  urine  having   been   tested  for 
sugar  for  two  successive  days,  and  none  being  found,  (a)  a  large 
quantity  of  cane-sugar  is  to  be  taken  in  the  form  which  is  most 
agreeable  to  the  student.     The  urine  of  the  next  twenty-four  hours 
is  to  be  collected  and  measured.     A  sample  of  it  is  then  to  be  tested 
for  reducing  sugar  by  Trommer's  and  the  phenyl  hydrazine  test.     If 
any  sugar  is  found,  the  reducing  power  of  a  definite  quantity  of  the 
urine  is  to  be  determined  by  titration  with  Fehling's  solution  (p.  427) 
(a)  before  and  (/?)  after  boiling  with  hydrochloric  acid  (p.  382). 

Or  (b)  a  large  meal  of  rice  or  arrowroot,  sweetened  with  as  much 
dextrose  as  the  observer  can  induce  himself  to  swallow,  is  to  be 
taken,  and  the  urine  treated  as  in  (a). 

Or  (c)  a  large  number  of  sweet  oranges  may  be  eaten. 

If  experiments  (a),  (b)  and  (c)  are  all  unsuccessful,  (a)  and  (b)  may 
be  repeated  on  a  dog. 

3.  Measurement  of  the  Quantity  of  Heat  given  off  in  Respiration. 
—This  may  be  done  approximately  as  follows :  Put  in  the  inner  copper 
vessel.  A,  of  the  respiration  calorimeter  (Fig.  137,  p.  484)  a  measured 
quantity  of  water  sufficient  to  completely  cover  the  series  of  brass 
discs.  Place  A  in  the  wider  outer  cylinder,  the  bottom  of  which  it 
is  prevented  from  touching  by  pieces  of  cork.  The  outer  cylinder 
hinders  loss  of  heat  to  the  air.  Suspend  a  thermometer  in  the  water 
through  one  of  the  holes  in  the  lid.  In  the  other  hole  place  a  glass 
rod  to  serve  as  a  stirrer.  Read  off  the  temperature  of  the  water.  Put 
the  glass  tube  connected  with  the  apparatus  in  the  mouth,  and  breathe 
out  through  it  as  regularly  and  normally  as  possible,  closing  the 
opening  of  the  tube  with  the  tongue  after  each  expiration  and 
breathing  in  through  the  nose.  Continue  this  for  five  to  ten  minutes, 
taking  care  to  stir  the  water  frequently.  Then  read  off  the  tern 
perature  again.  If  W  be  the  quantity  of  water  in  c.c.,  and  /  the 
observed  rise  of  temperature  in  degrees  Centigrade,  W/  equals  the 
quantity  of  heat,  expressed  in  small  calories  (p.  479),  given  off  by  the 
respiratory  tract  in  the  time  of  the  experiment,  on  the  assumptions 
(i)  that  all  the  heat  has  been  absorbed  by  the  water,  (2)  that  none 
of  it  has  been  lost  by  radiation  and  conduction  from  the  calorimeter 
*  This  experiment  is  only  suitable  for  advanced  students. 

33 


514  A  MANUAL  OF  PHYSIOLOGY 

to  the  surrounding  air.  Calculate  the  loss  in  twenty-four  hours  on 
this  basis;  then  repeat  the  experiment,  breathing  as  rapidly  and 
deeply  as  possible,  so  as  to  increase  the  amount  of  ventilation.  The 
quantity  of  heat  given  off  will  be  found  to  be  increased.* 

In  an  experiment  of  short  duration  (2)  is  approximately  fulfilled. 
As  to  (i),  it  must  be  noted  that  in  the  first  place  the  metal  of  the 
calorimeter  is  heated  as  well  as  the  water,  and  the  water-equivalent  of 
the  apparatus  must  be  added  to  the  weight  of  the  water  (p.  480).  The 
water  equivalent  is  determined  by  putting  a  definite  weight  of  water  at 
air  temperature  T  into  the  calorimeter,  and  then  allowing  a  quantity 
of  hot  water  at  known  temperature  T'  to  run  into  it,  stirring  well,  and 
noting  the  temperature  of  the  water  when  it  has  ceased  to  rise.  Call 
this  temperature  T".  Enough  hot  water  should  be  added  to  raise 
the  temperature  of  the  calorimeter  about  2°  C.  The  quantity  run 
in  is  obtained  by  weighing  the  calorimeter  before  and  after  the  hot 
water  has  been  added.  Suppose  it  is  m.  Let  the  mass  of  the  cold 
water  in  the  calorimeter  at  first  be  M,  and  let  M'  =  the  mass  of  water 
which  would  be  raised  i°  C.  in  temperature  by  a  quantity  of  heat 
sufficient  to  increase  the  temperature  of  all  the  metal,  etc.,  of  the  calori- 
meter by  i° — in  other  words,  the  water-equivalent  of  the  calorimeter. 
The  mass  m  of  hot  water  has  lost  heat  to  the  amount  of  m 
(T'-T"),  and  this  has  gone  to  raise  the 
temperature  of  a  mass  of  water  M  and  metal 
equivalent  to  a  mass  of  water  M'  by  (T"  -  T)  de- 
grees. . '.  m  (T  -  T")  =  M(T"  -  T)  +  M'(T"  -  T). 
Everything  in  this  equation  except  M'  is  known, 
and  .'.  M',  the  water-equivalent  of  the  calori- 
meter, can  be  deduced,  and  must  be  added 
in  all  exact  experiments  to  the  mass  of  water 
contained  in  it. 

Secondly,  all  the  excess  of  heat  in  the  ex- 
pired over  that  in  the  inspired  air  is  not  given 
off  to  the  calorimeter,  for  the  air  passes  out 
of  it  at  a  slightly  higher  temperature  than  that 
of  the  atmosphere.  At  the  beginning  of  the 
FIG.  142.  —  BOTTLE  experiment  this  excess  of  temperature  is  zero. 

ARRANGED         FOR         Trr  ,     .       .          0     ~         ,     r 

WATER-VALVE.  If  at  trie  end  it  is  i  C.,  the  mean  excess  is 

0-5°  C.  Now,  when  respiration  is  carried  on 

in  a  room  at  a  temperature  of  10°  C.,  the  expired  air  has  its 
temperature  increased  by  nearly  30°  C.  About  -^  of  the  heat  given 
off  by  the  respiratory  tract  in  raising  the  temperature  of  the  air  of 
respiration  would  accordingly  be  lost  in  such  an  experiment.  But 
since  the  portion  of  the  heat  lost  by  the  lungs  which  goes  to  heat  the 
expired  air  is  only  ^  of  the  whole  heat  lost  in  respiration  (p.  483),  the 
error  would  only  amount  to  T^  of  the  whole,  and  this  is  negligible. 

Thirdly,  the  air  leaves  the  calorimeter  saturated  with  watery  vapour 
at,  say,  10*5°,  while  the  inspired  air  is  not  saturated  for  10°  C. 

*  The  average  heat-loss  by  the  lungs  for  51  men  (calculated  for  the  24 
hours)  was  312,000  small  calories  for  normal,  919,000  for  the  fastest,  and 
195,000  for  the  slowest  breathing. 


PRACTICAL  EXERCISES  515 

Now,  the  quantity  of  heat  rendered  latent  in  the  evaporation  of  water 
sufficient  to  saturate  a  given  quantity  of  air  at  40°  C.  (the  expired  air 
is  saturated  for  body  temperature)  is  six  times  that  required  to  saturate 
the  same  quantity  of  air  at  10°.  If,  then,  the  inspired  air  is  half 
saturated,  the  error  under  this  head  is  ^ ,  or  8J  per  cent.  If  the 
inspired  air  is  three-quarters  saturated,  the  error  is  ^T,  or  about 
4  per  cent.  If  the  air  is  fully  saturated  before  inspiration,  as  is  the 
case  when  it  is  drawn  in  through  a  water- valve  (Fig.  142)  by  a  tube 
fixed  in  one  nostril,  the  only  error  is  that  due  to  the  slight  excess  of 
temperature  of  the  air  leaving  the  calorimeter  over  that  of  the  inspired 
air.  The  latent  heat  of  the  aqueous  vapour  in  saturated  air  at  10-5°  C. 
is  about  ^5-  more  than  the  latent  heat  of  the  aqueous  vapour  in 
the  same  mass  of  saturated  air  at  10°  C.,  or  about  —^  of  the  latent 
heat  in  saturated  air  at  40°.  The  error  in  this  case  would  therefore 
be  under  i  per  cent.  The  tubes  must  be  wide  and  the  bottle  large. 

4.  Variations  in  the  Quantity  of  Urea  excreted,  with  Variations 
in  the  Amount  of  Proteids  in  the  Food. — The  student  should  put 
himself,  or  somebody  else  if  he  can,  for  two  days  on  a  diet  poor  in 
proteids,  then  (after  an  interval  of  forty-eight  hours  on  his  ordinary 
food)  for  two  days  on  a  diet  rich  in  proteids.     A  suitable  table  of  diets 
will  be  supplied.    The  urine  should  be  collected  on  the  six  days  of  the 
period  of  experiment,  on  the  day  before  it  begins,  and  on  the  day  after 
it  ends.     Small  samples  of  the  mixed  urine  of  the  twenty-four  hours 
for  each  of  these  eight  days  should  be  brought  to  the  laboratory,  and 
the  quantity  of  urea  determined  by  the  hypobromite  method.     The 
volume  of  the  urine  passed  in  each  interval  of  twenty-four  hours 
being  known,  the  total  excretion  of  urea  for  the  twenty-four  hours 
can  be  calculated,  and  a  curve  plotted  to  show  how  it  varies  during 
the  period  of  experiment.* 

5.  Thyroidectomy. — Study  the  anatomy  of  the  neck  and  the  rela- 
tions and  blood-supply  of  the  thyroid  glands  in  a  dog  used  for  some 
previous  experiment. 

(i)  Then  select  a  half-grown  dog,  weigh  it,  inject  morphia  subcu- 
taneously  (p.  176),  and  fasten  on  the  holder  back  down.  Clip  the  hair 
from  the  neck,  and  shave  a  wide  space  on  each  side  of  the  middle 
line.  Scrub  with  soap  and  water,  then  with  corrosive  sublimate  solu- 
tion (o-i  per  cent.).  Sponges,  instruments,  ligatures,  etc.,  must  have 
been  boiled  in  water;  the  instruments  are  immersed  in  5  per  cent, 
carbolic  acid  solution,  everything  else  in  the  corrosive  solution.  The 
hands  and  nails  must  be  carefully  cleansed  and  washed  with  the  cor- 
rosive sublimate.  A  longitudinal  incision  is  made  through  the  skin  and 
subcutaneous  tissue  in  the  middle  line  of  the  neck,  beginning  a  little 
below  the  projecting  thyroid  cartilage.  By  separating  the  longitudinal 
muscles  just  external  to  the  trachea  on  one  side,  the  corresponding 
thyroid  lobe  will  be  seen  as  an  oval  red  body.  It  is  now  to  be  care- 

*  In  17  healthy  students  the  average  amount  of  urea  excreted  in  twenty- 
four  hours  on  the  ordinary  diet  was  29*51  grm.  (minimum  19*35  §Trm'> 
maximum  46*007  grm.)  ;  on  a  diet  poor  in  proteid,  average  2075  grm- 
(minimum  9-517  grm.,  maximum  32-857  grm.)  ;  on  a  diet  rich  in  proteid, 
average  38*83  grm.  (minimum  23*265  grm.,  maximum  67-82  grm.). 

33—2 


516  A  MANUAL  OF  PHYSIOLOGY 

fully  freed  from  its  attachments ;  all  vessels  connected  with  it  are  to 
be  tied  with  double  ligatures,  and  divided  between  the  ligatures.  In 
tying  the  superior  thyroid  artery  (a  short  large  vessel  coming  off  from 
the  carotid),  care  must  be  taken  not  to  put  the  ligatures  too  near  its 
origin,  as  the  rapid  current  in  the  carotid  may  prevent  closure  of  the 
vessel  by  clot,  and  secondary  haemorrhage  may  occur  some  days  after 
the  operation.  The  thyroid  lobe  is  thus  shelled  out  of  the  tissues  in 
which  it  lies.  If,  as  rarely  happens,  an  isthmus  is  present  (connecting 
the  two  lobes  across  the  front  of  the  trachea),  it  must  also  be  removed. 
All  bleeding  having  been  stopped,  the  wound  is  washed  out  with 
corrosive  solution,  and  the  muscles  brought  together  over  the  trachea 
by  a  row  of  interrupted  sutures,  which  should  not  be  drawn  too 
tight.  The  wound  in  the  skin  is  then  closed  by  a  similar  row, 
preferably  of  subcutaneous  sutures  (see  p.  190).  Collodion  is 
painted  over  the  wound,  and  the  animal  is  returned  to  its  cage.  It 
should  be  kept  for  a  week,  or,  better,  a  fortnight,  and  examined  care- 
fully during  that  time.  Probably,  unless  the  wound  has  become 
infected,  its  behaviour  will  be  perfectly  normal. 

(2)  The  second  part  of  the  experiment,  which  consists  in  removing 
the  remaining  thyroid  lobe,  is  now  to  be  performed  just  as  in  ( i ).  The 
animal  must  be  examined  next  morning,  and  then  twice  a  day  for  the 
following  week,  as  the  symptoms  of  cachexia  strumipriva  generally 
come  on  very  rapidly  in  young  dogs,  and  death  may  even  ensue 
within  two  days.  Trembling  of  the  limbs,  associated  with  instability 
of  movement,  spasms  resembling  those  of  tetany,  sometimes  passing 
into  general  epileptiform  convulsions,  and  progressive  emaciation, 
are  the  most  marked  symptoms.  The  animal  must  be  weighed  daily, 
the  temperature  taken  in  the  rectum,  the  thermometer  being  always 
pushed  in  to  the  same  distance  ;  and  it  will  also  be  well  to  determine 
the  number  of  the  red  corpuscles  in  samples  of  the  blood.  To 
obtain  the  samples  punctures  may  be  made  in  the  gluteal  region  with 
the  point  of  a  narrow-bladed  knife  or  lancet,  the  skin  having  been 
first  shaved  and  thoroughly  dried.  The  blood  should  flow  freely 
without  pressure  (p.  61).  A  record  of  the  experiment  from  the 
operation  to  the  autopsy  must  be  kept.  At  the  autopsy  search  must 
be  made  to  see  whether  the  thyroid  was  completely  removed,  and 
whether  any  accessory  thyroids  exist.  Such  are  occasionally  found 
in  the  form  of  small  reddish  masses,  either  in  the  neck  or  within  the 
chest  in  the  neighbourhood  of  the  aorta.  If  any  are  found,  they 
must  be  hardened  in  alcohol  and  sections  made.  Portions  of  the 
muscles,  spleen,  and  central  nervous  system  are  also  to  be  preserved  ; 
and  it  is  to  be  observed  whether  the  pituitary  body  has  undergone 
any  increase  in  size  or  other  change  (pp.  474,  475). 

6.  Thyroidectomy  with  Thyroid  Feeding. — Some  of  the  members 
of  the  class  should  modify  experiment  5  by  feeding  the  animal,  as 
soon  as  symptoms  have  appeared,  with  fresh  sheep's  thyroid  glands 
or  commercial  thyroid  extracts,  and  noting  any  alleviation  of  the 
symptoms.  If,  as  only  rarely  happens,  they  disappear,  the  animal  is 
to  be  allowed  to  live  for  a  considerable  time,  then  killed  by  chloro- 
form, an  autopsy  made,  and  portions  of  the  tissues  hardened  and 
compared  with  those  from  experiments  done  as  in  5. 


CHAPTER  IX. 
MUSCLE. 


IT  is  impossible  to  understand  the  general  physiology  of  muscle  and 
nerve  without  some  acquaintance  with  electricity.  It  would  be  out 
of  place  to  give  even  a  complete  sketch  of  this  preliminary  but 
essential  knowledge  here ;  and  the  student  is  expressly  warned  that  in 
this  book  the  elementary  facts  and  principles  of  physics  are  assumed 
to  be  part  of  his  mental  outfit.  But  in  describing  some  of  the 
electrical  apparatus  most  commonly  used  in  the  study  of  this  portion 
of  our  subject,  it  may  be  useful  to  recall  the  physical  facts  involved. 

Batteries. — The  Daniell  cell  is  perhaps  better  suited  for  physio- 
logical work  than  any  other 
voltaic  element,  although  for 
special  purposes  Bunsen,  Grove, 
Leclanche,  and  bichromate  of 
potassium  batteries  may  be  em- 
ployed. 

The  Daniell  is  a  two-fluid 
cell.  Saturated  solution  of  sul- 
phate of  copper  is  contained  in 
an  outer  vessel,  and  a  dilute 
solution  of  sulphuric  acid  in  a 
porous  pot  standing  in  the 
copper  sulphate  solution.  The 
latter  is  kept  saturated  by  a  few 
crystals  of  copper  sulphate.  A 
piece  of  sheet-copper,  generally 
bent  so  as  to  form  a  hollow 
cylinder,  dips  into  the  sulphate  of  copper,  and  a  piece  of  amalga- 
mated zinc  into  the  contents  of  the  porous  pot.  Inside  the  cell  the 
current  (the  positive  electricity)  passes  from  zinc  to  copper  ;  outside, 
from  copper  to  zinc.  The  copper  is  called  the  positive,  the  zinc  the 
negative,  pole.  When  the  current  is  passed  through  a  tissue,  the 
electrode  by  which  it  enters  is  termed  the  anode,  and  that  by  which 
it  leaves  the  tissue  the  kathode.  The  anode  is,  therefore,  the  elec- 
trode connected  with  the  copper  of  the  Daniell's  cell :  the  kathode 
is  connected  with  the  zinc. 


FIG.  143.— DANIELL  CELL. 
A,  outer  vessel ;   B,  copper  ;   C,  porous 
pot ;  D,   zinc  rod ;   D  is  supposed  to 
raised  a  little  so  as  to  be  seen. 


be 


5i8  A  MANUAL  OF  PHYSIOLOGY 

Potential — Current  Strength — Resistance. — We  do  not  know 
what  in  reality  electricity  is,  but  we  do  know  that  when  a  current 
flows  along  a  wire  energy  is  expended,  just  as  energy  is  expended 
when  water  flows  from  a  higher  to  a  lower  level.  Many  of  the 
phenomena  of  current  electricity  can,  in  fact,  be  illustrated  by  the  laws 
of  flow  of  an  incompressible  liquid.  The  difference  of  level,  in  virtue 
of  which  the  flow  of  liquid  is  maintained,  corresponds  to  the  difference 
of  electrical  level,  or  potential,  in  virtue  of  which  an  electrical  current 
is  kept  up.  The  positive  pole  of  a  voltaic  cell  is  at  a  higher  potential 
than  the  negative.  When  they  are  connected  by  a  conductor,  a  flow 
of  electricity  takes  place,  which,  if  the  difference  of  level  or  potential 
were  not  constantly  restored,  would  soon  equalize  it,  and  the  current 
would  cease ;  just  as  the  flow  of  water  from  a  reservoir  would  ulti- 
mately stop  if  it  was  not  replenished.  If  the  reservoir  was  small,  and 
the  discharging-pipe  large,  the  flow  would  only  last  a  short  time ;  but 
if  water  was  constantly  being  pumped  up  into  it,  the  flow  would  go  on 
indefinitely.  This  is  practically  the  case  in  the  Daniell  cell.  Zinc  is 
constantly  being  dissolved,  and  the  chemical  energy  which  thus  dis- 
appears goes  to  maintain  a  constant  difference  of  potential  between 
the  poles.  Electricity,  so  to  speak,  is  continually  running  down  from 
the  place  of  higher  to  the  place  of  lower  potential,  but  the  cistern  is 
always  kept  full. 

The  difference  of  electrical  potential  between  two  points  is  called 
the  electromotive  force ;  and  from  its  analogy  with  difference  of  pressure 
in  a  liquid,  it  is  easy  to  understand  that  the  intensity  or  strength  of  the 
current,  that  is,  the  rate  of  flow  of  the  electricity  between  two  points 
of  a  conductor,  does  not  depend  upon  the  electromotive  force  alone, 
any  more  than  the  rate  of  discharge  of  water  from  the  end  of  a  long 
pipe  depends  alone  on  the  difference  of  level  between  it  and  the 
reservoir.  In  both  cases  the  resistance  to  the  flow  must  also  be 
taken  account  of.  With  a  given  difference  of  level,  more  water  will 
pass  per  second  through  a  wide  than  through  a  narrow  pipe,  for  the 
resistance  due  to  friction  is  greater  in  the  latter.  In  the  case  of 
an  electrical  current,  a  wire  connecting  the  two  poles  of  a  Daniell's 
cell  will  represent  the  pipe.  A  thick  short  wire  has  less  resistance 
than  a  thin  long  wire ;  and  for  a  given  difference  of  potential,  of 
electric  level,  a  stronger  current  will  flow  along  the  former.  But  for 
a  wire  of  given  dimensions,  the  intensity  of  the  current  will  vary  with 
the  electromotive  force.  The  relation  between  electromotive  force, 

strength  of  current,  and  resistance  were  experimentally  determined  by 
•p 

Ohm,  and  the  formula  C  =  ^,  which  expresses  it,  is  called  Ohm's  Law. 
K. 

It  states  that  the  current  varies  directly  as  the  electromotive  force, 
and  inversely  as  the  resistance. 

Although  we  do  not  know  in  what  electrical  resistance  consists,  it 
may  be  defined  as  that  property  of  a  conductor  in  virtue  of  which  a 
flow  of  electricity  cannot  be  kept  up  through  it  without  the  expendi- 
ture of  energy.  In  treating  of  the  circulation  of  the  blood,  we  have 
already  seen  that  the  flow  of  a  liquid  along  a  tube  involves  the 
expenditure  of  energy  to  overcome  the  friction  of  the  liquid  molecules 


MUSCLE  519 

on  each  other,  and  that  this  energy  is  transformed  into  heat  (p.  72). 
In  like  manner  electrical  energy  is  transformed  into  heat  whenever  a 
current  flows  along  a  wire.  The  heat  produced  in  a  circuit  in  which 
no  external  work  is  done  is  exactly  equal  to  the  energy  which  has  dis- 
appeared in  the  transference  of  the  electricity  from  the  place  of  higher 
to  the  place  of  lower  potential ;  just  as  the  heat  produced  in  the  flow 
of  a  liquid  is  equal  to  the  difference  in  its  total  energy  at  the 
beginning  and  end  of  the  path.  If  C  is  the  current  strength,  and  E 
the  electromotive  force,  the  energy  represented  by  the  transference  of 
electricity  in  time  t  is  EC/,  or  (since  E  =  CR  by  Ohm's  Law),  C2R/; 
and  tnis  represents  the  heat  produced  in  the  circuit  when  no  work 
is  done. 

For  the  measurement  of  electrical  quantities  a  system  of  units  is 
necessary.  The  common  unit  of  resistance  is  the  ohm,  of  current  the 
ampere,  of  electromotive  force  the  volt.  The  electromotive  force  of  a 
Daniell's  cell  is  about  a  volt.  An  electromotive  force  of  a  volt, 
acting  through  a  resistance  of  an  ohm,  yields  a  current  of  one 
ampere ;  but  the  current  produced  by  a  Daniell's  cell,  with  its  poles 
connected  by  a  wire  of  i  ohm  resistance,  would  be  less  than  an 
ampere,  because  the  internal  resistance  of  the  cell  itself,  that  is,  the 
resistance  of  the  liquids  between  the  zinc  and  the  copper,  must  be 
added  to  the  external  resistance  in  order  to  get  the  total  resistance, 
which  is  the  quantity  represented  by  R  in  Ohm's  Law. 

Measurement  of  Resistance. — To  find  the  resistance  of  a  con- 
ductor, we  compare  it  with  known  resistances,  as  a  grocer  finds  the 


FIG.  144.—  WHEATS-TONE'S  FIG.  145.— DIAGRAM  OF  RESISTANCE 

BRIDGE.  Box. 

weight  of  a  packet  of  tea  by  comparing  it  with  known  weights.  The 
Wheatstone's  bridge  method  of  measuring  resistance  depends  on  the 
fact  that  if  four  resistances,  AB,  AD,  BC,  CD,  are  connected,  as  in 
Fig.  143,  with  each  other,  and  with  a  galvanometer  G  and  a  battery  F, 

A  T»       Tif 
no  current  will  flow  through  the  galvanometer  when  —-^  =  ^-^.- 

AU        v_y  LJ 

For  when  no  current  passes  through  the  galvanometer,  B  and  D 
are  at  the  same  potential.  Let  the  fall  of  potential  from  C  to  B  or 
from  C  to  D  be  a ;  then,  since  the  total  fall  of  potential  from  C  to  A 
must  be  the  same  along  either  of  the  paths  CBA  or  CDA,  the  fall  from 
B  to  A  must  be  equal  to  that  from  D  to  A.  Call  this  /?.  Now,  the 


52o  A  MANUAL  OF  PHYSIOLOGY 

fall  of  potential  which  takes  place  in  any  given  portion  of  a  circuit  is 
to  the  whole  fall  of  potential  in  the  circuit  as  the  resistance  of  the 
given  portion  is  to  the  whole  resistance.  That  is, 

a  BC 


a  +  ft     BC+AB' 
ft  AB  m      a_BC 

a+ft~BC+AB;     "     ft~AB' 
0.    ..    .      «     CD  BC     CD        AB     BC 

Similarly:     -.  .-.    £B  =  AD'  °r  AD  =  CD' 


In  making  the  measurement,  a  resistance-box,  containing  a  large 
number  of  coils  of  wire  of  different  resistances,  is  used  (Fig.  145). 
The  resistances  corresponding  to  AB  and  AD,  called  the  arms  of  the 
bridge,  may  be  made  equal,  or  may  stand  to  each  other  in  a  ratio 


FIG,  146. — SCHEME  OF  WIEDEMANN'S  GALVANOMETER  (WITH  TELESCOPE 

READING). 

T,  telescope  ;  S,  scale ;  M,  mirror ;  m,  ring  magnet  suspended  between  the  two 
galvanometer  coils  G,  the  distance  of  which  from  m  can  be  varied  ;  F,  fibre  suspending 
mirror  and  magnet. 

of  t  :  10,  i  :  ioo,  etc.  Then,  the  unknown  resistance  being  CD, 
BC  is  adjusted  by  taking  plugs  out  of  the  box  till,  on  closing  the 
current,  there  is  either  no  deflection,  or  the  deflection  is  as  small  as 
it  is  possible  to  make  it  with  the  given  arrangement. 

Galvanometer. — A  galvanometer  is  an  instrument  used  to  detect  a 
current,  to  determine  its  direction,  and  to  measure  its  intensity. 
Since,  by  Ohm's  law,  electromotive  force,  resistance,  and  current 
strength  are  connected  together,  any  one  of  them  may  be  measured 
by  the  galvanometer.  A  galvanometer  of  the  kind  ordinarily  used  in 
physiology  consists  essentially  of  a  small  magnet  suspended  in  the 
axis  of  a  coil  of  wire,  and  free  to  rotate  under  the  influence  of  a 
current  passing  through  the  coil.  The  most  sensitive  instruments 
possess  a  small  mirror,  to  which  the  magnet  is  rigidly  attached,  A 
ray  of  light  is  allowed  to  fall  on  the  mirror,  from  which  it  is  reflected 
on  to  a  scale  ;  and  the  rotation  of  the  mirror  is  magnified  and 
measured  by  the  excursion  of  the  spot  of  light  on  the  scale.  In 


MUSCLE  521 

the  Thomson  galvanometers  the  magnet  is  very  light.  A  strip  or 
two  of  magnetized  watch-spring  does  very  well.  The  magnet  is 
'  damped,'  that  is,  its  tendency,  when  once  displaced,  to  go  on 
oscillating  about  its  new  position  of  equilibrium  is  overcome  by 
enclosing  it  in  a  narrow  air  space.  In  the  Wiedemann  instrument  the 
magnet  is  heavier  (Fig.  146).  It  swings  in  a  chamber  with  copper 
walls.  Eve/y  movement  of  the  magnet  '  induces '  currents  in  the 
copper ;  these  tend  to  oppose  the  movement,  and  so  '  damping '  is 
obtained.  It  is  usual  to  read  the  deflections  of  the  Wiedemann 
galvanometer  by  means  of  a  telescope.  An  inverted  scale  is  placed 
over  the  telescope  at  a  distance  of,  say,  a  metre  from  the  mirror ;  an 
upright  image  of  the  scale  is  formed  in  the  telescope  after  reflection 
from  the  mirror,  and  with  every  movement  of  the  latter  the  scale 
divisions  appear  to  move  correspondingly.  The  method  of  reading 
by  a  telescope  can  be  applied  to  any  mirror  galvanometer,  and  is 
often  extremely  convenient  in  physiological  work.  Sometimes  a 
small  scale  is  fastened  on  the  mirror  itself,  and  observed  directly 
through  a  low-power  microscope. 

A  suspended  magnet,  if  no  other  magnets  are  near,  takes  up  a 
definite  position  under  the  influence  of  the  earth's  magnetism  ;  its 
long  axis,  in  the  position  of  rest,  lies  in  a  vertical  plane,  called  the 
plane  of  the  magnetic  meridian  at  the  given  place.  The  '  marked  ;  or 
north  pole  points  north,  the  south  pole  south.  If  the  magnet  is  dis- 
turbed from  this  position,  it  tends  to  return  to  it  as  soon  as  the  dis- 
turbing force  ceases  to  act.  If,  for  instance,  the  north  pole  is  displaced 
in  an  eastward  direction,  the  earth's  magnetism  will  produce  a  couple 
{a  pair  of  parallel  forces  acting  in  opposite  directions),  one  member 
of  which  may  be  considered  to  pull  the  north  pole  towards  the  west, 
and  the  other  to  pull  the  south  pole  towards  the  east.  Displacement 
of  the  magnet,  then,  is  opposed  by  this  couple  \  and  where  the  dis- 
placing force  is  small,  that  is,  the  current  passing  through  the  galva- 
nometer weak,  as  is  usually  the  case  in  physiological  observations,  it 
becomes  important  to  reduce  the  effect  of  the  magnetism  of  the 
•earth,  in  other  words,  the  strength  of  the  magnetic  field,  as  much  as 
possible.  This  can  be  done  by  bringing  a  magnet  into  the  neigh- 
bourhood of  the  galvanometer  with  its  north  pole  pointing  north. 
This  pole,  which  is  the  one  attracted  by  the  earth's  north  pole,  is 
magnetized  in  the  opposite  sense ;  and  by  properly  adjusting  its 
•distance  from  the  galvanometer  magnet,  the  influence  of  the  earth 
on  the  latter  can  be  almost  neutralized,  and  the  system  made  nearly 
'  astatic.'  In  many  galvanometers  the  magnets  attached  to  the  mirror 
form  an  *  astatic  '  pair  (Fig.  147).  Two  small  magnets  of  nearly  equal 
strength  are  connected  to  a  light  slip  of  horn  or  an  aluminium  wire, 
with  their  poles  in  opposite  directions.  The  earth's  magnetism  affects 
them  oppositely,  so  that  the  resultant  action  is  nearly  zero.  It  is  not 
possible  to  make  the  magnets  exactly  equal  in  strength,  nor  is  it 
desirable,  for  then  the  system  would  not  tend  to  come  to  rest  in 
any  definite  position,  and  the  zero  point  would  be  constantly  shifting. 
Either  one  or  both  magnets  may  be  surrounded  by  the  galvanometer 
coils.  If  both  are  so  surrounded,  each  must  be  within  a  separate 


522 


A  MANUAL  OF  PHYSIOLOGY 


FIG.  147. — ASTATIC  PAIR 
OF  MAGNETS. 


FIG.  149.— COMPENSATOR. 


FIG.  148. — DIAGRAM  OF  RHEOCORD 
(AFTER  Du  Bois  -  REYMOND'S 
MODEL). 


Description  of  Fig.  147.— SN  and  NS  are  the  magnets,  fixed  to  the  vertical  piece  P. 
M  is  a  mirror.  The  arrow-heads  show  the  direction  of  a  current  which  deflects  both 
magnets  in  the  same  direction. 

Description  of  Fig.  148.— I.  to  VII.  are  pieces  of  brass  connected  with  the  wires 
a  to/ in  such  a  way  that  by  taking  out  any  of  the  brass  plugs  i  to  5,  a  greater  or  less 
resistance  may  be  interposed  between  the  binding  screws  A  and  B.  The  two  wires  a 
are  connected  by  a  slider  s,  filled  with  mercury  or  otherwise  making  contact  between 
the  wires.  The  current  from  the  battery  B'  divides  at  A  and  B,  part  of  it  passing 
through  the  rheocord,  part  through  N,  the  nerve,  muscle,  or  other  conductor  which 
forms  the  alternative  circuit.  When  a  sufficient  resistance  R  is  interposed  in  the  chief 
circuit  to  make  the  total  strength  of  the  current  independent  of  changes  in  the 
resistance  of  the  rheocord,  the  strength  of  the  current  passing  through  N  will  vary 
inversely  as  the  resistance  of  the  rheocord.  When  all  the  plugs  are  in,  and  the  slider 
close  up  to  A,  there  is  practically  no  resistance  in  the  rheocord,  and  all  the  current 
passes  across  the  brass  pieces  and  plugs  to  B,  and  thence  back  to  the  battery.  As  s  is 
moved  further  away  from  A,  the  resistance  of  the  rheocord  is  increased  more  and 
more,  and  the  intensity  of  the  current  passing  through  N  becomes  greater  and  greater. 
The  scale  S  shows  the  length  of  wire  interposed  for  any  position  of  s,  and  this  gives  a 
rough  measure  of  the  fraction  of  the  current  passing  through  N.  When  plug  i  or  2  is 
taken  out,  a  resistance  equal  to  that  of  the  two  wires  a  is  interposed ;  plug  3,  twice  that 
of  a  ;  plug  4,  five  times  ;  plug  5,  ten  times. 

Description  of  Fig.  149. — W  is  a  wire  stretched  alongside  a  scale  S.  A  battery  B  is 
connected  to  the  binding  screws  at  the  ends  of  the  wire.  A  pair  of  unpolarizable  elect  rodes 
are  connected,  one  with  a  slider  moving  on  a  wire,  the  other  through  a  galvanometer 
with  one  of  the  terminal  binding  screws.  In  the  figure  a  nerve  is  shown  on  the  elec- 
trodes, one  of  which  is  in  contact  with  an  uninjured  portion,  the  other  with  an  injured 
part.  The  slider  is  moved  until  the  twig  of  the  compensating  current  just  balances  the 
demarcation  current  of  the  nerve  and  the  galvanometer  shows  no  deflection. 


MUSCLE  523 

coil,  and  the  current  must  pass  in  opposite  directions  in  the  two  coils, 
otherwise  they  would  neutralize  each  other. 

The  deflection  of  a  magnet  by  a  current  of  given  strength  is  pro- 
portional to  the  number  of  turns  of  wire  around  it.  Where  an 
increase  in  the  number  of  turns  does  not  sensibly  cut  down  the 
current,  as  in  experiments  on  tissues  like  nerves,  whose  resistance  is 
large  in  comparison  with  that  of  the  galvanometer,  an  instrument 
with  a  great  number  of  turns  of  wire,  that  is,  a  high-resistance 
galvanometer,  is  suitable.  The  resistance  of  the  galvanometers 
generally  used  in  electro-physiology  varies  from  3,000  or  4,000  ohms 
up  to  five  times  as  much. 

A  rheocord  is  an  instrument  by  means  of  which  a  current  may  be 
divided,  and  a  definite  portion  of 
it  sent  through  a  tissue  (Fig.  148). 

A  compensator  is  simply  a 
rheocord  from  which  a  branch  of 
a  current  is  led  off,  to  balance  or 
'  compensate  '  any  electrical  dif- 
ference in  a  tissue,  like  that  which 
gives  rise  to  the  current  of  rest  of 
a  muscle,  for  example  (Fig.  149). 

An  electrometer  is  an  instru- 
ment for  measuring  electromotive 
force,  that  is,  differences  of  electric 
potential.  Lippmann's  capillary 
electrometer  is  being  more  and  FIG.  ISO.-DIAGRAM  OF  A  SIMPLE 
more  employed  in  physiology.  A  ™™R  OF  CAPILLARY  ELECTR°- 
simple  form  can  be  conveniently  fi  parallel.sided  glass  bottle  containing 
made  as  follows.  A  glass  tube  IS  sulphuric  acid,  S  ;  Hg,  nvercury  in  glass 
drawn  OUt  to  a  capillary  at  One  tube,  the  capillary  end  of  which  projects 

end  and  filled  with  mercury.    The  £»j£*;*£B  SS&t! 

tube     IS      inserted     into     a     small   capillary  with  a  pressure  bottle ;  C,  capil- 

parallel- sided    glass    bottle,    and  lary  magnified, 
fastened  in  its  neck  with  a  plug 

of  sealing-wax.  The  bottle  is  partially  filled  with  10  to  20  per 
cent,  sulphuric  acid,  under  which  the  capillary  dips.  By  means  of 
a  small  pressure-bottle  filled  with  mercury,  and  connected  with  the 
glass  tube,  a  little  mercury  is  forced  through  the  capillary  so  as  to 
expel  the  air  in  it.  When  the  pressure  is  lowered  again,  sulphuric 
acid  is  drawn  up,  and  now  lies  in  the  capillary  in  contact  with  the 
meniscus  of  the  mercury.  A  platinum  wire  fused  through  the  tube 
dips  into  the  mercury.  Another,  passing  through  the  sealing-wax, 
makes  contact  with  the  sulphuric  acid  through  some  mercury  at  the 
bottom  of  the  bottle.  The  bottle  is  fastened  on  the  stage  of  a  micro- 
scope, the  capillary  brought  into  focus,  and  the  meniscus  adjusted 
by  raising  or  lowering  the  pressure-bottle.  When  the  platinum  wires 
are  connected  with  points  at  different  potential,  the  mercury  and 
sulphuric  acid  receive  charges  at  their  surfaces  of  contact  in  the 
capillary  tube,  by  which  the  equilibrium  previously  existing  between 
the  three  surface -tensions  (between  mercury  and  glass,  between 


524 


A  MANUAL  OF  PHYSIOLOGY 


sulphuric  acid  and  glass,  between  sulphuric  acid  and  mercury)  and 
the  hydrostatic  pressure  of  the  mercury  is  disturbed,  and  the 
mercurial  meniscus  moves  along  the  capillary.  If  the  mercury  is 
connected  with  a  surface  at  a  higher  potential  than  that  in  con- 
nection with  the  sulphuric  acid,  the  meniscus  moves  towards  the 
point  of  the  capillary,  and  vice  versa. 

Induced  Currents. — When  a  coil  of  wire  in  which  a  current  is 
flowing  is  brought  up  suddenly  to  another  coil,  a  momentary  current 
is  developed  in  the  stationary  coil  in  the  opposite  direction  to  that 
in  the  moving  coil.  Similarly,  if  instead  of  one  of  the  coils  being 
moved  a  current  is  sent  through  it,  while  the  other  coil  remains  at 
rest  in  its  neighbourhood,  a  transient  oppositely-directed  current  is 

It  consists  (i)  of  a  small 
table  carrying  a  parallel- 
sided  glass  vessel  con- 
taining mercury  and  sul- 
phuric acid.  (2)  The 
capillary  tube,  which  can 
be  moved  in  two  direc- 
tions at  right  angles  to 
each  other,  and  so  ad- 
justed in  the  field  of  the 
microscope.  (3)  A  pres- 
sure-vessel, and  a  mano- 
meter connected  with  it 
for  measuring  the  pres- 
sure. (4)  Two  binding- 
screws  connected  by  wires 
to  the  mercury  in  the 
capillary  tube  and  in  the 
parallel-sided  vessel.  The 
binding-screws  can  he 
short-circuited  by  closing 
the  friction-key  shown  at 
the  right  side  of  the  figure, 
thus  preventing  any  dif- 
ference of  electromotive 
force  between  two  points 
connected  with  the  screws 
from  affecting  the  eltctro- 
meter. 

FIG.  151. — CAPILLARY  ELECTROMETER  (AFTER  FREY),  AS  ARRANGED  FOR 
MOUNTING  ON  THE  MICROSCOPE  STAGE. 


set  up  in  the  latter.  When  the  current  in  the  first  coil  is  broken,  a 
current  in  the  same  direction  is  induced  in  the  other  coil. 

Du  Bois-Reymond's  Sledge  Inductorium  (Fig.  152). — This  consists 
of  two  coils,  the  primary  and  the  secondary,  the  former  having  a 
comparatively  small  number  of  turns  of  fairly  thick  copper  wire,  the 
latter  a  large  number  of  turns  of  thin  wire.  The  object  of  this  is 
that  the  resistance  of  the  primary,  which  is  connected  with  one  or 
more  voltaic  cells,  may  not  cut  down  the  current  too  much ;  while 
the  currents  induced  in  the  secondary,  having  a  high  electromotive 
force,  can  readily  pass  through  a  high  resistance,  and  are  directly 
proportional  in  intensity  to  the  number  of  turns  of  the  wire. 

By  means  of  various  binding-screws  and  the  electro-magnetic 
interrupter,  or  Neef's  hammer,  shown  in  the  figure  and  explained 


MUSCLE  525 

below  it,  the  current  can  be  made  once  in  the  primary  or  broken 
once,  or  a  constant  alternation  of  make  and  break  can  be  kept  up. 
We  can  thus  get  a  single  make  or  break  shock  in  the  secondary,  or  a 
series  of  shocks,  sometimes  called  an  interrupted  current.  Such  a 
series  of  stimuli  can  also  be  got  by  making  and  breaking  a  voltaic 
current  at  any  given  rate. 

A  *  self-induced  '  current  can  also  be  obtained  from  a  single  coil ; 
for  instance,  from  the  primary  coil  alone  of  the  induction  apparatus. 
The  reason  of  this  is,  that  when  a  current  begins  to  flow  through  any 
turn  of  a  coil  of  wire,  it  induces  in  all  the  other  turns  a  current  in  the 
opposite  direction,  and,  when  it  ceases  to  flow,  a  current  in  the  same 
direction  as  itself.  The  former  current,  '  the  make  extra  shock,' 
being  in  the  opposite  direction  to  the  inducing  current,  is  retarded  in 
its  development,  and  reaches  its  maximum  more  slowly  than  the  break 
extra  shock.  But,  as  we  shall  see,  the  suddenness  with  which  an 


FIG.  152. — Du  BOIS-REYMOND'S  INDUCTORIUM. 

B,  primary,  B',  secondary,  coil  ;  H,  guides  in  which  B'  slides,  with  scale ;  D,  electro- 
magnet ;  E,  vibrating  spring  ;  i,  wire  connecting  wire  of  D  to  end  of  primary  ;  v,  screw 
with  platinum  point,  connected  with  other  end  of  primary  ;  A,  A',  binding  screws  to 
which  are  attached  the  wires  from  battery.  A'  is  connected  with  the  wire  of  the  electro- 
magnet D,  and  through  it  and  i  with  the  primary. 

electrical  change  is  brought  about  is  one  of  the  most  important  factors 
in  electrical  stimulation,  and  therefore  the  break  extra  shock  is  a 
much  more  powerful  stimulus  than  the  make.  Owing  to  these  self-! 
induced  currents,  the  stimulating  power  of  a  voltaic  stream  may  be 
much  increased  by  putting  into  the  circuit  a  coil  of  wire  of  not  too 
great  resistance. 

The  self-induction  of  the  primary  also  affects  the  stimulating  power 
of  the  currents  induced  in  the  secondary  ;  the  shock  induced  in  the 
secondary  by  break  of  the  primary  current  is  a  stronger  stimulus 
than  that  caused  at  make  of  the  primary.  The  reason  is,  that  with  a 
given  distance  of  primary  and  secondary,  and  a  given  intensity  of  the 
voltaic  current  in  the  primary,  the  abruptness  with  which  the  induced 
current  in  the  secondary  is  developed  depends  upon  the  rapidity 


526  A  MANUAL  OF  PHYSIOLOGY 

with  which  the  primary  current  reaches  its  maximum  at  closing,  or 
its  minimum  (zero)  at  opening.  Now,  the  make  extra  current  retards 
the  development  of  the  primary  current,  while  in  the  opened  circuit 
of  the  primary  coil  the  current  intensity  falls  at  once  to  zero. 

The  inequality  between  the  make  and  break  shocks  of  the 
secondary  coil  can  be  greatly  reduced  by  means  of  Helmholtz's  wire. 
Connect  one  pole  of  the  battery  with  v  (Fig.  152),  and  the  other 
with  A'.  Join  A  and  A'  by  a  short,  thick  wire.  With  this  arrange- 
ment the  primary  circuit  is  never  opened,  but  the  current  is  alter- 
nately allowed  to  flow  through  the  primary,  and  short-circuited 
when  the  spring  touches  v.  The  'make'  now  corresponds  to  the 
sudden  increase  of  intensity  of  the  current  in  the  primary  when  the 
short-circuit  is  removed,  and  the  '  break '  to  its  sudden  decrease 
when  the  short-circuit  is  established.  In  both  cases  self-induced 
currents  are  developed,  and  therefore  both  shocks  are  weakened. 
But  the  opening  stimulus  is  now  slightly  the  weaker  of  the  two, 


FIG.  153. — UNPOLARIZABLE  ELECTRODES. 

A,  hook-shaped ;  B,  U-tubes  ;  C,  straight.  D,  clay  in  contact  with  tissue ;  S, 
saturated  zinc  sulphate  solution  ;  Z,  amalgamated  zinc  wire. 

because  the  opening  extra  shock  has  to  pass  through  a  smaller 
resistance  (the  short-circuit)  than  the  closing  extra  shock  (which 
passes  by  the  battery),  and  therefore  opposes  the  decline  of  current 
intensity  on  short-circuiting,  more  than  the  closing  shock  opposes 
the  increase  of  current  intensity  on  long-circuiting  through  the 
primary. 

By  means  of  wires  connected  with  the  terminals  of  the  secondary 
coil,  and  leading  to  electrodes,  a  nerve  or  muscle  may  be  stimulated ; 
and  it  is  usual  to  connect  the  wires  to  a  short-circuiting  key  (Fig. 
155),  by  opening  which  the  induced  current  is  thrown  into  the  tissue 
to  be  stimulated.  For  some  purposes  the  electrodes  may  be  of 
platinum ;  but  all  metals  in  contact  with  moist  tissues  become 
polarized  when  currents  pass  through  them,  that  is,  have  decom- 
position products  of  the  electrolysis  of  the  tissues  deposited  on  them. 
And  as  any  slight  chemical  difference,  or  even  perhaps  a  difference 
of  physical  state,  between  the  two  electrodes  will  cause  them  and  the 
tissues  to  form  a  battery  evolving  a  continuous  current,  it  is  often 
desirable  to  use  unpolarizable  electrodes. 

Unpolarizable  Electrodes. — Some  convenient  forms  of  these  are 
represented  in  Fig.  153.  A  piece  of  amalgamated  zinc  wire  dips  into 


MUSCLE  527 

saturated  zinc  sulphate  solution  contained  in  the  upper  part  of  a  glass 
tube.  The  lower  end  of  the  tube  may  be  straight,  but  drawn  out  so 
as  to  terminate  in  a  not  very  large  opening,  or  it  may  be  bent  into  a 
hook,  in  the  bend  of  which  a  hole  is  made.  Before  the  tube  is 
filled  with  the  zinc  sulphate  solution,  the  lower  part  of  it  is  plugged 
with  china  clay  made  up  with  normal  saline.  The  clay  just  projects 
through  the  opening,  and  thus  comes  in  contact  with  the  tissue. 
When  these  electrodes  are  properly  set  up,  there  is  very  little  polariza- 
tion for  several  hours,  but  for  long  experiments,  U-shaped  tubes,  filled 
with  saturated  zinc  sulphate  solution,  are  better.  The  amalgamated 
zinc  dips  into  one  limb,  and  a  small  glass  tube  filled  with  clay,  on 
which  the  tissue  is  laid,  into  the  other. 

Pohl's  Commutator  (Fig.  154)  consists  of  a  block  of  paraffin  or 
wood  with  six  mercury  cups,  each  in  connection  with  a  binding-screw 
(not  shown  in  the  figure).     Cups  i  and 
6  and  2  and  5  are  connected  by  copper 
wires,  which  cross  each  other  without 
touching.     The  bridge   consists    of  a 
glass    or    vulcanite    cross-piece   a,    to 
which  are  attached  two  wires  bent  into 
semicircles,    each    connected    with    a 
straight  wire  dipping  into  the  cups  3 
and  4  respectively.     With  the  bridge 
in  the  position  shown  in  the  figure,  a 
current  coming  in  at  4  would  pass  out          FIG.  154.— POHL'S  COM- 
by  the  wire  connected  with  i,  and  back  MUTATOR. 

again  by  that  connected  with  2,  in  the 

direction  shown  by  the  arrows.  When  the  bridge  is  rocked  to  the 
other  side  so  that  the  bent  wires  dip  into  5  and  6,  the  direction  of 
the  current  is  reversed.  The  cross-wires  may  be  taken  out  altogether, 
and  the  commutator  used  to  send  a  current  at  will  through  either  of 
two  circuits,  one  connected  with  i  and  2,  and  the  other  with  5 
and  6. 

Du  Bois-Reymond's  Short-circuiting  Key. — -A  cheap  and  convenient 
form  is  shown  in  Fig.  155. 

Time-Markers — Electric  Signal. — It  is  of  importance  to  know  the 
time  relations  of  many  physiological  phenomena  which  are  graphically 
recorded ;  for  example,  the  contraction  of  a  skeletal  muscle  or  the 
beat  of  a  heart.  For  this  purpose  a  tracing  showing  the  speed  of 
the  travelling-surface  in  a  given  time  is  often  taken  simultaneously 
with  the  record  of  the  movement  under  investigation.  For  a  slowly- 
moving  surface  it  is  sufficient  to  mark  intervals  of  one  or  two  seconds, 
and  this  is  very  readily  done  by  connecting  an  electro-magnetic 
marker  (such  as  the  electric  signal  of  Deprez)  with  a  circuit  which  is 
closed  and  broken  by  the  seconds  pendulum  of  an  ordinary  clock 
(Fig.  156)  or  a  metronome  (Fig.  60,  p.  170).  For  shorter  intervals 
a  tuning-fork  is  used,  which  makes  and  breaks  a  circuit  including  an 
electro-magnetic  marker,  or  writes  on  the  drum  directly  by  means  of 
a  writing-point  attached  to  one  of  the  prongs. 


528 


A  MANUAL  OF  PHYSIOLOGY 


In  all  the  great  functions  of  the  body  we  find  that  muscular 
movements  play  an  essential  part.  The  circulation  and  the 
respiration,  the  two  functions  most  immediately  essential  to 
life,  are  kept  up  by  the  contraction  and  relaxation  of  muscles. 
The  movements  of  the  digestive  canal,  the  regulation  of  the 
blood-supply  to  its  glands  and  to  all  parts  of  the  body,  and 
that  immense  class  of  movements  which  we  call  voluntary, 
are  all  dependent  upon  muscular  action,  which,  again,  is 
indebted  for  its  initiation,  continuance,  or  control,  to 
impulses  passing  along  the  nerves  from  the  nerve-centres. 


FIG.  155. — Du  BOIS-REYMOND'S  KEY. 


FIG.  156.— TIME-MARKER. 

Arrangement  for  marking  2  intervals. 
D,  seconds  pendulum,  with  platinum 
point  E  soldered  on ;  A,  mercury  trough, 
into  which  E  dips  at  end  of  its  swing ; 
B,  Daniell  cell;  C,  electro-magnets, 
which  draw  down  writing-lever  F  when 
the  current  is  closed  by  E  dipping  into 
A  ;  G,  spring  (or  piece  of  indiarubber), 
which  raises  F  as  soon  as  current  is 
broken. 


Hitherto  we  have  not  gone  below  the  surface  fact,  that 
muscular  fibres  have  the  power  of  contracting,  either  auto- 
matically, or  in  response  to  suitable  stimuli.  In  this  chapter 
and  the  two  next  we  shall  consider  in  detail  the  general 
properties  of  muscle,  nerve,  and  the  other  excitable  tissues. 
Lying  deeper  than  the  peculiarities  of  individual  muscles, 
muscular  tissue  has  certain  common  properties,  physical, 
chemical,  and  physiological.  The  biceps  muscle  flexes  the 
arm  upon  the  elbow,  and  the  triceps  extends  it.  The 
external  rectus  rotates  the  eyeball  outwards.  The  inter- 
costal muscles  elevate  the  ribs.  The  sphincter  ani  seals  up 
by  a  ring-like  contraction  the  lower  end  of  the  alimentary 


MUSCLE  529 

canal.  These  actions  are  very  different,  but  the  muscles 
that  carry  them  out  are  at  bottom  very  similar.  And  it 
cannot  be  doubted  that  the  functional  differences  are  due 
entirely,  or  almost  entirely,  to  differences  of  anatomical 
connection,  on  the  one  hand  with  bones  and  tendons,  on 
the  o>her  with  the  nerve-cells/of  the  spinal  cord  and  brain. 
The  common  properties  in  which  all  the  skeletal  muscles 
agree  are  the  subject-matter  of  the  general  physiology  of 
striated  muscle. 

The  cardiac  muscle  differs  more,  both  in  structure  and  in 
function,  from  the  skeletal  muscles  than  these  do  among 
themselves ;  the  smooth  muscle  of  the  intestines  and  blood- 
vessels still  more.  But  every  muscular  fibre,  striped  or 
unstriped,  resembles  every  other  muscular  fibre  more  than 
it  does  a  nerve-fibre  or  a  gland-cell  or  an  epithelial  scale. 
The  properties  common  to  all  muscle  make  up  the  general 
physiology  of  muscular  tissue. 

A  nerve-fibre  is  at  first  sight  very  different  from  a  muscular 
fibre.  It  has  diverged  more  widely  from  the  primitive  type 
of  undifferentiated  protoplasm.  It  has  lost  the  power  of 
contraction,  or  contractility,  but  it  retains,  in  common  with 
the  muscle-fibre,  susceptibility  to  stimulation,  or  excitability, 
the  capacity  for  growth,  and  to  a  limited  extent  the  capacity 
for  reproduction.  This  inheritance  of  primitive  properties, 
retained  alike  by  both  tissues,  is  the  basis  of  the  general 
physiology  of  muscle  and  nerve. 

The  electrical  organ  of  the  Torpedo  or  the  Malapterurus 
is  intermediate  in  some  respects  between  muscle  and  nerve, 
and  has  properties  common  to  both. 

In  the  gland-cell  the  chemical  powers  of  native  proto- 
plasm have  been  specialized  and  developed.  Contractility 
has  been,  in  general,  entirely  lost ;  but  excitability  remains. 
The  properties  shared  in  common  by  muscle,  nerve,  electrical 
organ,  gland,  and  certain  other  structures,  make  up  the 
general  physiology  of  the  excitable  tissues. 

Amoeboid  movement  is  the  most  primitive,  the  least  elabo- 
rated form  of  contraction. 

An  amoeba  may  be  seen  under  the  microscope  to  send  out 
pseudopodia,  or  processes,  of  its  substance,  and  to  retract 

34 


530  A  MANUAL  OF  PHYSIOLOGY 

them,  and  it  is  even  able  by  such  movements  to  change  its 
place.  Stimulation  with  induction  shocks  causes  the  whole 
of  the  processes  to  be  drawn  in,  and  the  amoeba  to  gather 
itself  into  a  ball.  This  illustrates  a  universal  property  of 
protoplasm,  excitability,  or  the  power  of  responding  to  certain 
external  influences,  or  stimuli,  by  manifestations  of  the 
peculiar  kind  which  we  distinguish  as  vital  or  physiological. 
Certain  of  the  white  blood-corpuscles  behave  like  the  amoeba; 
and  we  have  already  dwelt  upon  some  of  the  important 
functions  fulfilled  by  such  amoeboid  movement  in  the  higher 
animals  and  in  man.  But  a  great  distinction  between  this 
kind  of  contraction  and  that  of  a  muscular  fibre  is  that  it 
takes  place  in  any  direction. 

Cilia, — Cilia  possess  a  higher  and  more  specialized  grade 
of  contractility.  They  are  very  widely  distributed  in  the 
animal  kingdom ;  and  analogous  structures  are  also  found 
in  many  low  plants,  such  as  the  motile  bacteria. 

In  the  human  subject  ciliated  epithelium  usually  consists 
of  several  layers  of  cells,  the  most  superficial  of  which  are 
pear-shaped,  the  broad  end  being  next  the  surface  and 
covered  with  extremely  fine  processes,  or  cilia,  about  8  /JL  in 
length,  which  are  planted  on  a  clear  band.  It  lines  the 
respiratory  passages,  the  middle  ear  and  Eustachian  tube, 
the  Fallopian  tubes,  the  uterus  above  the  middle  of  the 
cervix,  the  epididymis,  where  the  cilia  are  extremely  long, 
and  the  central  cavity  of  the  brain  and  spinal  cord. 

Ciliary  motion  can  be  very  readily  studied  by  placing  a 
scraping  from  the  palate  of  a  frog,  or  a  small  portion  of  the 
gill  of  a  fresh-water  mussel  under  the  microscope  in  a  drop 
of  normal  saline  solution.  The  motion  of  the  cilia  is  at 
first  so  rapid  that  it  is  impossible  to  make  out  much,  except 
that  a  stream  of  liquid,  recognised  by  the  solid  particles 
in  it,  is  seen  to  be  driven  by  them  in  a  constant  direction 
along  the  ciliated  edge.  When  the  motion  has  become 
less  quick,  which  it  soon  does  if  the  tissue  is  deprived  of 
oxygen,  it  is  seen  to  consist  in  a  swift  bending  of  the  cilia 
in  the  direction  of  the  stream,  followed  by  a  slower  recoil 
to  the  original  position,  which  is  not  at  right  angles  to  the 
surface,  but  sloping  streamwards.  All  the  cilia  on  a  tract 


MUSCLE  531 

of  cells  do  not  move  at  the  same  time  ;  the  motion  spreads 
from  cell  to  cell  in  a  regular  wave.  The  energy  of  ciliary 
motion  may  be  considerable,  although  far  inferior  to  that 
of  muscular  contraction.  The  work  which  cilia  are  capable 
of  performing  can  be  calculated  by  removing  the  membrane, 
fixing  it  on  a  plate  of  glass,  cilia  outwards,  putting  weights 
on  the  glass  plate,  and  allowing  the  cilia,  like  an  immense 
number  of  feet,  to  carry  it  up  an  inclined  plane.  Bowditch 
found  in  this  way  that  the  cilia  on  a  square  centimetre  of 
mucous  membrane  did  nearly  7  gramme-millimetres  of  work 
per  minute  (equal  to  the  raising  of  7  grammes  to  a  height  of 
a  millimetre). 

Since  the  cilia  in  the  respiratory  tract  all  lash  upwards, 
they  must  play  an  important  part  in  carrying  up  foreign 
particles  taken  in  with  the  air,  and  the  mucus  in  which  they 
are  entangled,  as  well  as  pathological  products.  Engelmann 
found  that  the  energy  of  ciliary  motion  increases  as  the 
temperature  is  raised  up  to  about  40°  C.,  after  which  it 
diminishes  quickly.  Overheating  causes  cilia  to  come  to 
rest,  but  if  the  temperature  has  not  been  too  high,  and  has 
not  acted  too  long,  they  recover  on  cooling. 

Muscle.  —  Nearly  all  our  knowledge  of  the  physiology  of 
muscle  has  been  gained  either  from  striped  skeletal  muscle 
or  from  the  muscle  of  the  heart,  and  chiefly  from  the  former. 
Of  non-striped  muscle  we  know  comparatively  little  except 
by  inference,  owing  to  the  difficulty  of  obtaining  it  in  suffi- 
cient quantity  and  in  suitable  preparations  for  experiments. 
In  what  follows  we  always  refer  to  ordinary  skeletal  muscle, 
unless  it  is  otherwise  stated. 


Physical  Properties  of  Muscle  —  Elasticity.  —  All  bodies  may  have  ~]~ 
their  shape  or  volume  altered  by  the  application  of  force.  Some 
require  a  large  force,  others  a  small  force,  to  produce  a  sensible 
amount  of  distortion.  The  elasticity  of  a  body  is  the  property  in 
virtue  of  which  it  tends  to  recover  its  original  form  or  bulk  when 
these  have  been  altered.  Liquids  and  gases  have  only  elasticity  of 
volume  ;  solids  have  also  elasticity  of  form.  Most  solids  recover 
perfectly,  or  almost  perfectly,  from  a  slight  deformation.  The  limits 
of  distortion  within  which  this  occurs  are  called  the  limits  of  elasticity, 
and  they  vary  greatly  for  different  substances.  Living  muscle  has 
very  wide  limits  of  elasticity;  it  may  be  deformed  —  stretched,  for 

34—2 


532  A  MANUAL  OF  PHYSIOLOGY 

example — to  a  very  considerable  extent,  and  yet  recover  its  original 
length  when  the  stretching  force  ceases  to  act. 

The  extensibility  of  a  body  is  measured  by  the  ratio  of  the  increase 
of  length, [produced  by  unit  stretching  force  per  unit  of  area  of  the 
cross-section,1) to  the  original  length  of  a  uniform  rod  of  the  substance. 

If  e  is  the  extensibility,  £  =  :p™  where  /  is  the  increase  of  length, 

L  the  original  length,  s  the  cross-section,  and  F  the  stretching  force. 

J— *Jr 
The  reciprocal  of  this,  -y-,  is  called  Young's  modulus  of  elasticity, 

or  the  co-efficient  of  elasticity.  Suppose  we  wish  to  compare  the  ex- 
tensibility of  two  substances.  Let  A  and  B  be  strips  or  rods  of  the 
substances,  the  length  of  A  being  500  mm.,  that  of  B  1,000  mm.; 
the  cross-section  of  A,  100  sq.  mm.,  of  B,  200  sq.  mm.  Let  the  elon- 
gation produced  by  a  weight  of  i  kilo  be  10  mm.  in  each.  Then  the 

10  x 100  10  x  200 

extensibility  of  A  is  =  2  ;   and  that  of  B  is  =2  : 

500  x  i  1,000  x  i 

that  is,  the  substances  are  equally  extensible. 

Living  muscle  is  very  extensible ;  a  small  force  per  unit  area  of 

cross- section  of  a  prism  of  it  will  produce  a  comparatively  great 

elongation.  The  extensibility,  how- 
ever, diminishes  continually  with  the 
elongation,  so  that  equal  increments 
of  stretching  force  produce  always  less 
and  less  extension.  If,  for  instance, 
the  sartorius  or  semi-membranosus  of  a 
frog  be  connected  with  a  lever  writing 
on  a  blackened  surface,  and  weights 
increasing  by  equal  amounts  be  suc- 
cessively attached  to  it,  the  recording 

surface  being  allowed  to  move  the  same 

FIG.  I57.-CURVES  OF  EXTEN-     distance    after   the    addition    of    each 
SIBILITY.  weight,  a  series   of  vertical  lines,  re- 

M,  of  muscle  ;  S,  of  an  ordinary      presenting  the  amount  of  each  elonga- 

inorganic  solid.  tion,  will  be  traced.     When  the  lower 

ends  of  all  the  vertical  lines  are  joined 

by  a  smooth  curve,  it  is  found  to  be  a  hyperbola  with  the  concavity 
upwards  (Fig.  157).  This  is  a  property  common  to  living  and  dead 
muscle  and  to  other  animal  structures,  such  as  arteries.  Marey's 
method,  in  which  the  weight  is  continuously  increased  from  zero 
and  then  continuously  decreased  to  zero  again  by  the  flow  of  mercury 
into  and  out  of  a  vessel  attached  to  the  muscle,  gives  directly  the 
hyperbolic  curve  of  extensibility. 

The  elongation  of  a  steel  rod  or  other  inorganic  solid  is  propor- 
tional within  limits  to  the  extending  force  per  unit  of  cross-section ; 
and  a  curve  plotted  with  the  weights  for  abscissas  and  the  amounts 
of  elongation  for  ordinates  would  be  a  straight  line.  But  this  is  not 
a  fundamental  distinction  between  animal  tissues,  and  the  materials 
of  unorganized  nature,  as  some  writers  seem  to  suppose.  For  when 
the  slow  after- elongation  which  follows  the  first  rapid  increase  in 


MUSCLE  533 

length  in  the  loaded,  excised  muscle  is  waited  for,  the  curve  of 
extensibility  comes  out  a  straight  line  (Wundt),  and  within  limits 
this  is  also  the  case  for  human  muscles  in  the  intact  body.  And 
although  a  steel  rod  much  more  quickly  reaches  its  maximum  elon- 
gation for  a  given  weight  when  loaded,  and  its  original  length  when 
the  weight  is  removed,  than  does  a  muscle,  time  is  required  in  both 
cases,  and  the  difference  is  one  of  degree  rather  than  of  kind. 

Dead  muscle  is  less  extensible  and  much  less  elastic  than  living. 
In  the  state  of  contraction  the  extensibility  is  increased  in  frog's 
muscle ;  but  Donders  and  Van  Mansveldt  have  found  that  contrac- 
tion causes  little  difference  in  the  muscles  of  a  living  man,  although 
fatigue  increases  the  extensibility.  The  great  extensibility  and 
elasticity  of  muscle  must  play  a  considerable  part  in  determining  the 
calibre  of  the  vessels,  and  in  lessening  the  shocks  and  strains  which 
the  heart  and  the  vascular  system  in  general  are  called  upon  to  bear, 
and  must  contribute  much  to  the  smoothness  with  which  the  move- 
ments of  the  skeleton  are  carried  out,  and  immensely  reduce  the 
risk  of  injury  to  the  bones  as  well  as  to  the  muscles  themselves,  the 
tendons  and  the  other  soft  tissues.  And  not  only  is  smoothness 
gained,  but  economy  also ;  for  a  portion  of  the  energy  of  a  sudden 
contraction,  which,  if  the  muscles  were  less  extensible  and  elastic, 
might  be  wasted  as  heat  in  the  jarring  of  bone  against  bone  at  the 
joints,  is  stored  up  in  the  stretched  muscle  and  again  given  out  in  its 
elastic  recoil.  The  skeletal  muscles,  too,  are  even  at  rest  kept 
slightly  on  the  stretch,  braced  up,  as  it  were,  and  ready  to  act  at  a 
moment's  notice  without  taking  in  slack.  This  is  shown  by  the  fact 
that  a  transverse  wound  in  a  muscle  *  gapes,'  the  fibres  being  retracted, 
in  virtue  of  their  elasticity,  towards  the  fixed  points  of  origin  and 
insertion. 

If  a  muscle  is  so  overweighted  that  it  cannot  contract,  it  elongates 
slightly  on  stimulation  (Wundt).  This  has  by  some  been  held  to 
indicate  that  the  increase  of  extensibility  associated  with  contraction 
still  occurs  in  the  excited  state  when  actual  contraction  is  mechanically 
prevented. 

In  the  further  study  of  muscle  it  is  necessary  first  of  all  to  consider 
the  means  we  have  of  calling  forth  a  contraction — in  other  words,  the 
various  kinds  of  stimuli. 

Stimulation  of  Muscle. — A  muscle  may  be  excited  or 
stimulated  either  directly  or  through  its  motor  nerve  ;  and 
the  stimulus  may  be  electrical,  mechanical,  chemical,  or 
thermal.  Electrical  stimuli  are  by  far  the  most  commonly 
used,  and  will  be  discussed  in  detail.  A  prick,  a  cut,  or  a 
blow  are  examples  of  mechanical  stimuli.  A  fairly  strong 
solution  of  common  salt  or  a  dilute  solution  of  a  mineral 
acid  will  act  as  a  chemical  stimulus,  which  always  tends  to 
cause,  not  a  single  contraction,  but  a  tetanus.  Sudden  ; 
cooling  or  heating  acts  as  a  stimulus  for  muscle,  but  thermal 


534  A  MANUAL  OF  PHYSIOLOGY 

stimulation  is  somewhat  uncertain.  In  all  artificial  stimula- 
tion there  is  an  element  of  sudden  or  abrupt  change,  of  shock, 
in  other  words  ;  but  we  cannot  tell  in  what  the  '  natural ' 
or  '  physiological '  stimulus  to  muscular  contraction  in  the 
intact  body  really  consists,  nor  how  it  differs  from  artificial 
stimuli.  All  we  know  is  that  there  must  be  a  wide  difference, 
and  that  our  methods  of  excitation  must  be  very  crude  and 
inexact  imitations  of  the  natural  process. 

Direct  Excitability  of  Muscle. — The  famous  controversy  on 
the  existence  of  '  independent  muscular  irritability '  has  long 
been  forgotten,  and  has  no  further  interest  except  for  the 
antiquaries  of  science,  if  such  exist.  The  direct  excitability 
of  muscle  in  the  modern  sense  is  very  different  from  the 
question  which  occupied  Haller  and  his  contemporaries. 
What  the  modern  physiologists  have  been  called  upon  to 
decide  is  whether  muscular  fibres  can  be  caused  to  contract 
except  by  an  excitation  that  reaches  them  through  their 
nerves.  In  this  sense  there  can  exist  no  doubt  that  muscle 
is  directly  excitable,  and  the  proofs  are  as  follows : 

(i)  The  ends  of  the  frog's  sartorius  contain  no  nerves,  the 
apex  of  the  frog's  heart  contains  neither  nerves  nor  nerve- 
cells,  yet  both  respond  to  direct  stimulation.  (2)  Certain 
chemical  stimuli — ammonia,  for  instance — do  not  act  on 
nerve,  but  excite  muscle.  (3)  When  the  motor  nerves  of 
a  limb  are  cut  they  degenerate,  and  after  a  certain  time 
stimulation  of  the  nerve-trunk  causes  no  muscular  contrac- 
tion, while  the  muscles,  although  atrophied,  can  be  made 
to 'contract  by  direct  stimulation.  (4)  Finally,  there  is  the 
celebrated  curara  experiment  of  Claude  Bernard,  which  is 
described  in  a  somewhat  modified  form  in  the  Practical 
Exercises,  p.  593.  A  ligature  is  tied  firmly  round  one  thigh 
of  a  frog,  omitting  the  sciatic  nerve;  then  curara  is  injected, 
and  in  a  short  time  the  skeletal  muscles  are  paralyzed. 
That  the  seat  of  the  paralysis  is  not  the  muscles  themselves 
is  shown  by  their  vigorous  response  to  direct  stimulation. 
The  'block'  is  not  in  the  nerve-trunk,  nor  above  it  in 
the  central  nervous  system,  for  the  ligatured  leg  is  oftei 
drawn  up — that  is,  its  muscles  are  contracted,  although  th< 
poison  has  circulated  freely  in  the  sacral  plexus  and  th< 


MUSCLE  535 

spinal  cord.  Further,  if  the  nerve  of  the  ligatured  leg  be 
prepared  as  high  up  above  the  ligature  as  possible,  where 
the  curara  must  undoubtedly  have  reached  it  (just  above  the 
ligature  the  nerve  has  been  isolated  and  the  circulation  in  it 
more  or  less  interrupted),  stimulation  of  it  will  cause  con- 
traction of  the  muscles  of  the  limb ;  while  excitation  of  the 
other  sciatic  is  ineffective. 

It  can  be  also  shown,  by  means  of  the  negative  variation 
or  current  of  action  (p.  607),  that  a  nerve-trunk  on  which 
curara  has  acted  remains  excitable,  and  capable  of  conduct- 
ing the  nerve-impulse.  The  conclusion,  therefore,  is  that 
the  curara  paralyzes  neither  nerve-fibre  nor  muscular  fibre, 


FIG.  158. — TONIC  CONTRACTION  OF  MUSCLE  DURING  PASSAGE  OF  CONSTANT 

CURRENT. 

Two  sartorius  muscles  of  frog  connected  by  pelvic  attachments.  Current  from  12 
small  Daniell  cells  in  series  passed  through  their  whole  length.  Current  closed  at  mt 
opened  at  b.  Time  trace,  two-second  intervals. 

but  the  link  between  the  two  which  we  call  the  nerve- 
ending.  In  coming  to  this  conclusion,  the  assumption  is 
made  that  the  nerve-fibres  within  the  muscle,  since  they  are 
anatomically  similar  to  those  in  the  nerve-trunk  till  near 
their  terminations,  are  similarly  affected  by  curara.  We 
must  carefully  remember  that  the  '  nerve-endings '  which 
are  paralyzed  by  curara  do  not  necessarily,  nor  even  pro- 
bably, coincide  exactly  with  the  '  nerve-endings '  of  histology. 
Still,  it  is  significant  that  the  histological  differences  between 
the  nerve-terminations  in  striped  and  smooth  muscle  should 
correspond  to  a  physiological  difference  in  the  action  of 


536 


A  MANUAL  OF  PHYSIOLOGY 


curara  on  them.  This  drug  paralyzes  the  nerve-endings 
in  smooth  muscle — the  muscles  of  the  bronchi,  for  instance 
— with  much  greater  difficulty  than  those  in  ordinary  skeletal 
muscle,  and  the  same  is  true  of  the  vagus-endings  in  the 
heart. 

The  action  of  curara  gives  us  the  means  of  stimulating 
muscle  directly :  when  electrical  currents  are  sent  through 
a  non-curarized  muscle,  there  is  in  general  a  mixture  of 
direct  and  indirect  stimulation,  for  the  nerve-fibres  within 
the  muscle  are  also  excited.  Induced  currents  stimulate 

nerve  more  readily 
than  muscle.  Vol- 
taic currents  may 
excite  a  muscle 
whose  nerves  have 
degenerated,  while 
induced  currents 
are  entirely  with- 
out effect. 

For   direct 
stimulation,      a 
curarized    frog's 
sartorius  or  semi- 
FIG.    159.  —  TONIC    CONTRACTION    DURING   AND    membranosus       is 

AFTER    x*  LO^V. 
Curve    from    frog's    gastrocnemius.      At    M   constant    generally    USed    On 

account  of  their 
long  parallel 
fibres ;  for  indirect  excitation,  a  muscle-nerve  preparation, 
composed  of  a  frog's  gastrocnemius  with  the  sciatic  nerve 
attached  to  it,  is  commonly  employed,  as  it  is  easy  to  isolate 
the  muscle  without  hurting  its  nerve. 

Stimulation  by  the  Voltaic  Current. — While  the  current  con- 
tinues to  pass  through  a  nerve  without  any  sudden  or  great 
change  in  its  intensity,  there  is  no  stimulation,  and  the 
muscle  connected  with  the  nerve  remains  at  rest.  The 
same  is  generally  true  of  muscle  when  the  current  is  passed 
directly  through  it.  But  here  the  constancy  of  the  rule  is 
far  more  frequently  broken  by  exceptional  results  than  in 
nerve,  especially  if  the  current  is  at  all  strong,  when  a  state 


current  closed,  at  B  broken.     Contracture  continues  after 
opening  of  current.     Time  trace,  two-second  intervals. 


MUSCLE  537 

of  fibres  in  which  the  '  fixing '  reagent  has  caught  a  wave 
of  tetanus  is  very  apt  to  show  itself  during  the  whole  time 
of  flow  (Wundt)  (Fig.  158) ;  and  a  similar  condition,  the 
so-called  galvanotonus,  is  normally  seen  in  human  muscles 
when  traversed  by  a  stream  of  considerable  intensity. 

For  nerve,  and  with  these  qualifications  for  muscle,  too, 
we  may  lay  down  the  law  that  the  voltaic  current  stimulates 
at  make  and  at  break,  but  not  during  its  passage.     Or,  general- 
izing this  a  little,  since  it  has  been  shown  that  a  sudden 
increase  or  decrease  in  the  strength  of  a  current  already 
flowing  also  acts  as  a  stimulus,  we  may  say  that  the  voltaic  \ 
current  stimulates  only  when  its  intensity  is  suddenly  and  suffi- ' 
ciently  increased  or  diminished,  but  not  while  it  remains  constant.  ] 

A  second  law  of  great  theoretical  importance  is  that  at  v^tr 
make  the  stimulation  occurs  only  at  the  cathode;  at  break  only  *  ft^a'A 
at  the  anode;  and  that  the  make  is  stronger  than  the  break 
contraction.  This  is  true  both  for  muscle  and  nerve,  but  it 
is  most  directly  and  simply  demonstrated  on  muscle.  A 
long  parallel-fibred  curarized  muscle  is  supported  about  its 
middle ;  the  two  ends,  which  hang  down,  are  connected 
with  levers  writing  on  a  revolving  drum,  and  a  current  is 
sent  longitudinally  through  the  muscle.  It  is  not  difficult 
to  see  from  the  tracings  that  at  make  the  lever  attached  to 
the  cathodic  end  moves  first,  and  that  the  other  lever  only 
moves  when  the  contraction  started  at  the  cathode  has 
had  time  to  reach  it  in  its  progress  along  the  muscle. 
Similarly,  at  break  the  lever  connected  with  the  anodic  end 
moves  first. 

The  Muscular  Contraction. — When  a  muscle  contracts,  its 
two  points  of  attachment,  or,  if  it  be  isolated,  its  two  ends, 
come  nearer  to  each  other ;  and  in  exact  proportion  to  this 
shortening  is  the  increase  in  the  average  cross-section.  The 
contraction  is  essentially  a  change  of  form,  not  a  change  of 
volume.  The  most  delicate  observations  fail  to  detect  the 
smallest  alteration  in  bulk  (Ewald).  Living  fibres  kept 
contracted  by  successive  stimuli  can  be  examined  under  the 
microscope ;  or  fibres  may  be  '  fixed  '  by  reagents  like  osmic 
acid,  and  sometimes  a  very  good  opportunity  of  studying 
the  microscopic  changes  in  contraction  is  given  by  a  group 


538  A  MANUAL  OF  PHYSIOLOGY 

of  contraction,  and,  so  to  speak,  pinned  it  down.  It  is 
then  seen  that  the  process  of  contraction  in  the  fibre  is 
a  miniature  of  that  in  the  anatomical  muscle.  The  indi- 
vidual fibres  shorten  and  thicken,  and  the  sum-total  of  this 
shortening  and  thickening  is  the  muscular  contraction 
which  we  see  with  the  naked  eye.  The  phenomena  of  the 
muscular  contraction  may  be  classified  thus :  (i)  Optical, 
(2)  Mechanical,  (3)  Thermal,  (4)  Chemical,  (5)  Sonorous, 
(6)  Electrical.  (5)  v/ill  be  treated  under  '  Voluntary  Con- 
traction' ;  (6)  in  Chapter  XI. 

(i)  Optical  Phenomena  —  Microscopic  Structure  of  Striped 
Muscle. — The  structure  of  striped  muscle  has  long  been  the  enigma 
of  histology ;  and  the  labours  of  many  distinguished  men  have  not 
sufficed  to  make  it  clear.  On  the  contrary,  as  investigations  have 
multiplied,  new  theories,  new  interpretations  of  what  is  to  be  seen, 
have  multiplied  in  proportion,  and  a  resolute  brevity  has  become  the 
chief  duty  of  a  writer  on  elementary  physiology  in  regard  to  the 
whole  question. 

The  muscle-fibre,  the  unit  out  of  which  the  anatomical  muscle  is 
built  up,  is  surrounded  by  a  structureless  membrane,  the  sarcolemma. 
The  length  and  breadth  of  a  fibre  vary  greatly  in  different  situations. 
The  maximum  length  is  about  4  cm.  ;  the  breadth  may  be  as  much 
as  70  p  and  as  little  as  10  /x.  When  we  come  to  analyze  the  muscle- 
fibre  and  to  determine  out  of  what  units  it  is  built  up,  the  difficulty 
begins.  The  fibre  shows  alternate  dim  and  clear  transverse  stripes, 
and  can  actually  be  split  up  into  discs  by  certain  reagents.  It  also 
shows  a  longitudinal  striation,  and  can  be  separated  into  fibrils. 
Some  have  supposed  that  the  discs  are  the  real  structural  units 
which,  piled  end  to  end,  make  up  the  fibre.  The  fibrils  they  con- 
sider artificial.  Others  have  held  that  the  fibres  are  built  up  from 
fibrils  ranged  side  by  side,  and  that  the  discs  are  artificial.  The 
most  probable  view  is  that  the  contents  of  the  muscle-fibre  consist 
of  two  functionally  different  substances,  a  contractile  substance,  and 
an  interstitial,  perhaps  nutritive,  non- contractile  material  of  more 
fluid  nature.  The  contractile  substance  is  arranged  as  longitudinal 
fibrils  embedded  in  interfibrillar  matter  (sarcoplasm). 

According  to  Rutherford,  each  fibril  is  made  up  of  a  longitudinal 
row  of  segments  of  two  kinds  alternating  with  each  other  :  (i)  '  Bow- 
man's element,'  shaped  like  an  elongated  hour-glass,  and  containing 
a  substance  readily  stained  by  various  dyes  ;  (2)  an  '  intermediate 
segment '  of  cylindrical  shape,  the  general  substance  of  which  does 
not  readily  stain.  The  intermediate  segment  contains  in  its  centre  a 
globule  (Dobie's  globule),  which  is  easily  stained.*  The  fibrils  are 

*  In  the  muscles  of  certain  invertebrate  animals,  though  not  in  those 
of  vertebrates,  the  intermediate  segment  contains,  in  addition  to  Dobie's 
globule,  two  pear-shaped  bodies  (Flogel's  elements),  each  of  which 


MUSCLE  539 

regularly  arranged  in  bundles  within  the  fibre.     The  apposition  of 

Bowman's  elements  gives  rise  to  the  dim  stripe ;  the  apposition  of 

the  intermediate  segments  to  the  clear  stripe ;  the  apposition  of  the 

Dobie's  globules  to  a  line  in  the  middle  of  the  clear 

stripe  (Dobie's  line).     Some  have  supposed  that  this  line 

is  due  to  a  membrane  (Krause's  membrane)  stretching 

across  the  fibre  in  the  middle  of  each  light  disc,  dividing 

it  into  a  number  of  compartments.    Kiihne,  however,  was 

fortunate  enough  to  find  one  day  a  nematode  worm  in  the 

interior  of  a  fibre.     He  followed  its  movements,  and  saw 

it  pass  along  the  fibre  with  perfect  freedom,  ignoring 

Krause's  membrane ;  so  that  if  such  a  partition  exists,  it 

must  either  be  incomplete,  or  much  more  easily  ruptured  FlG     l6o  _ 

than  the  sarcolemma.  BUNDLE 

When  a  muscle  contracts,  the  intermediate  segment  OF  FIBRILS 
first  shortens,  so  that  the  ends  of  Bowman's  elements  come  °F  NEWT'S 
close  up  to  Dobie's  globules.  There  is,  apparently,  no 
lateral  bulging  of  the  intermediate  segments  while  this  FORD). 
shortening  is  going  on,  so  that  the  fluid  in  them  must  uncontracted 
enter  Bowman's  elements.  The  Bowman's  elements  condition ;  .6, 
begin  to  shorten  a  little  later  than  the  intermediate  seg-  ^en™  *  n  'd, 
ment.  The  easily-stainable  substance  in  them  passes  to  Dobie's  line, 
their  ends,  which  swell  and  become  dimmer,  while  their 
shafts  become  clear.  The  result  of  these  changes  is  that  in  the  fully 
contracted  fibril  the  clear  stripe  occupies  the  middle  of  what  was  the 
dim  stripe  in  the  uncontracted  fibril,  and  the  dim  stripe  of  the  con- 
tracted fibril  is  made  up  of  'the  swollen  ends  of  Bowman's  elements 
with  the  Dobie's  globules  and  other  tissue  elements  of  the  inter- 
mediate segments '  (Rutherford).  This  curious  phenomenon  is 
known  as  the  reversal  of  the  stripes.  Schafer  has  described  the 
contractile  elements  of  the  muscle-fibre  as  fine  columns  (sarcostyles) 
divided  by  septa,  in  the  position  of  Krause's  membrane,  into  segments 
(sarcomeres).  Each  sarcomere  contains  a  sarcous  element  with  a 
clear  fluid  at  its  ends,  which  produces  the  appearance  of  the  light 
tripes.  During  contraction,  according  to  him,  this  fluid  is  squeezed 
into  fine  longitudinal  canals,  which  pierce  the  sarcous  elements. 
Schafer's  muscle  columns  are  units  of  greater  transverse  diameter 
than  the  fibrils  of  Kolliker,  Rutherford,  etc. ;  and  Schafer  considers 
that  the  appearance  of  longitudinal  fibrillation  in  his  sarcous  ele- 
ments is  due  to  the  presence  of  these  canals,  and  does  not  indicate 
a  truly  fibrillar  structure. 

Some  observers,  using  chloride  of  gold  as  a  stain,  have  asserted 
that  an  apparent  network,  brought  out  by  that  reagent,  and  which  is 
stated  to  be  connected  with  the  nuclei  or  muscle-corpuscles,  is  the 
contractile  part  of  the  fibre.  But  this  view  has  met  with  great 
opposition  ;  and  the  substance  stained  by  the  gold  appears  to  be  only 
interstitial  material. 

occupies  an  intermediate  position  between  Dobie's  globule  and  the  end 
of  the  adjoining  Bowman's  element.  Flogel's  elements  also  stain  well, 
and  are  doubly  refracting. 


540 


A  MANUAL  OF  PHYSIOLOGY 


Appearance  of  the  Fibres  in  Polarized  Light. — A  ray  of  ordinary 
light  consists  of  vibrations  of  the  ether  in  all  planes  at  right  angles 
to  the  direction  of  the  ray.  In  a  ray  of  plane  polarized  light  all  the 
particles  vibrate  in  one  plane.  A  ray  of  light  which  has  been  polarized 
by  a  Nicol's  prism  cannot  pass  through  another  Nicol's  prism  with 
its  principal  plane  at  right  angles  to  that  of  the  first.  If  the  second 
or  analyzing  prism  be  rotated  so  that  the  principal  planes  are  no 
longer  at  right  angles,  some  of  the  light  will  pass  through.  The 
same  effect  is  produced  if,  without  altering  the  original  '  crossed  ; 
position  of  the  nicols,  a  substance  capable  of  rotating  the  polarized 
ray  is  introduced  between  the  prisms.  A  rough  illustration  will 
perhaps  tend  to  make  this  point  clearer.  Suppose  that  a  string  fixed 
at  one  end  is  set  vibrating  in  various  directions  by  a  twisting  move- 
ment. If  the  string  has  to  pass  through  a  narrow  vertical  slit,  e.g.y 
between  two  fingers  held  vertically,  all  vibrations  except  those  in  the 
vertical  plane  will  be  extinguished  ;  but  vertical  vibrations  will  be 
able  to  pass  beyond  the  slit.  The  movement  may  be  said  to  be 
plane  polarized,  and  the  effect  of  the  slit  corresponds  to  that  of  the 
first  nicol.  Now  make  the  string  pass  also  through  a  horizontal  slit ; 
the  vertical  vibrations  will  then  be  extinguished  too ;  in  other  words, 
none  of  the  movements  will  pass  beyond  the  '  crossed '  slits.  This 
corresponds  to  the  dark  field  of  the  crossed  nicols.  But  if  the  vertical 
vibrations  which  have  passed  the  first  slit  could  be  in  any  way 
changed  into  horizontal  vibrations,  they  would  no  longer  be  extin- 
guished by  the  second.  This  would  correspond  to  rotation  of  the 
plane  of  polarization  through  90°.  A  ray  of  light  polarized  by  the 

first  nicol  will,  if  its  plane  of 
polarization  be  rotated  through 
90°,  pass  entirely  (except  for 
'oss  by  ordinary  reflection  and 
absorption)  through  the 
second.  If  the  angle  of  rota- 
tion is  less  than  90°,  a  portion 
will  pass  through. 

The  substance  of  the  Bow- 
man's element,  and  particu- 
larly the  easily-stained  material 
in  it,  is  doubly  refracting,  and 
therefore  rotates  the  plane  of 
polarization.  The  same  is  true 
of  the  Dobie's  globule,  but 
the  rest  of  the  intermediate 
segment  is  singly  refracting. 
When  an  uncontracted  fibre 
is  viewed  with  crossed  nicols, 
the  dim  stripe  accordingly  ap- 
pears bright  in  the  otherwise  dark  field.  In  the  contracted  fibre 
the  stripe  that  is  dim  in  ordinary  light  is  bright  when  looked  at  with 
crossed  nicols,  since  the  ends  of  the  Bowman's  elements,  filled 
with  the  doubly  refractive  stainable  material,  and  the  doubly  re- 


FIG.    161.  — LIVING    MUSCULAR    FIBRE 
(FROM  GEOTRUPES  STERCORARIUS). 

i,  in  ordinary ;  2,  in  polarized  light.  (Van 
Gehuchten.)  In  living  muscle  (at  least  in 
fibres  which  are  not  extended)  in  contrast  to 
dead  muscle  after  treatment  with  reagents, 
the  doubly  refracting  or  anisotropous  sub- 
stance is  present  in  the  greater  part  of  the 
fibre  ;  and  with  crossed  nicols  the  position  of 
the  singly  refracting  or  isotropous  material  is 
indicated  only  by  narrow  transverse  black 
lines  or  rows  of  dark  dots. 


MUSCLE  541 

Tractive  Dobie's  globule  are  there  approximated.  The  stripe  which 
in  the  contracted  fibre  is  the  brighter  of  the  two  in  ordinary 
light  is  the  dimmer  of  the  two  in  the  field  of  the  crossed  nicols, 
although  it  is  not  absolutely  dark,  since  the  shafts  of  the  Bowman's 
elements  cause  some  rotation  of  the  plane  of  polarization  even  in  the 
absence  of  the  stainable  material  (Rutherford). 

Diffraction  Spectrum  of  Muscle. — When  a  beam  of  white  light 
passes  through  a  striped  muscle,  it  is  broken  up  into  its  constituent 
colours,  and  a  series  of  diffraction  spectra  are  produced,  just  as 
happens  when  the  light  passes  through  a  diffraction  grating  (a  piece 
of  glass  on  which  are  ruled  a  number  of  fine  parallel  equidistant 
lines).  The  nearer  the  lines  are  to  each  other,  the  greater  is  the  dis- 
placement of  a  ray  of  light  of  any  given  wave-length.  It  has  accord- 
ingly been  found  that  when  a  muscular  fibre  contracts,  the  amount 
of  displacement  of  the  diffraction  spectra  increases.  At  the  same 
time  the  whole  fibre  becomes  more  transparent. 

(2)  Mechanical  Phenomena. — The  muscular  contraction  may 
be  graphically  recorded  by  connecting  a  muscle  with  a  lever 
which  is  moved  either  by  its  shortening  or  by  its  thickening. 
The  lever  writes  on  a  blackened  surface,  which  must  travel 
at  a  uniform  rate  if  the  form  and  time-relations  of  the 
muscle-curve  are  to  be  studied,  but  may  be  at  rest  if  only 
the  height  of  the  contraction  is  to  be  recorded.  The  whole 
arrangement  for  taking  a  muscle-tracing  is  called  a  myograpb 
(Fig?f84).  The  duration  of  a  *  twitch  '  or  single  contraction 
(including  the  relaxation)  of  a  frog's  muscle  is  usually  given 
as  about  one-tenth  of  a  second,  but  it  may  vary  considerably 
with  temperature,  fatigue,  and  other  circumstances.  It  is 
measured  by  the  vibrations  of  a  tuning-fork  written  imme- 
diately below  or  above  the  muscle  curve.  When  the  muscle 
is  only  slightly  weighted,  it  but  very  gradually  reaches  its 
original  length  after  contraction,  a  period  of  rapid  relaxation 
being  followed  by  a  period  of  'residual  contraction,'  during 
which  the  descent  of  the  lever  towards  the  base  line  becomes 
slower  and  slower,  or  stops  altogether  some  distance 
above  it. 

Latent  Period. — If  the  time  of  stimulation  is  marked  on 
the  tracing,  it  is  found  that  the  contraction  does  not  begin 
simultaneously  with  it,  but  only  after  a  certain  interval, 
which  is  called  the  latent  period. 

This  can  be  measured  by  means  of  the  pendulum  myo- 
graph  or  the  spring  rnyograph,  in  both  of  which  the  carrier 


542 


A  MANUAL  OF  PHYSIOLOGY 


of  the  recording  plate  opens,  at  a  definite  point  in  its 
passage,  a  key  in  the  primary  coil  of  an  induction  machine, 
and  so  causes  a  shock  to  be  sent  through  the  muscle  or 
nerve,  which  is  connected  with  the  secondary.  The  precise 
point  at  which  the  stimulus  is  thrown  in  can  be  marked 
on  the  tracing  by  carefully  bringing  the  plate  to  the  position 
in  which  the  key  is  just  opened,  and  allowing  the  lever  to 
trace  here  a  vertical  line  (or,  rather,  an  arc  of  a  circle).  The 
portion  of  the  time-tracing  between  this  line  and  a  parallel 


FIG.  162. — SPRING  MYOGRAPH. 

A,  B,  iron  uprights,  between  which  are  stretched  the  guide-wires  on  which  tne 
travelling  plate  a  runs  ;  k,  pieces  of  cork  on  the  guides  to  gradually  check  the  plate  at 
the  end  of  its  excursion,  and  prevent  jarring  ;  b,  spring,  the  release  of  which  shoots  the 
plate  along  ;  h,  trigger-key,  which  is  opened  by  the  pin  d  on  the  frame  of  the  plate. 

line   drawn   through   the   point   at   which   the  contraction 
begins  gives  the  latent  period. 

Helmholtz  measured  the  length  of  the  latent  period  by 
means  of  the  principle  of  Pouillet,  that  the  deflection  of  a 
magnet  by  a  current  of  given  strength  and  of  very  short 
duration  is  proportional  to  the  time  during  which  the  current 
acts  on  the  magnet.  He  arranged  that  at  the  moment  of 
stimulation  of  the  muscle  a  current  should  be  sent  through 
a  galvanometer,  and  should  be  broken  by  the  contraction  of 
the  muscle  the  moment  it  began.  In  this  way  he  obtained 


MUSCLE 


543 


the  value  of  yj-g-  second  for  the  latent  period  of  frog's 
muscle.  The  tendency  of  later  observations  has  been  to 
make  the  latent  period  shorter.  Burdon  Sanderson  finds 


FIG.  163. — PENDULUM  MYOGRAPH. 

At  the  left  as  seen  from  the  side,  at  the  right  as  seen  from  the  front.  A,  bearings 
on  which  the  pendulum  swings  ;  P,  pendulum  ;  G,  G',  glass  plates  carried  in  the 
frames  T,  T',  ;  a,  pin  which  opens  the  trigger-key.  Trie  key,  when  closed,  is  in 
contact  with  c,  and  so  completes  the  circuit  of  the  primary  coil. 


that  the  change  of  form  probably  begins  in  muscle  with 
direct  stimulation  in  104QO  second  after,  and  the  electrical 
change  (p.  607)  simultaneously  with,  the  excitation.  It  is 


544  A  MANUAL  OF  PHYSIOLOGY 

known  that  the  apparent  latent  period  depends  upon  the  re- 
sistance which  the  muscle  has  to  overcome  in  beginning  its 
contraction.  A  heavily-weighted  muscle,  for  instance,  can- 
not begin  to  shorten  until  as  much  energy  has  been  developed 
as  is  necessary  to  raise  the  weight ;  and  its  latent  period 
will  be  distinctly  longer  than  that  of  unweighted  or  very 
slightly  weighted  muscles,  such  as  those  with  which  Sander- 
son worked. 

The  maximum  shortening,  or  '  height  of  the  lift/  depends 
upon  the  length  of  the  muscle,  the  direction  of  the  fibres, 
the  strength  of  the  stimulus,  the  excitability  of  the  tissue, 
and  the  load  it  has  to  raise. 

In  a  long  muscle,  other  things  being  equal,  the  absolute 
shortening,  and  therefore  the  maximum  height  of  the  curve 
will  be  greater  than  in  a  short  muscle  ;  in  a  muscle  with 


FIG.  164. — CURVE  OF  A  SINGLE  MUSCULAR  CONTRACTION  OR  TWITCH  TAKEN 
ON  SMOKED  GLASS  WITH  SPRING  MYOGRAPH  AND  PHOTOGRAPHED. 

Vertical  line  A  marks  the  point  at  which  the  muscle  was  stimulated  ,  time-tracing 
shows  T5o  of  a  section  (reduced). 

fibres  parallel  to  its  length — the  sartorius,  for  instance- 
it  will  be  greater  than  in  a  muscle  like  the  gastrocnemius 
with  the  fibres  directed  at  various  angles  to  the  long  axis 
For  stimuli  less  than  maximal,  the  absolute  contraction 
increases  with  the  strength  of  stimulation,  and  a  given 
stimulus  will  cause  a  greater  contraction  in  a  muscle  with 
a  given  excitability  than  in  a  muscle  which  is  less  excitable 
Finally,  increase  of  the  load  per  unit  of  cross-section  of  the 
muscle  diminishes  above  a  certain  limit  the  '  height  of  the 
lift/  although  below  that  limit  it  may  increase  it. 

Influences  which   affect  the  Time-relations   of  the   Muscu 
Contraction. — Many   circumstances    affect   the    form    of  th 
muscle-curve  and  its  time-relations. 

(a)  Influence  of  the  Load. — The  first  effect  of  contractio 
is  to  suddenly  stretch  the  muscle,  and  the  more  the  muscl 


MUSCLE  545 

is  loaded  the  greater  will  this  elongation  be.  So  that  at  the 
beginning  of  the  actual  shortening  part  of  the  energy  of 
contraction  is  already  expended  without  visible  effect,  and 
has  to  be  recovered  from  the  elastic  reaction  during  the 
ascent  of  the  lever. 

Then  the  inertia  of  the  lever  itself  and  of  its  load  comes 
into  play,  and  may  carry  the  curve  too  high  during  the 
up-stroke  and  too  low  during  the  down-stroke.  This  can 
be  minimized  by  making  the  lever  very  light,  and  attaching 
the  weight  close  to  the  fulcrum,  so  that  it  has  only  a  small 
range  of  movement,  and  never  acquires  more  than  a  smalL 
velocity.  The  contraction  of  a  muscle  loaded  by  a  weight 
which  is  not  increased  or  diminished  during  the  contraction 
is  said  to  be  iso-tonic,  for  here  the  tension  of  the  muscle 


FIG.  165. — INFLUENCE  OF  LOAD  ON  THE  FORM  OF  THE  MUSCLE  CURVE. 

i,  curve  taken  with  unloaded  lever ;  2,  3,  4,  weight  successively  increased  ; 
5,  abscissa  line ;  time-trace  ^  sec.  (reduced). 

is  the  same  throughout,  and  its  length  alters.  When  the 
muscle  is  attached  very  near  the  fulcrum  of  the  lever,  so 
that  it  acts  upon  a  short  arm,  while  the  long  arm  carrying 
the  writing-point  is  prevented  from  moving  much  by  a 
spring,  the  muscle  can  only  shorten  itself  very  slightly ;  but 
the  changes  of  tension  in  it  will  be  related  to  those  in  the 
spring,  and  therefore  to  the  curve  traced  by  the  writing- 
point.  Such  a  curve  is  called  iso-metric,  since  the  length  of 
the  muscle  remains  almost  unaltered. 

The  maximum  of  the  iso-metric  curve  (the  maximum  tension  with 
practically  constant  length)  is  sooner  reached  than  that  of  the  iso- 
tonic  (the  maximum  contraction  with  constant  tension).  From  this 
it  has  been  concluded  that  during  contraction  the  co-efficient  of 
elasticity  of  the  muscle  continuously  diminishes  (Fick),  or,  what 
comes  to  the  same  thing,  its  extensibility  continuously  increases. 

35 


546 


A  MANUAL  OF  PHYSIOLOGY 


The  work  done  by  a  muscle  in  raising  a  weight  is  equal  to  the 
product  of  the  weight  by  the  height  to  which  it  is  raised.  Beginning 
with  no  load  at  all,  it  is  found  that  the  weight  can  be  increased  up  to 
a  certain  limit  without  diminishing  the  height  of  the  contraction  ; 
perhaps  the  height  may  even  increase.  Up  to  this  limit,  then,  the 
work  evidently  increases  with  the  load.  If  the  weight  is  made  still 
greater,  the  contraction  becomes  less  and  less,  but  up  to  another 
limit  the  increase  of  weight  more  than  compensates  for  the  diminu- 
tion of  'lift,'  and  the  work  still  increases.  Beyond  this,  further 
increase  of  weight  can  no  longer  make  up  for  the  lessening  of  the 
lift,  and  the  work  falls  off  till  ultimately  the  muscle  is  unable  to  raise 
the  weight  at  all. 


FIG.  166.— INFLUENCE  OF  TEMPERATURE  ON  THE  MUSCLE  CURVE. 

2,  air  temperature  ;  i,  25°— 30°  C.  ;  3,  7°— 10°  C. ;  4,  ice  in  contact  with  muscle. 
Tfce  5th  curve  was  taken  at  a  little  above  air  temperature. 

The  manner  of  application  of  the  weight  has  an  influence  on  the 
work  done  by  the  muscle.  If  it  is  applied  before  the  contraction 
begins,  so  that  the  muscle  is  already  stretched  at  the  moment  of 
stimulation,  a  cause  of  error  and  uncertainty  is  introduced  ;  for  it  is 
known  that  mere  stretching  of  muscle  affects  its  metabolism,  and 
therefore  its  functional  power.  So  that  it  is  usual  in  experiments  of 
this  kind  to  after-load  the  muscle — that  is,  to  support  the  lever  and 
its  load  in  such  a  way  that  the  weight  does  not  come  upon  the 
muscle  till  contraction  has  just  begun.  The  'absolute  contractile 
force '  of  an  active  muscle  may  be  measured  on  this  principle  by 
determining  the  weight  which,  brought  to  bear  upon  the  muscle  at 
the  instant  of  contraction,  is  just  able  to  prevent  shortening  without 


MUSCLE 


547 


stretching  the  muscle.  It,  of  course, 
depends,  among  other  things,  on  the 
cross-section  of  the  muscle.  During 
the  contraction  the  absolute  force  di- 
minishes continually,  so  that  a  smaller 
and  smaller  weight  is  sufficient  to  stop 
any  further  contraction,  the  more  the 
muscle  has  already  shortened  before  it 
is  applied.  At  the  maximum  of  the 
contraction  the  absolute  force  is  zero. 
Hence  a  muscle  works  under  the  most 
favourable  conditions  when  the  weight 
decreases  as  it  is  raised,  and  this  is  the 
case  with  many  of  the  muscles  of  the 
body.  During  flexure  of  the  forearm 
on  the  elbow,  with  the  upper  arm 
horizontal,  a  weight  in  the  hand  is  felt 
less  and  less  as  it  is  raised,  since  its 
moment,  which  is  proportional  to  its  dis- 
tance from  a  vertical  line  drawn  through 
the  lower  end  of  the  humerus,  continu- 
ally diminishes. 

(b)  Influence  of  Temperature  on 
the  Muscular  Contraction. — Increase 
of  temperature  of  the  muscle  up 
to  a  certain  limit  diminishes  the 

latent  period  and  the  length  of  the 

,   .  .,       ,     .   ,  .      f    FIG.  167. — FATIGUE  CURVE  OF 

curve,  and  increases  the  height  of      MUSCLE    (FROG'S    GASTRO- 


the  contraction,  but  beyond  this 
limit  the  contractions  are  lessened 
in  height.  Marked  diminution  of 
temperature  causes,  in  general,  an 


CNEMIUS). 

Below  is  shown  the  arrangement 
with  which  the  curve  figured  was 
obtained.     A,  femur  with  gastro- 
cnemius    attached,    supported    in 
clamp  ;   C,  metal  hook  with  fine 
,     wire  attached  to  lever  F.     The  wire 
increase    in    the    latent    period  and     is  continued  along  the  lever  and 

length,   and    a    decrease    in    1 
height  of  the  contraction.     It 


s 


connected  with  a  sewing-needle, 

the  point  of  which  just  dips  into 

the  mercury  cup  D.     A  wire  from 
one  pole  of  the  Darnell  cell  E  dips 


. 

evident    that    much    depends    Upon  permanently  into  the  mercury  ;  the 

,    .  i  •    i  wire   B  from    the   other    pole    is 

the  normal   temperature  Which  We  attached  to  the  upper  end  of  the 

start  from,  and  moderate  cooling 

may    increase     the     height     Of    the 
Curve.       In  the    heart   the   effect    Of 


and  open  the  primary  circuit  of  an 
mductormm,  the  muscle  or  nerve 
being  connected  with  the  secon- 

i  t    •  .  ,         .          J  ,        .        .     .        dary.       Every    time     the     needle 

Cold   in    Strengthening   the    beat    IS     touches  the  mercury  the  muscle  is 


Often  Very  marked. 


stimulated  automatically. 


(c)  Influence  of  Previous  Stimulation.  —  If  a  muscle  is  stimu- 

35—2 


548 


A  MANUAL  OF  PHYSIOLOGY 


lated  by  a   series   of  equal   shocks   thrown   in   at   regular 

intervals,   and   the   contractions   recorded,   it   is  seen  that 

at  first  each  curve  overtops  its 
predecessor  by  a  small  amount. 
This  phenomenon,  which  is 
regularly  seen  in  fresh  skeletal 
muscle,  although  it  was  at  one 
time  supposed  to  be  peculiarly 
a  property  of  the  muscle  of  the 
heart,  is  called  the  '  staircase,' 
and  seems  to  indicate  that 
within  limits  the  muscle  is 
benefited  by  contraction  and 
its  excitability  increased  for  a 
new  stimulus.  Soon,  however, 
TAL  MUSCLE  (FROG).  in  an  isolated  preparation,  the 

Fl|li^7lationbyarrangementshownin  contractions    begin    to   decline 

in  height,  till  the  muscle  is  at 

length  utterly  exhausted,  and  reacts  no  longer  to  even  the 

strongest  stimulation. 

A  conspicuous  feature  of  the  contraction-curves  of  fatigued 

muscle  is  the  progressive  lengthening,  which  is  much  more 


FIG.  168. — 'STAIRCASE  '  IN  SKELE- 


FIG.  169. — 'STAIRCASE'  IN  CARDIAC  MUSCLE. 

Contractions  recorded  on  a  much  more  quickly  moving  drum  than  in  Fig.  168.  The 
contractions  were  caused  by  stimulating  a  heart  reduced  to  standstill  by  the  first 
Stannius'  ligature  (p.  175).  The  contractions  gradually  increase  in  height. 

marked  in  the  descending  than  in  the  ascending  period  ,- 
in  other  words,  relaxation  becomes  more  and  more 
difficult  and  imperfect.  It  is  by  no  means  so  easy  to  fatigue 
a  muscle  still  in  connection  with  the  circulation  as  an 
isolated  muscle.  But  even  the  latter,  if  left  to  itself,  will  to 


MUSCLE  549 

some  extent  recover,  and  be  again  able  to  contract,  although 
exhaustion  is  now  more  readily  induced  than  at  first. 

What  is  the  cause  of  muscular  fatigue  ?  An  exact  answer 
is  not  possible  in  the  present  state  of  our  knowledge,  but 
we  may  fairly  conclude  that  in  an  isolated  preparation  it  is 
twofold  :  (i)  The  material  necessary  for  contraction  breaks 
down  more  quickly  than  it  can  be  reproduced  or  brought 
to  the  place  where  it  is  required ;  (2)  waste  products  are 


FIG.  170.— FATIGUE  CURVE  OF  SKELETAL  MUSCLE 

(Gastrocnemius  of  frog,  indirect  stimulation),  taken  with  arrangement  shown  in 
Fig.  184.  Time-tracing,  T5o  of  a  second. 

formed  by  the  active  muscle  faster  than  they  can  be  removed. 
That  even  an  isolated  muscle  has  a  certain  store  of  the 
material  needed  for  contraction  which  cannot  be  all  exhausted 
at  once,  or  which  can  to  a  certain  extent  be  replenished  by 
processes  going  on  in  the  muscle,  is  shown  by  the  beneficial 
effect  of  mere  rest.  That  the  accumulation  of  fatigue 
products  has  something  to  do  with  the  exhaustion  is  shown 
by  the  fact  that  the  muscles  of  a  frog,  exhausted  in  spite  of 
the  continuance  of  the  circulation,  can  be  restored  by  bleed- 


550  A  MANUAL  OF  PHYSIOLOGY 

ing  the  animal,  or  washing  out  the  vessels  with  normal  saline 
solution,  while  injection  of  a  watery  extract  of  exhausted 
muscle  into  the  bloodvessels  of  a  curarized  muscle  renders  it 
less  excitable  (Ranke).  This  observer  supposed  that  it  was 
specially  the  removal  of  the  acid  products  of  contraction 
(sarcolactic  acid  and  acid  potassium  phosphate)  which 
restored  the  muscle.  Injection  of  arterial  blood,  or  even 
of  an  oxidizing  agent  like  potassium  permanganate,  into 
the  vessels  of  an  exhausted  muscle  also  causes  restoration 
(Kronecker). 

When  a  fatigued  muscle  responds  no  longer  to  indirect 
stimulation,  it  can  still  be  directly  excited.  The  seat  of 
exhaustion  must  therefore  be  either  the  nerve-trunk  or  the 
nerve-endings.  It  is  not  the  nerve-trunk  which  is  first 
fatigued,  for  this  still  shows  the  negative  variation  on  being 
excited.  And  if  the  two  sciatic  nerves  of  a  frog  or  rabbit 
be  stimulated  continuously  with  interrupted  currents  of 
equal  strength,  while  the  excitation  is  prevented  from  reach- 
ing the  muscles  of  one  limb  till  those  of  the  other  cease  to 
contract,  it  will  be  found  that  when  the  *  block '  is  removed 
the  corresponding  muscles  contract  vigorously  on  stimulation 
of  their  nerve.  The  passage  of  a  constant  current  through 
a  portion  of  the  nerve  or  the  application  of  ether  between 
the  point  of  stimulation  and  the  muscles  may  be  used  to 
prevent  the  excitation  from  passing  down  (p.  596). 

The  possible  seats  of  fatigue  caused  by  voluntary  muscular 
contraction  are  (i)  the  muscle,  (2)  the  nerve-endings,  (3)  the 
nerve-trunk,  and  (4)  the  central  nervous  system.  Actual 
experiments  (Mosso  and  Maggiora,  Lombard — p.  597)  have 
shown  that  fatigue  after  voluntary  effort  is  chiefly  central, 
and  not  in  the  muscles  and  nerves  themselves.  Electric; 
stimulation,  either  of  a  '  tired '  muscle  or  of  its  nerve,  is 
readily  responded  to  at  a  time  when  voluntary  contraction 
is  impossible. 

(d)  The  Influence  of  Drugs  on  the  Contraction  of  Muscle. — 
The  total  work  which  a  muscle  can  perform,  its  excitability 
and  the  absolute  force  of  the  contraction,  may  all  be  altered 
either  in  the  plus  or  the  minus  sense  by  drugs.  But  in 
connection  with  our  present  subject  those  drugs  which  con- 


MUSCLE 


55* 


spicuously  alter  the  form  and  time-relations  of  the  muscle- 
curve  have  most  interest.  Of  these  veratria  is  especially 
important.  When  a  small  quantity  of  this  substance  is 
injected  below  the  skin  of  a  frog,  spasms  of  the  voluntary 
muscles,  well  marked  in  the  limbs,  come  on  in  a  few  minutes. 
These  are  attended  with  great  stiffness  of  movement,  for 
while  the  animal  can  contract  the  extensor  muscles  of  its 
legs  so  as  to  make  a  spring,  they  relax  very  slowly,  and 
some  time  elapses  before  it  can  spring  again.  If  it  be  killed 
before  the  reflexes  are  completely  gone,  the  peculiar  altera- 
tions in  the  form  of  the  muscle-curve  caused  by  veratria 
will  be  most  marked.  The  poisoned  muscle,  stimulated 
directly  or  through 
its  nerve,  con- 
tracts as  rapidly  as 
a  normal  muscle, 
while  the  height 
of  the  curve  is  as 
great,  or  even  FlG.  17I._vERATRiA  CURVE. 

greater,      but      the  Frog's  gastrocnemius. 

relaxation  is  enor- 
mously prolonged  (Fig.  171).  This  effect  seems  to  be  to  a 
considerable  degree  dependent  on  temperature,  and  it  may 
temporarily  disappear  when  the  muscle  is  made  to  contract 
several  times  without  pause.  Barium  salts,  and  in  a  less 
degree  those  of  strontium  and  calcium,  have  an  action  on 
muscle  similar  to  that  of  veratria  (p.  598). 

(e)  The  individuality  of  the  muscle  itself  has  an  influence 
on  the  muscle-curve.  Not  only  do  the  muscles  of  different 
animals  vary  in  the  rapidity  of  contraction,  but  there  are 
also  differences  in  the  skeletal  muscles  of  the  same  animal. 
In  the  rabbit  there  are  two  kinds  of  striped  muscle,  the  red 
and  the  pale  (the  semitendinosus  is  a  red,  and  the  adductor 
magnus  a  pale  muscle),  and  the  contraction  of  the  former 
is  markedly  slower  than  that  of  the  latter. 

In  many  fishes  and  birds,  and  in  some  insects,  a  similar 
difference  of  colour  and  structure  is  present,  although  a 
physiological  distinction  has  not  here  been  worked  out. 

Even  where  there  is  no  distinct  histological  difference, 


552  A  MANUAL  OF  PHYSIOLOGY 

there  may  be  great  variations  in  the  length  of  contraction. 
In  the  frog,  for  instance,  the  hyoglossus  muscle  contracts 
much  more  slowly  than  the  gastrocnemius.  The  wave  of 
contraction,  which  in  frogs'  striped  muscle  lasts  only  about 
•07  second  at  any  point,  may  last  a  second  in  the  forceps 
muscle  of  the  crayfish,  though  only  half  as  long  in  the 
muscles  of  the  tail.  In  the  muscles  of  the  tortoise  the  con- 
traction is  also  very  slow.  The  muscles  of  the  arm  of  man 
contract  more  quickly  than  those  of  the  leg. 

Summation  of  Stimuli   and   Superposition  of  Contractions.  — 
Hitherto  we  have  considered  a  single  muscular  contraction 

as  arising  from  a  single 
stimulus,  and  we  have 
assumed  that  the  muscle 
has  completed  its  curve 
and  come  back  to  its 
original  length  before  the 
next  stimulus  was  thrown 
in.  We  have  now  to  in- 
FIG.  172.  —  SUPERPOSITION  OF  CONTRAC-  quire  what  happens  when 
TIONS*  a  second  stimulus  acts 

i  is  the  curve  when  only  one  stimulus  is  ,  i        j      • 

thrown  in  ;  2,  when  a  second  stimulus  acts       Upon     trie     mUSCle     during 


at  the  time  when  curve  i  has  nearly  reached       fae  mntrartinn    ransprl    hv 

its  maximum  height.  me  contraction  causea  Dy 

a  first  stimulus,  or  during 

the  latent  period  before  the  contraction  has  actually  begun  ; 
and  what  happens  when  a  whole  series  of  rapidly-succeeding 
stimuli  are  thrown  into  the  muscle. 

#)  First  let  us  take  two  stimuli  separated  by  a  smaller 
^interval  than  the  latent  period  (p.  541).  If  they  are  both 
maximal  (i.e.,  if  each  by  itself  would  produce  the  greatest 
amount  of  contraction  of  which  the  muscle  is  capable  when 
excited  by  a  single  stimulus),  the  second  has  no  effect  what- 
ever, the  contraction  is  precisely  the  same  as  if  it  had  never 
acted.  But  if  they  are  less  than  maximal,  the  contraction, 
although  it  is  a  single  contraction,  is  greater  than  would 
have  been  due  to  the  first  stimulus  alone;  in  other  words, 
the  stimuli  have  been  summed  or  added  to  each  other  during 
the  latent  period  so  as  to  produce  a  single  result. 

Next  let  us  consider  the  case  of  two  stimuli  separated  by 


MUSCLE  553 

a  greater  interval  than  the  latent  period,  so  that  the  second 
falls  into  the  muscle  during  the  contraction  produced  by  the 
first.  The  result  here  is  very  different :  traces  of  two  con- 
tractions appear  upon  the  muscle-curve,  the  second  curve 
being  that  which  the  second  stimulus  would  have  caused 
alone,  but  rising  from  the  point  which  the  first  had  reached 
at  the  moment  of  the  second  shock  (Fig.  172).  Although 
the  first  curve  is  cut  short  in  this  manner,  the  total  height 
of  the  contraction  is  greater  than  it  would  have  been  had 
only  the  first  stimulus  acted;  and  this  is  true  even  when 
both  stimuli  are  maximal.  Under  favourable  circumstances, 
when  the  second  curve  rises  from  the  apex  of  the  first,  the 


FIG.  173. — TETANUS. 

i,  5  stimuli  per  second  ;  2, 15  per  second ;  3,  15  per  second,  when  muscle  was  more 
exhausted  than  in  2. 

total  height  may  be  twice  as  great  as  that  of  the  contraction 
which  one  stimulus  would  have  caused  (p.  599). 

Not  only  may  we  have  superposition  or  fusion  of  two 
contractions,  but  of  an  indefinite  number;  and  a  series 
of  rapidly  following  stimuli  causes  complete  tetanus  of  the 
muscle,  which  remains  contracted  during  the  stimulation,  or 
till  it  is  exhausted  (Fig.  173). 

The  meaning  of  a  complete  tetanus  is  readily  grasped  if, 
beginning  with  a  series  of  shocks  of  such  rapidity  that  the 
muscle  can  just  completely  relax  in  the  intervals  between 
successive  stimuli,  we  gradually  increase  the  frequency 
(p.  600).  As  this  is  done,  the  ripples  on  the  curve  become 
smaller  and  smaller,  and  at  last  fade  out  altogether.  The 


554  A  MANUAL  OF  PHYSIOLOGY 

maximum  height  of  the  contraction  is  greater  than  that  pro- 
duced by  the  strongest  single  stimulus  ;  and  even  after  com- 
plete fusion  has  been  attained,  a  further  increase  of  the 
frequency  of  stimulation  may  cause  the  curve  still  to  rise. 

It  is  evident  from  what  has  been  said  that  the  frequency 
of  stimulation  necessary  for  complete  tetanus  will  depend 
upon  the  rapidity  with  which  the  muscle  relaxes ;  and 
everything  which  diminishes  this  rapidity  will  lessen  the 
necessary  frequency  of  stimulation.  A  fatigued  muscle  may 
be  tetanized  by  a  smaller  number  of  stimuli  per  second 
than  a  fresh  muscle,  and  a  cooled  by  a  smaller  number  than 
a  heated  muscle.  The  striped  muscles  of  insects,  which 
,  can  contract  a  million  times  in  an  hour,  require  300  stimuli 
per  second  for  complete  tetanus,  those  of  birds  100,  of  man 
40,  the  torpid  muscles  of  the  tortoise  only  3.  The  pale 
muscles  of  the  rabbit  need  20  to  40  excitations  a  second,  the 
red  muscles  only  10  to  20  ;  the  tail  muscles  of  the  crayfish 
40,  but  the  muscles  of  the  claw  only  6  in  winter  and  20  in 
summer.  The  gastrocnemius  of  the  frog  requires  30  stimuli  a 
second,  the  hyoglossus  muscle  only  half  that  number  (Richet). 

We  see,  then,  that  there  is  a  lower  limit  of  frequency  of  stimula- 
tion below  which  a  given  muscle  cannot  be  completely  tetanized,  and 
the  question  arises  whether  there  is  also  an  upper  limit  beyond  which 
a  series  of  stimuli  becomes  too  rapid  to  produce  complete  tetanus, 
or,  indeed,  to  cause  contraction  at  all.  We  may  be  certain  that  every 
stimulus  requires  a  finite  time  to  produce  an  effect,  and  it  is  possible 
that  if  the  duration  of  each  shock  were  reduced  below  a  certain 
minimum,  without  lessening  at  the  same  time  the  interval  between 
successive  excitations,  no  contraction  would  be  caused  by  any  or  all 
of  the  stimuli  in  the  series.  But  above  this  minimum  there  appar- 
ently lies  a  frequency  of  stimulation — at  least,  when  the  interval 
between  the  stimuli  is  reduced  exactly  in  the  same  proportion  as  the 
duration — at  which  an  interrupted  current  comes  to  act  like  a  constant 
current,  causing  a  single  twitch  at  its  commencement  or  at  its  end, 
but  no  contraction  during  its  passage. 

As  to  this  last  limit,  on  the  fixing  of  which  much  labour  has  been 
expended  without  any  harmony  of  result,  it  undoubtedly  does  not 
depend  upon  the  frequency  of  stimulation  alone  ;  the  intensity  of  the 
individual  excitations,  the  temperature  of  the  muscle,  and  probably 
other  factors,  affect  it.  For  Bernstein  found  that  with  moderate 
strength  of  stimulus  tetanus  failed  at  about  250  per  second,  and  was 
replaced  by  an  initial  contraction  ;  with  strong  stimuli  at  more  than 
1,700  per  second,  tetanus  could  still  be  obtained.  Kronecker  and 
Stirling,  stimulating  the  muscle  by  a  novel  and  ingenious  method 


MUSCLE  555 

(by  induced  currents  set  up  in  a  coil  by  the  longitudinal  vibrations  of 
a  magnetized  bar  of  iron),  saw  complete  tetanus  even  at  24,000 
stimuli  a  second ;  while  v.  Kries  in  a  cooled  muscle  found  tetanus 
replaced  by  the  simple  initial  twitch  at  100  stimuli  per  second, 
although  in  a  muscle  at  38°  C.  stimulation  of  ten  times  this  frequency 
still  caused  tetanus.  But  it  is  doubtful  whether  the  electrical  method 
of  stimulation  is  capable  of  solving  the  problem,  because  of  the 
difficulty  of  being  sure  that  the  number  of  excitations  is  the  same  as 
the  nominal  number  of  shocks,  all  the  more  that  even  very  short 
currents  leave  alterations  of  conductivity  and  excitability  behind 
them  (Sewall),  which  we  shall  have  to  discuss  in  another  chapter 
(P-  574)- 

It  is  only  while  the  actual  shortening  is  taking  place  that 
a  tetanized  muscle  can  do  external  work.  But  although 
during  the  maintenance  of  the  contraction  no  work  is  done, 
energy  is  nevertheless  being  expended,  for  the  metabolism  of 
a  muscle  during  tetanus  is  greater  than  during  rest.  Among 
other  changes,  the  carbon  dioxide  given  off  is  increased,  and 
lactic  acid  produced.  And  upon  the  whole  a  muscle  is 
more  quickly  exhausted  by  tetanus  than  by  successive  single 
contractions,  although  there  are  great  differences  between 
different  muscles.  For  example,  the  muscles  which  close  the 
forceps  of  the  crayfish  or  lobster  have,  as  everyone  knows, 
the  power  of  most  obstinate  contraction.  Richet  tetanized 
one  for  over  seventy  minutes,  and  another  for  an  hour  and 
a  half,  before  exhaustion  came  on,  while  a  tetanus  of  a 
single  minute  exhausted  the  muscles  of  the  crayfish's  tail. 
The  gastrocnemius  of  a  summer  frog  kept  up  for  twelve 
minutes,  and  a  tortoise  muscle  for  forty  minutes. 

Continuous  stimulation  is  not  always  necessary  for  the 
production  of  continuous  contraction ;  in  some  conditions 
a  single  stimulus  is  sufficient.  A  blow  with  a  hard  instru- 
ment  may  cause  a  dying  or  exhausted,  and  in  thin  persons 
even  a  fairly  normal,  muscle  to  pass  into  long-continued 
contraction.  This  so-called  '  idio-muscular '  contraction 
seems  to  depend,  in  part  at  least,  on  the  great  intensity  of 
the  stimulus. 

The  rate  at  which  the  wave  of  muscular  contraction  travels 
may  be  measured  by  stimulating  the  muscle  at  one  end,  and 
recording,  by  means  of  levers,  the  movements  of  two  points 
of  its  surface  as  far  apart  from  each  other  as  possible. 


556  A  MANUAL  OF  PHYSIOLOGY 

Time  is  marked  on  the  tracing  by  means  of  a  tuning-fork, 
and  the  distance  between  the  points  at  which  the  two 
curves  begin  to  rise  from  the  base-line  divided  by  the 
time  gives  the  velocity  of  the  wave.  Another  method  is 
founded  upon  the  measurement  of  the  rate  at  which  the 
negative  variation  (p.  607)  passes  over  the  muscle,  this  being 
jthe  same  as  the  velocity  of  the  contraction-wave.  In  frog's 
muscle  it  is  about  three  metres  a  second,  or  six  miles  an  hour. 
"fcise  of  temperature  increases,  fall  of  temperature  lessens  it. 

When  a  muscle  is  excited  through  its  nerve,  the  contrac- 
tion springs  up  first  of  all  about  the  middle  of  each  mus- 
cular fibre  where  the  nerve-fibre  enters  it,  and  then  sweeps 
out  in  both  directions  towards  the  ends.  But  so  long  is  the 
wave,  that  all  parts  of  the  fibre  are  at  the  same  time  in- 
volved in  some  phase  or  other  of  the  contraction.  And  this 
is  the  case  even  when  the  end  of  a  long  muscle  like  the 
sartorius  is  artificially  stimulated. 

The  wave  of  contraction  in  unstriped  muscle  lasts  a 
relatively  long  time  at  any  given  point,  and  in  tubes  like  the 
intestines  and  ureters,  the  walls  of  which  are  largely  com- 
posed of  smooth  muscle  arranged  in  rings,  the  wave  shows 
itself  as  a  gradually-advancing  constriction  travelling  from 
end  to  end  of  the  organ.  There  is  no  evidence  that  the  con- 
traction of  smooth  muscular  fibres  is  discontinuous — that  is, 
composed  of  summated  contractions  like  a  tetanus;  it  appears 
to  be  a  greatly-prolonged  simple  contraction  of  the  kind 
called  'tonic.'  An  artificial  stimulus,  mechanical  or  elec- 
trical, causes,  after  a  long  latent  period,  a  very  definitely- 
localized  contraction  in  a  rabbit's  ureter,  which  slowly 
spreads  in  a  peristaltic  wave  in  one  or  both  directions  along 
the  muscular  tube.  Here,  as  in  the  cardiac  muscle,  the 
excitation  passes  from  fibre  to  fibre,  while  in  striped  skeletal 
muscle  only  the  fibres  excited  directly  or  through  their 
nerves  seem  to  contract.  ^  That  the  rhythmical  contraction 
of  the  heart  isjiot  a  tetahusnas  already  been  seen.  It  is 
a  simple  contraction,  intermediate  in  its  duration  and  other 
characters  between  the  twitch  of  voluntary  muscle  and  the 
tonic  contraction  of  smooth  muscle.  The  contraction  both 
of  unstriped  and  of  cardiac  muscle  is  lengthened  and  made 


MUSCLE  557 

stronger  by  distension  of  the  viscera  in  whose  walls  they 
occur,  just  as  a  skeletal  muscle  contracts  more  powerfully 
against  resistance. 

Voluntary  Contraction. — It  is  often  stated  that  the  volun- 
tary contraction  is  a  tetanus,  but  in  favour  of  this  belief 
there  is  very  little  direct  evidence.     One  of  the  strongest 
buttresses  of  the  theory   of  natural   tetanus   has  been  the 
muscle-sound.     Discovered  about  eighty  years  ago,   first  by 
Wollaston  and  then  by  Erman,  half  a  century  passed  away 
before  it  was  investigated  more  fully  by  Helmholtz.     The 
latter  observer,  confirming  the  results  of  his  predecessors, 
put  down  the  pitch  of  the  low  rumbling  sound  heard  when 
the  masseter  contracts  in  closing  the  jaws  at  36  to  40  vibra- 
tions per  second.     He  found,  however,  that  little  vibrating 
reeds  with  a  rate  of  oscillation  of  about  19-5  per  second, 
were  more  affected,  when  attached  to  muscle  thrown  into 
voluntary  contraction,  than  those  that  vibrated  at  a  smaller 
or  a  greater  rate.     He  therefore  concluded  that  the  funda- 
mental tone  of  the  muscle  corresponded  to  this  frequency, 
although,  since  such  a  low  note  is  not  easily  appreciated,  the 
sound  actually  heard  was  really  its  octave  or  first  harmonic 
(p.  263).     The  objection  has  been  brought  forward  that  the 
resonance  tone  of  the  ear  also  corresponds  to  a  vibration 
frequency   of  36   to   40  a  second.     Now,   if  this  resonance 
tone  were  elicited  by  the  muscular  vibrations  in  sufficient 
strength  to  overpower  the  proper  note  of  the  muscle,  then, 
whatever  the  rate  of  these  vibrations  might  be,  the  resonance 
tone  would  appear  to  be  the  sound  produced  by  the  muscle. 
But  while  this  renders  it  highly  probable  that  the  resonance 
of  the  ear  contributes  to  the  production  of  the  muscle-sound, 
and  shows  that  we  cannot  from  the  pitch  of  the  muscle- 
sound   alone   deduce   the    rate    at   which  the   muscle-sub- 
stance is  vibrating,  it  does  not  invalidate  Helmholtz's  objec- 
tive observations  with  the  oscillating  reeds.     And  several 
observers  (Schafer,  Horsley,  v.  Kries)  have  noticed  periodic 
oscillations,  at  the  rate  of  8  to  10  per  second,  in  the  curves 
taken  from  voluntarily  contracted  muscles,  and  from  muscles 
excited  through  stimulation  of  the  motor  areas  of  the  surface 
of  the  brain.     Since  this   rate  remains   the   same  whether 


558  A  MANUAL  OF  PHYSIOLOGY 

the  motor  cortex,  the  corona  radiata,  or  the  spinal  cord  is 
excited,  and,  unlike  the  rate  of  response  to  excitation  of 
peripheral  nerves,  is  independent  of  the  frequency  of  stimu- 
lation, it  has  been  supposed  to  represent  the  rhythm  with 
which  impulses  are  discharged  from  the  motor  cells  of  the 
cord  (Fig.  174).  Other  observers  have  seen  a  rhythm  of  20 
per  second ;  while  Haycraft  denies  that  regular  oscillations 
occur  at  all,  and  thinks  that  irregularities  in  the  contraction, 
connected  with  a  want  of  co-ordination  of  all  the  fibres,  cause 
the  muscle-sound  by  drawing  forth  the  resonance  tone  of  the 
ear  itself.  Loven,  however,  found  the  rhythm  of  strychnia 
tetanus  in  the  frog  about  8  to  10  per  second,  and  asserted 
that  by  means  of  the  capillary  electrometer  (p.  524)  an 


FIG.  174.— CONTRACTIONS  CAUSED  BY  STIMULATION  OF  THE  SPINAL  CORD. 

electrical  oscillation  of  8  per  second  could  be  demonstrated 
in  voluntarily  contracted  muscle.  This  last  statement,  if 
confirmed,  would  be  strong  evidence  for  the  discontinuity  of 
at  least  some  voluntary  contractions.  But  against  it  we 
must  put  the  fact  that  secondary  tetanus  (p.  621)  is  not 
caused  by  muscle  in  voluntary  contraction,  except  (and  even 
this  is  doubtful)  just  at  the  beginning.  This,  indeed,  is  not 
incompatible  with  the  existence  of  natural  tetanus,  since 
chemical  stimulation,  which  certainly  sets  up  a  state  of  con- 
traction analogous  to  experimental  tetanus,  does  not  cause 
secondary  tetanus ;  but  we  still  lack  a  decisive  proof  that 
voluntary  contraction  is  maintained  by  a  strictly  intermittent 
outflow  of  nervous  energy,  and  not  by  a  continuous  outflow, 


MUSCLE  559 

which,  it  may  be,  remits  and  is  reinforced  at  intervals.  In 
any  case,  some  voluntary  contractions,  namely,  the  shortest 
possible,  do  not  seem  to  be  tetanic.  For  a  voluntary  move- 
ment can  be  executed  in  rV  to  ¥V  of  a  second,  which,  if  we 
take  the  greatest  frequency  of  discharge  in  natural  tetanus 
that  has  been  suggested,  would  allow  time  only  for  a  single 
oscillation,  caused  by  a  single  impulse. 

(3)  Thermal  Phenomena  of  the  Muscular  Contraction. — When 
a  muscle  contracts  its  temperature  rises ;  the  production  of 
heat  in  it  is  increased.  This  is  most  distinct  when  the 
muscle  is  tetanized,  but  has  also  been  proved  for  single  con- 
tractions. The  change  of  temperature  can  be  detected  by 
a  delicate  mercury  or  air  thermometer ;  and,  indeed,  a 
thermometer  thrust  among  the  thigh-muscles  of  a  dog  may 
rise  as  much  as  i°  to  2°  C.  when  the  muscles  are  thrown 
into  tetanus.  In  the  isolated  muscles  of  cold-blooded  animals 
the  increase  of  temperature  is  much  less  ;  and  electrical 
methods,  which  are  the  most  delicate  at  present  known, 
have  generally  been  used  for  its  detection  and  measurement. 

They  depend  either  upon  the  fundamental  fact  of  thermo-elec- 
tricity, that  in  a  circuit  composed  of  two  metals  a  current  is  set  up  if 
the  junctions  of  the  metals  are  at  different  temperatures ;  or  upon 
the  fact  that  the  electrical  resistance  of  a  metallic  conductor  varies 
with  its  temperature. 

On  the  former  principle  the  thermopile  has  been  constructed 
(Fig.  175),  on  the  latter  the  bolometer,  or  ''electrical-resistance  ther- 
mometer. ' 

Where  no  very  fine  differences  of  temperature  are  to  be  measured, 
a  single  thermo-j unction  of  German  silver  and  iron,  or  copper  and  iron, 
is  inserted  into  a  muscle  or  between  two  muscles.  But  the  electro- 
motive force,  and  therefore  the  strength  of  the  thermo-electric 
current,  is  proportional  for  any  given  pair  of  metals  to  the  number  of 
junctions,  and  for  delicate  measurements  it  may  be  necessary  to  use 
several  connected  together  in  series.  A  thermopile  of  antimony- 
bismuth  junctions  gives  a  stronger  current  for  a  given  difference  of 
temperature  than  the  same  number  of  German  silver-iron  couples, 
but  from  its  brittle  nature  is  otherwise  less  convenient. 

The  direction  of  the  current  in  the  circuit  is  such  that  it  passes 
through  the  heated  junction  from  bismuth  to  antimony,  and  from 
copper  or  German  silver  to  iron.  Knowing  this  direction,  we  are 
aware  of  the  changes  of  temperature  which  take  place  from  the  move- 
ments of  the  mirror  of  the  galvanometer  with  which  the  pile  is  con- 
nected. The  galvanometer  must  be  of  low  resistance,  since  thd 
electromotive  force  of  the  thermo-electric  currents  is  small,  and  a* 
high  resistance  would  cut  down  their  intensity  too  much. 


56o 


A  MANUAL  OF  PHYSIOLOGY 


The  muscle  which  is  to  be  excited  is  brought  into  close 
contact  with  one  junction  or  set  of  junctions,  the  other  set 
being  kept  at  constant  temperature  by  immersing  them  in 
water,  or  covering  them  with  muscle  that  is  not  to  be 
stimulated.  The  image  will  now  come  to  rest  on  the  scale ; 
and  excitation  of  the  muscle  will  cause  a  movement  indicat- 
ing an  increase  of  temperature  in  it,  the  amount  of  which 
can  be  calculated  from  the  deflection. 

In  this  way  Helmholtz  observed  a  rise  of  temperature  of 

•14°  to  -18°  C.  in  ex- 
cised frogs'  muscles 
when  tetanized  for  a 
couple  of  minutes. 

Heidenhain,  with  a 
very  delicate  pile, 
found  a  rise  of  '001° 
to  '005°  C.  for  a  single 
contraction  of  a  frog's 
muscle.  On  the  as- 
sumption that  the  pile 
had  time  to  take  on 
the  temperature  of  the 
muscle  before  there 
was  any  appreciable 
loss  of  heat,  this  would 


FIG.  175. 


A,  a  single  copper-iron  thermo-electric  couple  ; 
B/,  two  pairs,  one  inserted  into  the  tissue  b,  the 
other  dipping  into  water  in  a  beaker  a.  The  tem- 
perature of  the  water  may  be  adjusted  so  that  the 
galvanometer  shows  no  deflection.  The  temperature 
of  the  tissue  is  then  the  same  as  that  of  the  water. 


be  equal  to  the  pro- 
duction by  every  gramme  of  muscle  of  a  thousandth  to  five- 
thousandths  of  a  small  calorie  (p.  479)  of  heat.  From  Pick's 
observations  we  may  take  about  three-thousandths  of  a 
small  calorie  as  the  maximum  production  of  a  gramme  of 
frog's  muscle  in  a  single  contraction. 

It  is  certain  that  when  work  is  done  by  a  muscle  an  equi- 
valent amount  is  subtracted  from  its  sum-total  of  energy, 
and  we  might  therefore  expect  that  the  heat  produced  in 
contraction  should  diminish  as  the  work  increases.  But 
experiment  does  not  fulfil  this  expectation.  The  manner 
and  the  rate  of  its  expenditure  of  energy  depend  upon  the 
conditions  under  which  the  muscle  is  placed.  The  mere 
stretching  of  a  muscle  increases  its  metabolism,  and  there- 


MUSCLE  561 

fore  its  heat-production ;  and  a  stretched  muscle,  when 
caused  to  contract,  produces  more  heat  than  if  it  had  started 
without  tension,  and  still  more  heat  when  it  is  fixed  so  that 
it  cannot  shorten  during  stimulation.  This  last  fact  does 
not,  however,  prove  that  the  heat-production  is  greater 
when  no  work  is  done,  because  the  tension  increases  during 
excitation  when  contraction  is  prevented,  and  we  know  that 
increase  of  tension  alone  causes  more  heat  to  be  given  out. 
For  example,  more  heat  is  produced  by  a  muscle  when  it 
contracts  isometrically  than  when  it  contracts  isotonically. 

When  a  muscle,  excited  by  maximal  stimuli,  is  made  to 
lift  continuously  increasing  weights,  both  the  work  done  and 
the  heat  given  out  increase  up  to  a  certain  limit.  The 
muscle,  as  it  were,  burns  the  candle  at  both  ends.  This 
would  be  of  itself  enough  to  show  that  there  is  no  fixed 
relation  between  the  work  and  the  heat-production;  although 
the  latter  reaches  its  maximum  somewhat  sooner  than  the 
former. 

We  have  already  seen  that  when  a  muscle  is  cooled,  or 
fatigued,  or  poisoned  with  veratria  or  with  suprarenal  extract, 
the  stress  of  the  change  falls  chiefly  upon  the  relaxation. 
This  indicates  that  the  relaxation  is  by  no  means  a  mere 
elastic  recoil,  but  a  physiological  process  as  important  as 
the  contraction  itself;  and  this  conclusion  is  strengthened 
by  the  fact  we  have  now  to  mention,  that  not  only  is  heat 
produced  during  the  actual  shortening,  but  also  during  the 
relaxation.  If  a  muscle  is  allowed  to  contract  without 
raising  any  weight,  and  is  loaded  just  at  the  top  of  its  lift, 
so  that  the  load  acts  only  during  relaxation,  more  heat  is 
produced  than  when  no  weight  is  applied ;  and  the  heavier 
the  weight,  the  greater  is  the  heat-production. 

The  fraction  of  the  total  energy  transformed  which 
appears  as  muscular  work,  varies  with  the  conditions  of  the 
contraction.  The  greater  the  resistance,  the  larger  is  the 
proportion  of  the  energy  which  appears  as  work,  the  smaller 
the  proportion  which  appears  as  heat ;  but  even  in  the  most 
favourable  case,  an  excised  frog's  muscle  never  does  work 
equal  to  more  than  \  of  the  heat  given  off.  Generally  the 
ratio  is  much  less,  and  may  sink  as  low  as  -fj.  In  the  intact 

36 


562  A  MANUAL  OF  PHYSIOLOGY 

mammalian  body  it  is  probable  that  the  muscles  work  at 
least  as  economically  as  the  excised  frog's  muscle  under 
the  most  favourable  conditions;  for  both  experiment  and 
calculation  show  (p.  488)  that  in  a  normal  man  not  less 
than  ^,  nor  more  than  J,  of  the  whole  energy  transformed 
in  the  body  is  converted  into  work.  But  in  any  case 
the  heat -producing  mechanism  and  the  work -producing 
mechanism  of  muscle  are  certainly  in  some  respects  distinct, 
and  a  variation  in  the  activity  of  the  one  is  not  necessarily 
associated  with  a  corresponding  variation  in  the  activity  of 
the  other. 

(4)  Chemical  Phenomena  of  the  Muscular  Contraction. — We  as 
yet  know  but  little  regarding  the  chemical  composition  of  living 
muscle,  and  are  unlikely  ever  to  know  much,  since  most  chemical 
Orations  cause  the  immediate  death  of  the  tissue.     The  composition 
dead  mammalian  muscle  may  be  stated,  in  round  numbers,  as 
follows,  but  there  are  considerable  variations,  even  within  the  same 

Water 75  per  cent. 

Proteids          20       „ 

Fats 2 

Nitrogenous 
metabolites. 

Carbohydrates.   (£E3iSc  add 

Inosit 

vo~  Salts,  chiefly  carbonate  and  phosphate  of  potassium,  less)  than 

H  i  per  cent. 

-  *'\          There  is  more  water  in  the  muscles  of  young  than  of  old  anii 
__  ^^°   (v.  Bibra),  and  more  in  tetanized  than  in  rested  muscle  (Ranke) 
—          The  fats  probably  belong  to  a  small  extent  to  the  actual  muscl* 

fibres.     For  even  when  the  visible  fat  is  separated  with  the  utmoj 
n  care,  nearly  i  per  cent,  of  fat  still  remains  (Steil).     In  lean  horse 

flesh  Pfliiger  found  0*35  per  cent,  of  glycogen,  but  no  sugar.     Tl 
^"  total  nitrogen  was  3-21  per  cent,  of  the  moist  tissue. 

M 

'" ,  It  would  be  natural  to  expect  that  the  proteids,  whicl 

ftmJLj^    (A  t~*» 

bulk  so  largely  among  the  solids  of  the  dead  muscle,  am 
which  are  so  obviously  important  in  the  living  muscle, 
should  be  affected  by  contraction.  But  up  to  the  presenl 
time  no  quantitative  difference  in  the  proteids  of  resting  am 
exhausted  muscle  has  ever  been  made  out.  The  following 
chemical  changes,  however,  have  been  definitely  established, 
In  an  active  muscle — 


MUSCLE  563 

(a)  More  carbon  dioxide  is  produced. 

(b)  More  oxygen  is  consumed. 

(c)  Sarcolactic  acid  is  formed. 

(d)  Glycogen  is  used  up. 

(e)  The  substances  soluble  in  water  diminish  in  amount ;  those 

soluble  in  alcohol  increase. 

That  the  carbon  dioxide  is  not  formed  by  direct  oxida- 
tion, but  by  the  splitting  up  of  a  substance  or  substances 
with  which  the  oxygen  has  previously  combined,  is,  as  has 
already  been  shown  (pp.  247,  248),  highly  probable.  For  (to 
recapitulate)  (a)  no  free  oxygen  exists  in  muscle.  None  can 
be  pumped  out.  (6)  A  frog's  muscle  isolated  from  the  body 
will  go  on  contracting  for  a  long  time  in  an  atmosphere 
devoid  of  oxygen,  e.g.,  in  an  atmosphere  of  hydrogen. 
(c)  When  artificial  circulation  is  maintained  through  isolated 
muscles,  the  amount  of  carbon  dioxide  produced  does  not 
run  parallel  with  the  quantity  of  oxygen  consumed.  The 
latter  is  dependent  on  the  temperature  of  the  muscle, 
being  increased  when  the  muscle  is  heated,  diminished 
when  it  is  cooled.  The  production  of  carbon  dioxide,  on 
the  contrary,  is,  within  a  wide  range,  independent  of  the 
temperature. 

Formation  of  Sarcolactic  Acid — Reaction  of  Muscle. — To 
litmus  paper  fresh  muscle  is  amphicroic;  that  is,  it  turns 
red  litmus  blue  and  blue  litmus  red.  This  is  due,  partly 
at  least,  to  the  phosphates.  Monophosphate  (tribasic  phos- 
phoric acid  in  which  one  hydrogen  atom  is  replaced,  say 
by  sodium  or  potassium)  reddens  blue  litmus,  while  diphos-  <, 
phate  (where  two  hydrogen  atoms  are  replaced)  turns  red 
litmus  blue.  Litmoid  (lacmoid)  differs  from  litmus  in  not 
being  affected  by  monophosphates.  Diphosphates  turn  red 
litmoid  blue.  A  cross -section  of  fresh  muscle  is  about 
neutral  to  turmeric  paper  (sometimes  faintly  acid),  while 
that  of  a  rigid  or  tetanized  muscle  is  distinctly  acid,  brown 
turmeric  being  turned  strongly  yellow.  The  Sarcolactic  acid 
produced  in  rigor  and  activity  is  at  once  neutralized,  as  is 
shown  by  the  fact  that  blue  litmoid  paper  is  not  reddened, 
as  it  would  be  by  free  Sarcolactic  acid.  The  neutralization 
takes  place  at  the  expense  of  the  sodium  carbonate  and 
disodium  phosphate,  the  latter  being  changed  into  mono- 

36—2 


564  A  MANUAL  OF  PHYSIOLOGY 

phosphate,  which,  in  part  at  least,  causes  the  acid  reaction 
to  turmeric  (Rohmann). 

Glycogen  is  the  one  solid  substance  which  has  been 
definitely  proved  to  diminish  in  muscle  during  activity.  It 
accumulates  in  a  resting  muscle,  especially  in  a  muscle 
whose  motor  nerve  has  been  cut ;  rapidly  disappears  from 
the  muscles  of  an  animal  made  to  do  work  while  food  is 
withheld ;  or  from  the  muscles  of  an  animal  poisoned  by 
strychnia,  which  causes  violent  muscular  contractions. 

What  substance  is  the  sarcolactic  acid  formed  from? 
From  what  we  know  of  the  production  of  lactic  acid  both 
outside  the  body  and  in  the  intestine  from  carbo-hydrates, 
it  might  seem  a  most  plausible  suggestion  that  in  the  active 
muscle  it  comes  from  glycogen.  But  all  the  evidence  points 
the  other  way ;  e.g.,  in  rigor  mortis  sarcolactic  acid  is  pro- 
duced just  as  in  muscular  contraction.  Not  only  so,  but 
according  to  Ranke  every  isolated  muscle  has  a  certain 
maximum  of  acidity,  which  it  reaches  either  through  con- 
traction, or  through  rigor,  or  through  contraction  followed 
by  rigor.  Yet  in  rigor  mortis  the  quantity  of  glycogen  is 
unaltered  (Boehm).  The  probability  is  that  the  sarcolactic 
acid  is  formed  from  proteid,  perhaps  by  the  action  of  a 
Jerment. 

Source  of  the  Energy  of  Muscular  Contraction. — The  facts 
just  mentioned  show  that  glycogen  may  be  one  of  the 
sources  of  muscular  energy,  but  it  cannot  be  the  only 
source,  for  its  amount  is  too  small. 

For  example,  the  heart  of  an  average  man,  which  weighs  280 
grammes,  contains  about  60  grammes  solids,  and  among  these  not 
more  than  i  -5  grammes  glycogen.  In  twenty-four  hours  it  produces, 
even  on  a  low  estimate,  at  least  250,000  calories  of  heat,  equivalent 
to  the  complete  combustion  of  about  60  grammes  of  glycogen.  To 
supply  this  amount,  the  whole  store  of  glycogen  in  the  heart  would 
have  to  be  used  and  replaced  every  half-hour.  But  the  accumulation 
of  glycogen  is  immensely  slower  in  the  muscles  of  a  rabbit  made 
glycogen-free  by  strychnia,  and  therefore  we  have  to  look  around  for 
some  other  source  of  energy  to  supplement  the  glycogen.  We  have 
already  brought  forward  evidence  (p.  459)  that,  under  ordinary  cir- 
cumstances, not  a  great  deal,  at  any  rate,  of  the  energy  of  muscular 
contraction  comes  from  the  proteids.  Of  carbohydrates,  the  only 
one  except  glycogen  which  is  at  all  adequate  to  the  task  of  supplying 
so  much  energy  is  the  glucose  of  the  blood.  The  quantity  of  blood 


MUSCLE  565 

passing  through  the  coronary  circulation  has  been  estimated  at  30  c.c. 

per  100  grammes  of  cardiac  muscle  per  minute  (Bohr  and  Henriques), 

which  would  be  equivalent  for  an  average  man  to  about  120  litres   .          ^ 

intwenty-four  hours.     This  quantity  of  blood  will  contain  at  least 

150  grammes  of  glucose,  and  70  grammes  will  suffice  to  supply  all" 

the  heat  produced   by  the  heart.      Of  proteids  a  little  less  than 

60  grammes  would  be  needed,  of  fat  more  than  25  grammes.     We 

see,  therefore,  how  intense  must  be  the  metabolism  that  goes  on  in 

an  actively  contracting  muscle.     On  any  probable  assumption  as  to 

the  source  of  muscular  energy  a  quantity  of  material  equal  to  the 

whole  of  its  solids  must  be  used  up  by  the  heart  in  twenty-four  hours. 

Or,  to  put  it  in  another  way,  the  heart  requires  not  less  than  half  its 

weight,  possibly  its  weight,  of  ordinary  solid  food  in  a  day.     The  body 

as  a  whole  requires  -^  to  TV  of  its  weight. 

To  sum  up  :  It  is  universally  admitted  that  carbohydrates 
can  yield  energy  for  muscular  work.  It  has  been  demon- 
strated by  Zuntz  and  his  pupils  and  by  others  that  fat  can 
do  so.  The  experiments  of  Pfliiger,  to  which  we  have 
already  alluded  (p.  460),  have  shown  than  when  an  animal 
is  fed  on  lean  meat,  the  muscular  work  done  is  far  too  great 
to  have  come  from  non-proteid  substances.  We  must 
conclude,  therefore,  that  when  carbohydrates  and  fats  are 
plentiful  in  the  food,  the  greater  part  of  the  energy  of 
muscular  contraction  comes  from  them  ;  it  comes  on  the 
other  hand  from  proteids,  when  the  carbohydrates  and  the 
fats  are  restricted,  and  the  proteids  plentifully  supplied. 
Not  only  so,  but  these  three  groups  of  food  substances  yield 
muscular  energy  in  isodynamic  relation.  In  other  words,  a 
given  amount  of  muscular  work  requires  the  expenditure 
of  approximately  the  same  quantity  of  chemical  energy, 
whether  it  comes  almost  entirely  from  proteid,  or  chiefly 
from  carbohydrates,  or  chiefly  from  fat.  Some  observers  have 
stated  that  the  taking  of  even  a  comparatively  small  quantity 
of  sugar  vastly  increases  the  capacity  for  muscular  work  as 
measured  by  the  ergograph  (p.  597).  But  although  it  is  not 
to  be  doubted  that  sugar  is  under  normal  circumstances  one 
of  the  most  important  substances  used  up  in  muscular  con- 
traction, the  claim  that  sugar  is,  par  excellence,  the  food  for 
muscular  exertion  has  not  yet  been  made  out. 

Rigor  Mortis. — When  a  muscle  is  dying  its  excitability, 
after  perhaps  a  temporary  rise  at  the  beginning,  diminishes 


566  A  MANUAL  OF  PHYSIOLOGY 

more  and  more  until  it  ultimately  responds  to  no  stimulus, 
however  strong.  The  loss  of  excitability  is  not  in  itself  a 
sure  mark  of  death,  for,  as  we  have  seen,  an  inexcitable 
muscle  may  be  partially  or  completely  restored  ;  but  it  is 
followed,  or,  where  the  death  of  the  muscle  takes  place 
very  rapidly,  perhaps  accompanied,  by  a  more  decisive 
event,  the  appearance  of  rigor.  The  muscle,  which  was 
before  soft  and  at  the  same  time  elastic  to  the  touch, 
becomes  firm  ;  but  its  elasticity  is  gone.  The  fibres  are  no 
longer  translucent,  but  opaque  and  turbid.  If  shortening 
of  the  muscle  has  not  been  opposed,  it  will  be  somewhat 
contracted,  although  the  absolute  force  of  this  contraction 
is  small  compared  with  that  of  a  living  muscle,  and  a  slight 
resistance  is  enough  to  prevent  it.  The  reaction  is  now 
distinctly  acid.  This  is  rigor  mortis,  the  death-stiffening  of 
muscle. 

An  insight  into  the  real  meaning  of  this  singular   and 
sometimes  sudden  change  was  first  given  by  the  experiments 
of  Kiihne.     He  took  living  frog's  muscle,  freed  from  blood, 
froze  it,  and  minced  it  in  the  frozen  state.     The  pieces  were 
then  rubbed  up  in  a  mortar  with  snow  containing  i  per  cent, 
of  common  salt,  and  a  thick  neutral  or  alkaline  liquid,  the 
muscle-plasma,   was   obtained   by   filtration.     This  clotted 
into  a  jelly  when  the  temperature  was  allowed  to  rise,  but 
at  o°  C.  remained  fluid.     The  clotting  was  accompanied 
a  change  of  reaction,  the  liquid  becoming  acid.     An  eqnalb 
good,  or  better,  method  is  to  use  pressure  for  the  extractioi 
of  the  plasma  from  the  frozen  fragments  of  muscle.     A 
temperature  is  essential,  otherwise  the  plasma  will  coagulate 
rapidly  within  the  injured  muscle. 

A  similar  plasma  can  be  expressed  from  the  skelete 
muscles  of  warm-blooded  animals  (Halliburton),  and  wit! 
greater  difficulty  from  the  heart.  Attempts  to  obtain  il 
from  smooth  muscle  have  hitherto  failed,  possibly  because 
of  the  unfavourable  anatomical  conditions. 

When  the  muscle,  after  exhaustion  with  water,  is  covere( 
with  a  solution  of  a  neutral  salt,  a  5  per  cent,  solution  ol 
magnesium  sulphate  or  10.  per  cent,  solution  of  ammoniui 
chloride  being  probably  the  best,  a  proteid  passes  int< 


MUSCLE  567 

solution,  which  is  identical  with  the  myosin  of  the  clotted 
plasma.  If  the  solution  is  diluted,  it  clots  just  as  the  muscle- 
plasma  clots,  and  the  clot  or  precipitate  ca.ii  be  dissolved 
and  reproduced  at  will  (Practical  Exercises,  p.  602).  The 
addition  of  potassium  oxalate  does  not  prevent  coagulation 
of  muscle-extracts,  as  it  does  of  blood  and  blood-plasma. 

From  all  this  we  gather  that  rigor  mortis  is  essentially  a 
clotting  or  coagulation  of  a  substance  which  yields  myosin. 
What  this  substance  is  we  cannot  tell.     Some  have  sup- 
posed that  in  the  living  muscle  there  exists  a  body,  myo-       /^ 
sinogen,  which  is  the  direct  precursor  of  the  myosin  in  thei/'  .^ 
muscle-clot  or  within  the  fibres  in  rigor  mortis,  and  which  isl. 
related  to  it  as  fibrinogen  is  related  to  fibrin  in  the  clotting  \  - 
of  blood.     It  has  even  been  assumed  that  this  very  myosin- 
ogen  is  formed  when  myosin  is  dissolved  in  a  salt  solution  ; 
but  this  hypothesis  is  not  backed  by  sufficient  evidence. 

Why  does  coagulation  of  myosin  occur  at  the  death  of 
the  muscle?  To  this  question  no  clearer  answer  can  be 
given  than  to  the  question  why  blood  clots  when  it  is  shed. 
Just  as  a  fibrin  ferment  is  developed  when  blood  begins  to 
die,  a  myosin  ferment,  which  aids  coagulation,  is  perhaps 
developed  in  dead  or  dying  muscle. 

It  has  been  suggested  that  myosin,  sarcolactic  acid,  and 
carbon  dioxide  are  all  products  of  some  complex  body 
which  breaks  up  both  at  the  death  of  the  muscle,  and 
during  contraction,  and  that,  indeed,  contraction  is  only  a 
transient  and  removable  rigor  (Hermann).  But  it  cannot 
be  admitted  that  there  is  any  fundamental  connection 
between  rigor  and  contraction,  although  there  are  some 
superficial  resemblances.  In  both  there  is  (i)  shorten- 
ing ;  (2)  heat-production ;  (3)  formation  of  fixed  acid  and 
carbon  dioxide;  (4)  an  electrical  change  (p.  607).  Another 
analogy  might  be  forced  into  the  list  by  anyone  who 
was  determined  to  see  only  rigor  in  contraction  :  the  rigor 
passes  off  as  the  contraction  passes  off,  although  the  '  resolu- 
tion '  of  a  rigid  muscle  takes  days,  the  relaxation  of  an 
active  muscle  a  fraction  of  a  second.  The  disappearance  of 
rigor  is  not  dependent  on  putrefaction ;  it  takes  place  when 
growth  of  bacteria  is  prevented  (Hermann). 


568  A  MANUAL  OF  PHYSIOLOGY 

Various  influences  affect  the  onset  of  rigor.  Fatigue 
hastens  it ;  heat  has  a  similar  effect ;  the  contact  of  caffeine, 
chloroform  and  other  drugs  causes  most  pronounced  and 
immediate  rigor.  Blood  applied  to  the  cross-section  of  a 
muscle  first  stimulates  the  fibres  with  which  it  is  in  contact, 
and  then  renders  them  rigid.  But  it  is  to  be  remembered 
that  normally  the  blood  does  not  come  into  direct  contact 
even  with  the  sarcolemma,  much  less  with  its  contents. 

The  effect  of  heat  is  of  special  interest.  A  skeletal  muscle  of  a 
frog,  like  the  gastrocnemius,  if  dipped  into  normal  saline  solution  at 
40°  or  41°  C.  goes  into  rigor  at  once  ;  the  frog's  heart  requires  a 
temperature  3°  or  4°  higher ;  the  distended  bulbus  aortae  can  with- 
stand even  a  temperature  of  48°  for  a  short  time.  An  excised 
mammalian  muscle  passes  into  immediate  rigor  at  45°  to  50°.  In 
heat  rigor  the  reaction  of  the  muscle  becomes  strongly  acid,  and  the 
acidity  is  due  to  a  fixed  acid  (sarcolactic),  not  to  carbon  dioxide, 
although  the  production  of  the  latter  is  greatly  increased.  A  small 
quantity  of  heat  is  produced,  and  the  temperature  of  the  muscle  may 
be  raised  as  much  as  -^r°  C.  This  is  probably  due  chiefly  to  the 
increased  chemical  change,  and  only  to  a  slight  extent  to  the  physical 
alteration  in  the  myosin.  Heat  rigor  is,  in  fact,  a  greatly  accelerated 
rigor  mortis,  and  the  myosin,  although  clotted,  is  not  rendered 
insoluble  like  a  heat-coagulated  proteid  (p.  603). 

When  muscle  is  suddenly  raised  to  a  temperature  of  75°  to  100°  C., 
we  have  quite  a  different  series  of  events.  There  is  no  acid  reaction, 
no  evolution  of  carbon  dioxide ;  the  muscle  is  indeed  rigid,  but  true 
rigor  has  not  taken  place,  and  the  rigidity  is  due  to  coagulation  of 
the  proteids  by  heat.  Rigor  is  a  change  which  cannot  go  on  when 
once  the  comparatively  mobile  substance  of  the  living  muscle,  or  of 
the  muscle  in  the  act  of  dying,  has  been  converted  into  the  stable 
form  of  coagulated  proteid.  No  sarcolactic  acid  is  produced  in 
scalded  muscle,  perhaps  because  the  acid-forming  ferment  (p.  567) 
is  killed  by  the  high  temperature.  The  so-called  rigor  caused  by 
alcohol  and  by  acids  is  a  coagulation  of  the  proteids,  and  not  true 
rigor.  No  heat  is  produced,  and  no  carbon  dioxide  given  off. 

In  a  human  body  rigor  generally  appears  not  earlier  than 
an  hour,  and  not  later  than  four  or  five  hours,  after  death. 
In  exceptional  cases,  however,  it  may  come  on  at  once,  and 
the  annals  of  war  and  crime  contain  instances  where  a  man 
has  been  found  after  death  still  holding  with  a  firm  grip  the 
weapon  with  which  he  had  fought,  or  which  had  been  thrust 
into  his  hand  by  his  murderer.  It  is  related  that  after  one 
of  the  battles  of  the  American  Revolutionary  War  some  of 
the  dead  were  found  with  one  eye  open  and  the  other  closed 


MUSCLE  569 

as  in  the  act  of  taking  aim.  A  high  temperature  favours 
a  rapid  onset ;  a  body  wrapped  up  in  bed  will,  other  things 
being  equal,  become  rigid  sooner  than  a  body  lying  stripped 
in  a  field.  Muscular  exhaustion,  as  we  have  said,  is  another 
favouring  condition :  hunted  animals  and  the  victims  of 
wasting  diseases  go  quickly  into  rigor.  It  is  a  rule,  but  not 
an  invariable  one,  that  rigor,  when  it  comes  on  quickly,  is 
short,  and  lasts  longer  when  it  comes  on  late.  All  the 
muscles  of  the  body  do  not  stiffen  at  the  same  time ;  the 
order  is  usually  from  above  downwards,  beginning  at  the 
jaws  and  neck,  then  reaching  the  arms,  and  finally  the  legs. 
After  two  or  three  days  the  rigor  disappears  in  the  same 
order.  The  position  of  the  limbs  in  rigor  is  the  same  as 
at  death ;  the  muscles  stiffen  without  contracting.  This  can 
be  strikingly  shown  on  a  newly-killed  animal  by  cutting  the 
tendons  of  the  extensors  of  one  leg  and  the  flexors  of  the 
other;  when  natural  rigor  comes  on  the  legs  remain  just  as 
they  were.  If  heat  rigor,  however,  is  caused,  the  one  leg 
becomes  rigid  in  flexion  and  the  other  in  extension. 

The  Removability  of  Rigor, — It  has  been  asserted  that  rigor 
can  be  removed  and  excitability  restored.  After  interrupt- 
ing the  circulation  in  the  hind-legs  of  rabbits  by  compres- 
sion or  ligation  of  the  abdominal  aorta,  and  so  causing  the 
muscles  to  become  rigid,  Brown-Sequard  saw  them  recover 
their  irritability  when  the  blood  was  again  allowed  to  reach 
them.  He  performed  a  similar  experiment  with  artificial 
circulation  through  the  hand  of  an  executed  criminal,  with 
a  like  result.  But  grave  doubt  has  been  cast  upon  these 
experiments  by  later  observations,  and  it  is  now  almost 
universally  believed  that  no  really  rigid  muscle  has  ever 
been  restored,  and  that  the  apparent  recovery  which  Brown- 
Sequard  saw  was  due  to  the  muscles  not  having  been 
completely  rigid.  Heubel  has,  however,  stated  that  the 
rhythmical  contractions  of  the  frog's  heart  can  be  restored 
by  filling  its  cavity  with  blood,  after  rigor  has  been  caused 
by  heat  and  in  other  ways ;  and  although  we  cannot  transfer 
these  results  directly  to  skeletal  muscle,  they  would  show,  if 
confirmed,  that  the  question  is  not  yet  closed. 


CHAPTER  X. 

NERVE. 

> 

THE  voluntary  movements  are  originated  by  impulses  from 
the  brain,  which  reach  the  muscles  along  their  motor  nerves. 
The  involuntary  movements  are  in  many  cases  able  to  go 
on  in  the  absence  of  central  connections,  but  are  normally 
under  central  control.  Everywhere  the  connection  between 
the  brain  and  cord  and  the  peripheral  organs,  be  they 
muscles,  glands,  or  sensory  mechanisms,  is  made  by  nerve- 
fibres  ;  and  these  are  called  peripheral  nerve-fibres  to  dis- 
tinguish them  from  the  fibres  of  the  central  nervous  system 
itself. 

An  ordinary  peripheral  nerve  like  the  sciatic  is  made  up  of  a 
number  of  bundles  of  nerve-fibres.  Connective  tissue  surrounds 
and  separates  the  bundles,  and  also  penetrates  in  fine  septa  within 
them  and  between  the  individual  fibres,  forming  a  framework  for 
their  support,  and  carrying  the  bloodvessels  and  lymphatics. 

Each  medullated  nerve-fibre  (Plate  V.  i)  consists  of  two  sheaths 
enclosing  an  axis-cylinder,  which  runs  from  end  to  end  of  it  without 
break,  and  is  connected  centrally,  either  directly  or  indirectly,  with 
a  nerve-cell.  The  axis-cylinder  is  the  essential  conducting  part  of 
the  fibre,  for  it  is  present  in  every  nerve-fibre,  and  towards  the 
periphery  it  is  alone  present.  The  innermost,  and  by  far  the  thickest, 
of  the  sheaths  is  the  medullary  sheath,  or  white  substance  of 
Schwann,  which  is  of  fatty  nature,  and  is  blackened  by  osmic  acid. 
It  undergoes  a  kind  of  coagulation  at  death,  loses  its  homogeneity, 
and  shows  a  double  contour.  This  sheath  is  not  continuous,  but  is 
broken  by  constrictions  of  the  outer  sheath,  called  nodes  of  Ranvier, 
into  numerous  segments.  The  outer  sheath,  or  neurilemma,  is  a 
thin,  structureless  envelope  immediately  external  to  the  medulla.  It 
invests  the  nerve-fibre,  as  the  sarcolemma  does  the  muscle-fibre.  In 
each  internodal  segment  immediately  under  the  neurilemma  lies  a 
nucleus  surrounded  by  a  little  protoplasm.  Medullated  fibres  such 
as  those  described  are  by  far  the  most  numerous  in  the  cerebro- 


NERVE  571 

spinal  nerves ;  but  they  are  mixed  with  a  few  fibres  which  contain 
no  white  substance  .of  Schwann,  and  are,  therefore,  called  non- 
medullated  (Plate  VrxJ.  In  these  the  axis-cylinder  is  covered  only 
by  the  neurilemma.  In  the  sympathetic  system  the  non-medullated 
variety  is  present  in  greater  abundance  than  the  medullated.  In 
the  central  nervous  system  the  medullated  fibres  possess  no  neuri- 
lemma. 

So  far  as  we  know,  the  only  function  of  nerve-fibres  is  to 
conduct  impulses  from  nerve-centres  to  peripheral  organs, 
or  from  peripheral  organs  to  nerve-centres,  or  from  one 
nerve-centre  to  another.  And  in  the  normal  body  these 
impulses  never,  or  only  very  rarely,  originate  in  the  course 
of  the  nerve-fibres ;  they  are  set  up  either  at  their  peripheral 
or  at  their  central  endings.  By  artificial  stimulation,  how- 
ever, a  nerve-impulse  may  be  started  at  any  part  of  a  fibre, 
just  as  a  telegram  may  be  despatched  by  tapping  any  part  of 
a  telegraph  wire,  although  it  is  usually  sent  from  one  fixed 
station  to  another. 

The  Nerve-impulse:  its  Initiation  and  Conduction. 

What  the  nerve-impulse  actually  consists  in  we  do  not 
know.  All  we  know  is  that  a  change  of  some  kind,  of  which 
the  only  external  token  is  an  electrical  change,  passes  over 
the  nerve  with  a  measurable  velocity,  and  gives  tidings  of 
itself,  if  it  is  travelling  along  efferent  fibres  (that  is,  out  from 
the  central  nervous  system),  by  the  contraction  or  inhibition 
of  muscle  or  by  secretion ;  if  it  is  travelling  along  afferent 
fibres  (that  is,  up  to  the  central  nervous  system),  by  sensa- 
tion, or  by  reflex  muscular  or  glandular  effects. 

Whether  the  wave  which  passes  along  the  nerve  is  a  wave 
of  chemical  change,  or  a  wave  of  mechanical  (molecular) 
change,  there  is  no  definite  experimental  evidence  to  decide. 

That  chemical  changes  go  on  in  living  nerve,  we  need  not 
hesitate  to  assume ;  and,  indeed,  if  the  circulation  throughf 
a  limb  of  a  warm-blooded  animal  be  stopped  for  a  short 
time,  the  nerves  lose  their  excitability.  But  the  metabolism! 
appears  to  be  very  slight  compared  with  that  in  muscle  or 
gland.  Even  in  active  nerve  no  measurable  production  of 
carbon  dioxide  has  ever  been  observed,  nor,  in  fact,  has  any 
chemical  or  physical  difference  between  the  excited  and  the 


572  A  MANUAL  OF  PHYSIOLOGY 

resting  state  ever  been  unequivocally  made  out.  Neither  in 
cold-blooded  nor  in  mammalian  nerves  does  there  seem  to 
be  any  sensible  rise  of  temperature  during  stimulation. 

Stimulation  of  Nerve. — With  some  differences,  the  same 
stimuli  are  effective  for  nerve  as  for  muscle  (p.  533) ;  but 
chemical  stimulation  is  not  in  general  so  easily  obtained. 

Q  In  fact,  it  is  doubtful  whether  any  great  reliance  should  be  placed 
on  many  of  the  observations  hitherto  made  with  this  mode  of  excita- 
tion. For  it  has  been  shown  that  the  current  of  rest  of  the  nerve 
(p.  606),  when  a  short-circuit  is  formed  for  it  by  a  drop  of  any  con- 
ducting liquid  applied  to  a  fresh  cross-section  (the  usual  method  of 
experimenting  on  chemical  stimulation),  may  of  itself  cause  excitation 
(Hering). 

Griitzner  uses  equimolecular  solutions  for  experiments  on  chemical 
stimulation  —  i.e.,  solutions  which  contain  an  equal  number  of 
molecules  of  the  substances  to  be  tested  in  a  given  volume  of  water. 
He  has  found  that  for  motor  nerves  the  halogen  salts  have  a  stimu- 
lating power  in  the  order  of  their  molecular  weights;  e.g.,  sodium 
iodide  (Nal)  is  stronger  than  sodium  bromide  (NaBr),  and  sodium 
bromide  than  sodium  chloride  (NaCl).  Sensory  nerves  are  much 
less  susceptible  to  chemical  stimulation.  Bile  or  bile  salts,  for 
example,  which  stimulate  motor  nerves,  have  no  effect  on  sensory. 
A  sugar  solution,  which  excites  motor  nerves,  does  not  alter  the  rate 
of  respiration  when  applied  to  the  central  end  of  the  vagus,  which, 
however,  is  excited  by  potassium  chloride  (p.  214).  In  non-narcotized 
animals  reflex  secretion  of  saliva  is  caused  by  stimulation  of  the 
central  end  of  the  lingual  with  sodium  chloride  (Wertheimer). 

Mechanical  stimulation  has  been  carried  to  great  perfection  by 
Heidenhain,  and  especially  by  Tigerstedt.  By  means  of  an  instru- 
ment invented  by  the  latter,  not  only  may  a  regular  tetanus  be 
obtained,  but  the  strength  of  the  stimulus  (fall  of  a  weight)  can  be 
graduated  with  fair  accuracy  within  a  considerable  range.  He  found 
that  the  smallest  amount  of  work  spent  on  a  frog's  nerve  which  would 
suffice  to  excite  it  was  a  little  less  than  a  gramme-millimetre — that  is, 
the  work  done  by  a  gramme  falling  through  a  distance  of  a  milli- 
metre. No  doubt  a  great  part  of  this  is  wasted,  as  a  much  smaller 
quantity  of  work  done  by  an  electrical  current,  which  may  be 
supposed  to  act  more  directly  on  the  excitable  constituents,  suffices 
to  stimulate  a  nerve.  Thus,  while  the  minimal  mechanical  stimulus 

may  have  a  heat-equivalent  of  about  —  x  — -  gramme-degree,  the 
heat- equivalent  of  the  minimal  electrical  stimulus  may  easily  be  less 
than  —  x  — -  gramme-degree,  or  one-millionth  part  of  the  former. 

A  kilogramme-degree  is  equivalent  to  427  kilogramme-metres  of 
work;  therefore,  a  gramme -millimetre  of  work  is  equivalent  to 


NERVE  573 

gramme-degree,   or,  say,    —  x  — -  gramme-degree.     This 

427,000  4'2     Io 

corresponds  to  Tigerstedt's  minimum  mechanical  stimulus. 

A  piece  of  nerve  of  100,000  ohms'  resistance  may  be  excited  by 
a  current  passed  for  yj-^j-  second  when  the  difference  of  potential 
between  its  ends  is  only  T^  of  a  volt.  Taking  the  work  done  in 
this  case  as  measured  by  the  heat  produced,  we  get  work  (W)  =  H 

=  -~,  where  E  is  the  electromotive  force,  /  the  time  of  flow  of  the 

current,  J  Joule's  equivalent,  and  R  the  resistance.  Expressing 
these  in  C.G.S.  (centimetre — gramme — second)  units,  we  have 

(12!)2x-L. 

,__  Vioo/        TOO  ii 

W  = -. 5 =  —  x  — n  gramme-degree 

42  x  10°  x  ioj  x  100,000     4*2     iou 

as  the  work  done  by  an  electrical  stimulus  sufficient  to  excite  a  nerve. 
S.  P.  Langley  has  shown  that  the  work  done  by  the  minimal,  natural 
or  specific,  stimulus  for  the  retina  (green  light)  may  be  as  little  as 

„  erg*;  i.e.,  —  x  — -  gramme-degree,  or  10,000  times  less  than 
io8  4-2  io15 

the  minimal  electrical  stimulus,  on  our  assumptions,  for  the  naked 
nerve-trunk  of  a  frog.  But  these  assumptions  are  quite  rough,  and 
it  is  possible  that  the  energy  of  the  minimum  artificial  stimulus  is 
no  greater  than  that  of  the  minimum  natural  stimulus  of  the  retina. 

The  laws  of  electrical  stimulation  for  nerve  are  essentially  the  same 
as  those  we  have  already  discussed  for  muscle  (p.  537).  The  voltaic 
current  stimulates  a  nerve,  as  it  does  a  muscle,  at  closure  and 
opening,  and  not  in  general  during  the  flow,  but  the  exceptions  to 
this  rule  are  less  frequent  in  nerve  than  in  muscle.  Induction 
shocks  are  relatively  more  powerful  stimuli  for  nerve  than  the  make 
or  break  of  a  voltaic  current.  The  opposite,  as  we  have  seen,  is  true 
of  muscle ;  and,  upon  the  whole,  we  may  say  that  muscle  is  more 
sluggish  in  its  response  to  stimuli,  and  is  excited  less  easily  by  very 
brief  currents,  than  nerve  is.  An  apparent  illustration  of  this  differ- 
ence is  the  fact  that  the  nervous  excitation  has  no  measurable  latent 
period,  while  muscular  excitation  has.  But  it  is  quite  possible  that, 
if  the  conditions  of  experiment  were  as  favourable  in  nerve  as  in 
muscle,  a  sensible  latent  period  might  be  found  here  too. 

In  nerve  as  in  muscle,  strength  of  stimulus  and  intensity  of 
response  correspond  within  a  fairly  wide  range,  when  we  take  the 
height  of  the  muscular  contraction  or  the  amount  of  the  negative 
variation  (p.  607)  as  the  measure  of  the  nervous  excitation.  Super- 
position of  stimuli,  superposition  of  contractions,  and  complete 
tetanus,  are  caused  by  stimulating  a  muscle  through  its  nerve,  just 
as  by  stimulating  the  muscle  itself  (p.  552). 

The  excitability  of  nerve,  as  measured  by  the  muscular 
response  to  stimulation,  is  increased,  for  induction  shocks 
*  Here  we  take  an  erg  as  equivalent  to  njW  gramme-centimetre. 


574  A  MANUAL  OF  PHYSIOLOGY 

or  voltaic  currents  of  short  duration,  by  rise  of  temperature 
up  to  about  30°  C.t  and  diminished  by  fall  of  temperature. 
It  has  been  suggested  that  this  increase  of  excitability  is 
only  apparent,  and  due  to  the  strengthening  of  the  current 
by  diminution  of  the  resistance,  since  the  resistance  of  all 
animal  tissues,  like  that  of  electrolytic  conductors  in  general, 
diminishes  as  the  temperature  rises  (Gotch).  Cooling  of  the 
nerve,  even  to  5°  C.,  increases  the  excitability  for  currents 
of  long  duration  (several  hundredths  of  a  second).  The  con- 
ductivity for  the  nervous  impulse — that  is,  the  power  of  a 
portion  of  the  nerve  to  conduct  an  impulse  set  up  elsewhere 
— is  undoubtedly  increased  by  heat  and  diminished  by  cold. 

Drying  of  a  nerve  at  first  increases  its  excitability  ;  and 
the  same  is  true  of  separation  of  a  nerve  from  its  centre. 
In  the  latter  case  the  increase  of  irritability  begins  at  the 
proximal  end  of  the  nerve,  and  travels  towards  the  peri- 
phery. As  time  goes  on,  the  excitability  diminishes,  and 
ultimately  disappears  in  the  same  order  (Ritter-Valli  Law). 
At  a  certain  stage  it  may  be  found  that  a  given  stimulus 
causes  a  smaller  and  smaller  contraction  the  farther  down 
the  nerve — that  is,  the  nearer  to  the  muscle — it  is  applied. 
On  this  was  based  the  now  abandoned  '  avalanche  theory,' 
according  to  which  the  impulse  continually  unlocked  new 
energy  as  it  passed  along  the  nerve,  and  so  gathered  strength 
in  its  course  like  an  avalanche. 

Electrotonus. — Although  the  constant  current  does  not, 
unless  it  is  very  strong  or  the  nerve  very  irritable,  cause 
stimulation  during  its  passage,  it  modifies  profoundly  the 
excitability  and  conductivity  of  the  nerve.  (In  man  a 
certain  amount  of  tonic  contraction  —  galvanotonus  ^—  is 
normally  seen  during  the  passage  of  a  strong  current 
through  a  nerve).  In  the  neighbourhood  of  the  Jtathojde 
the  excitability  is  increased  (condition  of  katelectrotonus), 
while  around  the  anode  it  is  diminished  (anelectrotonus). 
Immediately  after  the  opening  of  the  current  these  relations 
are  for  a  brief  time  reversed,  the  excitability  of  the  post- 
kathodic  area  (area  which  was  at  the  kathode  during  the 
flow)  being  diminished,  and  that  of  the  post-anodic  in- 
creased. In  the  intrapolar  area  there  is  one  point  the 


NERVE 


575 


excitability  of  which  is  not  altered.  This  indifferent  point,  as 
it  is  called,  shifts  its  position  when  the  intensity  of  the 
current  is  varied. 

These  statements  have  been  made  on  the  strength  of  O 
experiments  in  which 
the  height  of  the  mus- 
cular contraction  was 
taken  as  the  index 
solely  of  the  excita- 
bility of  the  nerve  at 
any  given  point.  But 
it  is  now  known,  partly 
from  observations  on 
muscular  contraction 
in  which  changes  of 
excitability  of  the 
nerve  were  eliminated 
by  proper  choice  of  the 
point  of  stimulation, 
and  partly  from  obser- 
vations on  the  action 
stream  (p.  620),  that 
very  striking  altera- 
tions of.  conductivity 
are  also  produced  by 
the  constant  current, 
which  even  outlast  its 
flow.  For  all  currents 
except  the  weakest  the 
conductivity  at  the 
kathode  and  in  its  im- 
mediate  neighbour- 


FIG.  176.— DIAGRAM  OF  CHANGES  OF  EX- 
CITABILITY AND  CONDUCTIVITY  PRODUCED 
IN  A  NERVE  BY  A  VOLTAIC  CURRENT. 

E,  changes  of  excitability  during  the  flow  of  the 
current,  according  to  Pfluger.  The  ordinates  drawn 
from  the  abscissa  axis  to  cut  the  curve  represent  the 
amount  of  the  change.  C(i),  changes  of  conduc- 
tivity during  the  flow  of  a  moderately  strong  current. 
Conductivity  greatly  reduced  around  kathode  ;  little 
affected  at  anode.  C(2),  changes  of  conductivity 
during  flow  of  a  very  strong  current.  Conductivity 
reduced  both  in  anodic  and  kathodic  regions,  but 
less  in  the  former.  C,  changes  of  conductivity  just 
after  opening  a  moderately  strong  current.  Con- 
ductivity greatly  reduced  in  region  which  was 
formerly  anodic ;  little  affected  in  region  formerly 
kathodic. 


hood    is    diminished, 

and  with  currents  still  only  moderately  strong 
ampere,  e.g.)  the  block  deepens  into  utter  impassability. 
The  conductivity  at  the  anode  is,  during  all  this  stage,  but 
little  affected,  and  is  at  any  rate  much  higher  than  at  the 
kathode,  so  that  at  the  time  of  full  kathodic  block  the  nerve- 
impulse  still  freely  passes  through  the  region  around  the 
positive  pole.  With  still  stronger  currents  the  conduc- 


576 


A  MANUAL  OF  PHYSIOLOGY 


tivity  here,  too,  begins  to  diminish,  until  at  last  the  anode  is 
also  blocked  :  but  this  is  to  be  looked  upon  as  merely  an 
extension  of  the  defect  of  conductivity  which  has  been  creep- 
ing along  the  intrapolar  area  from  the  kathode.  After 
the  opening  of  the  current,  the  relation  between  kathodic 
and  anodic  conductivity  is  reversed,  for  now  the  post- 
kathodic  region  conducts  the  nerve-impulse  relatively  better 
than  the  post-anodic. 


FIG.  177. — KATELECTROTONUS. 
Weak  tetanus  of  muscle  (the  right-hand 
elevation ),  greatly  intensified  in  katelec- 
trotonus  of  the  motor  nerve  (the  left-hand 
elevation). 


FIG.  178. — ANELECTROTONUS. 

Strong  tetanus  of  muscle  (left-hand 
elevation),  lessened  in  strength  by  an- 
electrotonic  condition  of  the  motor  nerve 
(right-hand  elevation). 


The  above  facts  serve  to  explain  the  manner  in  which 
the  effects  of  stimulation  of  a  nerve  with  the  constant 
current  vary  with  the  strength  and  direction  of  the  stream. 
These  effects,  so  far  as  the  contraction  of  the  muscles 
supplied  by  the  nerve  is  concerned,  have  been  formulated 
in  what  has  been  somewhat  loosely  termed  the  law  of  con- 
traction. In  this  formula  the  direction  of  the  current  in  the 
nerve  is  commonly  distinguished  by  a  thoroughly  bad  bi 
now  ingrained  phraseology,  as  ascending  when  the  anode  if 
next  the  muscle,  and  descending  when  the  kathode  is  n< 

the  muscle. 

Law  of  Contraction. 


Current. 

Ascending. 

Descending. 

M. 

B. 

M. 

B. 

Weak    - 
Medium 
Strong  - 

C 
C 

C 

c 

C 
C 

c 

c 

Here  M  means  '  make,'  B,  '  break,'  of  the  current ;  C  means  'contraction  follows.' 


NERVE  577 

The  explanation  generally  given  of  the  facts  summed  up  0 
in  the  '  law  of  contraction  '  is  as  follows  :  Wherever  there 
is  an  increase  of  excitability  sufficiently  rapid  and  sufficiently 
large,  stimulation  is  supposed  to  take  place ;  where  there  is 
a  fall  of  excitability,  stimulation  does  not  occur.  Accord- 
ingly, at  closure  the  kathode  stimulates — the  anode  does 
not ;  while  at  opening,  the  anode,  at  which  the  depressed 
excitability  jumps  up  to  normal  or  more,  is  the  stimulating 
pole ;  the  kathode,  at  which  it  declines  to  normal  or  under 
it,  is  inactive. 

With  a  weak  current,  (i)  contraction  only  occurs  at  make,  and 
(2)  the  direction  of  the  current  is  indifferent.  The  explanation  of 
the  first  fact  is  that  the  make  is  a  stronger  stimulus  than  the  break, 
and  when  the  current  is  weak  enough  the  break  is  less  than  a  mini- 
mal stimulus.  No  sensible  change  of  conductivity  is  caused  by 
weak  currents,  which  suffices  to  explain  (2). 

With  a  '  medium '  current,  contraction  occurs  at  make  and  break 
with  both  directions.  Here  the  break  excitation  is  effective  as  well 
as  the  make.  With  anode  next  the  muscle  (ascending  current),  there 
is  of  course  nothing  to  prevent  the  opening  excitation,  which  starts 
at  the  anode,  from  passing  down  the  nerve  and  causing  contraction ; 
and  since  there  is  no  block  around  the  anode  or  in  the  intrapolar 
region  with  '  medium '  currents,  there  is  nothing  to  keep  the  closing 
(kathodic)  excitation  from  reaching  the  muscle  too.  With  the 
kathode  next  the  muscle  (descending  current),  the  closing  excita- 
tion, which  starts  from  the  kathode,  has  no  region  of  diminished 
conductivity  to  pass  through,  nor  has  the  opening  (anodic)  excitation, 
for  the  kathodic  block,  caused  by  moderately  strong  currents,  is 
removed  as  soon  as  the  current  is  broken. 

With  'strong'  currents  there  are  only  two  cases  of  contraction 
out  of  the  four,  just  as  with  '  weak,'  but  for  very  different  reasons. 
There  is  a  break-contraction  with  ascending,  and  a  make-contraction 
with  descending  current.  With  ascending  current  the  anode  is  next 
the  muscle,  and  the  break-excitation  starting  there  has  nothing  to 
hinder  its  course.  The  make-excitation,  although  as  strong  or 
stronger,  has  to  pass  through  the  whole  intrapolar  region  and  over 
the  anode,  and  here  the  conductivity  is  depressed  and  the  nerve- 
impulse  blocked.  With  descending  current  the  kathode  is  next  the 
muscle,  and  there  is  no  hindrance  to  the  passage  of  the  make  excita- 
tion. The  break-excitation,  however,  has  to  traverse  the  intrapolar 
region,  and  the  anodic  end  of  this  area  has  a  smaller  conductivity 
immediately  after  opening  than  during  the  flow,  while  the  kathodic 
end  does  not  at  once,  after  a  strong  current,  become  passable.  The 
break-excitation,  accordingly,  cannot  get  through  to  the  muscle. 

In  all  these  cases  of  complete  or  partial  block,  during  or  after  the 
flow  of  a  constant  current,  the  progress  of  the  nerve-impulse,  its 

37 


578 


A  MANUAL  OF  PHYSIOLOGY 


gradual  weakening,  and  final  extinction  can  be  very  well  shown  by 
means  of  the  action  stream  (p.  619). 

The  above  formula  can  only  be  verified  upon  isolated 
nerves,  and,  even  for  these,  exceptional  results  are  apt  to  be 
obtained  as  soon  as  the  nerves  begin  to  die. 

A  formula  similar  to  the  law  of  contraction  has  been 
shown  to  hold  for  the  inhibitory  fibres  of  the  vagus  (Donders), 
'  inhibition  '  being  substituted  for  *  contraction.'  There  is 
also  some  evidence  that  a  similar  law  obtains  for  sensory 
nerves. 

The  Law  of  Contraction  for  Nerves  '  in  Situ.' — When  a  nerve 
is  stimulated  without  previous  isolation — in  the  human  body, 

for  instance,  through  elec- 
trodes laid  on  the  skin — the 
current  will  not  enter  and 
leave  it  through  definite 
small  portions  of  its  sheath, 
nor  will  it  be  possible  to 
make  the  lines  of  flow  nearly 
parallel  to  each  other  and  to 
the  long  axis  of  the  nerve, 
as  is  the  case  in  a  slender 
strip  of  tissue  when  there  is 
a  considerable  distance  be- 
tween the  electrodes. 


FIG.  179. — DIAGRAM  OF  LINES  OF 
FLOW  OF  A  CURRENT  PASSING 
THROUGH  A  NERVE. 

A,  an  isolated  nerve  ;  B,  a  nerve  in 
situ.  Secondary  anodes  (+)  are  formed 
where  the  current  re-enters  the  nerve 
below  the  negative  electrode  after  passing 
through  the  tissues  in  which  it  is  em- 
bedded, and  secondary  kathodes  (— ) 
where  the  current  passes  out  of  the  nerve 
into  the  surrounding  tissues  below  the 
positive  electrode. 


On  the  contrary,  even  when  a 
single  electrode — say,  the  positive 
— is  placed  over  the  position  of 
the  nerve,  and  the  other  at  a 
distance  on  some  convenient  part 

of  the  body,  the  current  will  enter  the  nerve  by  a  broad  fan  of 
stream-lines  cutting  it  more  or  less  obliquely,  and  pass  out  again 
into  the  surrounding  tissues  :  so  that  both  an  anode  (surface  of 
entrance)  and  a  kathode  (still  larger  surface  of  exit)  will  correspond 
to  the  single  positive  pole.  Similarly,  the  single  negative  electrode 
will  correspond  to  an  anodic  surface  where  the  now  narrowing  sheaf 
of  lines  of  flow  enters  the  nerve,  and  a  smaller  kathodic  surface 
where  they  emerge. 

If  the  two  electrodes  were  on  the  course  of  the  nerve,  the  strear 
lines  would  still  cut  it  in  such  a  way  that  each  electrode  would  corn 
spond  both  to  anode  and  kathode  (Fig.  179). 


NERVE  579 

It  is  impossible  under  these  circumstances  to  define  the 
direction  of  a  current  in  a  nerve,  or  to  connect  direction  with 
any  specific  effect.  The  terms  *  ascending '  and  '  descending  ' 
current  are,  therefore,  meaningless.  When  we  place  one  of 
the  electrodes  over  the  nerve  and  the  other  at  a  distance, 
the  law  of  contraction  only  appears  in  a  disguised  form ; 
for  since  a  kathode  and  an  anode  exist  at  each  pole,  there 
is,  with  a  current  of  sufficient  strength,  excitation  at  each 
both  at  make  and  break.  The  negative  make-contraction 
is,  however,  stronger  than  the  positive,  for  the  excitation 
corresponding  to  the  latter  arises  at  the  secondary  kathodic 
surface,  where  the  sheaf  of  current-lines  spreading  from  the 
positive  electrode  passes  out  of  the  nerve.  Now,  this  is 
much  larger  than  the  primary  kathodic  surface,  through 
which  the  narrow  wedge  of  stream-lines  passes  to  reach  the 
negative  electrode,  and  the  current  density  at  the  latter  is 
accordingly  much  greater.  The  positive  break-contraction 
is,  for  a  similar  reason,  stronger  than  the  negative. 

With  a  '  weak '  current,  the  only  contraction  is  a  closing 
one  at  the  kathode ;  with  a  '  medium  '  current  there  are 
both  opening  and  closing  contractions  at  the  positive  pole, 
and  a  closing  but  no  opening  contraction  at  the  negative. 

The  conductivity  of  the  nerve,  as  we  have  seen  in  various 
examples,  is  not  necessarily  altered  in  the  same  sense  as 
the  excitability.  In  the  neighbourhood  of  the  kathode  it 
is  easier  to  cause  excitation  than  in  the  normal  nerve  (in- 
creased excitability),  but  it  is  less  easy  for  an  excitation  set 
up  elsewhere  to  pass  through  (diminished  conductivity). 
Change  of  temperature  seems  also,  for  stimuli  of  not  very 
short  duration,  to  act  in  the  opposite  way  on  these  two 
properties  of  nerve.  Carbon  dioxide  appears  to  depress 
the  excitability  without  affecting  the  conductivity,  and 
alcohol  to  have  the  contrary  effect  (Gad  and  Sawyer). 
Munk  found  that  in  a  dying  sciatic  nerve  certain  pointf.  may 
be  quite  inexcitable  to  the  strongest  stimuli,  while  weak 
stimulation  of  points  lying  nearer  the  central  end  may  cause 
muscular  contraction.  These  facts  seem  to  show  that  the 
process  by  which  the  nerve-impulse  is  propagated  (an  exci- 
tation of  each  nerve-element  by  the  one  next  it,  as  some 

37—2 


580  A  MANUAL  OF  PHYSIOLOGY 

have  supposed)  is  not  the  same  as  that  by  which  it  is 
originated. 

Double  Conduction. — When  a  nerve  is  stimulated  artificially, 
the  excitation  runs  along  it  in  both  directions  from  the 
point  of  stimulation  ;  so  that  fibres  which  in  the  intact  body 
are  afferent  can  conduct  impulses  towards  the  periphery, 
and  efferent  fibres  can  conduct  impulses  away  from  the 
periphery.  In  the  normal  state,  however,  double  conduc- 
tion must  seldom  occur,  for  efferent  fibres  are  connected 
centrally,  and  afferent  fibres  peripherally,  with  the  structures 
in  which  their  natural  stimuli  arise.  In  general,  too,  an 
impulse,  if  it  did  pass  centrifugally  along  an  afferent  fibre, 
would  not  give  any  token  of  its  existence,  for  the  peripheral 
organ  would  not  be  able  to  respond  to  it ;  and  we  have  no 
reason  to  believe  that  the  central  mechanisms  connected 
with  efferent  fibres  are  better  fitted  to  answer  such  foreign 
and  unaccustomed  calls  as  impulses  reaching  them  along 
normally  efferent  nerves.  There  is  some  evidence  that 
muscular  excitation  is  not  carried  over  to  the  motor  nerve- 
fibres  ;  in  other  words,  the  wave  of  action  flows  from  the 
nerve  to  the  muscle,  but  cannot  be  got  to  flow  backwards. 
Whether  such  an  organ  as  the  retina  can  be  excited  by 
impulses  reaching  it  '  the  wrong  way '  along  the  optic  nerve 
we  do  not  know,  although  the  point  might  possibly  be 
decided  by  means  of  the  retinal  currents  to  be  mentioned 
later  on  (p.  624).  We  shall  see  that  a  nutritive  influence  is 
exerted  over  afferent  fibres  by  the  spinal  ganglia  (p.  585), 
an  influence  which  must  spread  along  these  fibres  in  the 
opposite  direction  to  that  of  the  normal  excitation ;  but 
from  this  we  cannot  deduce  anything  as  to  the  behaviour 
of  ordinary  nerve-impulses. 

The  best  proofs  of  double  conduction  in  nerves,  with 
artificial  stimulation,  are :  (i)  The  propagation  of  the  nega- 
tive variation  or  action  current  in  both  directions.  This 
holds  for  sensory  as  well  as  for  motor  fibres,  as  du  Bois- 
Reymond  showed  on  the  posterior  roots  of  the  spinal  nerves 
of  the  frog  and  the  optic  nerves  of  fishes.  (2)  Stimulation 
of  the  posterior  free  end  of  the  electrical  nerve  of  Malap- 
terurus  (p.  625)  causes  discharge  of  the  electric  organ, 


NERVE  581 

although  the  nerve-impulse  travels  normally  in  the  opposite 
direction.  (3)  If  the  lower  end  of  the  frog's  sartorius  is  split 
into  two,  gentle  stimulation  of  one  of  the  tongues  causes 
contraction  of  individual  fibres  in  the  other.  This  is  supposed 
to  be  due  to  conduction  of  the  nerve-impulse  up  a  twig  of 
a  nerve -fibre  distributed  to  the  one  tongue,  and  down 
another  twig  of  the  same  fibre  going  to  the  other  tongue. 
A  similar  experiment  can  be  done  on  the  gracilis  of  the 
frog.  This  muscle  is  divided  by  a  tendinous  inscription  into 
two  parts,  each  supplied  by  a  branch  of  a  nerve  which  divides 
after  entering  the  muscle.  Stimulation  of  either  twig  is 
followed  by  contraction  of  both  parts  of  the  muscle  (Kiihne). 

Bert's  much -quoted  experiment  on  the  rat  is  valueless  as  a  proof 
of  double  conduction.  He  caused  union  of  the  point  of  the  tail 
with  the  tissues  of  the  back,  then  divided  the  tail  at  the  root,  and 
found  that  stimulation  of  what  was  now  the  distal  end  caused  pain. 
From  this  he  concluded  that  the  sensory  fibres  of  the  *  transposed ' 
tail  conducted  in  the  direction  from  root  to  tip.  But  the  conclusion 
is  not  warranted,  for  sensation  disappeared  in  the  tail  after  the 
section,  and  did  not  return  till  some  months  later,  when  the  nerve- 
fibres,  after  degenerating,  would  have  been  replaced  by  new  sensory 
fibres  growing  down  from  the  dorsal  nerves  (Ranvier).  For  a  similar 
reason  the  so-called  union  of  the  peripheral  end  of  the  cut  hypoglossal 
nerve  (motor)  with  the  central  end  of  the  cut  lingual  (sensory)  proves 
nothing  as  to  double  conduction,  nor  as  to  the  possibility  of  motor 
nerves  taking  on  a  sensory  function. 

Every  fibre  of  a  nerve  is  physiologically  isolated  from 
the  rest,  so  that  an  impulse  set  up  in  a  fibre  runs  its 
course  within  it,  and  does  not  pass  laterally  into  others 
(law  of  isolated  conduction).  In  connection  with  this  physio- 
logical fact  there  is  the  anatomical  fact  that  nerve-fibres 
do  not  branch  in  the  trunk  of  a  peripheral  nerve.  It 
has,  however,  been  shown  recently  that  bifurcation  of 
nerve  -  fibres  may  occur  in  the  spinal  cord  (Sherrington). 
The  axis-cylinder  of  a  peripheral  nerve-fibre  only  begins  to 
branch  where  isolation  of  function  is  no  longer  required,  as 
within  a  muscle.  The  experiment  of  Kiihne  on  double  con- 
duction, mentioned  above,  seems  to  show  that  an  excitation 
set  up  in  one  fibril  of  an  axis  cylinder  can  spread  to  the 
rest. 

Velocity  of  the  Nerve-impulse. — We  have  said  that  the  nerve- 


582  A  MANUAL  OF  PHYSIOLOGY 

impulse  travels  with  a  measurable  velocity.  It  is  now  time 
to  describe  how  this  has  been  ascertained  (p.  600).  For 
motor  fibres  the  simplest  method  is  to  stimulate  a  nerve  suc- 
cessively at  two  points,  one  near  its  muscle,  the  other  as  far 
away  from  it  as  possible,  and  to  record  the  contractions  on 
a  rapidly-moving  surface  (pendulum  or  spring  myograph) 
(p.  542).  The  apparent  latent  period  of  the  curve  corre- 
sponding to  the  nearer  point  will  be  less  than  that  of  the 
curve  corresponding  to  the  point  which  is  more  remote,  by 
the  time  which  the  impulse  takes  to  pass  between  the  two 
points.  The  distance  between  these  points  being  measured, 
the  velocity  is  known.  Helmholtz  found  the  velocity  for 
frog's  nerves  at  the  ordinary  temperature  of  the  air  to  be 
^Y  a  little  under,  and  for  human  nerves,  cooled  so  as  to  ap- 
^  ^  proximate  to  the  ordinary  temperature,  a  little  over  30 
metres  per  second.  For  observations  on  man  the  contrac- 
tion curves  of  the  flexors  of  one  of  the  fingers  or  of  the 
thumb  may  be  recorded,  first  with  stimulation  of  the 
brachial  plexus  at  the  axilla,  and  then  with  stimulation  of 
the  median  or  ulnar  nerve  at  the  elbow.  Probably  at  the 
same  temperature  there  is  little  difference  in  the  rate  of 
transmission  in  the  nerves  of  warm-blooded  and  cold-blooded 
animals,  but  temperature  has  an  enormous  influence. 

By  cooling  a  frog's  nerve  Helmholtz  reduced  the  rate  to  ~$  of  its 
value  at  the  ordinary  temperature,  and  in  the  human  arm  it  may 
vary  from  30  to  90  metres  per  second,  according  to  the  temperature, 
50  metres  being  about  the  normal  rate.  This  is  greater  than  the 
speed  of  the  fastest  train  in  the  world. 

The  passage  of  a  voltaic  current  through  an  isolated  nerve  also 
affects  the  velocity  of  the  nerve-impulse.     When  the  current  is  weak, 
the  velocity  is  increased  in  the  neighbourhood  of  the  kathode,  but 
diminished   near  the  anode;   when  it  is  stronger,  the   velocity   i 
diminished,  not  only  around  both  poles,  but  in  the  whole  intrapoh 
area.     This  agrees  with  what  we  have  already  seen  as  to  the  effect 
the  constant  current  on  the  conductivity  of  nerve. 

The  velocity  with  which  the  negative  variation  is  propa- 
gated (p.  610)  is  the  same  as  that  of  the  nerve-impulse. 

In  sensory  nerves  there  is  no  reason  to  believe  that  th( 
velocity  of  the  nerve-impulse  differs  from  that  in  motor 
nerves,  but  experiments  really  free  from  objection  are  as  yet 
wanting. 


NERVE  583 

The  usual  method  is  to  stimulate  the  skin  first  at  a  point  distant  Q 
from  the  brain,  and  then  at  a  much  nearer  point.  The  person 
experimented  on,  as  soon  as  he  feels  the  stimulation,  makes  a  signal, 
say,  by  closing  or  opening  with  the  hand  a  current  connected  with 
an  electric  time-marker,  writing  on  a  moving  surface.  There  is,  of 
course,  a  measurable  interval  between  the  excitation  and  the  signal, 
and  this  being  in  general  longer  the  more  remote  the  point  of  stimu- 
lation is  from  the  brain,  it  is  assumed  that  the  excess  represents  the 
time  taken  by  the  nerve-impulse  to  pass  over  a  length  of  sensory 
nerve  equal  to  the  difference  in  the  length  of  the  path.  But  there  is 
this  difficulty,  that  the  propagation  of  the  impulse  from  the  point  of 
stimulation  to  the  brain  is  only  one  link  in  the  chain  of  events  of 
which  the  signal  marks  the  end.  The  impulse  has  first  to  be  trans- 
formed into  a  sensation,  and  then  the  will  has  to  be  called  into  action, 
and  an  impulse  sent  down  the  motor  nerves  to  the  hand.  And  while 
the  time  taken  by  the  excitation  in  travelling  up  and  down  the 
peripheral  nerve-fibres  is,  perhaps,  fairly  constant,  the  time  spent  in 
the  intermediate  psychical  processes  is  very  variable. 

Chemistry   of  Nerve. — Our   knowledge   of  this   subject  is     - 
scanty  in  the  extreme ;  and  most  of  what  we  do  know  has 
been  obtained  from  analyses,  not  of  the  peripheral  nerves, 
but  of  the  white  matter  of  the  central  nervous  system. 

Proteids  are  present,  especially  in  the  axis  cylinder.  They  include 
a  globulin  and  a  nucleo-proteid. 

Substances  soluble  in  ether  include  cholesterin^  lecithin,  cerebrin, 
and  protagon,  which,  according  to  some,  is  a  mixture — to  others,  * 
compound  of  lecithin  and  cerebrin.  The  cholesterin  and  lecithin., 
at  least,  belong  chiefly  to  the  medullary  sheath,  which  further  con- 
tains a  kind  of  network  of  a  peculiar  resistant  substance  called 
neurokeratin  (Kiihne). 

The  neurilemma  consists  of  substances  insoluble  in  dilute  sodium 
hydrate. 

Gelatin  is  obtained  from  the  connective  tissue  which  binds  the 
nerve-fibres  together.  There  may  also  be  ordinary  fat  in  the  meshes 
of  the  epineurium  connecting  the  bundles.  Small  quantities  of 
xanthin,  hypoxanthin,  and  other  extractives,  can  also  be  obtained 
from  nerve. 

The  composition  of  the  white  matter  of  the  brain  is  as  follows : 

Water  .  68  per  cent, 

fProteids-  .      g' 

Cholesterin     -         -'       -     16 


Solids- 


Lecithin 


Cerebrin  -         -       3 

Salts  -    0-5 

.Other  substances    -         -    1-5 


32  per  cent. 


584  A  MANUAL  OF  PHYSIOLOGY 

An  analysis  of  the  sciatic  nerve  of  man  gave  in  round  numbers : 

Water     -  66  per  cent. 

{Cerebrin,  lecithin,  choles-         "\ 
terin,  and  fatty  acids    -     17 
Proteids  and  glutin          -     ,$[34  per  cent. 
Other  substances    -  1 1 

The  only  difference  between  living  and  dead  nerve  which  has  been 
made  out  with  any  degree  of  certainty  is  that  the  former  is  neutral  or 
faintly  alkaline,  and  the  latter  acid,  in  reaction. 

Nutrition  of  Nerve. — Nerve-fibres  are  '  bound  in  the  bundle 
of  life  '  with  certain  nerve-cells  on  their  course  ;  the  con- 
nection once  severed,  the  nerve-fibre  dies  inevitably.  In 
other  words,  fibre  and  cell  have  a  '  nutritive  unity ' ;  and 
this  is  what  we  should  expect,  for  they  also  have  a  mor- 
phological unity  ;  the  fibre  is  a  process  of  the  cell.  When 
a  spinal  nerve  is  cut  below  the  junction  of  its  roots, 
muscular  paralysis  and  impairment  of  sensation  at  once 
follow  in  the  region  supplied  by  the  nerve ;  but  for  a  time 
the  nerve  remains  excitable  to  direct  stimulation.  The 
excitability  gradually  diminishes,  and  in  a  few  days  is  com- 
pletely gone. 

If  portions  of  a  nerve  are  examined  at  different  periods 
after  section,  a  remarkable  process  of  degeneration  is  seen 
to  be  going  on.  The  nuclei  of  the  sheath  of  Schwann  pro- 
liferate, and  insinuate  themselves  into  the  medullary  sheath 
and  axis  cylinder,  which  break  up  into  detached  pieces,  and 
ultimately  disappear,  leaving  the  nerve-fibre  represented 
only  by  a  kind  of  mummy  of  connective  tissue.  This  process 
goes  on  simultaneously  along  the  whole  nerve,  from  the  cut 
end  to  the  periphery.  In  a  mammal  it  is  complete  injibout 
a  fortnight,  but  takes  longer  in  cold-blooded  animals. 

Degeneration  of  the  nerve  is  followed,  if  its  divided  ends 
are  not  kept  artificially  apart,  by  a  process  of  regenera- 
tion, already  distinct  in  from  three  to  four  weeks  after  the 
section,  but  in  some  cases  commencing  as  early  as  the 
second  week.  This  consists  in  the  outgrowth  of  new  axis 
cylinders,  in  the  form  of  fine  fibres,  from  the  ends  of  the 
divided  axis  cylinders  of  the  central  stump  of  the  nerve. 
These  push  their  way  into  and  along  the  degenerated  fibres, 
ultimately  acquire  a  medullary  sheath,  and  develop  into 


NERVE  585 

complete  nerve-fibres,  restoring  first  sensation,  and  later  on 
voluntary  motion,  to  the  paralyzed  part.  The  process  needs 
several  months  for  its  completion,  even  in  warm-blooded 
animals.  It  takes  place  under  the  influence  of  the  nutritive 
centre,  and  never  occurs  if  the  nerve  is  permanently  separ- 
ated from  its  cell.  It  is  a  remarkable  and  as  yet  unex- 
plained fact  that  regeneration  of  the  fibres  of  the  central 
nervous  system,  at  least  in  the  higher  animals,  either  does 
not  occur  at  all  or  is  exceedingly  uncommon. 

The  nutritive  centre  for  the  fibres  of  the  posterior  root  of 
a  spinal  nerve — i.e.,  for  the  afferent  fibres — is  the  ganglion  on 
that  root ;  the  centres  for  nearly  the  whole  of  the  fibres  of 
the  anterior  root  lie  in  the  spinal  cord  itself  (p.  657). 


FIG.  1 80.— DEGENERATION  OF  SPINAL  NERVES  AND  THEIR  ROOTS  AFTER 
SECTION. — The  shading  shows  the  degenerated  portions. 

The  proof  of  these   statements  is  contained  in  Waller's 
experiments,  which  may  be  summarized  as  follows  : 

(1)  Section  of  the  anterior  root  causes  degeneration  on 
the  peripheral,  but  not  on  the  central  side  of  the  lesion. 
Only  the  anterior  root  fibres  in  the  mixed  nerve  degenerate. 

(2)  Section  of  the  posterior  root  above  the  ganglion  causes 
degeneration  of  the  central  stump,  but  not  of  the  portion 
still  connected  with  the  ganglion,  nor  of  the  posterior  root 
fibres  below  the  ganglion  or  in  the  mixed  nerve. 

(3)  Section  of  the  posterior  root  below  the  ganglion  causes 
degeneration  of  the  fibres  of  the  root  below  the  section  and 
in  the  mixed  nerve,  but  not  above  it. 


586  A  MANUAL  OF  PHYSIOLOGY 

(4)  As  has  already  been  mentioned,  section  of  the  mixed 
nerve  causes  degeneration  on  the  peripheral,  but  not  on  the 
central  side  of  the  lesion. 

A  few  fibres  in  the  peripheral  stump  of  the  anterior  root 
do  not  degenerate  after  its  division,  and  a  few  fibres  in  the 
central  stump  do.  These  are  'recurrent  fibres'  (p.  669), 
which,  leaving  the  spinal  cord  by  the  posterior  root,  run  down 
the  nerve  for  a  short  distance,  and  then  pass  upwards  in  the 
anterior  root,  probably  to  the  pia  mater  and  the  connective 
tissue  of  the  root.  The  nutritive,  or  trophic,  centre  of  these 
fibres  being  the  spinal  ganglion,  they  do  not  degenerate  so 
long  as  the  connection  with  it  is  intact. 

Experimental  section  or,  in  man,  traumatic  division  or 
-  f\     compression  of  a  nerve  leads  not  only  to  its  degeneration, 
£u       but  ultimately,  if  regeneration  of  the  nerve  does  not  take 
tfvA>  f'place,  to  degeneration  of  the  muscles  supplied  by  it  as  well. 
The   muscle-fibres   dwindle   to  a  quarter   of  their   normal 
diameter ;   the  stripes  disappear ;   the  longitudinal  fibrilla- 
tion fades  out ;   and  at  length  only  hyaline  moulds  of  the 
fibres  are  left,  filled  and  separated  by  fatty  granules  and 
globules,  and  surrounded  by  engorged  capillaries.     Amidst 
the    general   decay,   the   muscular   fibres   of   the   terminal 
'  spindles,'  with  which  the  afferent  nerves  of  muscles  are 
connected,  alone  remain  unchanged  (Sherrington).     Certain 
diseases  of  the  cord  which  interfere  with  the  cells  of  the 
anterior    horn   cause   degeneration   of    motor   nerves,   and 
ultimately  of  muscles. 

Muscles  whose  motor  nerves  have  been  separated  from  their 
trophic  centres  show,  when  a  certain  stage  in  degeneration 
has  been  reached,  a  peculiar  behaviour  to  electrical  stimu- 
lation, called  the  'reaction  of  degeneration.'  To  the  constant 
current  the  muscles  are  more  excitable,  and  the  contraction 
slower  and  more  prolonged  than  normal ;  to  the  induced 
current  they  are  less  excitable  than  normal,  or  not  excitable 
at  all.  The  closing  anodic  contraction  is  stronger  than  the 
closing  kathodic — the  opposite  of  the  ordinary  law.  The 
nerves  are  inexcitable  either  to  constant  or  induced  currents. 
The  reaction  of  degeneration  is  only  obtained  from  paralyzed 
muscles  when  the  paralyzing  lesion  is  situated  below  the 


NERVE  587 

level  of  the  cells  of  the  anterior  horn  from  which  the  motor 
nerves  take  origin.  Accordingly,  it  is  sometimes  of  use  in 
localizing  the  position  of  a  lesion. 

Trophic  Nerves.  —  The  fact  that  the  proper  nutrition  of 
nerve-fibres  is  dependent  on  their  connection  with  nerve- 
cells  has  been  by  some  writers  generalized  into  the  doctrine 
that  all  tissues  are  provided  with  'trophic'  nerves,  which, 
apart  from  any  influence  on  functional  activity,  regulate 
the  nutrition  of  the  organs  they  supply.  But  the  evidence 
for  this  view,  when  weighed  in  the  balance,  is  found  want- 
ing ;  and  it  may  be  said  that  up  to  the  present  no  unequivocal 
proof,  experimental  or  clinical,  has  ever  been  given  of  the  existence 
of  specific  trophic  nerves. 

It  is  true  that  division  of  the  trigeminus  nerve  within  the 
skull  is  sometimes  followed  by  cloudiness  of  the  cornea, 
going  on  to  ulceration,  and  ultimately  inflammation  and 
destruction  of  the  eyeball.  Ulcers  also  form  on  the  lips  and 
on  the  mucous  membrane  of  the  mouth  and  gums ;  and  the 
nasal  mucous  membrane  on  the  side  corresponding  to  the 
divided  nerve  becomes  inflamed.  But  in  this  case  the  sen- 
sibility of  the  eye  is  lost,  and  reflex  closure  of  the  eyelids 
ceases  to  prevent  the  entrance  of  foreign  bodies.  The 
animal  is  no  longer  aware  of  the  contact  of  particles  of  dust 
or  bits  of  straw  or  accumulated  secretion  with  the  conjunc- 
tiva, and  makes  no  effort  to  remove  them.  The  lips,  being 
also  without  sensation,  are  hurt  by  the  teeth,  particularly  as 
the  muscles  of  mastication  on  the  side  of  the  divided  nerve 
are  paralyzed,  and  decomposed  food,  collecting  in  the 
mouth,  and  inhaled  dust  in  the  nose,  will  tend  still  further 
to  irritate  the  mucous  membranes.  There  is  thus  no  more 
need  to  assume  the  loss  of  unknown  trophic  influences  in 
order  to  explain  the  occurrence  of  the  ulcerative  changes 
than  there  is  to  explain  the  production  of  ordinary  bed- 
sores, bunions  or  corns  on  parts  peculiarly  liable  to  pressure. 
And,  as  a  matter  of  fact,  if  the  eye  be  artificially  protected, 
after  section  of  the  trigeminal  nerve,  the  ophthalmia  either 
does  not  occur  or  is  much  delayed. 

In  man,  too,  a  case  has  been  recorded  in  which  both  the 
fifth  and  the  third  nerves  were  paralyzed.  The  eye  was  still 


588  A  MANUAL  OF  PHYSIOLOGY 

shielded  by  the  contraction  of  the  orbicularis  oculi  supplied 
by  the  seventh  nerve,  as  well  as  by  the  drooping  of  the 
upper  eyelid  that  accompanies  paralysis  of  the  third.  It 
remained  perfectly  sound  for  many  months,  till  at  length 
the  tumour  at  the  base  of  the  brain  which  had  affected  the 
other  nerves  involved  the  seventh  too.  The  eye  was  now 
no  longer  completely  closed;  inflammation  came  on,  and 
vision  was  soon  permanently  lost  (Shaw).  In  another  case 
a  patient  lived  for  seven  years  with  complete  paralysis  of 
the  fifth  nerve,  yet  the  eye  remained  free  from  disease  and 
sight  was  unimpaired  (Gowers). 

The  so-called  '  trophic  '  effects  following  division  of  both 
vagi  we  have  already  discussed  (p.  221)  so  far  as  they  are 
concerned  with  the  respiratory  system.  The  degenerative 
changes  sometimes  seen  in  the  heart  are  perhaps  due  to  its 
being  overworked  in  the  absence  of  nervous  restraint  on  its 
functional  activity.  The  nutritive  alterations  in  muscles  and 
salivary  glands  after  section  of  motor  and  secretory  nerves 
seem  to  depend  largely  on  functional  and  vaso-motor  changes. 
In  muscles  they  may  be  in  part  due  to  the  loss  of  a  tonic 
influence  exerted  on  them  by  the  motor  cells  of  the  spinal 
cord,  through  the  ordinary  motor  nerves  (p.  683). 

Section  of  the  cervical  sympathetic  in  young  rabbits  and 
dogs  is  said  to  increase  the  growth  of  the  ear  and  of  the 
hair  on  the  same  side ;  but  it  is  impossible  to  separate  these 
consequences  from  the  vaso-motor  paralysis ;  and  the  same 
is  true  of  the  hypertrophy  following  section  of  the  vaso- 
motor  nerves  of  the  cock's  comb  and  of  the  nerves  of  bones. 
The  statement  has  been  made  that  on  section  of  the  superior 
laryngeal  nerve  in  the  horse  the  laryngeal  muscles  on  the 
corresponding  side  undergo  rapid  atrophy.  Since  the  nerve 
in  this  animal  is  destitute  of  motor  fibres  this  seemed  to 
indicate  either  that  the  nerve  contains  efferent  '  trophic ' 
fibres  for  the  muscles,  or  that  the  activity  of  its  afferent 
fibres  has  a  profound  influence  on  their  nutrition.  But  by 
means  of  the  laryngoscope  it  has  been  shown  that  after 
section  of  the  superior  laryngeal  the  vocal  cord  on  the  side 
of  the  section  is  at  once  rendered  motionless,  and  remains 
so.  The  atrophy  of  the  muscles  is  therefore  due  to  their 


NERVE 


589 


inaction  in  the  absence  of  the  sensory  impulses  by  which 
the  centre  controlling  them  is  normally  roused  to  activity. 
And  Mott  and  Sherrington  have  found  that,  although  section 
of  the  posterior  roots  in  monkeys  is  followed  after  a  time 
(three  weeks  to  three  months)  by  ulceration  over  certain 
portions  of  the  foot,  no  corresponding  lesions  occur  in  the 
hand.  They  believe,  therefore,  that  the  lesions  are  not  due 
to  the  withdrawal  of  a  reflex  trophic  tone,  but  are  accidental 
injuries  in  positions  specially  exposed  to  mechanical  or 
microbic  insults. 

Omitting  the  group  of  *  trophic '  nerves,  and  the  even  more  pro- 
blematical '  thermogenic '  fibres,  peripheral  nerves  may  be  classified 


as  follows 


Centripetal 

or  afferent 

fibres 


i.  Nerves  of  special  sensathon 


2.  Nerves  of  general  sensation 


'Smell. 
Taste. 


I  Hearing. 
ISii 


3.*  Possibly  nerves  other  than 
those  included  under  i 
and  2,  concerned  in  reflex' 


Sight. 

Tactile  sensation  (per- 
haps including  the 
nerves  of  muscular 
sense). 

Temperature. 

Pain. 

Calibre  of  small  arteries 
(pressor,  depressor). 

Action  of  heart. 

Visceral  movements. 

Respiratory-  move- 


changes  in 


i.  Motor  nerves  for 


I 
Glandular  secretion. 
Ordinary  skeletal 
,  \     muscles. 

/'Skeletal  muscles. 
Visceral       ,, 

{Vaso-constrictor. 
Cardio  -  augmen- 
tor. 

or  efferent  J  Erector    muscles    of    hairs    (pilo- 

fibres  [     motor  fibres). 

»fVisceral  muscles. 
2.  Inhibitory  nerves  for-J  fVaso-dilator. 

[Vascular     „        4  Cardio  -  inhi- 
.3.  Secretory  nerves.  [     bitory. 

*  It  is  not  known  whether  the  afferent  portion  of  a  reflex  arc  is  always 
composed  of  fibres  included  in  the  first  two  categories,  although 
undoubtedly  in  some  cases  it  is. 


590  A  MANUAL  OF  PHYSIOLOGY 


PRACTICAL  EXERCISES  ON  CHAPTERS  IX.  AND  X. 

i.  Difference  of  Make  and  Break  Shocks  from  an  Induction 
Machine. — Connect  a  Daniell  cell  B  (p.  173)  with  the  two  upper 
binding-screws  of  the  primary  coil  P,  and  interpose  a  spring  key  K 
m  the  circuit.  Connect  a  pair  of  electrodes  with  the  binding-screws 
of  the  secondary  coil  (Fig.  181). 

Electrodes  can  be  very  simply  made  by  pushing  copper  wires 
through  two  glass  tubes,  filling  the  ends  of  the  tubes  with  sealing- 
wax,  and  binding  them  together  with  waxed  thread.  The  projecting 
points  may  be  filed,  and  the  nerve  laid  directly  on  them,  or  they 
may  be  tipped  with  small  pieces  of  platinum  wire  soldered  on. 

(a)  Push  the  secondary  away  from  the  primary,  until  no  shock  can 
be  felt  on  the  tongue  when  the  current  from  the  battery  is  made  or 
broken  with  the  key.  Then  bring  the  secondary  gradually  up  towards 


FIG.  1 81.— ARRANGEMENT  OF  COIL  FOR  SINGLE  SHOCKS. 

the  primary,  testing  at  every  new  position  whether  the  shock  is  per- 
ceptible. It  will  be  felt  first  at  break.  If  the  secondary  is  pushed 
still  further  up,  a  shock  will  be  felt  both  at  make  and  at  break. 
From  this  we  learn  that  for  sensory  nerves  the  break  shock  is 
stronger  than  the  make.  The  same  can  easily  be  demonstrated  for 
motor  nerves  and  for  muscle. 

(b)  Smoke  a  drum  and  arrange  a  myograph,  as  shown  in  Fig.  184. 
But  omit  the  brass  piece  F,  and  do  not  connect  the  primary  through 
the  drum,  as  there  shown,  but  connect  it  as  in  Fig.  181.  Pith  a  fix 
(brain  and  cord),  and  make  a  muscle-nerve  preparation. 

To  make  a  Muscle-Nerve  Preparation. — Hold  the  frog  by  th< 
hind-legs  ;  the  front  part  of  the  body  will  hang  down,  making 
angle  with  the  posterior  portion.  With  strong  scissors  divide  th< 
backbone  anterior  to  this  angle,  and  cut  away  all  the  front  portion  of 
the  body,  which  will  fall  down  of  its  own  weight.  Make  a  circular  in- 
cision at  the  level  of  the  tendo  Achillis,  and  another  at  the  lower  en<* 
of  the  femur,  through  the  skin.  The  sciatic  nerve  must  now  be  dis- 


PRACTICAL  EXERCISES  591 

sected  out,  as  follows  :  Remove  the  skin  from  the  thigh,  and,  holding 
the  leg  in  the  left  hand,  slit  up  the  fascia  which  connects  the  external 
and  internal  groups  of  muscles  on  the  back  of  the  thigh.  Complete 
the  separation  with  the  two  thumbs.  Cut  through  the  iliac  bone, 
taking  care  that  the  blade  of  the  scissors  is  well  pressed  against  the 
bone,  otherwise  there  is  danger  of  severing  the  sciatic  plexus.  Now 
divide  in  the  middle  line  the  part  of  the  spinal  column  which  remains 
above  the  urostyle.  A  piece  of  bone  is  thus  obtained  by  means  of 
which  the  nerve  can  be  manipulated  without  injury.  Seize  this  piece 
of  bone  with  the  forceps,  and  carefully  free  the  sciatic  plexus  and 
nerve  from  their  attachments  right  down  to  the  gastrocnemius  muscle, 
taking  care  not  to  drag  upon  the  nerve.  The  muscles  of  the  thigh 
will  contract,  as  the  branches  going  to  them  are  cut.  This  is  an 
instance  of  mechanical  stimulation.  Now  pass  a  thread  under  the 
tendo  Achillis,  tie  it,  and  divide  the  tendon  below  it.  Strip  up  the 
tube  of  skin  that  covers  the  gastrocnemius,  as  if  the  finger  of  a  glove 
were  being  taken  off.  Tear  through  the  loose  connective  tissue 
between  the  muscle  and  the  bones  of  the  leg,  and  divide  the  latter 
with  scissors  just  below  the  knee.  Cut  across  the  thigh  at  its  middle. 

Fix  the  preparation  on  the  cork  plate  of  the  myograph  by  a  pin 
passed  through  the  cartilaginous  lower  end  of  the  femur,  and  attach 
the  thread  to  the  upright  arm  of  the  lever  by  one  of  the  holes  in  it. 
Hang  not  far  from  the  axis  by  means  of  a  hook  a  small  leaden  weight 
(5  to  10  grammes)  on  the  arm  of  the  lever  which  carries  the  writing- 
point,  and  move  the  myograph  plate  or  the  muscle-nerve  preparation 
until  this  arm  is  just  horizontal.  Fasten  the  electrodes  from  the 
secondary  coil  on  the  cork  plate  with  an  indiarubber  band  ;  lay  the 
nerve  on  them ;  and  cover  both  muscle  and  nerve  with  an  arch  of 
blotting-paper  moistened  with  normal  saline,  taking  care  that  the 
blotting-paper  does  not  touch  the  thread.  Adjust  the  writing-point: 
to  the  drum.  Begin  with  such  a  distance  between  the  coils  that  a 
break  contraction  is  just  obtained  on  opening  the  key  in  the  primary 
circuit,  but  no  make  contraction.  The  lever  will  trace  a  vertical  line 
on  the  stationary  drum.  Read  off  on  the  scale  of  the  induction 
machine  the  distance  between  the  coils,  and  mark  this  on  the  drum] 
Now  allow  the  drum  to  move  a  little,  still  keeping  the  writing-point 
in  contact  with  it;  then  push  up  the  secondary  coil  i  centimetre 
nearer  the  primary,  and  close  the  key.  If  there  is  a  contraction,  let 
the  drum  move  a  little  before  opening  the  key  again,  so  that  the  lines 
corresponding  to  make  and  break  may  be  separated  from  each  other. 
If  there  is  still  no  contraction  at  make,  go  on  moving  the  secondary 
up,  a  centimetre  (or  less)  at  a  time,  till  a  make  contraction  appears. 
When  the  coils  are  still  further  approximated,  the  make  may  become 
equal  in  height  to  the  break  contraction,  both  being  maximal,  i.e.,  as 
great  as  the  muscle  can  give  with  any  single  shock  (Fig.  182). 

(f)  Attach  a  thin  insulated  copper  wire  to  each  terminal  of  the 
secondary.  Loop  the  bared  end  of  one  of  the  wires  through  the 
tendo  Achillis,  and  coil  the  other  round  the  pin  in  the  femur,  so 
that  the  shocks  will  pass  through  the  whole  length  of  the  muscle. 
Repeat  the  experiment  of  (£),  with  direct  stimulation  of  the  muscle. 


592 


A  MANUAL  OF  PHYSIOLOGY 


2.  Stimulation  of  Nerve  and  Muscle  by  the  Voltaic  Current. — (a) 
Connect  a  Daniell  cell  through  a  key  with  a  pair  of  electrodes  on 
which  the  nerve  of  a  muscle-nerve  preparation  lies.  Observe  that 
the  muscle  contracts  when  the  current  is  closed  or  broken,  but  not 
during  its  passage. 

Connect  the  cell  with  a  simple  rheocord,  as  shown  in  Fig.  183,  so 


FIG.  182. — CONTRACTIONS  CAUSED  BY  MAKE  AND  BREAK  SHOCKS  FROM  AN 
INDUCTION  MACHINE. 

M,  make,  B,  break,  contractions.     The  numbers  give  the  distance  between  the 
primary  and  secondary  coils  in  centimetres. 

that  a  twig  of  the  current  of  any  desired  strength  may  be  sent  through 
the  nerve.  As  the  strength  of  the  current  is  decreased  by  moving 
the  slider  S,  it  will  be  found  that  it  first  becomes  impossible  to  obtain 
a  contraction  at  break.  The  current  must  be  still  further  reduced 
before  the  make  contraction  disappears,  for  the  closing  of  a  galvanic 
stream  is  a  stronger  stimulus  than  the  breaking  of  it.  The  break 
or  make  contraction  obtained  by  stimulating  a  nerve  with  an  in- 


FIG.  183. — SIMPLE  RHEOCORD  ARRANGED  TO  SEND  A  TWIG  OF  A  CURRENT 
THROUGH  A  MUSCLE  OR  NERVE. 

B,  battery :  R,  rheocord  wire  (German  silver)  ;  S,  slider  formed  of  a  short  piece  of 
thick  indiarubber  tubing  filled  with  mercury  ;  K,  spring  key  ;  W,  W,  wires  connected 
with  electrodes. 


duction-machine  must  not  be  confused  with  the  break  or  make 
contractions  caused  by  the  voltaic  current.  In  the  case  of  the 
induction-machine,  the  break  or  make  applies  merely  to  what  is  done 
in  the  primary  circuit,  not  to  what  happens  to  the  current  actually 
passing  through  the  nerve.  The  current  induced  in  the  secondary  at 
make  of  the  primary  circuit  is,  of  course,  both  made  and  broken  in 


PRACTICAL  EXERCISES  593 

the  nerve — made  when  it  begins  to  flow,  broken  when  the  flow  is 
over ;  the  shock  induced  at  break  of  the  primary  is  also  made  and 
broken  in  the  nerve.  And  although  make  and  break  of  the  actual 
stimulating  current  come  very  close  together,  the  real  make,  here,  too, 
is  a  stronger  stimulus  than  the  real  break. 

(fr)  Repeat  (a)  with  the  muscle  directly  connected  by  thin  copper 
wires,  or,  better,  unpolarizable  electrodes  (p.  526),  to  the  cell. 

3.  Mechanical  Stimulation. — Pith  a  frog.     Cut  away  the  anterior 
portion  of  the  body,  dissect  out  one  sciatic  nerve,  and  separate  the 
leg  to  which  it  belongs  from  the  other.     Pinch  the  end  of  the  nerve: 
or  prick  the  muscles,  and  they  contract. 

4.  Thermal  Stimulation. — Touch  the  nerve  of  the  same  prepara- 
tion with  a  hot  wire  ;  the  muscle  contracts.    The  nerve  is  killed  at  the 
point  of  contact,  but  can  be  again  stimulated  by  touching  it  with  the 
wire  lower  down. 

5.  Chemical  Stimulation. — (a)  Cut  off  the  injured  portion  of  the 
nerve  used  in  3  and  4.     App  y  to  the  cut  end  a  crystal  of  common 
salt,  or  let  the  nerve  dip  into  a  watch-glass  containing  a  saturated 
solution  of  salt.     In  a  short  time  the  muscles  supplied  by  the  nerve 
begin  to  twitch,  and  soon  enter  into  irregular   tetanus.      Take  a 
tracing  of  the  contractions.     Cut  off  the  piece  of  nerve  in  contact 
with  the  salt,  and  the  tetanus  stops.     This  shows  that  the  seat  of 
irritation  is  the  portion  of  the  nerve  into  which  the  salt  has  pene- 
trated, and  from  which  water  has  been  withdrawn  by  osmosis.     Con- 
traction can  also  be  caused  by  applying  the  salt  directly  to  the 
muscles. 

(<£)  Wrap  the  leg  in  blotting-paper  moistened  with  normal  saline, 
ind  expose  the  nerve  to  the  vapour  of  strong  ammonia ;  it  will  be 
killed,  but  not  stimulated,  for  the  muscles  will  not  contract.  Expose 
:he  muscles  themselves  to  the  ammonia,  and  contraction  will  occur. 
Accordingly  muscle  is  stimulated  by  ammonia,  while  nerve  is  not. 

6.  Ciliary  Motion. — Cut  away  the  lower  jaw  of  the  same  frog,  and 
place  a  small  piece  of  cork  moistened  with  normal  saline  on  the 
:iliated  surface  of  the  mucous  membrane  covering  the  roof  of  the 
nouth.     It  will  be  moved  by  the  cilia  down  towards  the  gullet.     Lay 
i  small  rule,  divided  into  millimetres,  over  the  mucous  membrane, 
ind  measure  with  the  stop-watch  the  time  the  piece  of  cork  takes  to 
ravel  over  10  millimetres.      Then   pour  normal  saline  heated   to 
]o°  C.  on  the  ciliary  surface,  rapidly  swab  with  blotting-paper,  and 
epeat  the  observation.     The  piece  of  cork  will  now  be  moved  more 
juickly  than  before,  unless  the  normal  saline  has  been  so  hot  as  to 
njure  the  cilia. 

7.  Direct  Excitability  of  Muscle— Action  of  Curara.—Y\\h  the 
•rain  of  a  frog,  and  prevent  bleeding  by  inserting  a  piece  of  match. 
Expose  the  sciatic  nerve  in  the  thigh  on  one  side.    Carefully  separate 
:,  for  a  length  of  half  an  inch,  from  the  tissues  in  which  it  lies.    Pass 

strong  thread  under  the  nerve,  and  tie  it  tightly  round  the  limb, 
xcluding  the  nerve.  Now  inject  into  the  dorsal  or  ventral  lymph- 
ac  a  few  drops  of  a  i  per  cent,  curara  solution.  As  soon  as  paralysis 
;  complete,  make  two  muscle-nerve  preparations,  isolating  the  sciatic 

38 


594  A  MANUAL  OF  PHYSIOLOGY 

nerves  right  up  to  the  vertebral  column.  Lay  their  upper  ends  on 
electrodes  and  stimulate;  the  muscle  of  the  ligatured  limb  will 
contract.  This  proves  that  the  nerve-trunks  are  not  paralyzed  by 
curara,  since  the  poison  has  been  circulating  in  them  above  the 
ligature.  The  muscle  of  the  leg  which  was  not  ligatured  will 
contract  if  it  be  stimulated  directly,  although  stimulation  of  its  nerve 
has  no  effect.  The  muscular  fibres,  accordingly,  are  not  paralyzed. 
The  seat  of  paralysis  must  therefore  be  some  structures  physio- 
logically intermediate  between  the  nerve-trunk  and  the  muscular 
fibres  (p.  534). 

8.  Graphic  Record  of  a  Single  Muscular  Contraction  or  Twitch. 
— Pith  a  frog  (brain  and  cord),  make  a  muscle-nerve  preparation, 
and  arrange  it  on  the  myograph  plate,  as  in  i  (b).     Lay  the  nerve  on 
electrodes  connected  with  the  secondary  coil  of  an  induction  machine 
arranged  for  single  shocks.    Introduce  a  short-circuiting  key  (Fig.  155) 
between  the  electrodes  and  the  secondary  coil,  and  a  spring  key  in 
the  primary  circuit.     Close  the  short-circuiting  key,  and  then  press 
down  the  spring  key  with  the  finger.     Let  the  drum  off  (fast  speed) ; 
the  writing-point  will  trace  a  horizontal  abscissa  line.     Open  the 
short-circuiting  key,  and  then  remove  the  finger  from  the  spring-key. 
The  nerve  receives  an  opening  shock,  and  the  muscle  traces  a  curve. 
Now  adjust  the  writing-point  of  an  electrical  tuning-fork  (Fig.  184), 
vibrating,  say,  100  times  a  second,  to  the  drum,  and  take  a  time- 
tracing  below  the  muscle-curve.     Stop  the  drum,  or  take  off  the 
writing-point,  the  moment  the  time-tracing  has  completed  one  cir- 
cumference of  the  drum,  so  that  the  trace  may  not  run  over  on  itself. 
Cut  off  the  drum-paper,  write  on  it  a  brief  description  of  the  experi- 
ment, with  the  time-value  of  each  vibration  of  the  fork,  the  date, 
and  the  name  of  the  maker  of  the  tracing,  and  then  varnish  it.     An 
exactly  similar  tracing  can  be  obtained  by  directly  stimulating  the 
muscle  (curarized  or  not). 

9.  Influence  of  Temperature  on  the  Muscle-curve. — Pith  a  frog 
(brain  and  cord),  make  a  muscle-nerve  preparation,  and  arrange  it 
on  a  myograph.     Lay  the  nerve  on  electrodes  connected  through  a 
short-circuiting  key  with  the  secondary  coil  of  an  induction-machine, 
or  connect  the  muscle  directly  with  the  key  by  thin  copper  wires. 
Take  a  Daniell  cell,  connect  one  pole  through  a  simple  key  with 
one  of  the  upper  binding-screws  of  the  primary  coil,  and  the  other 
pole   with   the  metal   of  the   drum.     A  wire,   insulated   from  the 
drum,  but  clamped  on  the  vertical  part  of  its  support,  and  with  its 
bare  end  projecting  so  as  to  make  contact  with  a  strip  of.  brass 
fastened  on  the  spindle,  is  connected  with  the  other  upper  terminal 
of  the  primary  (Fig.   184).     At  each  revolution  of  the  drum  the 
primary  circuit  is  made  and  broken  once  as  the  strip  of  brass  brushes 
the  projecting  end  of  the  wire.     The  object  of  this  arrangement  is  to 
ensure  that  when  the  writing-point  of  the  myograph  lever  has  been 
once  adjusted  to  the  drum,  successive  stimuli  will  cause  contractions, 
the  curves  of  which  all  rise  from  the  same  point.     Close  the  key  in 
the  primary,  set  the  drum  off  (fast  speed),  open  the  short-circuiting 
key,  and  as  soon  as  the  muscle  has  contracted  once,  close  it  again. 


PRACTICAL  EXERCISES 


595 


82 

fcj^ 


I 

o     J^llllS?^ 

pili&illl^ 


-. 


W-S.E 


**»       *"*     O     (VI     *»  **     CJ  (U  .S 

§  ;ss*E!|£|&a 
<  §gfcjfJ*li*> 

till 


3    C    O-C    Su-«—    O 

E  O  vfc  H  S  ^  ^  P..52 

Now  stop  the  drum,  mark  with  a  pencil  the  position  of  the  feet  of  the 
stand  carrying  the  myograph  plate,  take  the  writing-point  off  the  drum, 
and  surround  the  muscle  with  pounded  ice  or  snow.  After  a  couple 
of  minutes  brush  away  any  ice  which  would  hinder  the  movement  of 
the  muscle,  rapidly  replace  the  stand  in  exactly  its  original  position, 
with  the  writing-point  on  the  drum,  and  take  another  tracing.  Again 

38—2 


596  A  MANUAL  OF  PHYSIOLOGY 

take  off  the  writing-point,  and  remove  all  unmelted  ice  or  snow.  With 
a  fine-pointed  pipette  irrigate  the  muscle  with  normal  saline  at  30°  G, 
and  quickly  take  another  tracing.  Then  put  on  a  time-tracing  with 
the  electrical  tuning-fork.  Fig.  166,  p.  546,  shows  a  series  of  curves 
obtained  in  this  way. 

10.  Influence  of  Load  on  the  Muscle-curv*. — Arrange  everything 
as  in  9.     Take  a  tracing  first  with  the  L-ver  alone,  then  with  a  weight 
of  5  grammes,  then  with  10,  20,  50,  and  100  grammes  (Fig.  165, 

P-  545)- 

11.  Influence  of  Fatigue  on  the  Muscle-curve. — Arrange  as  in  10, 
but  leave  on  the  same  weight  (say,  TO  grammes)  all  the  time.     Place 
the  nerve  on  the  electrodes.     Leave  the  short-circuiting  key  open. 
The  nerve  will  be  stimulated  at  each  revolution  of  the  drum,  and  the 
writing-point  will  trace  a  series  of  curves,  which  become  lower,  and 
especially  longer,  as  the  preparation  is  fatigued.     Two  or  four  curves 
can  be  taken  at  the  same  time,  if  both  ends  of  one  or  of  two  brass 
slips  be  arranged  so  as  to  make  contact  with  the  projecting  wire  at 
an  interval  of  a  semicircumference  or  quadrant  of  the  drum  (Fig.  184). 
(For  specimen  curve,  see  Fig.  170,  p.  549.) 

12.  Seat  of  Exhaustion  in  Fatigue  of  the  Muscle-nerve  Prepara- 
tion for  Indirect  Stimulation. — When  the  nerve  of  a  muscle-nerve 
preparation  has  been  stimulated  until  contraction  no  longer  occurs, 
the  muscle  can  be  made  to  contract  by  direct  stimulation.     The  seat 
of  exhaustion  is,  therefore,  not  the  muscular  fibres  themselves.     To 
determine  whether  it  is  the  nerve-fibres  or  the  nerve-endings,  perform 
the  following  experiments  : 

(a)  Pith  a  frog ;   make  two  muscle-nerve  preparations  ;   arrange 
them  both  on  a  myograph  plate,  which  has  two  levers  connected 
with  it.     Attach  each  of  the  muscles  to  a  lever  in  the  usual  way,  and 
lay  both  nerves  side  by  s.'de  on  the  same  pair  of  electrodes.     Cover 
with  moist  blotting-paper.     The  electrodes  are  connected  with  the 
secondary  of  an  induction-machine  arranged  for  tetanus.     With  a 
camel's-hair  brush  moisten  one  of  the  nerves  between  the  electrodes 
and  the  muscle  with  a  mixture  of  equal  parts  of  ether  and  alcohol,, 
diluted  with  twice  its  volume  of  water,  to  abolish  the  conductivity. 
Or  put  the  mixture  in  a  small  bottle,  in  which  dips  a  piece  of  filter- 
paper.     The  projecting  end  of  the  filter-paper  is  pointed,  and  the 
nerve  is  laid  on  the  point.     As  soon  as  it  is  possible  to  stimulate 
the  nerves  without  obtaining  contraction  in  this  muscle,  proceed  to 
tetanize  both  nerves  till  the  contracting  muscle  is  exhausted.     If  the 
other  muscle  begins  to  twitch  during  the  stimulation,  more  of  the 
ether  mixture  must  be  painted  on  the  nerve.    As  soon  as  the  stimula- 
tion ceases  to  cause  contraction  in  the  non-etherized  preparation, 
wash  off  the  mixture  from  the  other  nerve  with  normal  saline,  and 
soon  contraction  may  be  seen  to  take  place  in  the  muscle  of  this 
preparation.      This    shows    that   the  nerve-trunk   is    still    excitable. 
Now,  both  nerves  have  been  equally  stimulated,  and  therefore  the 
exhaustion  in  the  non-etherized  preparation  was  not  due  to  fatigue 
of  the  nerve-fibres,  but  of  the  nerve-endings. 

(b)  Inject  f  gramme  chloral  hydrate  into  the  rectum  of  a  rabbit, 


PRACTICAL  EXERCISES  597 

and  put  a  pair  of  bulldog  forceps  on  the  anus.  Fix  the  animal  on  a 
holder  as  soon  as  the  chloral  has  taken  effect.  Clip  the  hair  from 
the  front  of  the  neck  and  insert  a  tracheal  cannula  (p.  177).  Now 
inject  subcutaneously  enough  of  a  i  per  cent,  solution  of  curara  to  just 
paralyze  the  skeletal  muscles.  As  soon  as  symptoms  of  paralysis  of 
the  muscles  of  respiration  have  appeared,  connect  the  tracheal  cannula 
with  the  artificial  respiration  apparatus.  Now  expose  the  sciatic  nerve 
(p.  1 86)  on  one  side,  put  on  a  ligature,  and  divide  it  above  the  ligature. 
Lay  the  nerve  on  electrodes  connected  with  the  secondary  coil  of 
an  induction  machine  arranged  for  tetanus,  and  stimulate  it.  If  the 
muscles  supplied  by  the  nerve  contract,  curara  must  be  injected  till 
contraction  is  no  longer  obtained.  Then  the  nerve  is  continuously 
stimulated  for  a  long  time.  After  some  hours  the  curara  action  will 
begin  to  wear  off,  and  it  may  be  seen  that  the  muscles  of  the  leg 
again  contract.  This  shows  that  even  a  very  prolonged  stimulation 
is  not  sufficient  to  exhaust  the  extra-muscular  nerve-fibres  (Bowditch). 


FIG.  185.— ARRANGEMENT  FOR  STUDYING  VOLUNTARY  MUSCULAR  FATIGUE. 


13.  Seat  of  Exhaustion  in  Fatigue  for  Voluntary  Muscular  Con- 
traction.— Support  the  arm,  extensor  surface  downwards,  on  a  rest 
such  as  that  shown  in  Fig.  184,  and  connect  the  middle  finger  of 
one  hand,  by  means  of  a  string  passing  over  a  pulley  on  the  edge 
of  a  table,  with  a  weight  of  3  or  4  kilos.  The  string  is  attached  to 
the  finger  by  a  leather  collar  surrounding  the  second  phalanx  of  the 
finger,  but  allowing  free  movements  of  the  joints.  The  extent  of  the 
vertical  movements  of  the  string  (and  therefore  the  work  done)  may 
be  registered  on  a  drum  by  a  writing-point  connected  with  it,  the 
whole  arrangement  forming  what  is  called  an  ergograph.  Two  collar 
electrodes  (strips  of  copper  covered  with  cotton-wool  soaked  in  salt 
solution,  and  bent  to  a  circular  form)  are  placed  on  the  forearm,  and 
connected  through  a  short-circuiting  key  with  the  secondary  coil  of  an 
induction  machine  arranged  for  tetanus  (p.  175),  and  having  a  battery 
of  four  or  five  Daniell  cells,  coupled  in  series,*  in  its  primary  circuit. 
The  middle  finger  is  now  made  to  raise  the  weight  repeatedly  by 
vigorous  contractions  of  the  flexor  muscles  until  at  length  a  failure 
*  /.*.,  the  copper  of  one  cell  connected  with  the  zinc  of  the  next. 


598  A  MANUAL  OF  PHYSIOLOGY 

occurs.  At  this  moment  the  short-circuiting  key  is  opened,  and  the 
flexor  muscles  stimulated  electrically.  They  again  contract  and  raise 
the  weight,  therefore  the  seat  of  exhaustion  in  voluntary  muscular 
effort  is  not  in  the  muscles.  That  it  is  not  usually  in  the  nerve- 
endings  nor  in  the  nerves  may  be  shown  by  inducing  fatigue  of  the 
finger  for  voluntary  contraction  in  the  same  way,  and  then  stimu- 
lating the  median  nerve  at  the  bend  of  the  elbow  by  sponge  elec- 
trodes. The  usual  seat  of  fatigue  for  voluntary  muscular  contraction 
must  therefore  be  in  the  spinal  cord  or  brain,  and  as  we  have  no 
reason  to  believe  that  the  nerve-fibres  of  the  central  nervous  system 
are  essentially  different  from  peripheral  nerve-fibres,  we  conclude  that 
the  fatigue  is  in  the  nerve-cells  or  the  network  of  fibrils  around  them 
(p.  640) . 

14.  Influence  of  Veratria  on  Muscular  Contraction. — Arrange  a 
drum  as  in  Fig.  184.     Pith  a  frog  (brain  only),  expose  the  sciatic 
nerve  in  one  thigh,  and  isolate  it  for  J  inch  from  the  surrounding 
tissues.    Pass  under  it  a  strong  thread,  and  ligature  everything  except 
the  nerve.     Now  inject  into  the  dorsal  or  ventral  lymph-sac  a  few 
drops  of  o'i  per  cent,  solution  of  sulphate  of  veratria.     In  a  few 
minutes  make  two  muscle-nerve  preparations  from  the  posterior  limbs. 
First  put  the  preparation  from  the  unligatured  limb  on  the  myograph 
plate.    Lay  the  nerve  on  electrodes  connected  through  a  short-circuit- 
ing key  with  the  secondary  of  an  induction  machine  arranged  as  in 
Fig.  184.     Put  the  writing-point  on  the  drum  and  set  it  off  (fast 
speed).     Open  the  short-circuiting  key  till  the  nerve  has  been  once 
stimulated,  then  close  it  again.     The  curve  obtained  differs  from  a 
normal  curve,  in  that  the  period  of  descent  (relaxation)  is  exceedingly 
prolonged.     Now  connect  the  preparation  from  the  ligatured  limb 
with  the  lever,  and  take  a  tracing  of  a  single  contraction.     Put  on  a 
time-tracing  with  the  electrical  tuning-fork  (see  Fig.  171,  p.  551). 

15.  Measurement  of  the  Latent  Period  of  Muscular  Contraction. 
— Use  the  spring  myograph  (Fig.  162,  p.  542),  raising  it  on  blocks  of 
wood.     Smoke  the  glass  plate  over  a  paraffin  flame,  or  cover  it  witli 
paper,  and  smoke  the  paper.     Connect  the  knock-over  key  of  the 
myograph  with  the  primary  circuit  of  an  induction  coil.     Pith  a  frog, 
and  make  a  muscle-nerve  preparation.     Arrange  it  on  the  myograph 
plate.      Place  electrodes  below  the  nerve  as  near  the  muscle   as 
possible,  and  connect  by  a  short-circuiting  key  with  the  secondary. 
Bring  the  writing-point  in  contact  with  the  smoked  surface  of  the 
spring  myograph,  so  as  to  get  the  proper  pressure.     See  that  the 
writing-point  of  the  tuning-fork  is  in  the  right  position  for  tracing 
time.     Then  push  up  the  plate  so  as  to  compress  the  spring,  till  the  rod 
connected  with  the  frame  which  carries  the  plate  is  held  by  the  catch. 

With  the  short-circuiting  key  closed,  press  the  release  and  allow 
an  abscissa  line  to  be  traced.  Again  shove  back  the  frame  till  it  is 
caught.  Push  home  the  rod  by  means  of  which  the  prongs  of  the 
tuning-fork  are  separated,  and  rotate  it  through  90°.  Close  the 
knock-over  key,  open  the  short-circuiting  key,  shoot  the  plate  again, 
and  a  muscle-curve  and  time-tracing  will  be  recorded.  Again  close 
the  short-circuiting  key,  withdraw  the  writing-point  of  the  tuning- 


PRACTICAL  EXERCISES  599 

fork,  push  back  the  plate,  close  the  trigger-key,  then  open  the  short- 
circuiting  key,  and  holding  the  travelling  frame  with  the  hand,  allow 
it  just  to  open  the  knock-over  and  stimulate  the  nerve.  The  writing- 
point  now  records  a  vertical  line  (or,  rather,  an  arc  of  a  circle),  which 
marks  on  the  tracing  the  moment  of  stimulation.  The  latent  period 
is  obtained  by  drawing  a  parallel  line  (or  arc)  through  the  point  of 
the  muscle-curve  where  it  just  begins  to  diverge  from  the  abscissa 
line.  The  value  of  the  portion  of  the  time-tracing  between  these  two 
lines  can  be  readily  determined,  and  is  the  latent  period. 

1 6.  Summation  of  Stimuli. — Arrange  two  knock-over  keys  on  the 
spring  myograph  at  such  a  distance  from  each  other  that  the  plate 
travels  from  one  to  the  other  in  a  time  less  than  the  latent  period. 
Connect  each  key  with  the  primary  circuit  of  a  separate  induction 
coil  having  a  couple  of  Daniells  in  it.    Join  two  of  the  binding-screws 
of  the  secondaries  together  :  connect  the  other  two  through  a  short- 
circuiting  key  with  electrodes,  on  which  the  nerve  of  a  muscle-nerve 
preparation  is  arranged.     Push  up  the  secondaries  till  the  break 
shocks  obtained  on  opening  the  two  knock-over  keys  are  maximal. 
Then  shoot  the  plate  as  described  in  15,  first  with  one  bigger  key 
closed,  and  then  with  both.     The  curves  obtained  should  be  of  the 
same  height  in  the  two  cases,  as  a  second  maximal  stimulus  falling 
within  the  latent  period  is  ignored  by  the  nerve  or  muscle.     Repeat 
the  experiment  with  submaximal  stimuli,  i.e.,  with  such  a  distance  of 
the  coils  that  opening  of  either  trigger  key  does  not  cause  as  strong 
a  contraction  as  is  caused  when  the  coils  are  closer.     The  curve  will 
now  be  higher  when  the  two  shocks  are  thrown  in  successively  than 
when  the  nerve  is  only  once  stimulated.      This  shows  that  (sub- 
maximal)  stimuli  can  be  summed  in  the  nerve.     The  same  could  be 
demonstrated  for  muscle  (p.  552). 

17.  Superposition  of  Contractions. — Smoke  a  drum  arranged  for 
automatic  stimulation  as  in  Fig.  184.     Adjust  the  brass  points  with 
a  distance  of,  say,  one  centimetre  between  them,  so  that  a  second 
stimulus  may  be  thrown  into  the  nerve  at  an  interval  greater  than  the 
latent  period  of  muscle.     Put  two  Daniells  in  the  primary  circuit. 
Lay  the  nerve  of  a  muscle-nerve  preparation  on  electrodes  connected 
through  a  short-circuiting  key  with  the  secondary.     Allow  the  drum 
to  revolve  (fast  speed) ;  open  the  short-circuiting  key  till  both  brass 
points  have  passed  the  projecting  wire,  then  close  it.     Now  bend 
back  the  second  brass  point,  and  take  a  tracing  in  which  the  first 
curve  is  allowed  to  complete  itself.     This  will  not  rise  as  high  as  the 
second  curve  obtained  when  the  two  stimuli  were  thrown  in.   Repeat 
the  experiment  with  varying  intervals  between  the  brass  points — 
that  is,  between  the  two  successive  stimuli.     Put  on  a  time-tracing 
with  the  electrical  tuning-fork.     (For  specimen  curve  see  Fig.  172, 
P-  552). 

18.  Composition  of  Tetanus. — (a)  Adjust  a  muscle-nerve  prepara- 
tion on  a  myograph  plate,  the  nerve  being  laid  on  electrodes  con- 
nected through  a  short-circuiting  key  with  the  secondary  of  an  induc- 
tion machine,  the  primary  circuit  of  which  contains  a  Daniell  cell 
and  is  arranged  for  an  interrupted  current  (Fig.  65,  p.  175).     The 


6oo 


A  MANUAL  OF  PHYSIOLOGY 


lever  should  be  shorter  than  that  used  for  the  previous  experiments, 
or  the  thread  should  be  tied  in  a  hole  farther  from  the  axis  of  rota- 
tion, so  as  to  give  less  magnification  of  the  contraction.  Set  the 
Neef's  hammer  going,  let  the  drum  revolve  (slow  speed),  and  open 
the  key  in  the  secondary.  The  writing-point  at  once  rises,  and  traces 
a  horizontal  or  perhaps  slightly-ascending  line.  Close  the  short- 
circuiting  key,  and  the  lever  sinks  down  again  to  the  abscissa  line. 
If  it  does  not  quite  return,  it  should  be  loaded  with  a  small  weight. 
This  is  an  example  of  complete  tetanus. 

(b)  Connect  the  spring  shown  in  Fig.  186  with  one  of  the  upper 
terminals  of  the  primary  coil,  and  the  mercury  cup  with  the  other. 

Fasten  the  end 
of  the  spring  in 
one  of  the 
notches  in  the 
upright  piece  of 
wood  by  means 
of  a  wedge,  so 
that  its  whole 
length  can  be 
made  to  vibrate. 
Let  the  drum  off 
set  the  spring 
vibrating  by  de 
pressing  it  with 
the  finger,  ther 
open  the  key  ir 
the  secondary 
The  muscle  is 
thrown  into  in 
complete  tetanus 
and  the  writing 

point  traces  a  wavy  curve  at  a  higher  level  than  the  abscissa  line.  Clost 
the  short-circuiting  key,  and  the  lever  falls  to  the  horizontal.  Repea 
the  experiment  with  the  spring  fastened,  so  that  only  j,  \,  J,  J  of  its 
length  is  free  to  vibrate.  The  rate  of  interruption  of  the  primarj 
circuit  increases  in  proportion  to  the  shortening  of  the  spring,  anc 
the  tetanus  becomes  more  and  more  complete  till  ultimately  the 
writing-point  marks  an  unbroken  straight  line.  Put  on  a  time-tracing 
by  means  of  an  electro-magnetic  marker  connected  with  a  metronome 
beating  seconds  or  half-seconds  (Fig.  60,  p.  170).  (For  specimer 
curves  see  Fig.  173,  p.  553.) 

19.  Velocity  of  the  Nerve-impulse. — Use  the  spring  myograph 
(Fig.  162,  p.  542).  Make  a  muscle-nerve  preparation  from  a  large 
frog  (preferably  a  bull-frog),  so  that  the  sciatic  nerve  may  be  as  long 
as  possible.  Connect  the  knock-over  key  with  the  primary  circuit  of 
an  induction  machine,  which  should  contain  a  single  Daniell  cell. 
Arrange  two  pairs  of  fine  electrodes  under  the  nerve  on  the  myograph 
plate,  one  near  the  muscle,  the  other  at  the  central  end.  Connect 
the  electrodes  with  a  Ponl's  commutator  (without  cross-wires),  the 


FIG.  186. — ARRANGEMENT  FOR  TETANUS. 

A,  upright  with  notches,  in  which  the  spring  S  is  fastened 
(shown  in  section) ;  C,  horizontal  board  to  which  A  is  attached, 
and  in  a  groove  in  which  the  mercury-cup  E  slides.  The  primary 
coil  P  is  connected  with  E,  and  through  a  simple  key,  K,  with 
the  battery  B,  the  other  pole  of  which  is  connected  with  the  end 
of  the  spring.  The  wires  from  the  secondary  coil,  P',  go  to  a 
short-circuiting  key,  K',  from  which  the  wires  F  go  off  to  the 
electrodes. 


PRACTICAL  EXERCISES  601 

side-cups  of  which  are  joined  to  the  terminals  of  the  secondary  coil, 
as  shown  in  Fig.  187.  By  tilting  the  bridge  of  the  commutator  the 
nerve  may  be  stimulated  at  either  point.  Great  care  must  be  taken 
to  keep  the  nerve  in  a  moist  atmosphere  by  means  of  wet  blotting- 
paper;  but  at  the  same  time  it  must  not  lie  in  a  pool  of  normal 
saline,  as  twigs  of  the  stimulating  current  would  in  this  case  spread 
down  the  nerve,  and  we  could  never  be  sure  that  the  apparent  was 
always  the  real  point  of  stimulation.  The  writing-points  of  the  lever 
and  tuning-fork  having  been  adjusted  to  the  smoked  plate,  as  in  15, 
the  bridge  of  the  Pohl's  commutator  is  arranged  for  stimulation  of 
the  distal  point  of  the  nerve,  the  plate  is  shot  with  the  short-circuit- 
ing key  in  the  secondary  closed,  and  an  abscissa  line  and  time-curve 
traced.  Then  the  writing-point  of  the  fork  is  removed  and  the  plate 
again  shot  with  the  key  in  the  secondary  open,  and  a  muscle-curve 


FIG.  187.— ARRANGEMENT  FOR  MEASURING  THE  VELOCITY  OF  THE  NERVE- 
IMPULSE. 

A,  travelling  plate  of  spring  myograph ;  M,  muscle  lying  on  a  myograph  plate ; 
N,  nerve,  lying  on  two  pairs  of  electrodes,  E  and  E' ;  C,  Pohl's  commutator  without 
<ross  wires  ;  K,  knock-over  key  of  spring  myograph  (only  the  binding-screws  shown) ; 
K',  simple  key  in  primary  circuit ;  B,  battery  ;  P,  primary  coil ;  S,  secondary  coil. 

is  obtained.  The  commutator  is  now  arranged  for  stimulation  of 
the  central  end  of  the  nerve,  and  another  muscle-curve  taken. 
Vertical  lines  are  drawn  through  the  points  where  the  two  curves 
just  begin  to  separate  out  from  the  abscissa  line.  The  interval 
between  these  lines  corresponds  to  the  time  taken  by  the  nerve- 
impulse  to  travel  along  the  nerve  from  the  central  to  the  distal  pair 
of  electrodes.  Its  value  in  time  is  given  by  the  tracing  of  the 
tuning-fork.  The  length  of  the  nerve  between  the  two  pairs  of 
electrodes  is  now  carefully  measured  with  a  scale  divided  in  milli- 
metres, and  the  velocity  calculated  (p.  582). 

20.  Chemistry  of  Muscle. — Mince  up  some  muscle  from  the  hind- 
legs  of  a  dog  or  rabbit  (used  in  some  of  the  other  experiments),  of 
which  the  bloodvessels  have  been  washed  out  by  injecting  normal 


602  A  MANUAL  OF  PHYSIOLOGY 

saline  solution  through  a  cannula  tied  into  the  abdominal  aorta  until 
the  washings  are  no  longer  tinged  with  blood.  To  some  of  the 
minced  muscle  add  twenty  times  its  bulk  of  distilled  water,  to  another 
portion  ten  times  its  bulk  of  a  5  per  cent,  solution  of  magnesium 
sulphate.  Let  stand,  with  frequent  stirring,  for  twenty-four  hours. 
Then  strain  through  several  folds  of  linen,  press  out  the  residue,  and 
filter  through  paper,  (i)  With  the  filtrate  of  the  watery  extract  make 
the  following  observations  : 

(a)  Reaction. — To  litmus  paper  acid. 

(b)  Determine  the  temperatures,  at  which  coagulation  of  the  various 
proteids  in  the  extract  takes  place,  according  to  the  method  described 
on  p.  21.     Put  some  of  the  watery  extract   in  the  test-tube,  and 
heat  the  bath,  stirring  the  water  in  the  beakers  occasionally  with  a 
feather.     Note  at  what  temperature  a  coagulum  first  forms.     It  will 
be  about  47°  C.     Filter  this  off,  and  again  heat ;  another  coagulum 
will  form  at  56°  to  58°.     Filter,  and  heat  the  filtrate ;  a  third  slight 
coagulum   may  be  formed  at  60°  to  65°  C.      A  fourth  precipitate 
(of  serum-albumin)  will  come  down  at  70°  to  73°.     Saturate  some 
of   the   watery   extract   with    magnesium    sulphate ;    a    large    pre- 
cipitate will  be   formed,  showing  the  presence    of  a    considerable 
amount  of  globulin.    Filter  off  the  precipitate  and  heat  the  filtrate ; 
coagulation  will  again  occur  at  very  much  the  same  temperatures  as 
before.     The  substance  coagulating  at  47°  to  48°  has  been  described 
by  Halliburton  as  a  globulin,  by  Demant  as  an  albumin.     If  it  is  a 
single  substance,  it  possesses  some  of  the  characters  of  both  globulins 
and  albumins,  for  it  is  partially  but  not  entirely   precipitated   by 
saturation   with   magnesium   sulphate,    and   is  not   precipitated   b; 
sodium  chloride. 

(2)  (a)  Test  the  reaction  of  the  magnesium  sulphate  extract.     I 
will  usually  be  faintly  acid. 

(b)  Heat  some  of  it.     Precipitates  will  be  obtained  at  the  same 
temperatures  as  in  (i)  (<£),  but  those  at  47°  to  48°  and  56°  to  58°  wil 
be  more  abundant.     Of  the  two,  that  at  47°  to  48°  will  be  the  large 
when  time  is  given  for  it  to  come  down  and  the  heating  is  gradual. 

(c)  Dilute  some  of  the  magnesium  sulphate  extract  with  three  times 
another  portion  with  four  times,  and  another  with  five  times,  its  volum 
of  water  in  a  test-tube,  and  put  in  a  bath  at  40°  C.    Coagulation  wil 
occur  in  one  or  all  of  these  test-tubes.     To  another  test-tube  of  the 
extract  diluted  in  the  proportion  which  has  given  the  best  *  muscle- 
clot  '  add  a  few  drops  of  a  dilute  solution  of  potassium  oxalate,  and 
place  in  the  bath  at  40°.     Coagulation  occurs  as  before.     Filter  off 
the  clot  from  all  the  test-tubes.     The  filtrate  is  the  '  muscle-serum/ 
and  yields  a  precipitate  of  serum-albumin  at  70°  to  73"  C.     Dissolve 
the  muscle-clot  in  5  per  cent,  magnesium  sulphate.     It  consists  of 
the  substances  which  coagulate  at  47°  to  48°  and  56°  to  58°.     These 
are  supposed  by  Halliburton  to  be  two  distinct  bodies — paramyosin 
and  myosin.     But  it  should  be  remembered  that  the  temperature  of 
heat-coagulation  of  any  substance  is  by  no  means  an  absolute  con- 
stant.   It  depends  on  the  reaction,  the  proportion  and  kind  of  neutral 
salts  present,  perhaps  on  the  strength  of  the  proteid  solution  and  the 


PRACTICAL  EXERCISES  603 

manner  of  heating.  A  solution  of  egg-albumin,  e.g.,  can  be  coagulated 
at  a  temperature  much  below  70°  when  it  is  heated  for  a  week.  Small 
differences  in  the  temperature  of  heat-coagulation,  unless  supported 
by  well-marked  chemical  reactions,  are  not  enough  to  characterize 
proteid  substances  as  chemical  individuals. 

(3)  Myosin,  like  other  globulins,  is  insoluble  in  distilled  water,  but 
soluble  in  weak  saline  solutions.  Saturation  with  neutral  salts  like 
sodium  chloride  and  magnesium  sulphate  precipitates  myosin,  but 
not  albumin,  from  its  solutions ;  saturation  with  ammonium  sulphate 
precipitates  both.  Myosin  is  said  to  be  dissolved  without  change  in 
very  weak  acids.  Stronger  acids  precipitate  it.  Verify  the  following 
reactions  of  myosin,  using  either  a  solution  of  the  muscle-clot,  or  the 
original  magnesium  sulphate  extract  of  the  muscle. 

(a)  Dropped  into  water,  it  is  precipitated  in  flakes,  which  can  be 
redissolved  by  a  weak  solution  of  a  neutral  salt  (say  5  per  cent,  mag- 
nesium sulphate). 

(b)  When  a  solution  of  myosin  is  dialysed,  it  is  precipitated  on 
the  inside  of  the  dialyser  as  the  salts  pass  out. 

(c)  If  a  piece  of  rock-salt  is  suspended  in  a  solution,  the  myosin 
gradually  gathers  upon  it,  diffusion  of  the  salt  out  through  the  precipi- 
tated myosin  always  keeping  a  saturated  layer  around  it. 

(d)  Saturate  a  solution  containing  myosin  with  crystals  of  mag- 
nesium  sulphate,   stirring   or   shaking  at  frequent  intervals.      The 
myosin  is  precipitated. 

(e)  Without   adding   any   salt,   simply   shake  a   myosin   solution 
vigorously ;  a  certain  amount  of  the  myosin  will  be  precipitated,  and 
the  solution  will  become  turbid.     This  reaction  can  also  be  obtained 
with  solutions  of  other  proteids,  such  as  albumin  (Ramsden). 

Extracts  in  all  essentials  similar  to  those  obtained  from  the  muscles 
of  a  freshly-killed  animal  can  be  got  from  muscles  that  have  entered 
into  rigor. 

21.  Reaction  of  Muscle  in  Rest,  Activity,  and  Rigor  Mortis. — 
(a)  Take  a  frog's  muscle,  cut  it  across,  and  press  a  piece  of  red  litmus 
paper  on  the  cut  end ;  it  is  turned  blue.     Yellow  turmeric  paper  is 
not  affected. 

(b)  Immerse  another  muscle  in  normal  saline  solution  at  40°  to 
42°  C.     It  becomes  rigid.     The  reaction  becomes  acid  to  litmus 
paper,  and  also  turns  brown  turmeric  paper  yellow. 

(c)  Plunge  another  muscle  into  boiling  normal  saline  solution.     It 
becomes  even  harder  than  in  (£),  but  its  reaction  remains  alkaline  to 
litmus  paper. 

(d)  Stimulate  another  muscle  with  an  interrupted  current  from 
an  induction  machine  (Fig.  65,  p.   175),  till  it  no  longer  contracts. 
The  reaction  is  now  acid  to  litmus  paper.     Brown  turmeric  paper 
may  also  be  turned  yellow. 

22.  Effect  of  Suprarenal  Extract  on  Muscular  Contraction — (i) 
On  Skeletal  Muscle.— Proceed  as  in  14,  but  instead  of  veratria  inject 
a  watery  solution  of  the  suprarenal  capsules  (calf,  sheep,  dog,  etc.). 
The  curve  of  the  gastrocnemius  acted  upon  by  the  extract  is  pro- 
longed as  in  veratria  poisoning,  although  not  to  such  a  great  extent. 


604  A  MANUAL  OF  PHYSIOLOGY 

(2)  On  the  Smooth  Muscle  of  the  Bloodvessels. — Make  the  arrange- 
ments for  a  blood-pressure  tracing  from  a  dog  as  in  19,  p.  185.  Put 
a  cannula  in  the  carotid  and  another  in  the  femoral  vein  or  one  of 
its  branches  (p.  177).  Expose  both  vagi  in  the  neck,  and  pass 
threads  loosely  under  them.  Connect  the  carotid  with  the  mano- 
meter and  take  a  tracing.  Then,  while  the  tracing  is  continued, 
inject  slowly  into  the  femoral  vein  an  amount  of  watery  extract 
corresponding  to  about  -g-th  gramme  of  suprarenal.  The  blood- 
pressure  rises*  owing  to  constriction  of  the  arterioles  by  direct 
action  of  the  extract  on  their  muscular  tissue.  The  heart  is  greatly 
slowed  owing  to  stimulation  of  the  cardio-inhibitory  centre.  At 
once  cut  both  vagi  while  a  tracing  is  being  taken  ;  the  blood-pressure 
rises  still  more  (p.  475).  The  rise  is  not  long  maintained,  but  a 
second  injection  causes  a  renewed  increase  of  pressure. 

*  The  amount  of  the  initial  rise  of  pressure  is  very  variable,  since  the 
slowing  of  the  heart  tends  to  diminish  the  pressure,  while  the  constriction 
of  the  arterioles  tends  to  increase  it.  Thus,  in  one  experiment  the  increase 
of  pressure  on  injection  of  the  extract  was  only  6  mm.  of  mercury,  while 
in  another  it  was  56  mm.  On  section  of  the  vagi  in  this  second  experi- 
ment, there  was  an  additional  rise  of  64  mm.,  and  after  a  second  injection 
a  further  rise  of  70  mm.,  making  an  increase  of  190  mm.  in  all  above  the 
original  pressure. 

<,*l 


CHAPTER  XL 
ELECTRO-PHYSIOLOGY. 

A  LITTLE  more  than  a  hundred  years  ago  the  foundation  both  of 
electro-physiology  and  of  the  vast  science  of  voltaic  electricity  was 
laid  by  a  chance  observation  of  a  professor  of  anatomy  in  an  Italian 
garden.     It  is  indeed  true  that  long  before  this  electrical  fishes  were 
not  only  popularly  known,  but  the  shock  of  the  torpedo  had  been  to 
a  certain  extent  scientifically  studied.     But  it  was  with  the  discovery 
of  Galvani  of  Bologna  that  the  epoch  of  fruitful  work  in  electro- 
physiology  began.     Engaged  in  experiments  on  the  effect  of  static 
electricity  in  stimulating  animal  tissues,  he  happened  one  day  to 
notice  that  some  frogs'  legs,  suspended  by  copper  hooks  on  an  iron 
railing,  twitched  whenever  the  wind  brought  them  into  contact  with 
one  of  the  bars  (p.  627).     He  concluded  that  electrical  charges  were 
developed  in  the  animal  tissues  themselves,  and  discharged  when  the 
circuit  was  completed.     Volta,  professor  of  physics  at  Padua,  fixing  his 
attention  on  the  fact  that  in  Galvani's  experiment  the  metallic  part  of 
the  circuit  was  composed  of  two  metals,  maintained  that  the  contact 
of  these  was  the  real  origin  of  the  current,  and  that  the  tissues  served 
merely  as  moist  conductors  to  complete  the  circuit ;  and  he  clinched 
his  argument  by  constructing  the  voltaic  pile,  a  series  of  copper  and 
zinc  discs,  every  two  pairs  of  which  were  separated  by  a  disc  of 
wet  cloth.      The  pile  yielded  a  continuous  current  of  electricity. 
'  So,'  said  Volta,  '  it  is  clear  that  the  tissue  in  Galvani's  experiment 
only  acts  the  part  of  the  cloth.'     Galvani,  however,  showed  that  con- 
traction without  metals  could  be  obtained  by  dropping  the  nerve  of  a 
preparation  on  to  the  muscle  (p.  627);  and  it  soon  began  to  be  recog- 
nised that  both  Galvani  and  Volta  were  in  part  right,  that  two  brilliant 
discoveries  had  been  made  instead  of  one  ;  in  short,  that  the  tissues 
produce  electricity,  and  that  the  contact  of  different  metals  does  so 
too.     Although  it  is  curious  to  note  how  completely  the  growth  of 
that  science  of  which  Volta's    discovery  was  the  germ   has   over- 
shadowed the   parent   tree  planted   by  the  hand   of  Galvani,  yet 
animal  electricity  has  been   deeply  studied  by  a  large  number   of 
observers,   and  many  interesting  and   important   facts   have   been 
brought  to  light. 


6o6 


A  MANUAL  OF  PHYSIOLOGY 


Since  it  is  in  muscle  and  nerve  that  the  phenomena  of 
electro-physiology  are  seen  in  their  simplest  expression,  and 
have  been  chiefly  studied,  we  shall  develop  the  fundamental 
laws  with  reference  to  muscle  and  nerve  alone,  and  after- 
wards apply  them  to  other  excitable  tissues. 

i.  All  points  on  the  surface  of  an  uninjured  resting  muscle  are 
approximately  at  the  same  potential.  In  other  words,  if  any 
two  points  are  connected  with  a  galvanometer  by  means  of 
unpolarizable  electrodes,  little  or  no  current  is  indicated. 
(Although  it  is  scarcely  possible  to  isolate  a  muscle  without 
its  showing  some  current,  the  more  carefully  the  isolation 
is  performed  the  feebler  is  the  current ;  and  between  two 
points  of  the  inactive,  uninjured  ventricle  of  the  frog  no 
electrical  difference  has  been  found.) 


FIG.  188. — A,  uninjured,  B,  injured, 
portion  of  nerve  ;  G,  galvanometer. 
The  large  arrows  show  direction  of 
demarcation  current  or  current  of  rest, 
the  small  arrows  direction  of  negative 
variation  or  action  current. 


FIG.  189.— DIAGRAM  OF  CURRENTS 
OF  REST  IN  A  REGULAR  MUSCLE, 
OR  MUSCLE  CYLINDER. 

E,  equator.  The  dotted  lines  join 
points  at  the  same  potential,  between 
which  there  is  no  current. 


I  2.  Any  uninjured  point  on  the  surface  of  a  resting  muscle  or 
\nerve  is  at  a  higher  potential  than  any  injured  point ;  so  that  a 
current  will  pass  through  the  galvanometer  from  uninjured 
to  injured  point,  and  in  the  tissue  from  the  latter  to  the 
former  (current  of  rest  or  demarcation  current — Fig.  188). 

3.  Any  unexcited  point  on  the  surface  of  a  muscle  or  nerve  is 
at  a  higher  potential  than  any  excited  point,  and  any  less  excited 
point  is  at  a  higher  potential  than  any  more  excited  point. 

The  best  object  for  experiments  on  the  demarcation 
current  is  a  straight-fibred  muscle  like  the  frog's  sartorius. 
If  this  muscle  be  taken,  and  the  ends  cut  off  perpendicularly 
to  the  surface,  a  muscle-prism  is  obtained  (Fig.  189).  The 
strongest  current  is  got  when  one  electrode  is  placed  on 
the  middle  of  either  cross-section  and  the  other  on  the 
'  equator  ' — that  is,  on  a  line  passing  round  the  longitudinal 


ELECTRO-PHYSIOLOGY  607 

surface  midway  between  the  ends.  The  direction  of  this 
current  is  from  the  cross-section  towards  the  equator  in  the 
muscle.  If  the  electrodes  are  placed  on  symmetrical  points 
on  each  side  of  the  equator,  there  is  no  current. 

A  particular  case  of  this  symmetrical  or  '  streamless '  arrangement 
is  where  the  middle  points  of  the  two  cross-sections  are  led  off  to 
the  galvanometer ;  here,  if  the  sections  are  similar,  their  potential 
is  the  same,  and  the  needle  remains  at  zero.  Between  two  points 
of  the  longitudinal  surface  at  unequal  distances  from  the  equator 
there  is  a  current  in  the  galvanometer  from  the  nearer  to  the  more 
distant  point,  the  potential  of  a  longitudinal  point  nearer  a  cross-section 
being  lower  than  that  of  one  more  remote.  Between  two  points  on 
the  same  cross-section  there  is  a  current  if  they  are  not  symmetrically 
placed  with  reference  to  its  centre,  the  direction  in  the  muscle  being 
from  more  central  to  more  peripheral  point. 

The  above  may  be  taken  as  applying  to  nerve  also,  with 
the  proviso  that  less  is  known  as  to  electrical  differences 
between  points  on  the  same  cross-section,  since  ordinary 
cold-blooded  nerves  are  too  small  for  such  experiments. 

Current  of  Action,  or  Negative  Variation. — When  a  muscle 
or  nerve  is  excited,  a  wave  of  diminished  potential  (nega- 
tivity) sweeps  over  it.  Suppose  two  points,  A  and  B 
(Fig.  190),  on  the  longitudinal  surface  of  a  muscle  to  be  con- 
nected with  a  capillary  electrometer  (p.  524),  the  movements 
of  the  mercury  being  photographed  on  a  travelling  sensitive 
surface.  Let  the  muscle  be  excited  at  the  end,  so  that  the 
wave  of  excitation  will  be  propagated  in  the  direction  of 
the  arrow.  The  wave  will  reach  A  first,  and  while  it  has  not 
yet  reached  B,  A  will  become  negative  to  B.  If  there  is  a 
resting  difference  of  potential  between  A  and  B,  this  will 
be  altered,  the  new  and  transitory  difference  adding  itself 
algebraically  to  the  old.  When  the  wave  reaches  B,  it  may 
already  have  passed  over  A  altogether,  and  B  now  becoming 
negative  to  A,  there  will  be  a  movement  of  the  meniscus  of 
the  electrometer  in  the  opposite  direction.  This  is  called 
the  diphasic  current  of  action.  If  the  wave  has  not  passed 
over  A  before  it  reaches  B,  as  would  in  general  be  the  case 
in  an  actual  experiment,  there  will  be  first  a  period  during 
which  A  is  more  negative  than  B  (first  phase) ;  this  will  end 
as  soon  as  B  has  become  equally  negative  with  A,  and  will 
be  succeeded  by  a  period  during  which  B  is  more  negative 


608  A  MANUAL  OF  PHYSIOLOGY 

than  A  (second  phase).  Since  the  wave  takes  time  to  reach 
its  maximum,  it  is  evident  that  a  well-marked  first  phase 
will  be  favoured  when  the  interval  between  its  arrival  at 
A  and  B  is  long,  for  in  this  case  A  will  have  a  chance  of 
becoming  strongly  negative  while  B  is  still  normal.  Simi- 
larly, if  A  has  again  become  normal,  or  nearly  normal, 
before  the  maximum  negativity  has  passed  over  B,  a  strong 
second  phase  will  be  favoured.  The  heart-muscle,  accord- 
ingly, where  the  wave  of  contraction,  and  its  accompanying 
electrical  change,  move  with  comparative  slowness,  is  better 


FIG.  190.— DIAGRAM  TO  ILLUSTRATE  PROPAGATION  OF  THE  NEGATIVE 
CHANGE  ALONG  AN  ACTIVE  MUSCLE  OR  NERVE. 

Suppose  A  B  to  be  a  horizontal  bar  representing  the  muscle  or  nerve.  Let  C  be  a 
curved  piece  of  wood  representing  the  curve  of  the  electrical  change  at  any  point. 
Let  W  W  be  two  glass  cylinders  connected  by  a  flexible  tube,  the  whole  being 
filled  with  water.  Suppose  the  rims  of  the  cylinders  originally  to  touch  A  B  at  the 
points  A  and  B,  and  let  them  be  movable  only  in  the  vertical  direction.  The  level  of 
the  water  being  the  same  in  both,  there  is  no  tendency  for  it  to  flow  from  one  to  the 
other.  This  represents  the  resting  state  of  the  tissue  when  A  and  B  are  symmetrical 
points.  Now  let  C  be  moved  along  the  bar  at  a  uniform  rate.  The  cylinder  W,  being 
free  to  move  down,  but  not  horizontally,  will  be  displaced  by  C,  and,  if  it  is  kept 
always  in  contact  with  its  curved  margin,  will,  after  describing  the  curve  of  the 
electrical  variation,  come  again  to  rest  in  its  old  position  at  A.  B  will  do  the  same 
when  C  reaches  it.  But  since  C  reaches  A  before  B,  the  level  of  the  water  in  B  will 
at  first  be  higher  than  that  in  A,  and  water  will  flow  from  B  to  A.  This  will  corre- 
spond to  the  time  during  which  the  point  of  the  tissue  represented  by  A  would  be 
negative  to  a  point  represented  by  B.  Later  on,  when  C  has  reached  the  position 
shown  by  the  dotted  lines,  the  level  of  the  water  in  A  will  be  higher  than  that  in  B, 
and  a  flow  will  take  place  in  the  opposite  direction  to  the  first  flow.  This  corresponds 
to  a  second  phase  of  the  negative  variation. 

suited  for  showing  a  well-marked  diphasic  variation  than 
skeletal  muscle,  and  still  better  suited  than  nerve.  In  the 
gastrocnemius  muscle  of  the  frog,  when  excited  through  its 


ELECTRO-PHYSIOLOGY  609 


nerve,  the  electrical  response  begins  about  yuW  second,  and 
the  change  of  form  of  the  muscle  about  y^V^  second  after 
the  stimulation.  The  apex  of  the  curve,  or  change  of  sign, 
corresponds  to  y^j-  second  after  excitation.  It  is  believed 
that  in  a  rnuscle  directly  excited  the  electrical  change  begins 
in  less  than  roW  second,  and  the  mechanical  change  in 
TWIT  second  (Burdon  Sanderson).  (Figs.  192-194.) 

When  one  electrode  is  placed  on  an  injured  part,  the 
wave  of  action  and  of  electrical  change  diminishes  as  it 
reaches  the  injured  tissue  ;  and  if  the  tissue  is  killed  at  this 
part,  it  diminishes  to  zero  ;  so  that  here  the  second  phase 
may  be  greatly  weakened  or  may  disappear  altogether. 

In  this  case  the  current  of  action  can  be  demonstrated, 
even  for  a  single  excitation,  but  still  better  for  a  tetanus, 
with  the  galvanometer,  which  in  general  is  not  quick  enough 
to  analyze  a  diphasic  variation  with  equal  phases,  and  gives, 
therefore,  only  their  algebraic  sum  —  that  is,  zero.  When 
the  muscle  or  nerve  is  tetanized,  the  negative  variation 
appears,  while  stimulation  is  kept  up,  as  a  permanent 
deflection  representing  the  '  sum  '  of  the  separate  effects. 
The  action  current  of  the  phrenic  nerve  which  accompanies 
the  natural  respiratory  discharge  has  been  recently  demon- 
strated (Reid  and  Macdonald). 

When  the  current  of  rest  is  compensated  by  a  branch  of  an 
external  current  just  sufficient  to  balance  it  and  bring  the  galva- 
nometer image  back  to  zero,  the  action  current  appears  alone  in 
undiminished  strength.  This  shows  that  the  latter  is  not  due  to  a 
'change  of  electrical  resistance  during  excitation,  since  such  a  change 
would  equally  affect  current  of  rest  and  compensating  current,  and 
they  would  still  balance  each  other.  The  action  current  is  really  due 
to  a  change  of  potential,  which  can  be  measured  by  determining 
what  electromotive  force  is  just  required  to  balance  it,  and  which 
may  actually  exceed  that  of  the  current  of  rest.  Thus,  Sanderson  and 
Gotch  found  an  average  of  0*08  of  a  Daniell  cell  (the  electromotive 
force  of  the  Daniell  would  be  about  a  volt)  as  the  electromotive  force 
of  the  action  current  due  to  a  single  indirect  excitation  of  a  vigorous 
frog's  gastrocnemius,  and  about  0-04  Daniell  as  that  of  the  current  of 
rest.  The  electromotive  force  of  the  current  of  rest  in  rabbit's  nerve 
was  found  by  du  Bois-Reymond  to  be  0*026  ;  Gotch  and  Horsley 
found  the  average  for  the  cat  o'oi,  and  for  the  monkey  only  0-005. 

Before  Burdon  Sanderson  introduced  the  capillary  electro- 
meter for  the  study  of  the  electrical  phenomena  of  living 

39 


6io 


A  MANUAL  OF  PHYSIOLOGY 


tissues,  and  Burch  perfected  a  method  for  the  measurement 
of  the  curves,  the  differential  rheotome,  originally  constructed 
by  Bernstein,  was  the  most  valuable  instrument  we  pos- 
sessed for  experiments  on  the  time -relations  of  these 
phenomena.  By  its  aid,  for  instance,  it  was  shown  that 
the  rate  of  propagation  of  the  electrical  change  in  muscle  is 
the  same  as  that  of  the  mechanical  change,  and  in  nerve  the 
same  as  that  of  the  nervous  impulse. 


The  differential  rheotome  consists  essentially  of  a  stationary  metal 
ring,  the  whole  or  part  of  which  is  graduated,  and  of  a  portion  which 
can  be  made  to  revolve  at  a  known  rate.  The  latter  carries  two 
contacts :  a,  an  obliquely-placed  platinum  wire  which  touches  at 

every  revolution  a  horizontal 
wire  b  on  the  fixed  ring,  thu 
making  and  breaking  the  pri 
mary  circuit  P  of  an  indu 
tion  machine,  and  so  causing 
stimulation  of  a  muscle  or 
nerve  M  connected  with  the 
secondary  S ;  and,  c,  a  double 
contact,  either  in  the  form  of 
two  platinum  wires,  which  dip 
into  two  mercury  troughs,  or 
of  two  wire  brushes  rubbing 
on  copper  blocks  d,  at  a 
certain  part  of  the  revolution. 
The  troughs  or  blocks  are  con- 
nected with  a  circuit  contain- 
ing a  galvanometer  G,  and  a 
portion  of  the  muscle  or  nerve 
arranged  so  as  to  give  a  strong 
action  current.  This  circuit 
is  completed  by  the  wires  or 
brushes,  which  are  in  metallic 
contact  with  each  other ;  and  the  relative  position  of  the  fixed  con- 
tact in  the  primary  circuit  and  of  the  troughs  or  copper  blocks  can 
be  altered  so  as  to  alter  at  will  the  interval  between  stimulation  and 
closure  of  the  galvanometer  circuit.  The  proportion  of  the  whole 
revolution  during  which  this  circuit  is  closed  can  be  varied  by 
changing  the  relative  position  of  the  two  copper  blocks.  Suppose 
the  tissue  is  stimulated  at  one  end  while  the  leading-off  electrodes 
are  at  the  other.  When  the  contact  «,  b,  is  made  at  the  same  time 
as  c,  d,  no  deflection  will  be  shown  by  the  galvanometer  if  the 
rheotome  is  revolving  rapidly  (the  demarcation  current  being 
accurately  compensated),  because  the  circuit  will  be  opened  before 
the  negative  change  has  time  to  travel  to  the  leading-off  electrodes. 
But  as  the  distance  between  b  and  d  is  increased,  a  small  deflection 


FIG.  191.— DIAGRAM   OF   DIFFERENTIAL 
RHEOTOME. 


ELECTRO-PHYSIOLOGY  6n 

will  appear,  which,  with  further  increase  of  the  distance,  will  become 
larger,  reach  a  maximum,  and  then  begin  to  fall  off  again.  The 
first  small  deflection  corresponds  to  the  position  in  which  the  negative 
change  has  just  had  time  to  reach  the  leading-off  electrodes  before 
the  galvanometer  circuit  is  opened.  The  maximum  deflection  cor- 
responds to  a  period  a  little  later  than  this,  because  the  electrical 
variation  does  not  at  once  reach  its  maximum  at  any  point. 

In  human  muscles  the  current  of  action  has  been  demonstrated  by 
connecting  a  galvanometer  with  ring  electrodes  passing  round  the 
forearm,  and  throwing  the  muscles  into  contraction.  A  diphasic 
variation  is  thus  obtained ;  and  the  electrical  change  travels  with  a 
velocity  of  as  much  as  12  metres  per  second,  which  is  greater  than 
the  velocity  in  frogs'  muscles. 

As  to  the  interpretation  of  the  facts  we  have  been  de- 
scribing, and  which  are  summed  up  in  the  three  propositions 
on  p.  606,  two  chief  doctrines  have  divided  the  physiological 
world :  (i)  the  theory  of  du  Bois-Reymond,  the  pioneer  of 
electro-physiology,  and  (2)  the  theory  of  Hermann.  It  was 
believed  by  du  Bois-Reymond  that  the  current  of  rest  seen 
in  injured  tissues  is  of  deep  physiological  import,  and  that 
the  electrical  difference  which  gives  rise  to  it  is  not  de- 
veloped by  the  lesion  as  such,  but  only  unmasked  when  the 
•electrical  balance  is  upset  by  injury.  He  looked  upon  the 
muscle  or  nerve  as  built  up  of  electromotive  particles,  with 
definite  positive  and  negative  surfaces  arranged  in  a  regular 
manner  in  a  sort  of  ground-substance  which  is  electrically 
indifferent.  The  '  negative  variation  '  he  supposed  to  depend 
on  an  actual  diminution  of  previously-existing  electromotive 
forces ;  and  from  this  conception  arose  its  historic  name. 
This  theory  has  been  highly  elaborated  and  extended  to 
include  new  facts  as  they  have  arisen,  and  it  explains  certain 
phenomena,  such  as  the  currents  of  a  prism  of  muscle, 
better  than  the  simpler  theory  associated  with  the  name 
of  Hermann.  The  latter  observer  and  his  school  assume 
that  the  uninjured  muscle  or  nerve  is  '  streamless,'  not 
because  equal  and  opposite  electromotive  forces  exactly 
balance  each  other  in  the  substance  of  the  tissue,  but 
because  electromotive  forces  are  absent  until  they  are  called 
into  existence  at  the  boundary,  or  plane  of  demarcation, 
between  sound  and  injured  tissue.  For  this  reason  in  the 
terminology  of  Hermann  du  Bois-Reymond's  current  of  rest 
is  called  the  '  demarcation '  current. 

39—2 


612 


A  MANUAL  OF  PHYSIOLOGY 


The  experiments  of  Burdon  Sanderson,  who  photographed 
the  excursions  of  the  capillary  electrometer  on  a  sensitive 

plate  carried  by  a  rapidly- 
moving  pendulum,  have  tended 
to  revive  under  new  and  striking 
aspects  the  old  '  pre-existence  ' 
theory  of  du  Bois-Reymond, 
which  some  physiologists  seem 
to  have  regarded  as  moribund, 
FlG  I92  if  not  actually  defunct.  For 

Electrical   response  to  single  mo-  Sanderson   has  shown  that   in 

mentary    excitations     of     an    injured  a^if-Jon     fn    fn~    npp-ativp   wav^ 

gastrocnemius  by  its  nerve,  as  projected  ncgat 

on  a  plate  moving  at  a  comparatively  (excitation   Wave    of    Bernstein) 

slow  rate,  showing  a  contour  like  that 

of   a   spike  in  optical   section.      The  which    IS    Set    Up    by    a   momen- 

'  spike' is  followed  by  a  'hump,'  'and  ,  ,.         ,  ,  .  ,. 

if  the  former  be  taken  to  mean  a  sudden  tary  Stimulus,  and    runs   rapidly 

electrical  swing  of  such  a  character  as  P1nno.  fUp    mncirlp  in  hnth  Hirpr 

to  indicate  that  the  proximal  electrode  along  tne    H1USC1 

becomes  first  negative,  then  positive,  tions,  there   occurs   in   injured 

the    latter    must    indicate    that    it    is 

followed  by  a  change  in  the  same  direc-    muscle  a  more  slowly-developed 

tion,    but    of   slower    progress.    .    .   .  ,  .  ,  . 

This   slower   change  not  only  cui-  and  more  persistent  change  of 

minates,  but  begins  later,  and  is  there-    nnt~nfia1    ;n  fV,^   CamA   rlir^H'™ 

fore  called  the  "after-effect."'   The  potential  in  tne  same  directioi 

upper  curves  show  the  excursion  of  the    as    the    first     phase     of    the    CX 

meniscus  of  the  electrometer,  the  lower 

the  vibrations  of  a  tuning-fork  (Burdon    Citation  wave,  when  the   HlUSCk 

is    excited    through    its    nerve 

either  continuously  or  by  recurring  stimuli,   or  even,  in  a 
less  degree,  by  a  single  momentary  stimulus.     The  amount 


FIG.  193. 

The  '  spike '  and  '  hump '  of  a  gastrocnemius  muscle,  whose  lower  end  had  been 
injured  by  dipping  it  into  water  just  sufficiently  warmed  to  produce  rigor.  The  record 
was  taken  on  a  plate  moving  ten  times  faster  than  that  with  which  Fig.  192  was  obtained. 
The  lowest  curve  shows  the  movements  of  the  meniscus,  the  one  above,  the  vibrations 
of  the  tuning-fork  marking  time  (Burdon  Sanderson). 


of  this  more  permanent  difference  of  potential  is  roughl} 
proportional  to    the  intensity   of  the    injury  as  measurec 


ELECTRO-PHYSIOLOGY 


613 


by  the  previously-existing  difference  of  potential  between 
the  two  electrodes,  and,  according  to  Sanderson,  it  repre- 
sents a  true  negative  variation  in  du  Bois-Reymond's 
sense — that  is,  a  diminution  of  the  electrical  difference  to 


A.  B. 

FIG.  194.— 'SPIKE'  OF  UNINJURED  GASTROCNEMIUS  (BURDON  SANDERSON). 
A  photographed  on  slow,  B  on  fast-moving  plate. 

which  the  current  of  rest  is  due.  In  an  uninjured  muscle 
only  the  passage  of  the  transient  excitation  wave  is  indi- 
cated by  the  electrometer.  But  there  is  reason  to  believe 
that  even  in  intact  muscles  excitation,  both  momentary  and 


FIG.  195.— CURVE  OF  AN  INJURED  MUSCLE  EXCITED  SIXTY  TIMES  A  SECOND. 

'  Shows  the  characteristic  curve  of  the  negative  variation  of  du  Bois-Reymond.  The 
previous  difference  of  potential  exceeded  0*03  volt.  At  the  end  of  the  period  of  excita- 
tion the  diminution  amounted  to  0*054  volt.  Each  excitation  was  followed  by  an  after- 
effect in  the  same  direction,  the  character  of  which  is  best  seen  after  the  tenth  excita- 
tion '  (Burdon  Sanderson). 

recurrent,  as  in  experimental  tetanus,  causes  electromotive 
effects  that  outlast  the  excitation  wave,  although,  since  the 
muscle  is  everywhere  equally  affected,  these  do  not  influence 
the  electrometer.  Injured  parts  of  a  muscle,  on  the  other 
hand,  are  less  capable  of  responding  to  these  changes  than 


6i4  A  MANUAL  OF  PHYSIOLOGY 

the  intact  tissue,  so  that  they  become  less  negative  towards 
the  uninjured  tissue  than  they  were  before  excitation,  and 
the  demarcation  current  is  thus  diminished. 

Although  the  electromotive  changes  caused  by  excitation 
are  much  more  transient  than  those  caused  by  injury, 
everything  suggests  that  there  must  be  some  deep  analogy 
between  the  two  conditions.  But  we  cannot  say  definitely 

how  far  whatever 
chemical  or  physical 
changes  underlie  the 
electrical  phenomena 
are  alike  in  injured  or 
dying,  and  in  active 
muscle  or  nerve. 

Some  writers  seem  to 
FIG.  196.  suppose  that  an  increase 

'  The  normal  response  to  a  series  of  excitations  of       chemical       activity 

recurring  with  a  frequency  of  84  per  second  in  a  -i       u 

wholly  uninjured  muscle,  in  which  there  was  no  HlUSt    necessarily    DQ   at 

previous  difference  of  potential  between  the  middle  tup      hnrrnm       nf      hnth 

and  terminal  contacts.     Each  excitation  produces  a  me 

spike  which  is  the  expression  of  the  passage  of  a  changes  ;     in    the    dying 

wave  of  excitation  of  which  the  direction  is  alter-  .                   . 

minal  [i.e.,   towards  the  ends].     The  first   phase  muscle,    it    is    Said,     the 

expresses  a  change  in  the  direction  of  propagation,  ,                 ,       , 

the  second  opposed  to  it.     But  after  the  wave  has  Chemical   Changes    must 

passed,  the  contacts  are  equipotentiai,  as  they  were  up      inrrpaspH      and 

before' (Burdon  Sanderson).  increased,     ana 

know  that  they  are  in 

creased  in  the  living  active  muscle.  This  may  be  so,  bu 
the  electrical  changes  are  very  marked  in  injured  and  ir 
active  nerve,  and  here  we  know  nothing  of  measurable 
chemical  changes.  And  warmed  living  muscle  is  positive  tc 
muscle  less  warm,  although  the  metabolism  must  in  genera 
be  more  active  in  the  former.  It  is,  of  course,  quite  clear 
that  energy  must  be  running  down,  for  electrical  currents 
capable  of  doing  work  are  being  produced ;  but  whether 
this  energy  comes  from  chemical  changes  or  from  physical 
changes,  or  from  both,  or  how  much  of  it  comes  from  either, 
we  cannot  tell. 

Others  have  said  that  there  is  really  a  subdued  kind  of 
more  or  less  permanent  excitation  in  the  neighbourhood  of 
the  injured  tissue,  and  that  this  explains  the  similarity  of 
electrical  condition  in  activity  and  injury.  This  pushes  the 


ELECTRO-PHYSIOLOGY  615 

inquiry  a  step  further  back,  but  does  not  touch  the  question 
of  the  nature  of  the  changes  underlying  both  action  and 
injury.  Physical  explanations  of  the  action  current  of  muscle 
have  been  based  on  the  hypothesis  that  in  contraction 
variations  in  surface-tension,  with  accompanying  electrical 
changes,  occur  at  certain  surfaces  (surface  of  separation 
between  light  and  dim  discs,  or  between  fluid  contents 
and  wall  of  sarcous  capillary  tubes).  A  great  objection  to 
these  theories  is  that  in  nerve,  so  far  as  we  know,  no 
sensible  mechanical  change  whatever  takes  place  during 
excitation,  and  that  differences  of  potential  exist  or  may  be 
developed  in  tissues  of  the  most  diverse  structure. 

Polarization  of  Muscle  and  Nerve.* — We  have  already  spoken 
of  electrical  excitation  and  of  the  changes  of  excitability 
caused  by  the  passage  of  a  constant  current  (p.  574).  We 
are  now  to  see  that  these  physiological  effects  are  accom- 
panied by,  and  indeed  very  closely  related  to,  more  physical 
changes  which  the  galvanometer  or  electrometer  reveals  to 
us.  When  a  current  is  passed  by  means  of  unpolarizable 
electrodes  (Fig.  153,  p.  526)  through  a  muscle  or  nerve  for 
several  seconds,  and  the  tissue  thrown  on  to  the  galvano- 
meter immediately  after  this  polarizing  current  is  opened,  a 
deflection  is  seen  indicating  a  current  (negative  polarization 
current)  in  the  opposite  direction. 

This  negative  polarization  differs  from  the  polarization  of  the 
electrodes  seen  after  passage  of  a  current  through  any  ordinary  elec- 
trolytic conductor,  like  dilute  sulphuric  acid.  The  latter  is  due  to  the 
deposition  of  hydrogen  on  the  kathode  and  oxygen  on  the  anode, 
the  electrodes  being  converted  for  the  time  into  the  plates  of  a 
secondary  battery.  But  in  muscle,  nerve,  and  other  animal  tissues, 
as  well  as  in  vegetable  structures,  and  indeed,  to  a  certain  extent,  in 
unorganized  porous  bodies  soaked  with  electrolytes,  the  polarization 
is  not  confined  to  the  neighbourhood  of  the  electrodes,  but  distributed 
all  the  way  between  them  ;  in  other  words,  it  is  an  internal  polariza- 
tion depending  on  the  separation  of  ions  in  the  mass  of  the  tissue.  In 
muscle  and  nerve  this  internal  negative  polarization  is  very  strongly 
marked ;  and  although  it  is  not  bound  up  with  the  life  of  the  tissue, 
and  may  be  obtained  when  this  has  become  quite  inexcitable,  it  is 
nevertheless  dependent  on  the  preservation  of  the  normal  structure, 
for  a  boiled  muscle  shows  but  little  negative  polarization. 

*  The  portions  in  small  type  on  pp.  61 5-620  may  be  omitted  except  by 
students  interested  in  the  subject  or  reading  for  a  special  purpose. 


6i6 


A  MANUAL  OF  PHYSIOLOGY 


When  the  polarizing  current  is  strong,  and  its  time  of  closure 
short,  we  obtain,  on  connecting  the  tissue  with  the  galvanometer 
after  opening  the  current,  not  a  negative,  but  a  positive  deflection, 
indicating  a  so-called  positive  polarization  current  in  the  same  direc- 
tion as  that  of  the  polarizing  stream.  The  '  positive  polarization  '  is 
only  obtained  when  the  tissue  is  living ;  and  it  is  far  more  strongly 
marked  in  the  anodic  than  in  the  kathodic  region.  There  is,  in  fact, 
a  great  weight  of  evidence  that  the  '  positive  polarization '  current  is 
really  an  action  stream,  due  to  the  opening  excitation  set  up  at  the 
anode  (p.  537). 

Suppose  that  the  nerve  in  Fig.  197  is  stimulated  by  the  opening 

of  the  battery  B,  and  that,  immediately 
after,  the  nerve  is  connected  with  the 
galvanometer  G  by  the  electrodes  E,  Er 
Suppose,  further,  that  the  shaded  region 
near  the  anode  remains  more  excited 
for  a  short  time  than  the  rest  of  the 
nerve,  and  we  have  seen  (p.  577)  that 
after  the  opening  of  a  strong  current 
there  is  a  defect  of  conductivity,  espe- 
cially in    the    neighbourhood   of  the 
anode,   which  would  tend  to  localiz 
excitation.     The   portion  of  nerve  a 
E  being  negative  relatively  to  that  a 
E1?  an  action  current  will  pass  through 
the  galvanometer  from  Ej  to  E,  anc 
through  the  nerve  in  the  same  direc 
tion  as  the  original  stimulating  stream 
that  is,  it  will  have  the  direction  of  the 
positive  polarization  current. 

Under  certain  conditions  a  state  ol 
continuous  excitation  in  the  anodic 
region  of  a  nerve  is  shown  by  a  tetanus  of  its  muscle  (Ritters  tetanus^ 
p.  633,  and  Fig.  198). 

Griitzner  and  Tigerstedt  have  put  forward  a  different  theory  of  the 
break  contraction.  They  say  it  is  really  a  closing  contraction  due  to 
the  closure  of  the  negative  polarization  current  through  the  tissue 
itself,  as  soon  as  the  polarizing  current  is  opened.  In  fact,  they 
admit  only  one  kind  of  electrical  stimulus,  the  kathodic,  or  make. 
But  this  theory  does  not  adequately  take  account  of  positive  polari- 
zation, and  there  are  also  other  objections  to  it. 

Electrotonic  Currents. — During  the  flow  of  the  polarizing 
current,  there  are  very  remarkable  galvanoscopic  evidences 
of  the  changes  produced  by  it.  And  although  it  is  not 
possible  directly  to  demonstrate  polarization  in  the  region 
between  the  electrodes  while  the  current  continues  to  pass, 
this  is  easily  done  in  the  extrapolar  regions,  although  much 
more  readily  on  nerve  than  on  muscle. 


FIG.  197. — DIAGRAM  TO  SHOW 
DISTRIBUTION  OF  'POSITIVE 
POLARIZATION  '  AFTER  OPEN- 
ING POLARIZING  CURRENT. 
B,    battery ;    G,    galvanometer. 
The  dark  shading  signifies  that  the 
excitation  to  which    the    positive 
polarization    current     is    due    is 
greatest  in  the  immediate  neigh- 
bourhood of  the  anode,  and  fades 
away  in  the  intrapolar  region. 


ELECTRO-PHYSIOLOGY 


617 


If  a  current  be  passed  from  the  battery  (Fig.  199)  in  the 
direction  indicated  by  the  arrows,  while  a  galvanometer  is 
connected  with 
either  of  the  extra- 
polar  areas,  as 
shown  in  the  figure, 
a  current  will  pass 
through  the  galva- 
nometer, in  the 
same  direction  in 
the  nerve  as  the 
polarizing  current, 
so  long  as  the  latter 
continues  to  flow. 


FIG.    198. — RITTER'S 
TETANUS. 


These  currents  are 
called  electrotonic,  and 
seem  to  depend  on 
the  spread  of  the  polar- 
izing stream  along  the 
nerve  outside  the  elec- 
trodes, owing  to  a 
polarization  taking 
place  at  the  boundary 
between  some  part  of 
the  nerve-fibre  which 
may  be  called  a  core, 
ind  another  part  which 

lay  be  called  a  sheath.  The  exact  seat  of  this  polarization  is 
unknown  ;  it  may  be  between  axis-cylinder  and  medullary  sheath,  or 
between  the  latter  and  the  neurilemma.  In  any  case,  such  a  polari- 
sation would  practically  act  as  a  resistance  to  the  direct  passage  of 


A  strong  voltaic  current  was 
passed  for  some  time  through  the 
nerve  of  a  muscle-nerve  prepara- 
tion. On  opening  the  circuit, 
the  muscle  gave  one  strong  con- 
traction, and  then  entered  into 
irregular  tetanus,  which  con- 
tinued for  four  minutes.  (Only 
the  first  part  of  the  tracing  is 
reproduced. ) 


FIG.  199. — DIAGRAM  SHOWING  DIRECTION  OF  THE  EXTRAPOLAR  ELEC- 
TROTONIC CURRENTS. 

the  current  from  the  anode  down  into  the  'core,'  or  from  the  core 
out  to  the  kathode,  and  would  cause  it  to  spread  longitudinally  along 
the  sheath  in  the  extrapolar  regions.  On  this  view  the  electrotonic 
currents  are  really  twigs  of  the  polarizing  stream.  And,  as  a  matter 
of  fact,  such  currents  can  be  produced  on  a  model  in  which  a  platinum 
wire  is  surrounded  with  a  sheath  of  saturated  zinc  sulphate  solution. 


618  A  MANUAL  OF  PHYSIOLOGY 

A  current  led  into  the  latter  tries,  so  to  speak,  to  pass  mostly  by  the 
good  conducting  wire.  If  this  is  not  polarizable — if  it  is,  e.g.,  a  zinc 
wire — there  is  little  or  no  spreading  of  the  current  outside  the  elec- 
trodes ;  it  passes  at  once  into  the  core,  and  so  on  to  the  other 
electrode.  If,  however,  there  is  polarization  when  the  current  passes 
from  the  liquid  into  the  wire,  as  is  the  case  when  the  latter  is 
platinum,  the  stream  spreads  longitudinally.  Indeed,  we  know 
that  both  nerve  and  muscle,  and  especially  the  former,  are  far 
more  polarizable  in  the  transverse  than  in  the  longitudinal  direc- 
tion; the  apparent  transverse  resistance*  of  nerve  may  be  seven 
times  the  longitudinal  resistance,  and  this  is  a  condition  which  favours 
electrotonus. 

This  physical  electrotonus  must  be  distinguished  from  the 
changes  of  excitability  produced  by  the  constant  current,  ta 
which  the  name  of  electrotonus  is  also  sometimes  given. 
For  although  the  decline  in  the  intensity  of  the  electrotonic 
currents  as  we  pass  away  from  the  electrodes,  has  its 
analogue  in  the  distribution  of  the  electrotonic  changes  o 
excitability,  and  there  are  other  facts  which  suggest  a  rela 
tion  between  the  two,  we  are  ignorant  of  the  real  nature  o 
this  relation. 

The  electrotonic  currents  cannot  spread  beyond  a  ligature 
they  are  stopped  by  anything  which  destroys  the  structure 
of  the  tissue ;  they  are  affected  by  reagents  such  as  carbon 
dioxide  and  ether.  But  this  does  not  show  that  they  are 
other  than  physical  in  origin,  for  what  destroys  the  structure 
of  the  tissue  or  modifies  its  molecular  condition  may  destroy 
or  diminish  its  capacity  for  polarization. 

Stimulation  of  the  nerve  while  the  polarizing  current  is  flowing 
causes  in  general  in  the  extrapolar  regions  a  negative  variation  of  the 
electrotonic  current,  but  in  the  intrapolar  region  a  positive  variation. 
The  latter  is  undoubtedly  an  action  stream.  Hermann  has  explained 
its  direction  on  the  assumption  that  the  excitation  diminishes  in 
intensity  as  it  approaches  the  kathode  or  recedes  from  the  anode, 
and  increases  in  intensity  as  it  passes  towards  the  anode  or  away 
from  the  kathode  (law  of  polarization  increment).  But  the  fact  that 

*  The  great  apparent  transverse  resistance  of  nerve  may  be  due,  in. 
part  if  not  wholly,  to  the  resistance  of  the  neurilemma,  if  that  membrane, 
like  the  boundary  of  a  red  blood  corpuscle,  has  a  much  higher  resistance 
than  the  contents  of  the  fibre  or  the  lymph  between  the  fibres.  Or  it 
may  be  that  the  resistance  of  the  medullary  sheath  is  greater  than  that 
of  the  axis  cylinder.  Examples  of  such  differences  of  resistance  even 
in  the  fluid  constituents  of  one  and  the  same  animal  structure  are  not 
wanting.  For  instance,  the  resistance  of  the  yolk  of  a  hen's  egg  may 
be  three  times  greater  than  that  of  the  white. 


ELECTRO-PHYSIOL  OG  Y 


619 


during  the  flow  of  a  current  the  conductivity  of  the  nerve  is  far 
more  depressed  around  the  kathode  than  near  the  anode  affords  a 
sufficient  explanation. 

The  nerve-impulse,  starting  from  the  stimulating  electrodes  S 
(Fig.  200),  will  pass  over  E,  the  anode,  in  greater  intensity  than  over 
EI,  the  kathode  ;  and  therefore,  upon  the  whole,  during  tetanus  E 
will  be  negative  to  Ep  and 
a  current  of  action  will  be 
developed  in  the  same 
direction  as  the  polarizing 
current,  and  reinforcing  it. 
When  the  kathodic  block 
is  complete,  and  the  excita- 
tion has  to  pass  over  the 

kathode    before    reaching 

FIG.  200.— DIAGRAM  SHOWING  DIRECTION 

the  mtrapolar  region,  no  OF  THE  STIMULATION  EFFECT  IN  THE 
effect  is  produced  by  stimu-  INTRAPOLAR  REGION  DURING  THE  FLOW 
lation.  OF  THE  POLARIZING  CURRENT. 

The  stimulation    effects 

in  the  extrapolar  regions  are  probably  due  partly  to  action  currents, 
as  is  shown  by  the  fact  that  when  the  polarizing  current  is  strong 
enough  to  markedly  depress  the  conductivity  in  the  neighbourhood 
of  the  anode,  the  variation  becomes  positive  instead  of  negative 
when  one  of  the  galvanometer  electrodes  lies  near  the  anode.  For 
here  the  excitation  coming  from  S  passes  E2  in  far  less  intensity  than  E;5 
(Fig.  201).  E3  is  therefore,  on  the  whole,  during  tetanus  negative  to  E2, 
and  the  direction  of  the  action  current  in  the  nerve  is  from  E3  to  E2. 

The  negative  variation  in  the  extrapolar  kathodic  region  could 
also  be  explained  as  an  action  current  due  to  diminished  conduc- 
tivity in  the  neighbourhood  of  the  kathode.  But  the  negative  anodic 
variation  cannot  be  an 
action  current,  unless  we 
suppose  that  with  the 
weaker  polarizing  currents 
the  conductivity  is  in- 
creased around  the  anode  ; 
and  for  this  there  is  not 
sufficient  proof.  It  is  pro- 
bable, therefore,  that  there 
is  another  factor  mixed  up  FlG-  201.— DIAGRAM  TO  SHOW  DIRECTION 
f  .  J  OF  THE  POSITIVE  STIMULATION  EFFECT 

with  the  currents  of  action,          IN  THE   ANODIC    EXTRAPOLAR    REGION 
and  in  part  opposing  them.          DURING  THE  FLOW  OF  A  STRONG  POLARI- 
Some  have  supposed   that         ZING  CURRENT. 
the   capacity   for   polariza- 
tion between  core  and  sheath  is  diminished  during  excitation,  and 
that,  accordingly,  less  of  the  current  spreads  beyond  the  electrodes, 
and  an  apparent  negative  variation  is  caused  in  the  extrapolar  regions 
by  stimulation  ;  but  there  is  no  direct  evidence  for  this. 

After  the  opening  of  the  polarizing  current,  electromotive  changes 

in,  as  we  have  seen,  be  recognised  for  a  short  time  in  the  intrapolar 


62O 


A  MANUAL  OF  PHYSIOLOGY 


area.  This  is  also  true  of  both  extrapolar  regions.  The  main  after- 
current in  the  anodic  region  is  in  the  opposite  direction  to  the 
polarizing  stream ;  but  this  is,  under  certain  circumstances,  preceded 
by  a  very  short  kick  of  the  galvanometer  magnet  in  the  same  direc- 
tion. The  kathodic  after-current  is  in  the  same  direction  as  the 
polarizing  stream,  and  is,  except  with  strong  currents  and  a  compara- 
tively long  time  of  closure,  much  weaker  than  the  main  anodic. 
The  latter  is  to  be  looked  upon  as  having  the  same  origin  as  the 
positive  polarization  current  of  the  intrapolar  region,  a  state  of  open- 
ing excitation  around  the  anode ;  in  other  words,  it  is  an  action 
current.  The  kathodic  and  the  preliminary  anodic  after-currents  are 
probably  due  to  negative  polarization. 

Stimulation  of  the  nerve  after  opening  the  polarizing  current  causes 

well-marked  effects; 
in  the  intrapolar 
region  the  stimula- 
tion effect  is  in  the 
opposite  direction 
to  the  polarizing 
current;  in  the  ex- 
trapolar anodic 
area,  in  the  same 
direction  as  the 
polarizing  stream 
In  the  extrapolai 
kathodic  region,  it 
is  in  the  opposite 
direction,  and,  ex 
cept  with  strong 
polarizing  currents,  and  a  more  than  momentary  time  of  closure,  less 
in  amount  than  the  stimulation  effect  in  the  anodic  region. 

All  these  cases  are  readily  explained  by  the  fact  that  immediately 
after  opening  the  polarizing  current  the  conductivity  of  the  nerve  is 
more  depressed  in  the  anodic  than  in  the  kathodic  region,  although 
with  strong  currents  it  is  depressed  in  both.  An  excitation  reaching 
the  extrapolar  anodic  area  from  S  will  pass  over  E3  in  greater  intensity 
than  over  E4  (Fig.  202).  E4  will  therefore  be  positive  to  E3,  and  the 
action  current  will  go  through  the  nerve  in  the  direction  of  the  arrow. 
An  excitation  reaching  the  kathodic  extrapolar  area  from  S'  will 
arrive  at  Ef>  in  greater  intensity  then  at  E5.  The  resultant  action 
stream  will  therefore  have  the  direction  in  the  nerve  from  E6  to  E5. 
And  the  effects  in  the  intrapolar  region  can  be  similarly  explained. 

A  nerve  may  be  stimulated  by  an  electrotonic  current 
produced  in  nerve-fibres  lying  in  contact  with  it.  A  well- 
known  illustration  of  this  is  the  experiment  known  as  the 
paradoxical  contraction  (Practical  Exercises,  p.  630). 

The  current  of  action  of  a  nerve  can  also,  under  certain 
conditions,  stimulate  another  nerve,  as  Hering  has  shown. 


FIG.  202. — DIAGRAM  SHOWING  THE  DIRECTION  OF 
THE  STIMULATION  EFFECTS  AFTER  OPENING  THE 
POLARIZING  CURRENTS  IN  THE  ANODIC  AND 
KATHODIC  EXTRAPOLAR  REGIONS  (A  AND  K),  AND 
IN  THE  INTRAPOLAR  REGION  E15  E2. 


ELECTRO-PHYSIOLOG  Y 


621 


This  comes  under  the  head  of  secondary  contraction.  But 
the  best-known  form  of  secondary  contraction  is  where  a 
nerve,  placed  on  a  muscle  so  as  to  touch  it  in  two  points 
(Fig.  203),  is  stimulated  by  the  action-current  of  the  muscle, 
and  causes  its  own  muscle  to 
contract.  A  secondary  tetanus 
can  be  obtained  in  this  way  by 
dropping  a  nerve  on  an  arti- 
ficially tetanized  muscle.  The 
beat  of  the  heart  causes  usually 
only  a  single  secondary  con- 
traction when  the  sciatic  nerve 
of  a  frog  is  allowed  to  fall  on  it 
(p.  179).  But  when  the  diphasic 
variation  is  well  marked,  as  it  is 
in  an  uninjured  heart,  there  may 
be  a  secondary  contraction  for 
each  phase,  i.e.,  two  for  each 
heart-beat.  Excitation  of  one 
muscle  may  in  the  same  way 
cause  secondary  contraction  of 
another  with  which  it  is  in  close  contact. 

The  electromotive  phenomena  of  the  heart  and  of  the 
central  nervous  system  are  naturally  included  under  those 
of  muscle  and  nerve. 

Bteart. — The  current  of  action  has  been  chiefly  studied.  In  the 
's  heart  the  variation  shown  by  the  capillary  electrometer  is 
diphasic.  During  the  first  phase  the  base  is  negative  to  the  apex ; 
during  the  second  phase  the  apex  is  negative  to  the  base.  The 
meaning  of  this  is  that  the  negative  electrical  change,  like  the  con- 
traction, starts  at  the  base,  and  passes  on  to  the  apex.  Sometimes  a 
third  phase  is  seen  (triphasic  variation),  in  which  the  base  again 
becomes  negative  to  the  apex.  It  has  been  supposed  that  this  is  due 
to  the  contraction  of  the  arterial  bulb,  which  follows  that  of  the  rest 
of  the  heart.  If  the  tissue  is  injured  at  either  leading-off  electrode, 
the  corresponding  phase  disappears. 

In  the  uninjured  mammalian  heart,  beating  as  far  as  possible 
under  normal  conditions,  the  sequence  is  the  same,  the  diphasic 
variation  showing  first  base  negative  to  apex,  then  apex  negative  to 
base.  Statements  to  the  contrary  seem  to  have  been  founded  on 
observation  of  injured  hearts,  or  hearts  placed  under  abnormal 
conditions.  For  example,  when  the  base  of  the  heart  is  cooled,  the 


FIG.    203.  —  SECONDARY    CON- 
TRACTION. 

The  nerve  of  muscle  M  touches 
muscle  M'  at  a  and  b.  Stimulation 
of  the  nerve  of  M'  at  S  causes  con- 
traction of  M. 


622 


A  MANUAL  OF  PHYSIOLOGY 


variation  first  becomes  triphasic,  the  sequence  of  the  relative  nega- 
tivity being  base — apex — base;  and  finally  diphasic  with  a  sequence 
the  reverse  of  the  normal,  the  apex  being  first  negative,  then  the  base. 
An  electrical  change  accompanies  every  beat  of  the  human  heart. 
Waller  has  shown  how  this  may  be  demonstrated  by  means  of  the 
capillary  electrometer.  His  experiments  seemed  to  indicate  a 

diphasic  variation  in  which 
the  apex  first  became  nega- 
tive to  the  base  and  the  base 
then  negative  to  the  apex. 
From  later  work  by  Bayliss 
and  Starling,  however,  it 
would  seem  that  this  is  incor- 
rect, the  variation  being  really 
triphasic,  first  base  negative 
to  apex,  then  apex  negative  tc 
base,  and  then  again  base 
negative  to  apex. 

When  the  heart  is  directlj 
stimulated  by  induction  shocks 
at  the  rate  of  about  three  pei 
second,  an  artificial  rhythm- 
is  set  up.  The  interval  which 
elapses  between  stimulation 

FIG.    204.  -  ELECTRO  -  CARDIOGRAMS       eit^er,   °*  auricle  or, 
FROM  MAN  (EiNTHovEN).  — Lower      and  the  beginning  of  the 
led  off  in  opposite  way  from  upper.  trical  change  is  about 

a  second. 

Central  Nervous  System. —It  was  discovered  by  du  Bois-Rey 
mond  that  the  spinal  cord,  like  a  nerve,  shows  a  current  of  res! 
between  longitudinal  surface  and  cross-section,  and  that  a  current  o 
action  is  caused  by  excitation.  Setschenow  stated  that  when  the 
medulla  oblongata  of  the  frog  was  connected  with  a  galvanometer 
spontaneous  variations  occurred  which  he  supposed  due  to  periodic 
functional  changes  in  its  grey  matter.  Gotch  and  Horsley  have 
made  elaborate  experiments  on  the  spinal  cord  of  cats  and  monkeys 
Leading  off  from  an  isolated  portion  of  the  dorsal  cord  to  the  capil 
lary  electrometer,  and  stimulating  the  motor  part  of  the  cortex  cerebri 
they  obtained  a  persistent  negative  variation  followed  by  a  series  ol 
intermittent  variations.  This  agrees  remarkably  with  the  musculai 
contractions  in  an  epileptiform  convulsion  started  by  a  similar  excita 
tion  of  the  cortex,  which  consist  of  a  tonic  spasm  followed  by  clonic 
(interrupted)  contractions,  and  suggests  that  it  is  the  nature  of  the 
cortical  discharge  which  determines  the  character  of  the  convulsion. 

By  means  of  the  galvanometer  the  same  observers  have  made 
investigations  on  the  paths  by  which  impulses  set  up  at  differen 
points  travel  along  the  cord.  To  these  we  shall  have  to  refer  again 
(p.  671). 

On  the  currents  of  the  cerebral  cortex  only  a  few  experiments  have 
hitherto  been  made  by  Caton,  Beck,  and  Fleischl.  But  if  well- 


ELECTRO-PHYSIOLOGY  623 

marked  changes  of  potential  could  be  localized  on  the  cortex  as  a 
result  of  stimulation  of  sensory  fibres,  the  method  would  probably  be 
of  great  value  for  tracing  these  to  their  central  connections. 

Glandular  Currents. — These  have  been  studied  with  any  care  only 
in  the  submaxillary  gland  and  in  the  skin,  although  the  liver,  kidney, 
spleen,  and  other  organs,  also  show  currents  when  injured.  In  the  sub- 
maxillary  gland  the  hilus  is  positive  to 
any  point  on  the  external  surface  of  the 
gland  ;  a  current  passes  from  hilus  to 
surface  through  the  galvanometer,  and 
from  surface  to  hilus  through  the  gland 
(Fig.  205).  When  the  chorda  tympani 
is  stimulated  with  rapidly  -  succeeding 
shocks  of  moderate  strength,  there  is  a 
positive  variation ;  i.e.,  the  surface  be- 
comes still  more  negative  to  the  hilus  FlG-  205. -CURRENT  OF  SUB- 
This  variation  can  be  abolished  by  a  MAXILLARY  GLAND. 

small  dose  of  atropia,  and  then  stimula- 
tion causes  a  slight  negative  variation.  A  further  dose  of  atropia 
abolishes  this,  too.  With  slowly-interrupted  shocks  (not  more  than 
five  per  second)  a  large  negative  variation  is  caused,  and  no  positive 
variation,  and  the  same  is  true  of  rapid  stimuli  too  weak  to  excite 
secretion. 

Single  induction  shocks  cause  a  diphasic  variation,  the  surface  of 
the  gland  becoming  first  more  negative  and  then  more  positive  to  the 
hilus,  so  that  a  positive  deflection  of  the  galvanometer  is  followed  by 
a  negative. 

In  nearly  all  circumstances  stimulation  of  the  sympathetic  causes 
a  negative  variation.  Bradford,  to  whom,  and  to  Bayliss,  we  are 
indebted  for  our  knowledge  of  this  subject,  explains  the  different 
behaviour  of  the  chorda  tympani  to  different  kinds  of  stimulation  as 
due  to  the  existence  in  it  of  anabolic  fibres,  which  increase  the  build- 
ing up  of  the  proper  substance  of  the  gland,  in  addition  to  the 
katabolic  fibres,  which  increase  destructive  metabolism  and  cause 
secretion  (p.  339). 

Skin  Currents. — So  far  as  has  been  investigated,  the  integument 
of  all  animals  shows  a  permanent  current  passing  in  the  skin  from  the 
external  surface  inwards.  This  is  feebler  in  skin  which  possesses  no 
glands.  In  skin  containing  glands  the  current  is  chiefly,  but  not 
altogether,  secretory.  As  such,  it  is  affected  by  influences  which 
affect  secretion,  a  positive  variation  being  caused  by  excitation  of 
secretory  nerves,  e.g.,  in  the  pad  of  the  cat's  foot  by  stimulation  of 
the  sciatic.  The  deflection  obtained  when  a  finger  of  each  hand  is 
led  off  to  the  galvanometer,  which  was  at  one  time  looked  upon  as 
a  proof  of  the  existence  of  currents  of  rest  in  intact  muscles,  is  due 
to  a  secretion  current,  and  the  variation  seen  during  voluntary  con- 
traction of  the  muscles  of  one  arm  is  certainly  in  part,  and  probably 
altogether,  a  secretion  stream. 

Of  more  doubtful  origin  is  the  current  of  ciliated  mucous  mem- 
brane, which  has  the  same  direction  as  that  of  the  skin  of  the  frog 


624  A  MANUAL  OF  PHYSIOLOGY 

and  the  mucous  membrane  of  the  stomach  of  the  frog  and  rabbit — 
viz.,  from  ciliated  to  under  surface  through  the  tissue,  or  from  ciliated 
surface  to  cross-section,  if  that  is  the  way  in  which  it  is  led  off.  The 
current  is  strengthened  by  induction  shocks,  by  heating,  and  in 
general  by  influences  which  increase  the  activity  of  the  cilia.  Some 
circumstances  point  to  the  goblet-cells  in  the  membrane  as  the  source 
of  the  current ;  but,  on  the.  whole,  the  balance  of  evidence  is  in 
favour  of  the  cilia  being  the  chief  factor  (Engelmann),  although  the 
mucin-secreting  cells  may  be  concerned,  too. 

Eye-currents. — If  two  electrodes  connected  with  a  galvanometer 
are  placed  on  the  excised  eye  of  a  frog  or  rabbit,  one  on  the  cornea 
and  the  other  on  the  cut  optic  nerve,  it  is  found  that  a  current  of 
rest  due  to  the  injury  passes  in  the  eye  from  optic  nerve  to  cornea. 
The  same  is  true  if  the  anterior  electrode  is  placed  on  the  retina 
itself,  the  front  of  the  eyeball  being  cut  away.  There  is  nothing  of 
interest  in  this  ;  but  the  important  point  is  that  if  light  be  now 

allowed  to  fall  upon  the  eye,  an  elec- 
trical change  is  caused  (Holmgren, 
Dewar  and  McKendrick),  generally  first 
a  positive  and  then  a  negative  varia 
tion,  succeeded  by  another  positive 
movement  when  the  light  is  cut  off. 

The  variation  depends  upon  the 
retina  alone,  and  does  not  occur  when  it 
is  removed.  Bleaching  of  the  visual 
purple  does  not  much  affect  the  varia- 
tion, so  that  it  is  not  connected  with 

chemical    changes   in   this    substance. 

FIG.  206. -EYE-CURRENT.        And   of    the   spectral   colours,    yellow 

light,  which  affects  the  visual  purple 
comparatively  little,  causes  the  largest  variation  ;  blue,  the  least ; 
but  white  light  is  more  powerful  than  either.  (For  '  visual  purple ' 
see  Chapter  XIII.) 

Electric  Fishes. — Except  lightning,  the  shocks  of  these  fishes  were 
probably  the  first  manifestations  of  electricity  observed  by  man. 
The  Torpedo,  or  electrical  ray,  of  the  coasts  of  Europe  was  known  to 
the  Greeks  and  Romans.  It  is  mentioned  in  the  writings  of  Aris- 
totle and  Pliny,  and  had  the  honour  of  being  described  in  verse  1,500 
years  before  Faraday  made  the  first  really  exact  investigation  of  the 
shock  of  the  Gymnotus,  or  electric  eel,  of  South  America.  The 
third  of  the  electric  fishes,  Malapterurus  electricus,  although  found 
in  many  of  the  African  rivers,  the  Nile  in  particular,  and  known  for 
ages,  was  scarcely  investigated  till  forty  years  ago. 

In  all  these  fishes  there  is  a  special  bilateral  organ  immediately 
under  the  skin,  called  the  electrical  organ.  It  is  in  this  that  the 
shock  is  developed.  It  consists  of  a  series  of  plates  arranged  parallel 
to  each  other.  To  one  side  of  each  plate  a  branch  of  the  electrical 
nerve  supplying  each  lateral  half  of  the  organ  is  distributed.  This 
side  of  the  plate  during  the  shock  becomes  negative  to  the  other 
(Pacini's  rule),  so  that  each  half  of  the  organ  represents  a  battery  of 


ELECTRO-PHYSIOLOGY. 


625 


many  cells  arranged  in  series.  The  direction  of  the  shock  through 
the  organ  depends  on  the  side  of  the  plate  to  which  the  nerve-supply 
goes,  and  the  arrangement  of  the  plates  with  reference  to  the  natural 
position  of  the  animal. 

Thus,  in  Gymnotus  the  plates  are  vertical,  and  at  right  angles  to 
the  long  axis  of  the  fish,  and  the  nerves  are  distributed  to  their  pos- 
terior surface ;  the  shock  accordingly  passes  in  the  animal  from  tail 
to  head.  In  Malapterurus,  although  the  arrangement  of  the  plates  is 
the  same,  the  nerve-supply  is  to  the  anterior  surface;  for  Max 
Schultze  has  shown  that  although  the  nerve  appears  to  sink  into  the 
posterior  surface,  it  really  passes  through  a  hole  in  the  plate,  and 
spreads  out  on  its  anterior  face.  The  shock  passes  from  head  to  tail. 

In  Torpedo,  the  plates  or  septa  dividing  the  vertical  hexagonal 
prisms  of  which  each  lateral  half  of  the  organ  consists  are  horizontal; 
the  nerve-supply  is  to  the  lower  or  ventral  surface ;  and  the  shock 


FIG.  207  —DIAGRAM  SHOWING  DIRECTION  OF  SHOCK  IN  GYMNOTUS. 

passes  from  belly  to  back  through  the  organ.     In  all  electric  fishes 

the  discharge  is  interrupted;  an  active  fish  may  give  as  many  as 

200  shocks  per  second. 
The  electrical  nerve  of  Malapterurus  is  very  peculiar.     It  consists 

of  a  single  gigantic  nerve-fibre  on  each  side,  arising  from  a  giant 

nerve  -  cell.     The  fibre  has 

an  enormously  thick  sheath, 

the  axis  cylinder  forming  a 

relatively  small  part  of  the 

whole;    and    the    branches 

which  supply  the  plates  of 

the  organ  are   divisions   of 
this  single  axis  cylinder. 

The    electromotive    force 
of  the  shock  of  the  Gym- 
notus may  be  very  consider-     FlG>  2o8. -DIAGRAM  SHOWING  DIRECTION 
able;  and  even  Torpedo  and  OF  SHOCK  IN  MALAPTERURUS. 

Malapterurus  are  quite  able 

to  kill  other  fish,  their  enemies  or  their  prey.  Indeed,  Gotch  has 
estimated  the  electromotive  force  of  i  cm.  of  the  organ  of  Torpedo 
at  5  volts,  and  Schonlein  finds  that  the  electromotive  force  of  the 

40 


626  A  MANUAL  OF  PHYSIOLOGY 

whole  organ  may  be  equal  to  that  of  31  Daniell  cells,  or  o'o8  volt  for 
each  plate,  and  it  is  one  of  the  most  interesting  questions  in  the 
whole  of  electro-physiology,  how  they  are  protected  from  their  own 
currents.  There  is  no  doubt  that  the  current  density  inside  the  rish 
must  be  at  least  as  great  as  in  any  part  of  the  water  surrounding  i 
and  probably  much  greater.  The  central  nervous  system  and  the 
great  nerves  must  be  struck  by  strong  shocks,  yet  the  fish  itself  is  not 
injured  ;  nay  more,  the  young  in  the  uterus  of  the  viviparous  Torpedo 
are  unharmed.  The  only  explanation  seems  to  be  that  the  tissues  ol 
electric  fishes  are  far  less  excitable  to  electrical  stimuli  than  the  tissues 
of  other  animals ;  and  this  is  found  to  be  the  case  when  their  muscles 
or  nerves  are  tested  with  galvanic  or  induction  currents.  It  requires 

extremely  strong  currents  to 
stimulate  them ;  and  the  elec- 
trical nerves  are  more  easily 
excited  mechanically,  as  by  liga- 
turing or  pinching,  than  elec- 
trically. In  general,  too,  the 
shock  is  more  readily  called 

forth     by     reflex     mechanical 

FIG.  200. — DIAGRAM  SHOWING  DIREC-       ..      ,  ,.          r  iU      ,  .     ,,        , 
TION  OF  SHOCK  IN  TORPEDO.  stimulation  of  the  skin  than  by 

electrical  stimulation.    But  that 

the  organ  itself  is  excitable  by  electricity,  has  been  shown  by  Gotch. 
He  proved  that  in  Torpedo  a  current  passed  in  the  normal  direction 
of  the  shock  is  strengthened,  and  a  current  passed  in  the  opposite 
direction  weakened,  by  an  action  current  in  the  direction  of  the 
shock.  And  indeed  a  single  excitation  of  the  electrical  nerve  is 
followed  by  a  series  of  electrical  oscillations  in  the  organ  which 
gradually  die  away. 

Whether  the  electrical  organ  is  the  homologue  of  muscle  or  of 
nerve-ending,  or  whether  it  is  related  to  either,  has  not  been 
definitely  settled.  That  curara  does  not  affect  the  electrical  organ  in 
Torpedo,  although  it  paralyzes  the  motor  nerve-endings,  is,  as  far  as 
it  goes,  against  the  nerve-ending  theory.  That  there  is  a  measurable 
latent  period  (about  ^J^  second)  cannot  be  considered  as  in  favoui 
of  the  muscle  theory,  for  the  latent  period  is  probably  determinec 
more  by  functional  than  by  morphological  considerations. 

The  skate  must  now  be  added  to  the  list  of  electric  fishes 
Although  its  organ  is  relatively  small,  and  its  electromotive  fora 
relatively  feeble,  yet  it  is  in  all  respects  a  complete  electrical  organ 
It  is  situated  on  either  side  of  the  vertebral  column  in  the  tail.  Th 
plates  or  discs  are  placed  transversely  and  in  vertical  planes.  Th 
nerves  enter  their  anterior  surfaces ;  the  shock  passes  in  the  orgai 
from  anterior  to  posterior  end.  Gotch  and  Sanderson  have  estimate' 
the  maximum  electromotive  force  of  a  length  of  I  cm.  of  th 
electrical  organ  of  the  skate  at  about  half  a  volt. 


PRACTICAL  EXERCISES  627 


PRACTICAL  EXERCISES  ON  CHAPTER  XL 

1.  Galvani's  Experiment. — Pith  a  frog  (brain  and  cord).      Cut 
through  the  backbone  above  the  urostyle,  and  clear  away  the  anterior 
portion  of  the  body  and  the  viscera.     Pass  a  copper  hook  beneath 
the  two  sciatic  plexuses,  and  hang  the  legs  by  the  hook  on  an  iron 
tripod.     If  the  tripod  has  been  painted,  the  paint  must  be  scraped 
away  where  the  hook  is  in  contact  with  it.     Now  tilt  the  tripod  so 
that  the  legs  come  in  contact  with  one  of  the  iron  feet.     Whenever 
this  happens,  the  current  set  up  by  the  contact  of  the  copper  and 
iron    is   completed,    the   nerves   are   stimulated,    and   the   muscles 
contract  (p.  605). 

2.  Make  a  muscle-nerve  preparation  from  the  same  frog.     Crush 
the  muscle  near  the  tendo  Achillis,  so  as  to  cause  a  strong  demarcation 
current.     Cut  off  the  end  of  the  sciatic  nerve.     Then  lift  the  nerve 
with  a  small  brush  or  thin  glass  rod,  and  let  its  cross-section  fall  on 
the  injured  part  of  the  muscle.     Every  time  the  nerve  touches  the 
muscle  a  part  of  the  demarcation  current  passes  through  it,  stimulates 
the  nerve,  and  causes  contraction  of  the  muscle  (p.  605). 

3.  Make  a  muscle-nerve  preparation.     Lay  it  on  a  glass  plate  A, 
supported   on   a   block  of  wood. 

Snip  off  the  end  of  the  nerve  N,  and 

arrange  the  cut  surface  on  a  pad  of 

kaolin  B,  moistened  with  normal 

saline.     Another  pad  B'  is  placed 

under  the  nerve  a  little  way  from 

its  cut  end.      Both  pads   project 

down  over  the  edge  of  the  glass 

plate.     A  watch-glass  C  filled  with 

normal  saline  solution  is  lifted  up 

below  the  projecting  ends  till  they 

are    immersed.      Whenever    this 

happens,  a  circuit  is  completed  for 

the    demarcation    current   of  the 

nerve  itself,  by  which  it  is  stimu-     FiG.2io. -STIMULATION  OF  A  NERVE 

lated,  and  the  muscle  M  contracts        ™  "s  OWN  DEMARCATION  CUR- 

,  _.      '  KSHT« 

(Fig.  209). 

4.  Secondary  Contraction. — Make  two  muscle-nerve  preparations, 
Lay  the  cross-section  of  one  of  the  sciatic  nerves  on  the  muscle  of 
the  other  preparation  (Fig.  203,  p.  621).    Place  under  the  nerve  near 
its  cut  end  a  small  piece  of  glazed  paper  or  of  glass  rod,  and  let  the 
longitudinal  surface  of  the  nerve  come  in  contact  with  the  muscle 
beyond  this.     Lay  the  nerve  of  the  other  preparation  on  electrodes 
connected  with  an  induction  machine  arranged  for  single  shocks,  with 
a  Daniell  cell  and  a  spring  key  in  the  primary  circuit  (Fig.  181). 
On  closing  or  opening  the  key  both  muscles  contract.     Arrange  the 
induction  machine  for  an  interrupted  current.     When  it  is  thrown 
into  one  nerve,  both  muscles  are  tetanized ;  the  nerve  lying  on  the 
muscle  whose  nerve  is  directly  stimulated  is  excited  by  the  action 
current  of  the  muscle. 

40 — 2 


628 


A  MANUAL  OF  PHYSIOLOGY 


5.  Demarcation  Current  and  Current  of  Action  with  Capillary 
Electrometer. — (a)  Study  the  construction  of  the  capillary  electro- 
meter (Fig.  151,  p.  524).  Raise  the  glass  reservoir  by  the  rack  and 
pinion  screw,  so  as  to  bring  the  meniscus  of  the  mercury  into  the  field. 
Place  two  moistened  fingers  on  the  binding-screws  of  the  electrometer, 
open  the  small  key  connecting  them,  and  notice  that  the  mercury 
moves,  a  difference  of  potential  between  the  two  binding-screws 
being  caused  by  the  moistened  fingers. 

(b)  Demarcation  Current. — Set  up  a  pair  of  unpolarizable  elec- 
trodes (Fig.  153,  p.  526).  Fill  the  glass  tubes  about  one-third  full  of 
kaolin  mixed  with  normal  saline  solution  till  it  can  be  easily  moulded. 
To  do  this,  make  a  piece  of  the  clay  into  a  little  roll,  which  will  slip 
down  the  tube.  Then  with  a  match  push  it  down  until  it  forms  a 


FIG.  2ii.— MOIST  CHAMBER. 

E,  unpolarizable  electrodes  supported  in  the  cork  C  ;  M,  muscle  stretched  over  tf 
electrodes  and  kept  in  position  by  the  pins  A  B  stuck  in  the  cork  plate  P  ;  B,  binding- 
screws  connected  with  galvanometer  or  capillary  electrometer.     The  other  pair 
binding-screws  serves  to  connect  a  pair  of  stimulating  electrodes  inside  the  chamt 
with  the  secondary  coil  of  an  induction  machine. 

firm  plug.     Next  put  some  saturated  zinc  sulphate  solution  in  the 
tubes,  above  the  clay,  with  a  fine-pointed  pipette.     Fasten  the  tubf 
in  the  holder  fixed  in  the  moist  chamber  (Fig.  211).     Now  amal- 
gamate the  small  pieces  of  zinc  wire  (p.  173),  which  are  to  be  con- 
nected with  the  binding-screws  of  the  chamber. 

The  zincs  are  now  placed  in  the  tubes,  dipping  into  the  zim 
sulphate.     A  piece  of  clay  or  blotting-paper  moistened  with  normal 
saline  is  laid  across  the  electrodes  to  complete  the  circuit  between  theii 
points,  and  they  are  connected  with  the  electrometer  to  test  whethf 
they  have  been  properly  set  up.     There  ought  to  be  little,  if  an] 
movement  of  the  mercury  on  opening  the  side-key  of  the  electn 
meter.     If  the  movement  is  large,  the  electrodes  are  '  polarized,'  anc 
must  be  set  up  again.     The  second  pair  of  binding-screws  in  th< 
chamber  are  connected  with  a  pair  of  platinum-pointed  electrodes  or 


PRACTICAL  EXERCISES  629 

the  one  side,  and  on  the  other,  through  a  short-circuiting  key,  with 
the  secondary  coil  of  an  induction  machine  arranged  for  tetanus. 

Next  pith  a  frog  (cord  and  brain),  and  make  a  muscle-nerve  pre- 
paration. Injure  the  muscle  near  the  tendo  Achillis.  Lay  the 
injured  part  over  one  unpolarizable  electrode,  and  an  uninjured  part 
over  the  other.  Put  a  wet  sponge  in  the  chamber  to  keep  the  air 
moist,  and  place  the  glass  lid  on  it.  Focus  the  meniscus  of  the 
mercury,  and  open  the  key  of  the  electrometer ;  the  mercury  will 
move,  perhaps  right  out  of  the  field.  Note  the  direction  of  move- 
ment, and  remembering  that  the  real  direction  is  the  opposite  of  the 
apparent  direction,  and  that  when  the  mercury  in  the  capillary  tube 
is  positive  to  the  sulphuric  acid,  the  movement  is  from  capillary  to 
acid,  determine  which  is  the  positive  and  which  the  negative  portion 
of  the  muscle  (p.  606). 

(c]  Action  Current. — Now  fasten  the  muscle  to  the  cork  or  paraffin 
plate  in  the  moist  chamber,  without  disturbing  its  position  on  the 
electrodes,  by  pins  thrust  through  the  lower  end  of  the  femur  and 
the   tendo   Achillis.     Lay  the   nerve   on  the   platinum   electrodes. 
Open  the  key  of  the  electrometer,  and  let  the  meniscus  come  to  rest. 
This  happens  very  quickly,  as  the  capillary  electrometer  has  but  little 
inertia.    If  the  meniscus  has  shot  out  of  the  field,  it  must  be  brought 
back  by  raising  or  lowering  the  reservoir.     Stimulate  the  nerve  by 
opening  the  key  in  the  secondary  circuit ;  the  meniscus  moves  in  the 
direction  opposite  to  its  former  movement. 

(d)  Repeat  (b)  and  (c)  with  the  nerve  alone,  laying  an  injured  part 
(crushed,  cut,  or  over-heated)  on  one  electrode,  and  an  uninjured 
part  on  the  other.     Of  course  the  nerve  does  not  need  to  be  pinned. 

Clean  the  unpolarizable  electrodes,  and  be  sure  to  lower  the  reser- 
voir of  the  electrometer ;  otherwise  the  mercury  may  reach  the  point 
of  the  capillary  tube  and  run  out. 

In  5  a  galvanometer  may  be  used  instead  of  the  electrometer,  the 
unpolarizable  electrodes  being  connected  to  it  through  a  short- 
cicuiting  key.  The  spot  of  light  is  brought  to  the  middle  of  the 
scale  by  moving  the  control-magnet ;  or  if  a  telescope-reading 
(Fig.  146,  p.  520)  is  being  used,  the  zero  of  the  scale  is  brought  by 
the  same  means  to  coincide  with  the  vertical  hair-line  of  the  tele- 
scope. The  short-circuiting  key  is  then  opened. 

6.  Action-current  of  Heart. — Pith  a  frog  (brain  and  cord).    Excise 
the  heart,  and  lay  the  base  on  one  unpolarizable  electrode,  and  the 
apex  on  the  other,  having  a  sufficiently  large  pad  of  clay  on  the  tips 
of  the  electrodes  to  ensure  contact  during  the  movements  of  the 
heart,  or  having  little  cups  hollowed  in  the  clay  and  filled  with  normal 
saline,  into  which  the  organ  dips.     Connect  the  electrodes  with  the 
capillary  electrometer  and  open  its  key.     At  each  beat  of  the  heart 
the  mercury  will  move  (p.  622). 

7.  Electrotonus. — Set  up  two  pairs  of  unpolarizable  electrodes  in 
the  moist  chamber.     Connect  two  of  them  with  a  capillary  electro- 
meter (or  galvanometer),  and  two  with  a  battery  of  three  or  four  small 
Daniell  cells,  as  in  Fig.  199.     Lay  a  frog's  nerve  on  the  electrodes. 
When  the  key  in  the  battery  circuit  is  closed,  the  mercury  (or  the 


630 


A  MANUAL  OF  PHYSIOLOGY 


needle  of  the  galvanometer)  moves  in  such  a  direction  as  to  indicate 
that  in  the  extrapolar  regions  parts  of  the  nerve  nearer  to  the  anode 
are  positive  to  parts  more  remote,  and  parts  nearer  to  the  kathode  are 
negative  to  parts  more  remote.  The  direction  of  movement  of  the 
mercury  (or  galvanometer  needle)  must  be  made  out  first  for  one 
direction  of  the  polarizing  current.  Then  the  latter  must  be  reversed, 
and  the  movement  of  the  mercury  (or  needle)  on  closing  it  again 
noted  (p.  617). 

8.  Paradoxical  Contraction. — Pith  a  frog  (brain  and  cord).     Dis- 
sect out  the  sciatic  nerve  down  to  the  point  where  it  splits  into  two 

divisions,  one  for  the  gastrocnemius  /',  and  the 
other  for  the  peroneal  muscles  a.  Divide  the 
peroneal  branch  as  low  down  as  possible,  and 
make  a  muscle-nerve  preparation  in  the  usual 
way.  Lay  the  central  end  of  the  peroneal 
nerve  on  electrodes  connected  through  a 
simple  key  with  a  battery  of  two  Daniell  cells. 
When  the  peroneal  nerve  is  stimulated  the 
gastrocnemius  muscle  contracts.  This  result 
is  not  due  to  the  current  of  action,  for  it  is 
not  obtained  with  mechanical  stimulation  of 
the  nerve  ;  but  it  is  not  the  result  of  an 
escape  of  current,  for  if  the  peroneal  nerve 
be  ligatured  between  the  point  of  stimulation 
and  the  bifurcation,  no  contraction  is  obtained. 
The  contraction  is  really  due  to  a  part  of  the 
electrotonic  current  set  up  in  the  peroneal 
nerve  passing  through  the  fibres  for  the 
gastrocnemius,  where  they  lie  side  by  side  in  the  trunk  of  the  sciatic. 

9.  Alterations   in  Excitability  and  Conductivity  produced  ir 
Nerve  by  the  Passage  of  a  Voltaic  Current  through  it. — (a)  Sei 
up  two   pairs  of  unpolarizable  electrodes   in  the   moist   chamber. 


FIG.   212.  —  PARADOXI- 
CAL CONTRACTION. 


FIG.  213. — ARRANGEMENT  FOR  SHOWING  CHANGES  OF  EXCITABILITY 
PRODUCED  BY  THE  VOLTAIC  CURRENT. 

M,  muscle  ;  N,  nerve  ;  EL  Ez,  electrodes  connected  .with  secondary  coil  S  ;  E3,  E 
unpolarizable  electrodes  connected  with  Pohl's  commutator  (with  cross-wires)  C 
B',  '  polarizing'  battery  ;  B,  'stimulating  '  battery  in  primary  circuit  P  ;  K,  K",  simp' 
keys  ;  K',  short-circuiting  key. 

Connect  a  battery  of  two  or  three  Daniell  cells,  arranged  in  sene 
through  a  simple  key  with  the  side-cups  of  a  Pohl's  commutator  wit 


PRACTICAL  EXERCISES  631 

cross-wires  in.  Connect  the  commutator  to  one  pair  of  the  unpolar- 
izable  electrodes  ('the  polarizing  electrodes'),  as  in  Fig.  213.  The 
other  pair  of  unpolarizable  electrodes  ('the  stimulating  electrodes') 
are  to  be  connected  through  a  short-circuiting  key  with  the  secondary 
of  an  induction  machine  arranged  for  tetanus.  A  single  Daniell  is 
put  in  the  primary  coil.  Pith  a  frog  (brain  and  cord),  make  a  muscle- 
nerve  preparation,  pin  the  lower  end  of  the  femur  to  the  cork  plate 
in  the  moist  chamber,  attach  the  thread  on  the  tendo  Achillis  to  the 
lever  connected  with  the  chamber  through  the  hole  in  the  glass  pro- 
vided for  this  purpose,  and  arrange  the  nerve  on  the  electrodes  so 
that  the  stimulating  pair  is  between  the  muscle  and  the  polarizing 
pair.  By  moving  the  secondary,  seek  out  such  a  strength  of  stimulus 
as  just  suffices  to  cause  a  weak  tetanus  when  the  polarizing  current 
is  not  closed.  Set  the  drum  off  (slow  speed),  and  take  a  tracing  of 
the  contraction.  Then  close  the  polarizing  current  with  the  Pohl's 
commutator  so  arranged  that  the  anode  is  next  the  stimulating 
electrodes,  i.e.,  the  current  ascending  in  the  nerve.  Again  open  the 
short-circuiting  key  in  the  secondary ;  the  contraction  will  now  be 
weaker  than  before,  or  no  contraction  at  all  may  be  obtained.  Allow 
the  preparation  two  minutes  to  recover,  then  stimulate  again,  as  a 
control,  without  closing  the  polarizing  current.  If  the  contraction  is 
of  the  same  height  as  at  first,  close  the  polarizing  current  with  the 
bridge  of  the  commutator  reversed,  so  that  the  kathode  is  now  next 
the  stimulating  electrodes.  On  stimulating,  the  contraction  will  now 
be  increased  in  height.  (See  Figs.  177,  178,  p.  576.) 

(b)  Arrange  everything  as  in  (a),  except  that  one  of  the  polarizing 
electrodes   is   placed   at  each  end,   and  the  two   stimulating  elec- 
trodes close  together  in  the  middle  of  the  nerve.     A  large  carbon 
resistance  (say  500,000  ohms)  is  introduced  into  the  circuit  of  the 
secondary  coil,  to  prevent  more  than  a  very  small  fraction  of  the 
polarizing  current    from    passing   through  the  coil.     Seek  out  the 
strength   of  stimulation   which  just   causes   contraction   when   the 
polarizing  current  is  not  closed.     Now  close  the  polarizing  current  in 
such  a  direction  that  the  anode  is  between  the  stimulating  electrodes 
and  the  muscle.     If  no  contraction  occurs  on  stimulation,  push  up 
the  secondary  towards  the  primary  till  the  muscle  contracts.     Then 
stop  stimulation,  open  the  polarizing  current,  and  allow  an  interval 
of  two  minutes.     Now  pass  the  polarizing  current  through  the  nerve 
in  the  opposite  direction,  so  that  the  kathode  is  between  the  stimu- 
lating electrodes  and  the  muscle.     No  contraction  will  be  obtained 
on  exciting  with  the  same  strength  of  stimulus  as  caused  contraction 
when  the  anode  was  next  the  muscle.     The  kathode  has  diminished 
the  conductivity  of  the  nerve ;  and  if  four  or  five  small  Daniell  cells 
are  put  on  in  the  polarizing  circuit,  no  contraction  may  be  obtained, 
even  with  the  coils  close  together,  while  the  excitation  will  still  pass 
the  anode  and  cause  contraction. 

(c)  Connect  a  galvanometer  or  capillary  electrometer  by  unpolar- 
izable electrodes  with  a  frog's  sciatic  nerve,  as  shown  in  Fig.  214,  the 
cut  end  being  on  one  electrode,  the  longitudinal  surface  on  the  other. 
Arrange  two  polarizing  electrodes  (unpolarizable)  one  at  each  end  of 


632 


A  MANUAL  OF  PHYSIOLOGY 


the  remaining  portion  of  the  nerve,  and  connected  through  a  simple 
key  and  a  commutator  with  cross-wires  with  a  battery  of  two  or  three 
small  Daniells.  A  pair  of  fine  platinum,  or  a  third  pair  of  very  fine- 
pointed  unpolarizable  electrodes  is  placed  under  the  nerve  midway 
between  the  two  polarizing  electrodes,  and  connected,  through  a 
large  carbon  resistance,  with  the  secondary  of  an  induction-machine 
arranged  for  tetanus.  Let  the  mercury  of  the  electrometer  or  the 
spot  of  light  on  the  scale  of  the  galvanometer  (or  the  telescope  image 
of  the  scale)  come  to  rest  when  the  demarcation  current  of  the  nerve 
is  thrown  in.  On  stimulating  the  nerve  when  the  polarizing  circuit 
is  open,  a  movement  of  the  mercury  in  the  capillary  electrometer  or 
of  the  spot  of  light  (or  telescope  image,  as  the  case  may  be)  in  the 
galvanometer  takes  place  (current  of  action).  Now  close  the  polariz- 
ing current  in  such  a  direction  that  the  anode  is  next  the  leading-off 
electrodes.  An  action  current  is  still  indicated  on  stimulation. 
Reverse  the  polarizing  current  so  as  to  bring  the  kathode  next  the 


B,  battery  ;  C,  Pohl's 
commutator  with  cross- 
wires  ;  Ej,  E2,  unpolar- 
izable electrodes  con- 
nected with  C  ;  D, 
platinum  electrodes 
connected  with  S,  the 
secondary  coil,  through 
the  large  carbon  resist- 
ance R;  £3,  E4,  unpo- 
larizable electrodes  con- 
nected with  Hg  and 
H2SO4,  the  mercury  and 
sulphuric  acid  of  the 
capillary  electrometer  ; 
K',  simple  key  ;  K",  a 
short-circuiting  key ;  N, 
nerve. 


FIG.  214.— ARRANGEMENT  FOR  SHOWING,  BY  MEANS 
OF  THE  CAPILLARY  ELECTROMETER,  THAT  THE 
KATHODE  BLOCKS  THE  NERVE-IMPULSE. 


leading-off  electrodes.  The  excitation  is  now  blocked  by  the  kathode, 
and  no  movement  of  the  mercury  or  of  the  spot  of  light  takes  place. 
10.  Pfliiger's  Formula  of  Contraction  (p.  576). — To  demonstrate 
this,  connect  two  unpolarizable  electrodes,  through  a  spring  key  and 
a  commutator,  with  a  simple  rheocord  (Fig.  183),  so  as  to  lead  off 
a  twig  of  a  current  from  a  Daniell  cell.  The  unpolarizable  elec- 
trodes are  placed  in  a  moist  chamber.  A  muscle-nerve  preparation 
is  arranged  with  the  nerve  on  the  electrodes  and  the  muscle  attached 
to  a  lever.  The  effects  of  make  and  break  of  a  weak  current,  ascend- 
ing and  descending,  can  be  worked  out  with  the  simple  rheocord. 
The  effects  of  a  medium  current  will  probably  be  obtained  with 
a  single  Daniell  connected  directly  with  the  electrodes  through  a 
key.  The  effects  of  a  strong  current  will  be  got  when  three  or  four 
Daniells  are  connected  with  the  electrodes.  Care  must  be  taken  to 
keep  the  preparation  in  a  moist  atmosphere,  and  more  than  one 
preparation  may  be  needed  to  verify  the  whole  formula. 


PRACTICAL  EXERCISES 


633 


11.  Ritter's  Tetanus. — Lay  the  nerve  of  a  muscle-nerve  prepara 
tion  on  a  pair  of  unpolarizable  electrodes  connected  through  a  simple 
key  with  a  battery  of  three  or  four  small  Daniells.     Connect  the 
muscle  with  a  lever.     Pass  an  ascending  current  (anode  next  the 
muscle)  for  a  few  minutes  through  the  nerve,  and  let  the  writing-point 
trace  on  a  slowly-moving  drum.     When  the  current  is  closed  there 
may  be  a  single  momentary  twitch,  or  the  muscle  may  remain  same- 
what  contracted  (galvanotonus)  as  long  as  the  current  is  allowed  to 
pass,  or  it  may  continue  to  contract  spasmodically  ('  closing  tetanus '). 
When  the  current  is  opened  the  muscle  will  contract  once,  and  then 
immediately  relax,  or  there  may  be  a  more  or  less  continued  tetanus 
{Ritter's  or  'opening   tetanus').     If  opening  tetanus   is  obtained, 
divide  the  nerve  between  the  electrodes :   the   tetanus   continues. 
Divide  it  between  the  anode  and  the  muscle :  the  tetanus  at  once 
disappears.     This  shows  that  the  seat  of  the  excitation  which  causes 
the  tetanus  is  in  the  neighbourhood  of  the  anode  (p.  617).    That  there 
is  a  state  of  excitation  in  this  region  after  a  voltaic  current  is  opened 
may  be  shown  electrically  thus  : 

12.  Positive  Polarization. — Connect  a  pair  of  unpolarizable  elec- 
trodes by  double  leads  with  a  battery  of  twelve  or  fifteen  small  Daniells 
and   a    galvanometer    or 

capillary  electrometer,  as 
in  Fig.  215.  A  Pohl's 
commutator  without 
cross-wires  is  introduced 
in  such  a  way  that  when 
the  bridge  is  in  one  direc- 
tion the  battery  circuit  is 
made  and  the  galvano- 
meter or  electrometer 
circuit  broken,  and  vice 
versa  when  the  bridge  is 
tilted  in  the  other  direc- 
tion. A  frog's  nerve  is 
laid  on  the  electrodes  in 
the  moist  chamber,  with 
its  cut  ends  at  the  same 
distance  from  the  elec- 
trodes (streamless  arrange- 
ment), to  eliminate  as  far 
as  possible  the  demarcation  current.  The  battery  current  is  now 
passed  for  an  instant  through  the  nerve ;  the  commutator  is  at  once 
reversed,  and  the  electrometer  or  galvanometer  shows  a  movement 
indicating  that  the  anodic  area  is  negative  to  the  kathodic  ('positive 
polarization').  The  positive  polarization  current  is  in  the  same 
direction  as  the  polarizing  current.  The  positive  polarization  effect 
may  be  preceded  by  a  'kick'  in  the  opposite  direction  ('negative 
polarization ').  The  negative  polarization  effect  is  much  increased  if 
the  polarizing  current  be  allowed  to  flow  for  some  time.  For  accu- 
rate experiments  it  is  better  to  employ  two  pairs  of  unpolarizable 


FIG.  215.  —  SCHEME  FOR  DEMONSTRATING 
'  POSITIVE  POLARIZATION  '  BY  THE  CAPIL- 
LARY ELECTROMETER. 

EI,  £2,  unpolarizable  electrodes  connected  with 
the  'polarizing'  battery  B  through  a  Pohl's  com- 
mutator (without  cross-wires)  C  ;  K,  simple  key  ; 
Hg  and  H2SO4,  the  mercury  and  sulphuric  acid  of 
the  capillary  electrometer ;  N,  nerve ;  K',  key  in 
electrometer  circuit. 


634  A  MANUAL  OF  PHYSIOLOGY 

electrodes,  one  for  leading  in  the  polarizing  current  to  the  tissue,  and 
the  other  for  leading  off  the  polarization  current  to  the  galvanometer 
or  electrometer. 

13.  Galvanotropism. — Place  at  each  end  of  a  rectangular  trough 
filled  with  tap-water  a  metallic  plate,  or  a  plate  of  carbon,  connected 
through  a  commutator  and  key  with  the  poles  of  a  Grove  or  bichro- 
mate battery  of  several  cells,  or,  if  the  laboratory  is  provided  with  a 
current  from  the  street,  with  the  switch  through  one  or  more  incan- 
descent lamps.  Put  into  the  water  a  number  of  tadpoles,  which 
should  not  be  too  young.  When  the  current  is  closed,  the  tadpoles 
will  arrange  themselves  in  a  definite  way  with  their  long  axes  in  the 
direction  of  the  lines  of  flow,  the  head  being  turned  towards  the 
anode.  Reverse  the  current,  and  they  turn  their  heads  in  the 
opposite  direction.  If  the  current  is  taken  from  the  laboratory 
supply,  the  anode  may  be  known  as  the  electrode  at  which  leas 
gas  comes  off,  or  at  which  a  mixture  of  potassium  iodide  and  starch 
becomes  blue. 


2.  Cover-glass  preparation  of  spinal  oord  of  ox,  x  250.    (Stained  with  methyl  blue.) 


Axis-cylinder 


Dendritic  processes 


\         Bipolar  mtrve-cell 


Anterior  column 


Anterior  nerve-root 

Nerve-cells  of 
anterior  cornu 


Nerve-fibres  qf 
vhite  -natter 


r 


ij 

*  j  "  nerve- 


Nuclei 


Mcdul 


--  Neuritemma 
Medullar 


•§      ,    1.  Nerve-iiores  of  frog,  teased 

osmic  acid,  x  300. 
(Stained  with  hffimatoxylin.) 


Posterior  nerve-root 


Posterior  column 


3.  Transverse  section  of  spinal  cord.     (Stained  with  aniline  blue-black.) 


Sylvian  fissure 


Internal  carefid.  _ 


.Rasilar  artery  - 
Hedulla  obloiyat 


Anterior  cerebral 


Base  of  brain,  with  arteries  injected. 


West  Newm, 


CHAPTER  XII. 
THE  CENTRAL  NERVOUS  SYSTEM. 

IN  other  divisions  of  our  subject  we  have  been  able  to 
follow  to  a  greater  or  less  extent  the  processes  which  take 
place  in  the  organs  described.  The  chemistry  and  the 
physics  of  these  processes  have  bulked  more  largely  in  our 
pages  than  the  anatomy  and  histology  of  the  tissues  them- 
selves. In  dealing  with  the  central  nervous  system  we  must 
adopt  a  method  the  very  reverse  of  this.  Its  anatomical 
arrangement  is  excessively  intricate.  The  events  which 
take  place  in  that  tangle  of  fibre,  cell,  and  fibril  are,  on  the 
other  hand,  almost  unknown.  So  that  in  the  description  of 
the  physiology  of  the  central  nervous  system  we  can  as  yet 
do  little  more  than  trace  the  paths  by  which  impulses  may 
pass  between  one  portion  of  the  system  and  another,  and  from 
the  anatomical  connections  deduce,  with  more  or  less  pro- 
bability, the  nature  of  the  physiological  nexus  which  its 
parts  form  with  each  other  and  the  rest  of  the  body.  And 
here  it  may  be  well  to  remark  that,  although  for  convenience 
of  treatment  we  have  considered  the  general  properties  of 
nerves  in  a  separate  chapter,  there  is  not  only  no  funda- 
mental distinction  between  the  central  nervous  system  and 
the  outrunners  which  connect  it  with  the  periphery,  but 
obviously  a  central  nervous  system  would  be  meaningless 
and  useless  without  afferent  nerves  to  carry  information  to 
it  from  the  outside,  and  efferent  nerves  along  which  its 
commands  may  be  conducted  to  the  peripheral  organs. 


636  A  MANUAL  OF  PHYSIOLOGY 

I.  Structure  of  the  Central  Nervous  System.* 

In  unravelling  the  complex  structure  of  the  central  nervous 
system,  we  avail  ourselves  of  information  derived  (i)  from 
its  gross  anatomy ;  (2)  from  its  microscopical  anatomy ; 
(3)  from  its  development  ;  (4)  from  what  we  may  call, 
although  the  term  is  open  to  the  criticism  of  cross-division, 
its  physiological  and  pathological  anatomy,. 

The  study  of  development  enables  us  not  only  to  determine  the 
homology,  the  morphological  rank,  of  the  various  parts  of  the  brain 
and  cord,  but  also,  by  comparison  of  animals  of  different  grades  of 
organization,  sometimes  to  decide  the  probable  function  and  physio- 
logical importance  of  a  strand  of  nerve-fibres  or  a  column  of  nerve- 
cells.  It  is  of  special  value  in  helping  us  to  differentiate  and  to 
trace  the  various  tracts  or  paths  into  which  the  white  matter  of  the 
central  nervous  system  may  be  divided.  For  the  medullary  sheath 
is  not  developed  at  the  same  time  in  all  the  tracts,  and  a  strand  of 
nerve-fibres  without  a  medulla — e.g.,  the  pyramidal  tract  (p.  650)  at 
birth — is  readily  distinguished  under  the  microscope. 

Then,  again — and  this  is  what  we  propose  to  include  under  the 
fourth  head — experimental  physiology  and  clinical  and  pathological 
observation  throw  light  not  only  on  the  functions,  but  also  on  the 
structure,  of  the  central  nervous  system.  For  instance,  complete  or 
partial  section,  or  destruction  by  disease,  of  the  white  fibres  of  the 
cord  or  brain,  or  of  the  nerve  roots,  or  removal  of  portions  of  the 
grey  matter,  is  followed  by  degeneration  in  definite  tracts.  And 
since,  as  we  have  already  seen,  degeneration  of  a  nerve-fibre  is  caused 
when  it  is  cut  off  from  the  cell  of  which  it  is  a  process,  the  amount 
and  distribution  of  such  degeneration  teaches  us  the  extent  and 
position  of  the  central  connections  of  the  given  tract.  And,  particu- 
larly in  young  animals,  removal  of  a  peripheral  organ — an  eye  or  a 
limb — may  be  followed  by  atrophy  of  portions  of  the  central  nervous 
system  immediately  related  to  it.  Certain  tracts  of  white  or  grey 
matter  are  also  differentiated  from  each  other  by  the  size  of  their 
fibres  or  cells.  For  example,  the  postero-median  column  of  the 
spinal  cord  has  small  fibres,  the  direct  cerebellar  tract  large  fibres ; 
the  pyramidal  cells  in  what  we  shall  afterwards  have  to  distinguish  as 
the  '  leg  area'  (p.  707)  of  the  cerebral  corcex  are  large  ;  those  of  the 
*  face  area '  are  comparatively  small. 

Certain  tracts  may  also  be  marked  out  by  means  of  the  electrica) 
variation,  which  gives  token  of  the  passage  of  nervous  impulses  along 
them  when  portions  of  the  central  nervous  system  or  peripheral 
nerves  are  stimulated  (Horsley  and  Gotch). 

*  It  is  unnecessary  to  say  that  a  complete  description  of  the  structure 
of  the  brain  and  cord  from  the  anatomical  standpoint  would  be  out  of  place 
in  a  book  like  this.  As  in  the  other  divisions  of  our  subject,  a  knowledge 
of  anatomy  is  assumed  on  the  part  of  the  reader. 


THE  CENTRAL  NERVOUS  SYSTEM 


637 


Development  of  the  Central  Nervous  System. — Very  early  in 
development  (Fig.  216)  the  keel  of  the  vertebrate  embryo  is  laid 
dawn  as  a  groove  or  gutter  in  the  epiblast  of  the  blastodermic  area 
(Chap.  XIV.).  The  walls  of  this  'medullary  groove'  grow  inwards, 
and  at  length  there  is  formed,  by  their  coalescence,  the  *  neural  canal > 
(Fig.  217),  which  expands  at  its  anterior  end  to  form  four  cerebral 


FIG.  216. — FORMATION  OF  THE  NEURAL  CANAL  AT  AN  EARLY  STAGE. 

vesicles  (Fig.  218).  Thus  there  is  a  continuous  tunnel  from  end  to 
end  of  the  primary  cerebro- spinal  axis;  and  this  persists  in  the  adult 
as  the  central  canal  of  the  spinal  cord  and  the  ventricles  of  the  brain, 
whose  ciliated  epithelium  represents  the  epiblastic  lining  of  the  primi- 
tive neural  canal*  From  the  wall  of  this  canal  is  developed  the 
cerebro-spinal  axis,  with  the  motor  roots  of  the  spinal  nerves.  The 


, 


\ 


SK2: 


FIG.  217. — NEURAL  CANAL  AT  A  LATER  STAGE. 

ganglia  on  the  posterior  roots  arise  from  a  series  of  epiblastic  thicken- 
ings arranged  along  the  neural  canal,  but  outside  its  wall.  From  both 
poles  of  each  ganglion  cell  a  process  grows  out,  one  towards  the 
periphery,  which  forms  a  peripheral  nerve-fibre,  the  other  centrally 

*  Gaskell  and  Bland  Sutton  regard  the  central  canal  as  the  representa- 
tive of  the  alimentary  canal  of  the  (crustacean)  ancestor  of  the  verte- 
brates. 


638 


A  MANUAL  OF  PHYSIOLOGY 


to  connect  the  cell  with  the  cord.  From  the  after-brain  is  developed 
the  medulla  oblongata,  from  the  hind-brain  the  cerebellum  and  pons, 
from  the  mid-brain  the  corpora  quadrigemina  and  crura  cerebri. 

The  fore-brain,  or  primary  fore- 
lh.  Oj      brain,  gives  rise  of  itself  only 

zj^J  I  "  /ti\   *  1     <""n™>    '       to  the  third  ventricle  and  optic 

thalamus,  but  a  secondary  fore- 
brain  buds  off  from  it  and  soon 
divides  into  two  chambers, 
from  the  roof  of  which  the 
cerebral  hemispheres,  and  from 
the  floor  the  corpora  striata, 
are  derived.  Their  cavities 
persist  as  the  lateral  ventricles, 
which  communicate  with  the 
third  ventricle  by  the  foramen 
of  Monro.  The  olfactory  tracts 
are  formed  as  buds  from  the 
secondary  fore-brain. 

To  complete  the  story  of 
the  development  of  the  brain, 
it  may  be  added  that  the  retina 
is  really  an  expansion  of  its 
nervous  substance.  A  hollow 
process,  the  optic  vesicle,  buds 
out  on  each  side  from  the 
primary  fore  brain.  A  button 
of  epiblast,  which  afterwards 
becomes  the  lens,  grows  against 
the  vesicle  and  indents  it,  so 
that  it  becomes  cup-shaped,  the  inner  concave  surface  of  the  cup 
representing  the  retina  proper,  the  outer  convex  surface  the  choroidal 
epithelium.  The  stalk  becomes  the  optic  nerve. 

Histological  Elements  of  the  Central  Nervous  System. — The 
central  nervous  system  is  built  up  (i)  of  true  nervous  elements,  (2)  of 
supporting  tissue.  The  nervous  elements  have  usually  been  described 
as  consisting  of  nerve-fibres  and  nerve-cells,  but  the  antithesis  of  a 
time-honoured  distinction  must  not  lead  us  to  forget  that  the  essential 
part  of  a  nerve-fibre,  the  axis-cylinder,  is  a  process  of  a  nerve  cell, 
and  the  medullary  sheath  perhaps  a  product  of  the  axis-cylinder.* 
In  strictness,  the  term  'nerve-cell '  ought  to  include  not  only  the  cell- 
body,  but  all  its  processes,  out  to  their  last  ramifications.  But  the 
habit  of  speaking  of  the  position  of  the  cell-body  as  that  of  the  nerve- 

*  Although  each  internode  of  the  medullary  sheath  of  a  peripheral 
nerve-fibre  has  been  supposed  to  be  formed  from  a  cell  that,  in  the  course 
of  development,  comes  in  contact  with  the  axis-cylinder  and  ultimately 
encircles  it,  a  similar  origin  can  hardly  be  admitted  for  the  medulla  of  the 
fibres  of  the  spinal  cord  and  brain,  where,  indeed,  a  segmental  genesis 
seems  excluded  by  the  absence  of  regularly  placed  internodal  nuclei  and 
nodes  of  Ranvier. 


FIG.  218.  —  DIAGRAM  TO  ILLUSTRATE 
THE  FORMATION  OF  THE  CEREBRAL 
VESICLES. 

A.  i  indicates  the  cavity  of  the  secondary 
fore-brain,  which  eventually  becomes  the 
lateral  ventricles.  In  B  the  secondary  fore- 
brain  has  grown  backwards  so  as  to  overlap 
the  other  vesicles.  I,  first  cerebral  vesicle 
(primary  fore-brain  or  'tween  brain) ;  II, 
second  cerebral  vesicle  (mid-brain)  ;  III, 
third  cerebral  vesicle  (hind-brain) ;  IV,  fourth 
cerebral  vesicle  (after-brain). 


THE  CENTRAL  NERVOUS  SYSTEM 


639 


cell  is  so  ingrained  that  it  seems  better  to  continue  the  use  of  the 
latter  term  in  its  old  signification,  and  to  speak  of  the  cell  and 
branches  together  as  a  nervous  element.  A  nerve-cell  from  the 
anterior  horn  of  the  spinal  cord  (Plate  V.,  2),  which  may  be  taken  as 
a  typical  nerve-cell,  is  a  knot  of  granular  protoplasm,  apparently 
destitute  of  a  cell-wall,  but  containing  a  large  nucleus  inside  of  which 
lies  a  highly  refractive  nucleolus.  Pigment  may  also  be  present, 
especially  in  old  age.  By  certain  methods  of  staining  it  may  be 
shown  that  fibrils  run  through  the  cell-substance,  while  between  the 
fibrils  lie  round  or  spindle-shaped  bodies  (Nissl's  bodies)  which  stain 


FIG,  219  -if 

a— e  shows  the  development  of  the  pyramidal  nerve-cells  of  the  cerebral  cortex  in  a 
typical  mammal ;  a,  neuroblast  with  commencing  neuron  ;  b,  dendrons  appearing  ; 
d,  commencing  collaterals.  A — D  shows  the  different  degree  of  complexity  in  the  fully- 
developed  pyramidal  cells  in  different  vertebrates  :  A,  frog;  B,  lizard ;  C,  rat ;  D,  man. 
(Donaldson,  after  Ram6n  y  Cajal.) 

with  basic  dyes.  These  bodies  vary  in  appearance  in  different  kinds 
of  nerve-cells,  and  in  the  same  nerve-cell  under  different  conditions. 
Several  processes — it  may  be  five  or  six — pass  off  from  the  cell-body, 
one  of  which  is  distinguished  from  the  rest  by  the  fact  that  it  main- 
tains its  original  diameter  for  a  comparatively  great  distance  from  the 
cell,  and  gives  off  comparatively  few  branches.  This  process,  which 
in  favourable  preparations  can  be  traced  on  till  it  becomes  the  axis- 
cylinder  of  a  nerve-fibre,  is  called  the  axis-cylinder  process,  or  more 
shortly  the  neuron.  The  few  slender  branches  that  come  off  from  it, 
usually  at  right  angles,  are  called  collaterals.  Both  the  main  thread 
of  the  neuron  and  the  collaterals  end  by  breaking  up  into  brushes  of 
fibrils.  The  rest  of  the  processes  of  the  cell,  which  are  termed 


640 


A  MANUAL  OF  PHYSIOLOGY 


dendrons,  or  protoplasmic  processes,  very  rapidly  diminish  in  diameter, 
as  they  pass  away  from  the  cell,  by  breaking  up  into  fibrils  like  the 
branches  of  a  tree.  They  lose  themselves  at  a  little  distance  from 
the  cell  in  the  surrounding  network,  which  forms  the  greater  portion 
of  the  ground  material  of  the  grey  substance,  and  in  which  the 
dendritic  systems  of  neighbouring  cells  come  into  relation  with  each 
other,  and  with  the  terminal  brushes  of  the  neurons.  Probably  the 
relation  is  not  one  of  actual  anatomical  continuity,  but  the  processes 
come  so  close  together  that  nerve  impulses  are  able  to  pass  across 
from  the  terminal  brush  of  the  neuron  of  one  nervous  element  to  the 
dendrons  of  another.  All  the  nerve-cells  of  the  cerebro-spinal  axis 
are  believed  to  agree  with  the  cells  of  the  anterior  horn  in  the  pos- 
session of  a  neuron  and  one  or  more  dendrons.  In  the  cerebral 
cortex  the  typical  cells  are  of  pyramidal  shape.  From  the  base 
comes  off  the  neuron,  and  from  the  angles  the  dendritic  processes. 


FIG.  220, 

Cells  from  the  Gasserian  ganglion  of  a  developing  guinea  pig.  The  originally  bipolar 
cells  are  seen  changing  into  cells  apparently  unipolar.  The  same  process  occurs  in  the 
cells  of  the  spinal  ganglia.  (Van  Gehuchten.) 

Sometimes  a  nreuon,  instead  of  ending  in  a  brush  of  fibrils  which 
come  into  relation  with  the  dendrons  of  another  nervous  element, 
breaks  up  into  a  sort  of  basket-work  of  fibrils  surrounding  the  cell- 
body.  The  cells  of  Purkinje,  for  instance,  in  the  cerebellum,  are 
surrounded  by  such  pericellular  baskets.  The  cells  of  the  spinal 
ganglia  have  two  neurons,  which  in  the  embryo  arise  one  from  each 
end  of  the  bipolar  cell,  but  in  the  adult  are  connected  to  the  cell 
by  a  single  process  (Fig.  220).  They  have  no  dendrons.  The 
sympathetic  ganglion  cells  seem  also  to  be  often  devoid  of  true  den- 
dritic processes,  although  it  is  not  certain  that  this  is  always  the  case. 
Another  kind  of  cell  which  seems  undoubtedly  to  be  of  nervous 
nature  is  the  'granule-cell.'  Granule-cells  are  much  smaller  than 
the  nerve-cells  we  have  been  describing.  Their  processes  are  much 
less  easily  followed,  but  all  appear  to  give  off  a  neuron  and  one  or 
more  dendrons.  They  contain  a  relatively  large  nucleus  (5  to  8  //  in 
diameter),  with  only  a  mere  fringe  of  cell-substance.  The  nucleus, 
unlike  that  of  a  large  nerve-cell,  stains  deeply  with  haematoxylin. 
Some  parts  of  the  grey  matter  are  crowded  with  these  granule- 
cells,  e.g.,  the  nuclear  layer  of  the  cerebellum  and  the  substantia 


THE  CENTRAL  NERVOUS  SYSTEM  641 

gelatinosa,  or  substance  of  Rolando,  which  caps  the  posterior  horn 
in  the  cord.  In  other  parts  they  are  more  thinly  scattered,  but  pro- 
bably they  are  as  widely  diffused  as  the  large  nerve-cells  proper,  and 
no  extensive  area  of  the  grey  matter  is  wholly  without  them. 

The  layer  of  ciliated  epithelium  lining  the  central  canal  of  the 
spinal  cord  and  the  ventricles  of  the  brain  in  the  lower  animals  and 
in  early  life  in  man,  has  also  been  considered  by  some  as  of  nervous 
nature ;  and  the  fact  that  the  deep  ends  of  the  cells  are  continued 
into  processes  which  pierce  far  into  the  grey  substance  lends  weight 
to  this  opinion. 

Growth  of  Nerve-cells. — The  growth  of  a  nervous  element  is 
a  comparatively  slow  process.  Early  in  foetal  life  (about  the  third 
or  fourth  week  in  man)  certain  round  germinal  cells  make  their 
appearance  amid  the  columnar  epiblastic  cells  surrounding  the 
neural  canal.  From  their  division  are  formed,  in  the  first  months  of 
embryonic  life,  the  primitive  nerve-cells  or  neuroblasts.  These  soon 
elongate  and  push  out  processes,  first  the  neuron  or  neurons,  and 
then  the  dendrons  (Fig.  219).  As  development  goes  on  the  cell- 
body  grows  larger,  and  the  processes  longer  and  more  richly 
branched.  The  neuron,  in  the  case  of  the  great  majority  of  the 
nervous  elements  of  the  brain  and  cord,  ultimately  acquires  a  medul- 
lary sheath,  although,  as  we  have  said,  the  time  at  which  medullation 
is  completed  varies  in  different  groups  of  elements,  and  in  some 
nervous  tracts  it  is  even  wanting  at  birth.  At  birth,  too,  the 
branches  of  many  of  the  cells  are  less  numerous,  and  the  connections 
between  different  nervous  elements  therefore  less  intimate  than  they 
will  afterwards  become.  For  many  years  the  processes,  and  par- 
ticularly the  neurons,  continue  not  only  to  grow  longer,  but  also  to 
grow  thicker.  The  cell-body  also  enlarges,  and  the  quantity  of 
material  in  it  that  stains  with  basic  dyes  increases.  Even  after 
puberty  is  reached  the  anatomical  organization  of  the  nervous  system 
may  still  continue  to  advance,  although  at  an  ever-slackening  rate, 
and  the  finishing  touches  may  only  be  given  to  its  architecture  in 
adult  life.  In  old  age  the  nervous  elements  decay  as  the  body  does. 
The  cell-body  diminishes  in  size ;  the  stainable  material  lessens  in 
amount ;  vacuoles  form  in  the  protoplasm  and  pigment  accumulates  ; 
the  nucleus  shrinks;  the  nucleolus  is  obscured  or  may  disappear 
altogether.  At  the  same  time  the  processes  of  the  cell,  and  espe- 
cially the  dendrons,  tend  to  atrophy  (Fig.  221). 

Nerve-cells  are  the  most  distinctive  histological  feature  of  the  grey 
nervous  substance.  Sown  thickly  in  the  cerebral  cortex,  the  basal 
ganglia,  the  floor  of  the  fourth  ventricle,  and  the  cervical  and  lumbar 
enlargements  of  the  cord,  they  are  scattered  more  sparingly  wherever 
the  grey  matter  extends.  They  also  occur  in  the  spinal  ganglia  and 
their  cerebral  homologues,  in  the  ganglia  of  the  sympathetic  system 
and  the  sporadic  ganglia  in  general.  But  wide  as  is  their  distribution 
and  great  as  is  the  size  of  the  individual  cells,  they  yet  make  up  but 
a  small  portion  of  the  whole  of  the  central  nervous  substance.  And 
although  it  is  not  to  be  wondered  at  that  objects  so  notable  when 
viewed  under  the  microscope  should  have  struck  the  imagination  of 

41 


642 


A  MANUAL  OF  PHYSIOLOGY 


physiologists,  it  is  probable  that  the  very  high  powers  which  it  is  so 
common  to  attribute  exclusively  to  them  ought  to  be,  in  part  at  least, 
shared  with  the  nervous  plexus  woven  from  their  processes  and  of 
which  they  form  the  nodes. 

In  addition  to  non-medullated  fibres  and  filaments  arising  from  the 
nerve-cells,  the  grey  matter  contains  also,  as  may  be  seen  in  prepara- 
tions stained  by  Weigert's  method,*  great  numbers  of  exceedingly 
fine  medullated  fibres. 

Only  medullated  nerve-fibres  are  met  with  in  the  white  matter  of 
the  cerebro-spinal  axis.  They  are  devoid  of  a  neurilemma.  In 


FIG.  221. 

i,  spinal  ganglion  cells  of  a  still-born  male  child ;  2,  of  a  man  ninety-two  years 
old  (X  250) — N,  nuclei;  3,  nerve-cells  from  the  antennary  ganglion  of  a  honey-bee 
just  emerged  in  the  perfect  form ;  4,  of  an  old  honey-bee.  The  nucleus  is  black  in 
the  figure.  In  3  it  is  very  large,  in  4  it  is  shrunken,  and  the  cell-substance  contains 
vacuoles.  (Hodge.) 

diameter  they  vary  from  2  /x  to  20  ft.  In  Malapterurus  electricus  the 
fibre  in  the  cord  which  supplies  the  electrical  organ  is  of  immense 
size  ;  and  in  the  anterior  column  of  many  fishes  may  also  be  seen  a 
single  gigantic  fibre  on  each  side  with  a  diameter  of  nearly  100  /*. 
It  cannot  be  said  that  any  relation  between  the  functions  of  nerve 
fibres  and  their  size  has  been  definitely  established.  Many  afferent 
fibres,  it  is  true,  are  small — this  is  notably  the  case  with  the  fibres  of 
the  posterior  column  and  posterior  root — and  many  motor  fibres  are 
large.  But  the  distinction  can  by  no  means  be  generalized,  for  the 

*  Weigert's  is  a  special  method  of  staining  the  medullary  sheath  with 
hrematoxylin. 


THE  CENTRAL  NERVOUS  SYSTEM  643 

fibres  of  the  cerebellar  tract,  which  certainly  are  afferent,  are  among 
the  largest  in  the  spinal  cord  ;  and  the  vaso-motor  fibres,  which  pass 
from  the  cord  into  the  sympathetic,  are  smaller  than  the  fibres  of  the 
posterior  column.  Even  the  motor  nerve-fibres  of  striated  muscles 
vary  considerably  in  diameter,  those  of  the  tongue,  e.g.,  being  smaller 
than  those  of  the  muscles  of  the  limbs.  Further,  the  medullated 
fibres  of  the  brain  are,  without  reference  to  function,  in  general  finer 
than  the  fibres  of  the  cord.  The  cause  of  these  differences  in  the 
size  of  nerve-fibres  is  quite  unknown.  It  is  more  likely  to  be  morpho- 
logical than  physiological. 

The  supporting  tissue  of  the  central  nervous  system  consists 
partly  of  ordinary  connective  tissue  derived  from  the  mesoblast,  and 
partly  of  a  peculiar  form  of  tissue  derived  from  the  epiblast,  and 
called  neuroglia.  The  whole  cerebro-spinal  axis  is  wrapped  in  four 
concentric  sheaths.  Next  the  walls  of  the  bony  hollow  in  which  it 
lies  is  the  dura  mater.  Next  the  nervous  substance  itself,  following 
the  convolutions  of  the  brain  and  the  fissures  of  the  cord,  and  giving 
off  bloodvessels  supported  in  connective-tissue  septa  to  both,  is  the 
pia  mater.  Between  the  dura  and  the  pia,  separated  from  the  latter 
by  a  jacket  of  cerebro-spinal  fluid,  is  the  double  layer  of  the  arachnoid. 
The  comparatively  coarse  processes  that  run  into  the  nervous  sub- 
stance from  the  pia  mater  are  the  main  beams  in  the  scaffolding  of 
non-nervous  material  with  which  that  substance  is  interwoven,  and 
by  which  it  is  supported.  The  interstices  are  filled  in  by  a  thick-set 
feltwork  of  interlacing  but  unbranched  neuroglia  fibres,  which  lie  close 
against  the  small  glia  cells,  but  in  the  adult  at  least  are  perfectly 
distinct  from  them.  In  preparations  impregnated  by  the  Golgi 
method*  the  fibres  appear  to  be  processes  running  out  from  the 
attenuated  cell-body  like  the  arms  of  a  microscopic  crab  or  spider. 
But  this  is  a  deceptive  appearance,  as  Weigert  has  shown  by  means 
of  a  special  method  in  which  the  neuroglia  fibres  are  alone  stained. 
It  is  possible,  however,  that  in  the  embryo  the  fibres  are  formed  by 
the  cells,  and  afterwards  become  detached  from  them.  The  glia 
fibres  are  perfectly  distinct  from  the  nervous  substance  proper,  but 
they  are  not  ordinary  connective  tissue.  In  the  white  matter  nearly 
every  medullated  nerve-fibre  is  divided  from  its  neighbours  by  glia 
fibres,  which  form  a  wide-meshed  network.  The  network  is  denser 
in  most  parts  of  the  grey  substance,  though  not  in  all.  The 
neuroglia  is  present  in  greatest  abundance  in  the  grey  matter  imme- 
diately surrounding  the  central  canal  of  the  cord  and  the  ventricles 
of  the  brain  (the  ependyma,  as  it  is  called).  Contrary  to  the  common 
opinion,  the  substance  of  Rolando  is  poor  in  neuroglia  (Weigert). 
Another  kind  of  tissue,  consisting  only  of  a  granular  mass,  entirely 

*  The  method  depends  upon  the  deposition  of  mercury,  or  silver,  in  or 
around  the  cell-bodies  and  their  processes  in  tissues  which  have  been 
hardened  in  bichromate  of  potassium  and  then  soaked  in  a  solution  of 
mercuric  chloride  or  silver  nitrate.  In  Pal's  improvement  of  Golgi's 
method  a  solution  of  sodic  sulphide  follows  the  mercuric  chloride. 

41—2 


644  A  MANUAL  OF  PHYSIOLOGY 

devoid  of  cells,  has  been  described  as  filling  in  the  spaces  of  the 
grey  matter  not  occupied  by  the  other  elements.  It  is  for  this 
substance  that  some  authors  reserve  the  name  of  neuroglia.  But 
it  is  probable  that  the  granular  appearance  seen  in  microscopic 
preparations  is  due  to  nothing  else  than  the  cross-sections  of  the 
fine  neuroglia  fibrils  or  of  the  nervous  plexus. 

^ 

General  Arrangement  of  the  White  and  Grey  Matter  in  the 
Central  Nervous  System. — (i)  Around  the  central  canal,  as  we 
have  seen,  a  tube  of  grey  matter  sheathed  with  white  fibres 
is  developed.  This  tube,  from  optic  thalamus  to  conus 


FIG.  222. — NEUROGLIA  FIBRES  AND  CELLS  (from  a  human  embryo  30  cm.  in 
length).  The  small  cell  on  the  right  is  from  the  grey,  the  other  two  from  the 
white  substance ;  Golgi's  method  (Kolliker). 

medullaris,  may  be  conveniently  referred  to  as  the  central 
grey  axis  or  stem,  which,  in  the  lowest  vertebrates,  e.g.,  fishes, 
is  much  the  most  important  part  of  the  central  nervous 
system. 

(2)  On  the  outer  surface  of  the  anterior  portion  of  the 
neural  axis,  but  not  in  the  part  corresponding  to  the  spinal 
cord,  is  laid  down  a  second  sheet  of  cortical  grey  matter. 
Between  this  and  the  primitive  grey  stem  are  interposed 
(a)  the  sheath  of  white  fibres  that  clothes  the  latter,  and 
connects  its  various  parts,  and  (6)  a  new  development  of 
white  matter  (corona  radiata,  cerebellar  peduncles),  which 


THE  CENTRAL  NERVOUS  SYSTEM  645 

serves  to  bring  the  cortex  into  relation  with  the  primitive 
axis,  and  through  it  with  the  rest  of  the  body. 

Although  there  are  histological  and  developmental  differ- 
ences between  the  cerebral  and  the  cerebellar  cortex,  we 
may,  for  some  purposes,  classify  them  together  as  cortical 
formations.  And  we  may  also  include  under  this  head  the 
corpora  striata,  which,  although  generally  grouped  with  the 
optic  thalami  and  the  other  clumps  of  grey  matter  at  the 
base  of  the  brain,  as  the  basal  ganglia,  are  to  be  regarded  as 
cortical  in  character.  As  we  mount  in  the  vertebrate  scale, 
the  cortex  formation  of  the  secondary  fore-brain  and  hind- 
brain  acquires  prominence. 

In  other  words,  the  grey  matter  developed  in  the  roof  of  the 
cerebral  vesicles  i  and  III.  (Fig.  218)  (the  grey  matter  of  the  cere- 
bral and  cerebellar  cortex)  comes  to  overshadow  the  superficial  grey 
matter  hitherto  present  only  in  the  roof  of  vesicle  II.  (in  the  corpora 
bigemina).  And  this  cortex  formation  becomes  larger  in  amount, 
and,  in  the  case  of  the  cerebral  grey  matter,  more  richly  convoluted, 
the  higher  we  ascend,  until  it  reaches  its  culmination  in  man.  As 
the  anterior  cerebral  vesicles  develop,  they  spread  continually  back- 
ward until  at  length  the  cerebral  hemispheres  cover  over,  and  almost 
completely  surround,  the  primary  fore-brain,  and  the  mid-  and  hind- 
brains,  so  that  the  anterior  portion  of  the  primitive  stem  comes, 
as  it  were,  to  be  invaginated  into  the  second  wider  tube  of  cortical 
grey  matter.  This  development  of  the  cortical  grey  substance  is 
accompanied  with  a  corresponding  development  of  white  fibres,  for 
an  isolated  nerve-cell  is  no  more  conceivable  than  a  railway-station 
the  track  from  which  leads  nowhere  in  particular,  or  a  harbour  on 
the  top  of  a  hill. 

But  it  is  to  be  particularly  observed  that  the  new  forma- 
tion does  not  supplant  the  old,  but  works  through  and 
directs  it.  The  nerve-cells  of  the  cortex  do  not  throw  out 
their  neurons  to  make  direct  junction  with  muscles  and 
sensory  surfaces.  Such  junction  the  cortex  finds  already 
established  between  the  primitive  cerebro-spinal  axis  and  the 
periphery.  It  joins  itself  on  by  new  white  substance  to  the 
cells  of  the  central  stem  ;  and  we  have  reason  to  believe 
that  no  fibres  pass  either  from  the  periphery  to  the  cortex, 
or  from  the  cortex  to  the  periphery,  without  being  broken  in 
the  cells  of  this  primitive  grey  tube. 

The  fibres  from  the  cortex  of  each  cerebral  hemisphere  (corona 
radiata),  radiating  out  like  a  fan  below  the  grey  matter,  are  gathered 


646  A  MANUAL  OF  PHYSIOLOGY 

together  into  a  compact  leash  as  they  sweep  down  through  the 
isthmus  of  the  brain  in  the  internal  capsule,  to  join  the  crura 
cerebri.  The  cortex  of  each  cerebellar  hemisphere,  and  the  ribbed 
pouch  of  grey  matter,  known  as  the  corpus  dentatum,  which  is  buried 
in  its  white  core,  are  also  connected  by  strands  of  fibres  with  the 
central  stem  and  the  cerebral  mantle.  The  restiform  body  or  inferior 
peduncle  brings  the  cerebellum  into  communication  with  the  spinal 
cord.  The  superior  peduncle  by  one  path,  and  the  middle  peduncle 
by  another,  connect  it  with  the  cerebral  cortex.  A  great  transverse 
commissure,  the  corpus  callosutn,  unites  the  cerebral  hemispheres 
across  the  middle  line,  while  transverse  fibres  that  pass  into  the  pons, 
as  well  as  other  fibres  that  break  through  the  middle  lobe  or  worm, 
form  a  similar  junction  between  the  two  hemispheres  of  the  cere- 
bellum. 

The  fibres  of  the  nervous  system  may  be  divided  into 
(i)  fibres  connecting  the  peripheral  organs  with  nerve-cells 
in  the  central  grey  axis ;  (2)  fibres  connecting  nerve-cells  in 
this  central  axis  with  cells  in  the  external  or  cortical  grey 
tube  ;  and  (3)  fibres  linking  cortex  with  cortex,  or  central 
ganglia  with  each  other.  Our  first  task  is,  therefore,  to  trace 
the  peripheral  nerves  to  their  cells  or  centres  in  the  nervous 
stem.  And  although  there  is  reason  to  believe  that  the 
whole  of  the  peripheral  nerves,  cerebral  and  spinal  (with 
the  exception  of  the  olfactory  and  optic,  which  are  rather 
portions  of  the  brain  than  true  peripheral  nerves),  form  an 
unbroken  morphological  series,  it  will  be  well  to  begin  with 
the  spinal  nerves,  since  their  motor  and  sensory  fibres  are 
gathered  into  different  and  definite  roots,  whose  course 
within  the  cord  is,  in  general,  more  easily  traced  than  the 
course  of  the  cerebral  root-bundles  within  the  brain. 
"*  Arrangement  of  the  Grey  and  White  Matter  in  the  Spinal 
Cord. — The  grey  matter  of  the  spinal  cord  is  arranged  on 
each  side  in  a  great  unbroken  column  of  roughly  crescentic 
section  (Plate  V.,  3),  joined  with  its  fellow  across  the  middle 
line  by  a  grey  bar  or  bridge,  which  springs  from  the  con- 
vexity of  the  crescent,  and  is  pierced  from  end  to  end  by 
the  central  canal.  The  anterior  horn  of  the  crescent, 
although  it  varies  in  shape  at  different  levels  of  the  cord,  is, 
in  general,  broad  and  massive  in  comparison  with  the 
slender  and  tapering  posterior  horn.  In  the  lower  cervical 
and  upper  dorsal  region  a  moulding  or  projection,  forming 


THE  CENTRAL  NERVOUS  SYSTEM 


647 


a  lateral  horn,  springs  from  the  fluted  outer  side  of  the  grey 
substance.  Within  the  grey  matter  nerve-cells  are  found, 
sometimes  so  regularly  arranged  that  they  form  veritable 
cellular  or  vesicular  strands.  Of  these  the  best  marked  are: 
(i)  The  tract  or  tracts  made  up  by  the  cells  of  the  anterior 
horn  (Fig.  223),  which  practically  run  from  end  to  end  of  the 


Enlargement 


Lum&ar 
Enlarement 


Sailings  Cervical 
mid  eus 


-Lateral  cell-column 
(column  cf  the  tnt£r- 
medtc-lateral  tract) 

-Stilling's  dorsal 
nucleu. 
Column 


in  te  rm  edtc  -I a  fa  r 
tract. 


FIG.  223. — DIAGRAM _OF  GREY  TRACTS  OF  CORD. 

cord,  swell  out  in  the  cervical  and  lumbar  enlargements, 
where  the  cells  are  very  numerous  and  of  great  size  (70  /-t  to 
140  fi  in  diameter),  and  contract  to  a  thin  thread  in  the 
thoracic  region,  where  they  are  relatively  few,  scattered,  and 
small.  (2)  Clarke's  column,  whose  cells  are  situated  at  the 
inner  side  of  the  root  of  the  posterior  horn  just  where  it 


648  A  MANUAL  OF  PHYSIOLOGY 

joins  on  to  the  grey  cross-bar.  It  gradually  increases  in 
size  from  above  downwards,  usually  appearing  first  at  the 
level  of  the  seventh  or  eighth  cervical  nerve,  attaining  its 
maximum  development  at  the  eleventh  or  twelfth  dorsal  and 
disappearing  altogether,  as  a  continuous  strand,  at  the  level 
of  the  second  or  third  lumbar  nerves.  The  so-called 
cervical  and  sacral  nuclei  of  Stilling,  however,  occupy  the 
same  position  towards  the  upper  and  lower  ends  of  the 
cord,  and  may  be  looked  upon  as  isolated  portions  of 
Clarke's  column.  (3)  A  tract  called  the  intermedia-lateral 
tract,  which  is  best  marked  in  the  thoracic  region,  but 
extends  also  down  into  the  lumbar  swelling  and  up  until  it 
blends  with  certain  cells  of  the  anterior  horn  of  the  cervical 
cord.  (4)  The  cells  of  the  posterior  horn  are  less  numerous 
and  smaller  than  those  of  the  anterior  horn.  Throughout 
the  whole  cord,  however,  two  small  groups  of  cells  may  be 
distinguished,  one  on  the  lateral  and  the  other  on  the  mesial 
side  of  the  isthmus  or  neck  of  the  horn  a  little  in  front  of 
(i.e.,  ventral  to)  the  edges  of  the  substance  of  Rolando. 

The  white  matter  of  the  cord  is  anatomically  divided  by 
the  position  of  the  nerve-roots  and  the  anterior  and  posterior 
fissures  into  three  columns  on  each  side  :  the  anterior,  lateral, 
and  posterior  columns  (Plate  V.,  3).  The  first  two  are  often 
grouped  together  as  the  antero-lateral  column.  In  the 
cervical  region  it  may  be  seen  with  the  microscope  that 
the  posterior  white  column  is  almost  bisected  by  a  septum 
running  in  from  the  pia  mater  towards  the  grey  commissure. 
The  inner  half  is  called  the  postero-median  column,  or 
column  of  Goll ;  the  outer  half  the  postero-external  column. 
or  column  of  Burdach  (Fig.  224).  No  localization  of  any 
of  the  other  conducting  paths  in  the  cord  is  possible  by 
anatomical  examination ;  but  by  means  of  the  develop- 
mental method  and  the  method  of  degeneration  the  columns 
of  Goll  and  Burdach  can  be  followed  throughout  the  cord, 
and  several  similar  areas  can  be  mapped  out.  We  shall 
only  mention  those  that  are  physiologically  the  most  im- 
portant. 

When  the  spinal  cord  is  divided,  and  the  animal  allowed 
to  survive  for  a  time,  certain  tracts  are  picked  out  by  the 


THE  CENTRAL  NERVOUS  SYSTEM 


649 


degeneration  of  their  fibres,  although  in  every  degenerated 
tract  some  fibres  remain  unaffected.  We  may  distinguish 
the  tracts  that  degenerate  above  the  lesion  (ascending  de- 
generation) from  those  that  degenerate  below  the  lesion 
(descending  degeneration). 

Ascending  Tracts. — Above  the  lesion  degeneration  is  found 
both  in  the  posterior  and  the  antero-lateral  columns. 
Immediately  above  the  section  nearly  the  whole  of  the 


Antero-lateral 

ground-bundle 


FIRST  CERVICAL. 


Direct  pyramidal 


SIXTH  CERVICAL. 


Antero-lateral,     ascend- 
ing and  descending 

Crossed  pyramidal 
Direct  cerebellar 


Postero-external  (Burdach's)   6UJ  C 
Postero-median  (Goll's)  6t/o  O 

SIXTH  DORSAL.  FOURTH  LUMBAR. 


FIG.  224.— DIAGRAMMATIC  SECTIONS  OF  THE  SPINAL  CORD  TO  SHOW  THE 
TRACTS  OF  WHITE  MATTER  AT  DIFFERENT  LEVELS. 


* 


'Sterior  column  is  involved.  Higher  up  the  degeneration 
clears  away  from  Burdach's  tract,  and,  shifting  inwards, 
comes  to  occupy  a  position  in  the  column  of  Goll.  In  the 
antero-lateral  column  two  degenerated  regions  are  seen,  both 
at  the  surface  of  the  cord,  one  a  compact,  sickle-shaped  area 
extending  forwards  from  the  neighbourhood  of  the  line  of 
entrance  of  the  posterior  roots,  and  the  other  an  area  of 
scattered  degeneration,  embracing  many  intact  fibres,  and 
completing  the  outer  boundary  of  the  column  almost  to  the 


650  A  MANUAL  OF  PHYSIOLOGY 

anterior  median  fissure.  The  compact  area  is  called  the 
direct  cerebellar  tract,  the  diffuse  area  the  (micro-lateral  ascend- 
ing tract,  or  tract  of  Gowers. 

Descending  Tracts. — When  the  cord  is  divided,  say  in  the 
upper  dorsal  or  cervical  region,  the  following  tracts  de- 
generate below  the  lesion : 

(1)  A  small  group  of  fibres  close  to  the  antero-median 
fissure,  which  has  received  the  name  of  the  direct  pyramidal 
tract — pyramidal,  because  higher  up  in  the  medulla  oblongata 
it  forms  part  of  the  pyramid  ;  direct,  because  it  does  not 
cross  over  at  the  decussation  of  the  pyramids,  but  continues 
down  on  the  same  side. 

(2)  A  tract  of  degenerated  fibres  in  the  posterior  part  of 
the  lateral  column.     This  is  the  lateral  or  crossed  pyramidal 
tract,  and  is  much  larger  than  the  direct.     In  the  medulla  it 
also  lies  within  the  pyramid,  but,  unlike  the  direct  pyramidal 
tract,  it   crosses  to  the  opposite  side  of  the   cord  at  the 
decussation. 

(3)  A   tract    of    scattered   degeneration   overlapping   the 
tract  of  Gowers,  and  called  the  antero-lateral  descending  tract. 

(4)  A  small  comma-shaped  island  of  degeneration  (comma 
tract)  can  be  followed  downwards  for  a  short  distance  in  the 
posterior  column. 

When  we  have  deducted  the  long  ascending  and  descend- 
ing tracts  which  have  been  described,  there  still  remains, 
both  in  the  anterior  and  in  the  lateral  column,  a  balance  of 
white  matter  unaccounted  for.  This  white  substance,  which 
does  not  degenerate  for  any  great  distance  either  above  or 
below  a  lesion,  is  called  the  antero-lateral  ground-bundle,  and 
lies  chiefly  in  the  form  of  an  incomplete  ring  around  the 
anterior  cornu.  It  is  believed  to  consist  of  fibres  which  run 
only  a  comparatively  short  course  in  the  cord,  and  serve  to 
connect  nerve-cells  at  different  levels. 

The  next  question  which  arises  is  :  How  are  the  long 
tracts  connected  below,  i.e.,  with  the  periphery,  and  above, 
i.e.,  with  the  higher  parts  of  the  central  nervous  system  ? 
The  answer  to  this  question,  partly  derived  from  clinical 
records  and  partly  from  experimental  results,  is  in  the  case 
of  some  of  the  tracts  unexpectedly  full  and  minute,  though 


THE  CENTRAL  NERVOUS  SYSTEM 


651 


meagre  in  regard  to  others.     But  to  render  it  intelligible  it 
is  necessary,  first  of  all,  to  describe  briefly — 

The  Arrangement  of  the  Grey  and  White  Matter  in  the  Upper 
Portion  of  the  Cerebro-spinal  Axis. — In  the  medulla  oblongata 
the  grey  and  white  matter  of  the  spinal  cord  is  rearranged, 
and,  in  addition,  new  strands  of  fibres  and  new  nuclei  of 
grey  substance  make  their  appearance.  Of  these  nuclei  the 
most  conspicuous  is  the  dentate  nucleus  of  the  inferior  olive, 
which,  covered  by  a  crust  of  white  fibres,  appears  as  a  pro- 
jection on  the  antero- 
lateral  surface  of  the  me- 
dulla. In  front  of  the 
olive,  between  it  and  the 
continuation  of  the  an- 
terior median  fissure,  is 
another  projection,  the 
pyramid,  which  looks  like 
a  prolongation  of  the  an- 
terior column  of  the  cord, 
but  is  made  up  of  very 
different  constituents. 
Dorsal  to  the  olive  is  the 
restiform  body  or  inferior 
peduncle  of  the  cere- 
bellum, and  behind  the 

restiform  body  lie  two  thin  columns,  the  funiculus  cuneatus, 
which  continues  the  postero-external  column  of  the  cord, 
and  the  funiculus^  graciligj  which  continues  the  postero- 
internal  column.  In  these  funiculi  are  contained  respec- 
tively the  nucleus  cuneatus  and  the  nucleus  gracilis.  The 
rearrangement  of  the  constituents  of  the  cord  is  due  mainly 
to  two  causes  :  (i)  The  opening  up  of  the  central  canal  to 
form  the  fourth  ventricle,  and  the  folding  out,  on  either  side, 
of  the  grey  matter  which  lies  posterior  to  it  in  the  cord 
(2)  the  breaking  up  of  the  grey  matter  of  the  anterior  horn 
by  strands  of  fibres  as  they  sweep  through  it  from  the  lateral 
pyramidal  tract  to  take  up  a  position  in  the  pyramid  of  the 
opposite  side  (decussation  of  the  pyramids). 

The    cerebro-spinal   axis   passes   up   from    the    medulla 


FIG.  225. — DIAGRAMMATIC  TRANSVERSE 
SECTION  OF  MEDULLA  OBLONGATA. 

a,  nucleus  gracilis  ;  bt  nucleus  cuneatus ; 
e,  internal  arcuate  fibres  crossing  the  middle 
line  from  a  and  b  to  the  fillet,  d ;  e,  anterior 
median  fissure. 


652  A  MANUAL  OF  PHYSIOLOGY 

through  the  pons,  encircled  and  traversed  by  the  transverse 
pontine  fibres  derived  from  the  middle  cerebellar  peduncle 
or  commissure,  which  enclose  everywhere  between  them 
numerous  collections  of  nerve-cells  (nuclei  pontis).  En- 
larged by  the  accession  of  many  of  these  fibres  which  come 
from  the  cortex  of  the  cerebellum  on  the  opposite  side,  as 
well  as  of  fibres  from  the  nuclei  of  the  cranial  nerves  that 
take  origin  in  this  neighbourhood  (fifth  and  eighth),  the 
central  nervous  stem  bifurcates  above  the  pons  into  the  two 
diverging  crura  cerebri.  From  each  crus  a  great  sheet  of 
fibres  passes  up  between  the  optic  thalamus  and  the  caudate 
nucleus  of  the  corpus  striatum  on  the  one  hand,  and  the 
globus  pallidus  of  the  lenticular  nucleus  on  the  other,  as 
the  internal  capsule,  from  which  they  are  dispersed,  in  the 
corona  radiata,  to  the  cerebral  cortex.  Both  in  the  upper 
part  of  the  pons  and  in  the  crus  a  ventral  portion,  or  crusta, 
containing  the  fibres  of  the  pyramidal  tract,  and  a  dorsal 
portion,  or  tegmentum,  can  be  distinguished,  the  line  of 
separation  being  marked  in  the  crus  by  a  collection  of  grey 
matter,  called  from  its  usual,  though  not  invariable,  colour 
the  substantia  nigra  (Fig.  22|).  A  portion  of  the  tegmentum 
is  continued  below  the  optic  thalamus. 

Coming  back  now  to  our  question  as  to  the  connec- 
tions of  the  long  tracts  of  the  cord,  let  us  consider,  first 
of  all, 

The  Connections  of  the  Postero-median  and  Fostero-external 
Columns. — When  a  single  posterior  root  is  divided,  say  in  the 
dorsal  region,  between  the  cord  and  the  ganglion,  its  fibres, 
as  we  have  already  seen  (p.  585),  degenerate  above  the 
section.  If  a  series  of  microscopic  sections  of  the  spinal 
cord  be  made,  well-marked  degeneration  will  be  found  at 
the  level  of  entrance  of  the  root  on  the  same  side  of  the 
cord,  while  below  that  level  there  will  be  only  a  few 
degenerated  fibres  in  the  comma  tract.  Immediately  above 
the  plane  of  the  divided  root  the  degeneration  will  be 
confined  to  Burdach's  column  and  to  its  external  border. 
Higher  up  it  will  be  found  in  the  internal  portion  of 
Burdach's  and  the  external  rim  of  Coil's  column.  Still 
higher  up  the  degenerated  fibres  will  be  confined  to  the 


THE  CENTRAL  NERVOUS  SYSTEM 


653 


postero-median  column ;  the  postero-external  will  be  entirely 
free  from  degeneration. 

When  a  number  of  consecutive  posterior  roots  are  cut,  the  whole 
of  the  postero-external  column  in  the  sections  immediately  above  the 
highest  of  the  divided  roots  will  be  found  occupied  by  degenerated 
fibres,  while  Coil's  column  may  be  free  from  degeneration,  or  de- 
generated only  at  its  outer  border.     Higher  up  degeneration  will  be 
found  to  have  involved  the  whole  of 
the  postero-median  column,  and  to 
have  cleared  away  altogether  from 
the  postero-external.     The  degene- 
ration in  the  column  of  Goll  may 
be  traced  along  the  whole  length  of 
the  cord  to  the  medulla,  although 
the  number   of  degenerated  fibres 
diminishes  as  we  pass  upward.   The 
explanation    of    these   appearances 
seems  to  be  as  follows.     It  may  be 
seen   in   preparations  of  the   cord 
impregnated     by    Golgi's     method 
that  the  fibres  of  the  posterior  roots 
soon  after  their  entrance  into  the 
cord  divide  into  two  processes,  one 
of   which   runs   up  and   the  other 
down  in  the  posterior  column,  or  in 
the  adjoining   portion  of  the  pos- 
terior horn.      From  both  of   these 
collaterals  are  given  off  at  intervals. 
The  descending  branches  probably 
run  downwards  only  for  a  short  dis- 
tance, and  the  degeneration  in  the  comma  tract  seen  after  section  of 
the  cord  may  be  due  to  the  division  of  these  branches.     Many  of  the 
ascending  branches  pass  up  for  a  short  distance  in  the  postero-external 
column,  sweeping  obliquely  through  it  to  gain  the  tract  of  Goll.     In  i 
this  tract  some  of  them  run  right  on  to  the  medulla  oblongata,  to  end 
in  a  collection  of  grey  matter,  the  nucleus  gracilis.     Others  must  end  j 
at  various  levels  in  the  cord,  their  collaterals,  and  ultimately  the  main 
branches  themselves,  coming  into  relation  with  nerve-cells  in  the 
grey  matter.     When  the  cervical  posterior  roots  are  cut,  many  of  the\ 
degenerated  fibres  remain  in  Burdach's  column  up  to  the  medulla,  j 
where  they  make  junction  with  the  nucleus  cuneatus.     In  the  pos- : 
terior  column,  then,  the  fibres  of  the  posterior  roots  which  do  not 
suffer  interruption  in  nerve-cells  in  the  spinal  cord  are  arranged  in 
layers,  the  fibres  from  the  lower  roots  being  nearest  the  median 
fissure,  and  those  from  the  higher  roots  farthest  away  from  it.    Other 
collaterals  from  the  posterior  root-fibres,  and  many  of  the  root-fibres 
themselves,  run  into  the  anterior  horn ;  some  pass  into  the  posterior 
horn,   and   doubtless    come   into   relation    with  its    scattered  cells. 


FIG.    226.— POSTERIOR    ROOTS 

ENTERING     SPINAL    CORD    (at    the 

left  of  the  figure).  (From  a  prepara- 
tion stained  with  aniline  blue- 
black.) 


654  A  MANUAL  OF  PHYSIOLOGY 

Other  collaterals  cross  the  middle  line  in  the  posterior  commissure 
and  end  in  the  grey  matter  of  the  opposite  side. 

We  may,  therefore,  conclude  without  hesitation  that  some 
of  the  fibres  of  the  posterior  roots  ascend  to  the  medulla  in 
the  posterior  column  of  the  cord  without  making  junction 
with  any  cells  until  they  reach  the  gracile  and  cuneate 
nuclei,  where  they  end  by  breaking  up  into  terminal  brushes 
of  fibrils.  The  cell -bodies  of  these  neurons  lie  in  the 
posterior  root-ganglia. 

Connections  of  the  Direct  Cerebellar  Tract. — Since  the  direct 
cerebellar  tract  does  not   degenerate  after   section  of  the 
posterior  nerve-roots,  but  does  degenerate  above  the  level 
of  the  lesion  after  section  of  the  spinal  cord,  the  nerve-cells 
of  which  its  fibres  are  the  neurons  must  be  situated  some- 
where or  other  in  the  cord.     The  cells  of  the  anterior  horn 
are  known,  in  great  part  at  any  rate,  to  be  connected  with 
other  tracts,  so  that  there  are  left  over,  to  all  intents  and 
purposes,  only  the  scattered  cells  of  the  posterior  horn  and 
the  vesicular  column  of  Clarke.     Now,  it  has  been  observed 
that  the  column  of  Clarke  first  becomes  prominent  in  the 
lower  dorsal  region,  and  that  in  this  same  region  the  direct 
cerebellar  tract  begins.     Atrophy  of  the  cells  of  Clarke's 
column    has    sometimes   been   shown    to   accompany   de- 
generation of  the  direct   cerebellar  fibres.     Further,   axis- 
cylinder  processes  may  be  seen  sweeping  out  from  Clarke's 
column  in  the  direction  of  the  direct  cerebellar  tract,  and 
although,  in  all  probability,  nobody  has  as  yet  been  able 
definitely  to  follow  any  of  those  axis-cylinder  processes  into 
fibres  of  the  tract,  the  evidence  when  put  together  is  pretty 
strong  that  the  cells  of  Clarke's  column,  or  some  of  them 
at  least,   are  their  cells  of  origin.     Clarke's  cells  are  sur- 
rounded by  a  fibrillar  network  which  seems  to  represent  the 
terminations  of  some  of  the  posterior  root-fibres  and  of  their 
collaterals.     The  direct  cerebellar  tract  runs  right  up  to  the 
cerebellum  through  the  restiform  body,  without  crossing  and 
without  being  further  interrupted  by  nerve-cells.     The  fibres 
of  the  restiform  body  end  partly  in  the  dentate  nucleus  of^ 
the  cerebellum,  partly  in  the  vermis.  {^}  -"^  ^  <\« 

Connections  of  the  Antero-lateral  Ascending  Tract. — It  is  not 


THE  CENTRAL  NERVOUS  SYSTEM  655 

known  with  any  certainty  with  what  cells  in  the  spinal  cord 
this  tract  is  connected.  All  we  can  say  is  that  none  of  its 
fibres  can  come  directly  from  the  posterior  nerve-roots,  since 
no  degeneration  is  seen  in  the  tract  on  section  of  the  roots 
alone. 

It  passes  up  through  the  medulla,  where  it  perhaps  makes  junction  i 
with  the  cells  of  the  lateral  nucleus,  a  collection  of  grey  matter  in 
the  lateral  portion  of  the  spinal  bulb.     Thence  through  the  formatio 
reticularis  it  is  supposed  to  reach  the  pons,  and,  turning  back  through 
the  superior  peduncle,  ends  in  the  cerebellum. 

The  formatio  reticularis  is  the  mosaic  of  grey  and  white  matter 
formed  in  the  medulla  by  the  interlacing  of  longitudinal  and  trans- 
verse fibres  with  each  other  and  with  the  relics  of  the  grey  matter  of 
the  anterior  horn.  Its  longitudinal  fibres  are  derived  from  the  fillet 
and  from  the  remains  of  the  anterior  and  lateral  columns  after  the 
direct  and  crossed  pyramidal  tracts  have  taken  up  their  position 
in  the  pyramid  and  the  direct  cerebellar  tract  has  passed  into  the 
restiform  body.  The  antero-lateral  ascending  tract  seems  to  pass 
bodily  into  the  formatio  reticularis  and  to  form  part  of  its  longitudinal 
fibres.  The  transverse  fibres  sweep  in  bold  curves  towards  the  raphe 
from  the  gracile  and  cuneate  nuclei  and  the  dentate  nucleus  of  the 
olive.  The  reticular  formation  occupies  the  whole  of  the  anterior 
and  lateral  portions  of  the  medulla  behind  the  pyramids  and  olivary 
bodies,  and  is  continued  upwards  in  the  dorsal  portion  of  the  pons 
and  crura. 

Through  the  gracile  and  cuneate  nuclei,  but  particularly 
the  latter,  the  postero-internal  and  postero- external  columns 
of  the  cord  are  further  connected  on  the  one  hand  with  the '' 
cerebellar  hemisphere  by  fibres  passing  up  in  the  restiform 
body  of  the  same,  and  to  a  smaller  extent  of  the  opposite  side, 
and  on  the  other  hand  with  the  fillet  by  fibres  which  sweep 
in  wide  arches  (internal  arcuate  fibres)  across  the  mesial 
raphe  to  the  opposite  side.  The  fillet  is  a  well-marked 
bundle  which  is  formed  from  those  fibres  and  lies  imme- 
diately behind  the  pyramid.  Receiving  fibres  from  other 
sources  on  its  way,  and  also  giving  off  fibres,  it  runs  upwards 
in  the  dorsal  or  tegmental  portion  of  the  pons  and  crura 
cerebri,  posterior  to  the  formatio  reticularis,  with  the  longi- 
tudinal fibres  of  which  it  blends  in  the  region  below  the 
optic  thalamus.  One  well-marked  strand  of  these  longi- 
tudinal fibres  receives  the  name  of  the  posterior  longitudinal 
bundle  (Fig.  227).  In  the  subthalamic  region  and  in  the 


656  A  MANUAL  OF  PHYSIOLOGY 

optic  thalamus  itself  the  neurons  of  the  fillet,  whose  cells 
of  origin  lie  in  the  gracile  and  cuneate  nuclei,  end  for  the 
most  part.  Their  terminal  brushes  come  into  relation  with 
nerve-cells  whose  neurons,  entering  into  the  corona  radiata, 
continue  the  path  to  the  cerebral  cortex.  A  few  of  the  fibres 
of  the  fillet  may,  however,  pass  straight  on  to  the  cortex 
without  being  interrupted  in  nerve-cells  (Monakow). 

Connections  of  the  Pyramidal  Tracts. — When  the  cortex 
around  the  fissure  of  Rolando  is  destroyed  by  disease  in 
man,  or  removed  by  operation  in  animals,  it  is  found  that  in 

1 


FIG.  227.— DIAGRAMMATIC  TRANSVERSE  SECTION  OF  CRURA  CEREBRI  AND 
AQUEDUCT  OF  SYLVIUS. 

a,  anterior  corpora  quadrigemina ;  b,  aqueduct ;  c,  red  nucleus ;  d,  fillet ;  e,  sub- 
stantia  nigra  ;  /,  pyramidal  tract  in  the  crusta  of  the  crura  cerebri  ;  g,  fibres  from 
frontal  lobe  of  cerebrum  ;  h,  fibres  from  temporo-occipital  lobe ;  i,  posterior  longi- 
tudinal bundle. 

a  short  time  degeneration  has  taken  place  in  the  fibres  of  the 
corona  radiata  which  pass  off  from  this  area.  The  degenera- 
tion can  be  followed  down  through  the  genu  and  the  anterior 
two-thirds  of  the  posterior  limb  of  the  internal  capsule 
(Fig.  2*l|),  and  the  crusta  of  the  cerebral  peduncle  of  the 
corresponding  side  into  the  medulla  oblongata.  Below  the 
decussation  of  the  pyramids  it  is  found  that  the  degenera- 
tion, has  involved  the  two  pyramidal  tracts,  and  only  these — 
the  crossed  pyramidal  tract  on  the  side  opposite  the  cortical 
lesion,  the  direct  pyramidal  tract  on  the  same  side — and 


THE  CENTRAL  NERVOUS  SYSTEM  657 

that  the  cross-section  of  the  two  degenerated  tracts  goes 
on  continually  diminishing  as  we  pass  down  the  cord.  (We 
overlook,  for  the  moment,  in  the  interest  of  simplicity  of 
statement,  the  fact  that  in  the  monkey  and  in  man,  at  any 
rate,  some  degenerated  fibres  may  be  found  in  the  crossed 
pyramidal  tract  on  the  same  side  as  the  lesion.)  This  is 
proof  positive  that  the  trophic  cells  of  these  tracts  are 
situated  in  the  cerebral  cortex.  The  fact  that  the  degenera- 
tion does  not  spread  to  the  anterior  roots  is  proof  probable 
that  nerve-cells  intervene  between  the  pyramidal  fibres  and 
the  root-fibres.  The  results  both  of  normal  and  morbid 
histology  complete  the  proof,  and  enable  us  to  identify  the 
cells  of  the  anterior  horn  as  the  cells  in  question.  For 

(1)  Axis-cylinder  processes  have  been  actually  observed 
passing  out  from  certain  of  the  so-called  motor  cells  of  the 
anterior  horn  to  become  the  axis-cylinders  of  fibres  of  the 
anterior  root. 

(2)  In    the    pathological    condition    known   as   anterior 
poliomyelitis,  the  cells  of  the  anterior  horn  degenerate,  and 
so  do  the  anterior  roots  of  the  affected  region,  the  motor 
fibres  of  the  spinal  nerves,  and  the  muscles  supplied  by  them. 

(3)  An  enumeration  has  been  made  in  a  small   animal 
{frog)  of  the  cells  of  the  anterior  horn  and  of  the  anterior 
root-fibres,  and  it  has  been  found  that  the  numbers  agree  in 
a  remarkable  manner.     From  all  this  it  cannot  be  doubted 
that  most,  at  any  rate,  of  the  cells  of  the  anterior  horn  are 
connected  with  fibres  of  the  anterior  root.     But  since  the 
number  of  fibres  in  the  pyramidal  tracts  falls  far  short  of 
the  number  of  cells  in  the  anterior  horn,  and  of  the  number 
of  fibres  in  the  anterior  roots,  it  is  necessary  to  assume  that 
one  pyramidal  fibre  may  be  connected  with  several  cells. 

Connections  of  the  Antero-lateral  Descending  Tract. — Degenera- 
tion is  caused  in  this  tract  by  a  lesion  in  the  cerebellum  on  the  same 
side.  The  degeneration  lessens  as  we  pass  down  the  cord.  From 
this  we  conclude  that  the  trophic  cells  of  the  antero-lateral  descending 
tract  lie  in  the  cerebellum.  It  is  said  that  some  degenerated  fibres 
are  found  in  the  anterior  roots.  This  would  point  to  a  direct  con- 
nection between  the  cortex  of  the  cerebellum  and  the  motor  nerves, 
but  recent  observations,  on  the  whole,  cast  doubt  upon  the  state- 
ment. The  descending  antero-lateral  tract  passes  down  from  the 
cerebellum  in  the  restiform  body. 

42 


658  A  MANUAL  OF  PHYSIOLOGY 

Thus  far,  then,  we  have  been  able  to  map  out  two  great 
paths  from  the  cerebral  cortex  to  the  periphery,  one  efferent, 
the  other  afferent. 

(1)  The  great  efferent  or  motor  path,  which,  starting  in  the 
cortex  around  the  fissure  of  Rolando,  and  sweeping  down 
the  broad  fan  of  the  corona  radiata,  passes  through  the 
narrow  isthmus  of  the  posterior  limb  of  the  internal  capsule 
into  the  crusta  of  the  crus  cerebri,  and   thence   into   the 
pyramid  of  the  bulb.     Here  the  greater  part  (usually  about 
90   per   cent.)   of  the  fibres    decussate,   appearing   in   the 
cervical  cord  as  the  massive  crossed  pyramidal  tract  of  the 
opposite  side.     A  few  (usually  about  10  per  cent.)  remain 
on  the  same  side,  as  the  slender  direct  pyramidal  tract ;  but 
the  breadth  of  this  tract  constantly  diminishes  as  its  fibres 
continue  to  decussate  across  the  anterior  white  commissure, 
and  to  reinforce  the  crossed  tract  of  the  opposite  side.     The 
fibres  of  this  crossed  tract  are,  in  their  turn,  continually 
passing  off  into  the  grey  matter  of  the  anterior  horn,  where 
they  break  up  into  fibrils,  and  thus  make  connection  (physio- 
logical if  not  anatomical)  with  the  fine  nerve-plexus  in  the 
vicinity  of  the  cells,  whose  axis-cylinder  processes  enter  the 
anterior  roots  of  the  spinal  nerves.     The  losses  which  it 
suffers  as  it  passes  along  the  cord  may  be  partly  compen- 
sated by  the  bifurcation  of  some  of  its  fibres  (geminal  fibres), 
but  ultimately  the  whole  tract  makes  junction  with  the  grey 
matter,  and  dwindles  away  as  the  lumbar  region  is  reached 
(Fig.  224).     It  has  been  asserted  that  on  their  way  down 
the  cord  the  two  crossed  pyramidal  tracts  exchange  some 
fibres  with  each  other  (recrossed  fibres) ;  and  it  was  sup- 
posed that  this   would    explain   the  escape   in   hemiplegia 
(paralysis  of  one  side  of  the  body)  of  those  muscles  which 
are  accustomed  to  work  with  the  corresponding  muscles  on 
the  opposite  side.     But  although  there  is  no   doubt  that 
such   muscles   are   innervated   to   some  extent   from   both 
cerebral  hemispheres,  it  is  more  probable  that  this  is  due  to 
uncrossed  (homolateral)  than  to  recrossed  fibres. 

(2)  A  great  afferent  or  sensory  path  by  which  some,  at  least, 
of  the  impulses  carried  up  through  the  posterior  roots  of  the 
spinal  nerves,  after  passing  through  various  relays  of  nerve- 


THE  CENTRAL  NERVOUS  SYSTEM  659 

cells,  reach  the  cortex  of  the  cerebellum  ;  or  the  upper 
portions  of  the  central  grey  tube,  the  corpora  quadrigemina 
and  optic  thalamus ;  or,  finally  (both  indirectly  and  by  a 
more  direct  route  which  certain  fibres  of  the  fillet  and  the 
formatio  reticularis  follow  through  the  tegmentum  and  the 
posterior  limb  of  the  internal  capsule  behind  the  motor 
fibres),  the  cerebral  cortex  itself. 

The  efferent  path  from  the  cortex  of  the  brain  is  broken 
by  but  one  relay  of  nerve-cells,  the  motor  cells  of  the  anterior 
horn.  The  afferent  path  is  interrupted  by  at  least  two 
relays,  one  in  the  ganglion  on  the  posterior  root,  another  in 
the  medulla ;  and  on  some  of  the  routes  another,  or  even 
more  than  one,  between  the  medulla  and  the  cortex. 

Connections  of  the  Grey  Matter  of  the  Cerebellum  with  the 
Periphery  and  other  Parts  of  the  Central  Nervous  System. — 
Numerous  as  are  the  nervous  ties  of  the  cerebral  cortex,  those  of  the 
grey  matter  of  the  cerebellum  are,  in  proportion  to  its  mass,  still 
more  extensive,  and  perhaps  not  less  important.  Speaking  broadly, 
we  may  say  that  the  restiform  body  connects  chiefly  the  dentate 
nucleus  and  the  grey  matter  of  the  worm  with  both  sides  of  the 
spinal  cord,  and  through  it  with  the  periphery.  The  middle 
peduncle  is  in  the  main  a  link  between  the  cerebellar  cortex  and  the 
cerebral  cortex  of  the  opposite  side,  through  the  relay  of  the  pontine 
grey  matter,  and,  to  a  smaller  extent,  a  link  between  the  cortical 
matter  of  the  two  cerebellar  hemispheres.  The  superior  peduncle 
connects  mainly  the  dentate  nucleus  of  one  side  with  the  cortex  of 
the  opposite  cerebral  hemisphere  through  the  red  nucleus  of  the 
tegmentum  of  the  crus  cerebri  on  the  opposite  side.  Through  the 
restiform  body  afferent  impulses  pass  up  to  the  cerebellum.  From 
the  cerebellum  they  may  proceed  to  the  cerebrum.  So  that  the 
path  by  the  restiform  body,  dentate  nucleus,  and  superior  peduncle 
may  form  an  alternative  route  for  afferent  impressions  passing  from 
the  periphery  to  the  great  brain — a  path  broken  by  at  least  four 
relays  of  nerve-cells.  The  cerebellar  cortex  may  be  connected  by  an 
efferent  path  through  the  restiform  body  and  the  descending  antero- 
lateral  tract  with  the  motor  roots  of  the  same  side.  An  uncrossed 
connection  also  exists  between  the  cerebellum  and  the  vestibular 
branch  of  the  auditory  nerve,  through  one  of  its  nuclei  of  origin,  and 
possibly  between  it  and  other  cranial  nerves,  such  as  the  optic  and 
trigeminal. 

The  Internal  Capsule. — We  must  now  learn  that  the  internal 
capsule  embraces  other  fibres  than  those  which  pass  down 
into  the  spinal  cord  as  the  pyramidal  tracts,  and  up  from  it 
as  the  afferent  tegmental  path.  In  the  first  place,  it  contains 

42 — 2 


660  A  MANUAL  OF  PHYSIOLOGY 

numerous  fibres  running  from  the  Rolandic  area,  and 
destined  to  make  connection  with  the  motor  nuclei  of  the 
cranial  nerves  in  the  grey  matter  underlying  the  aqueduct 
of  Sylvius  and  the  fourth  ventricle. 

The  cranial  and  spinal  fibres,  indeed,  form  but  one  com- 
pact bundle  (pyramidal  tract)  in  their  passage  through  the 
corona  radiata  and  internal  capsule,  the  knee  of  which  is 
occupied  by  the  former,  the  posterior  limb  by  the  latter,  and 
may  be  followed  as  a  distinct  strand  through  the  middle  of 


, 


FIG.  228.— DIAGRAMMATIC  HOOTZONTAL  SECTION  OF  LEFT  HALF  OF  BRAIN 
TO  SHOW  INTERNAL  CAPSULE. 

the  crusta  into  the  pons.     Here  the  fibres  for  the  nuclei  of 
the  cranial  nerves  decussate. 

But  we  have  not  yet  exhausted  the  constituents  of  the 
internal  capsule.  Two  great  cones  of  fibres  sweep  down 
into  it,  one  from  the  frontal,  the  other  from  the  occipital 
and  temporal  portions  of  the  cerebral  cortex.  The  first 
passes  through  its  anterior  limb,  the  second  behind  the 
sensory  path  in  its  posterior  limb.  Running  on  through  the 
crusta  of  the  cerebral  peduncle  (Fig.  227),  the  frontal  tract 


THE  CENTRAL  NERVOUS  SYSTEM 


661 


internal,  the  occipito-temporal  external,  they  end  in  the  grey 
matter  of  the  pons,  and  probably  serve  as  one  segment  of  an 
extensive  commissural  connection  between  the  cerebral  and 
the  cerebellar  cortex  of  the  opposite  side,  the  other  segment 
being  formed  by  fibres  which  reach  the  pons  through  the 
middle  cerebellar  peduncle.  Although  their  further  con- 
nections are  unknown,  it  is  evident  that  the  junction  of  the 
cerebral  cortex  with  this  pontine  grey  matter,  through  and 
into  which  so  many  nerve-tracts  pass,  multiplies  the  number 


FIG.  229. — ASSOCIATION  FIBRES  (AFTER  STARR). 

Cerebral  hemisphere  seen  from  the  side.  A,  A.  association  fibres  between  adjacent 
convolutions  ;  B,  between  frontal  and  occipital  lobes  ;  C.  cingulum,  connecting  frontal 
and  temporo-sphenoidal  lobes  ;  D,  uncinate  fasciculus  ;  E,  inferior  longitudinal  bundle ; 
O.T.,  optic  thalamus  ;  C.N.,  caudate  nucleus, 

of  possible  routes  by  which  impulses  may  travel  between  one 
part  of  the  brain  and  another.  The  pons  itself  is  in  part  a 
transverse  commissure  between  the  two  halves  of  the  cere- 
bellum, as  the  corpus  callosum  is  between  the  two  cerebral 
hemispheres.  And  intertwined  in  the  corona  radiata  with 
the  callosal  fibres  are  other  systems,  of  which  it  is  especially 
necessary  to  mention  the  fibres  that  link  nearly  every  part  of 
the  cerebral  cortex  with  the  optic  thalamus.  These  fibres 
pass  from  the  frontal  and  parietal  regions  through  the 
anterior,  and  from  the  occipital  region  through  the  posterior 
border  of  the  internal  capsule,  those  from  the  occipital 
cortex  forming  what  is  called  the  optic  radiation.  The 
thalamus  is  also  connected  with  the  cortex  of  the  temporal 


662  A  MANUAL  OF  PHYSIOLOGY 

lobe,  with  the  cerebellum,  and  through  the  fillet  with  the 
posterior  part  of  the  tegmental  system,  the  medulla  oblon- 
gata  and  the  spinal  cord  (p.  656). 

We   have   purposely  omitted  to  enumerate  many  other 
paths  by  which  the  various  tracts  of  grey  matter  in  the  brain 
are  brought  into  communication  with  each  other,  and  our 
knowledge  of  such  connections  is  constantly  augmenting. 
When  we  add  that  not  only  are  the  cerebral  hemispheres 
united   by  many  ties  to   the  subordinate   portions   of  the 
cerebro-spinal  axis  and  to  each  other,  but  that  cortical  areas 
of  one  and  the  same  hemisphere  are  in  communication  by 
short  connecting  loops  of  'association'  fibres  (Fig.  229),  it  will 
be  seen  that  the  linkage  of  the  various  parts  of  the  central 
nervous  system  is  extremely  complex;  that  an  excitation, 
blocked  out  from  one  path,  may  have  the  choice  of  many 
alternative  routes;    and  that  the  apparent  simplicity  and 
isolation  of  the  pyramidal  tracts  must  not  be  allowed  too  far 
to  govern  our  views  of  the  possibilities  open  to  a  nervous 
impulse  once  it  has  been  set  going  in  the  labyrinth  of  the 
nervous  network.     Nor  is  it  only  by  the  white  fibres  that 
nervous  impulses  can  be  conducted.     There  is  the  clearest 
evidence  that  they  can  also  spread  along  continuous  sheets 
of  grey  matter.     And  the   actual  route  taken  by  a  given 
impulse  is,  in  all  probability,  determined  as  much  by  mole- 
cular conditions,  particularly  in  the  terminal  fibrils  of  the 
neurons  and  dendrons  and  in  the  substance,  whatever  it 
may  be,  which  intervenes  between  them,  as  by  anatomical 
relations ;  so  that  a  road  open  at  one  moment  may  be  closed 
at  another.     We  may  suppose  that  the  greater  the  numb< 
of  connections   between  the  cells  of  the   central   nervous 
system,  the  greater  is  the  complexity  of  the  processes  whicl 
may  be  carried  on  within  it.     And,  indeed,  comparison  oi 
the  brains  of  different  animals  shows  us  that  it  is  not  so 
much  by  excess  in  the  quantity  of  grey  matter  as  by  the 
increased   complexity  of  linkage,  that  a   highly  developed 
brain  differs  from  a  brain  of  lower  type ;   the  higher  the 
brain,  the  smaller  is  the  proportion  of  grey  to  white  sub- 
stance, but  the  greater  is   the  number  of  possible  paths 
between  one  nerve-cell  and  another. 


THE  CENTRAL  NERVOUS  SYSTEM  663 

II.  Functions  of  the  Central  Nervous  System. 

Much  of  our  knowledge  of  the  functions  of  the  central 
nervous  system  and  of  its  divisions  has  been  gained  by  the 
removal  or  destruction  of  more  or  less  extensive  tracts  of 
nervous  substance,  or  the  cutting  off  of  connection  between 
one  part  and  another.  But  it  is  well  to  warn  the  reader  at 
the  very  outset  that  in  no  other  part  of  physiology  is  such 
caution  required  in  making  deductions  as  to  the  working 
of  the  intact  mechanism  from  the  phenomena  which  mani- 
fest themselves  after  such  lesions. 

In  the  first  place,  every  operation  of  any  magnitude  on  the  brain 
or  cord  is  immediately  followed  by  a  depression  of  the  functional 
power  of  the  nervous  tissue,  a  depression  which  may  extend  far  from 
the  actual  seat  of  injury  and  manifest  itself  by  various  phenomena,  nj 
which  are  grouped  together  under  the  name  of  '  shock.'  Thus,  when  x"^ 
the  spinal  cord  of  a  dog  is  divided,  e.g.,  in  the  dorsal  region,  all  power, 
all  vitality,  one  might  almost  say,  seems  to  be  for  ever  gone  from  the 
portion  of  the  body  below  the  level  of  the  section.  The  legs  hang 
limp  and  useless.  Pinching  or  tickling  them  calls  forth  no  reflex 
movements.  The  vaso-motor  tone  is  destroyed,  and  the  vessels 
gorged  with  blood.  The  urine  accumulates,  overfills  the  paralyzed 
bladder,  and  continually  dribbles  away  from  it.  The  sphincter  of 
the  anus  has  lost  its  tone,  and  the  faeces  escape  involuntarily.  And 
if  we  were  to  continue  our  observations  only  for  a  short  time,  a  few 
hours  or  days,  we  should  be  apt  to  appraise  at  a  very  low  value  the 
functions  of  that  part  of  the  cord  which  still  remains  in  connection 
with  the  paralyzed  extremities.  But  these  symptoms  are  essentially 
temporary.  They  are  the  results  of  shock ;  they  are  not  true  *  defi- 
ciency '  phenomena.  And  if  we  wait  for  a  time,  we  shall  find  that 
this  torpor  of  the  lower  dorsal  and  lumbar  cord  is  far  from  giving  a 
true  picture  of  its  normal  state ;  that,  cut  off  as  it  is  from  the  in- 
fluence of  the  brain,  it  is  still  endowed  with  marvellous  powers.  If 
we  wait  long  enough,  we  shall  see  that,  although  voluntary  motion 
never  returns,  reflex  movements  of  the  hind-limbs,  complex  and 
co-ordinated  to  a  high  degree,  are  readily  induced.  Vaso-motor 
tone  comes  back.  The  functions  of  defaecation  and  micturition  are 
normally  performed.  Erection  of  the  penis  and  ejaculation  of  the 
semen  take  place  in  a  dog.  A  man  with  complete  paralysis  below 
the  loins  and  destitute  of  all  sensation  in  the  paralyzed  region  has 
been  known  to  become  a  father  (Brachet).  Pregnancy  carried  on  to 
labour  at  full  term  has  been  observed  in  a  bitch  whose  cord  was 
completely  divided  above  the  lumbar  enlargement. 

We  cannot  doubt  that  the  spinal  cord  takes  an  important  share  in 
this  recovery  of  function.  But  here  again  it  would  be  erroneous  to 
conclude  that  everything  is  due  to  the  cord.  For  Goltz  and  Ewald 


664  ^  MANUAL  OF  PHYSIOLOGY 

have  been  able  to  keep  dogs  alive  for  long  periods  after  preliminary 
section  of  the  cord  in  the  cervical  region  and  subsequent  removal  of 
large  portions  of  it.  They  find  that  even  after  destruction  of  the 
lumbar  and  sacral  regions  of  the  cord  the  external  sphincter  of  the 
anus,  striped  and  even  voluntary  muscle  though  it  be,  regains  its 
tone,  although  it  is  temporarily  lost  after  the  first  cervical  section. 
The  bladder  ultimately  recovers  the  power  of  emptying  itself  spon- 
taneously and  at  regular  intervals.  A  pregnant  bitch  in  which  the 
lumbar  enlargement  and  the  whole  cord  below  it  to  the  cauda  equina 
had  been  removed,  and  therefore  all  the  nerve-roots  supplying 
fibres  to  the  uterus  cut,  whelped  in  a  normal  manner,  and  the 
corresponding  mammary  glands  behaved  exactly  as  the  rest.  Diges- 
tion went  on  as  usual  when  practically  nothing  of  the  cord  except 
its  cervical  portion  was  left.  Certain  vaso-motor  phenomena  were 
also  observed  which  suggest  that  the  sympathetic  system,  inde- 
pendently of  the  cerebro-spinal  system,  is  itself  possessed  of  regula- 
tive powers. 

Secondly,  we  must  not  run  into  the  opposite  error,  and  assume, 
without  proof,  that  all  the  functions  which  the  brain  or  cord  is  capable 
of  manifesting  under  abnormal  circumstances  are  actually  exercised 
by  either  when,  under  ordinary  conditions,  it  is  working  along  with 
and  guiding,  or  being  guided  by,  the  other.  For  example,  in  many 
animals  the  reflex  powers  of  the  cord  are,  if  not  increased,  at  all 
events  more  freely  exercised  when  the  controlling  influence  of  the 
higher  centres  has  been  cut  off  than  when  the  central  nervous  system 
is  intact. 

Thirdly,  there  is  another  class  of  phenomena  which  we  must  make 
allowance  for,  and  perhaps  more  frequently  in  the  case  of  patho- 
logical lesions  in  man  than  in  experimental  lesions  in  the  lower 
animals.  This  is  the  class  of  '  irritative '  phenomena.  The  irritation 
set  up  by  a  blood  clot  or  a  collection  of  pus,  or  in  any  other  way,  in 
a  wound  of  the  grey  or  white  matter,  may  cause  a  stimulation  of 
nervous  tracts  by  which,  for  a  time,  the  '  deficiency '  effects  of  the 
lesion  may  be  masked. 

In  the  fourth  place,  we  must  not  hastily  conclude  that  when  no 
obvious  deficiency  seems  to  follow  the  removal  of  a  portion  of  the 
central  nervous  system,  the  function  of  that  portion  must  necessarily 
be  of  such  a  nature  as  to  give  rise  to  no  objective  signs.  For  we 
have  reason  to  believe  that,  to  a  certain  extent,  the  function  of  one 
part  may,  in  its  absence,  be  vicariously  performed  by  another. 

Bearing  in  mind  the  cautions  we  have  just  been  empha- 
sizing, we  may  broadly  distinguish  between  the  functions  of 
the  cord  (including  the  bulb)  and  those  of  the  brain  proper 
by  saying  that  the  cord  is  essentially  the  seat  of  reflex 
actions,  the  brain  the  seat  of  automatic  actions  and  con- 
scious processes.  But  neither  of  these  conceptions  is 


THE  CENTRAL  NERVOUS  SYSTEM  665 

entirely  correct.  Both  err  by  defect  and  by  excess.  The 
brain,  it  is  true,  is  pre-eminently  automatic.  The  move- 
ments which  are  started  in  the  grey  matter  of  the  cerebral 
cortex  are  pre-eminently  voluntary  (p.  704),  but  we  cannot 
deny  to  the  brain  the  possession  of  reflex  powers  as  well. 
The  movements  in  which  the  only  neive  centres  concerned 
are  those  of  the  spinal  cord  are  above  all  reflex  (p.  674). 
But  some  of  its  centres,  and  especially  those  lying  in  the 
medulla — for  example,  the  respiratory  centre — are  perhaps, 
much  as  they  are  influenced  by  afferent  impulses,  capable  of 
discharging  automatic  impulses  too.  And  while  conscious- 
ness is  certainly  bound  up  with  the  integrity  of  the  brain, 
and  in  all  the  higher  mammals  is  probably  associated  with 
cerebral  activity  alone,  it  has  been  plausibly  maintained 
that  the  spinal  cord,  even  of  such  an  animal  as  the  frog,  is 
also  endowed  with  something  which  might  be  called  a  kind 
of  hushed  consciousness.  If  this  is  so  for  the  frog,  with  its 
distinct  though  relatively  ill-developed  cerebral  hemispheres, 
it  must  be  still  more  likely  in  the  case  of  fishes  and  animals 
below  them,  which  are  practically  devoid  of  a  cerebral  cortex 
altogether. 

Functions  of  Spinal  Cord  (including  Medulla  Oblongata). 

The  functions  of  the  spinal  cord  may  be  classified  thus  : 

1.  The  conduction  of  impulses  set  up  elsewhere — either 

in  the  brain  or  at  the  periphery. 

2.  The  modification  of  impulses  set  up  elsewhere  (reflex 

action). 

3.  The  origination  of  impulses  (?). 

i.  Conduction  of  Nervous  Impulses  by  the  Cord. — The  old 
controversy  as  to  whether  the  white  fibres  of  the  spinal 
cord  are  directly  excitable  may  be  considered  as  definitely 
settled  in  the  affirmative.  Long  strands  of  white  matter 
have  been  isolated,  and  laid  on  electrodes,  and  contractions 
of  distant  muscles  have  been  seen  to  follow  stimulation, 
even  when  every  precaution  has  been  taken  to  avoid  escape 
of  current  on  to  the  anterior  roots.  And  indeed,  apart  from 
direct  experimental  evidence,  the  fact  that  the  white  fibres 


666  A  MANUAL  OF  PHYSIOLOGY 

of  the  brain  are  universally  admitted  to  be  excitable  by 
artificial  means  would  be  of  itself  almost  sufficient  to  decide 
the  question,  for  we  know  of  no  essential  difference  between 
the  cerebral  and  the  spinal  fibres.  But  the  conditions  must 
rarely  occur  under  which  direct  stimulation  of  white  fibres 
in  their  course  is  possible  in  the  intact  body ;  and  the  only 
impulses  with  which  we  need  concern  ourselves  here  are 
those  that  reach  the  conducting  paths  from  grey  matter 
in  the  cord  itself  or  in  the  brain,  or  from  the  peripheral 
organs. 

What  sort  of  impulses,  then,  do  the  various  tracts  of  the 
spinal  cord  conduct  ?  For  the  posterior  roots  this  question 
was  first  fully  answered  by  Magendie ;  for  the  anterior  roots 
by  Sir  Charles  Bell.  Bell  observed  that,  when  he  cut  the 
motor  roots  in  an  animal  just  killed,  and  stimulated  the 
peripheral  ends,  muscular  contractions  were  obtained.  He 
concluded  from  this  that  the  anterior  roots  are  motor ;  but 
although  he  is  often  credited  with  the  discovery  of  the 
functions  of  the  posterior  roots  as  well,  he  was  not  the  first 
to  make  the  decisive  experiment  necessary  to  show  that 
they  are  the  conductors  of  sensory  impulses. 

When  the  posterior  roots  are  divided,  loss  of  sensation 
occurs  in  the  region  to  which  they  are  distributed.  If  only 
one  root  is  cut,  the  loss  of  sensation  is  never  complete  in 
any  part  of  the  skin ;  and  Sherrington  has  found  that  the 
areas  of  distribution  of  consecutive  nerve  roots  are  not 
sharply  marked  off  from  each  other,  but  to  some  extent 
overlap.  Stimulation  of  the  peripheral  end  of  the  divided 
posterior  root  has  no  effect.  Stimulation  of  the  central  end 
gives  rise,  if  the  animal  be  conscious,  to  evidences  of  pain, 
and  other  signs  of  the  passage  of  afferent  impulses,  e.g., 
a  rise  in  blood-pressure.  The  latter  may  also  be  observed 
when  the  animal  is  anaesthetized. 

Head's  clinical  observations  have  thrown  light  on  the  distribution 
of  the  sensory  nerves  of  the  viscera  and  their  relation  to  the  sensory 
nerves  of  the  skin.  It  has  long  been  known  that  in  disease  of  an 
internal  organ  the  pain  is  often  referred  to  some  superficial  part  at 
a  distance  from  the  actual  seat  of  the  lesion.  Head  finds  that  the 
pain  is  referred  to  definite  regions  of  the  skin  for  each  organ.  In 


THE  CENTRAL  NERVOUS  SYSTEM 

these  regions  the  excitability  for  impressions  of  touch  or  temperature 
is  increased,  and  the  reflexes  elicited  by  stimulation  are  exaggerated. 
For  example,  in  diseases  of  the  larynx,  hyperalgesia  (increased  sensi- 


ire  connecting 
Cere  be  /  wRe  d  nu  ele  u  s 
kthus  ur  cerelral  cortex 


,PyramiduJ  Cell 


<)/  cerebral  cortt 


ires  connecting 


Fibre  of  Direct 


Fibre  of  Qoll's  Col- 


Get  n  glio  n-Cell 
onPost-Root--~(± 

Post.Pook  &£ 

Fibres       1    ^< 


t  I  / 


Fibre  ofPyram.  /n 
'~ut short) 

k- -Fibre-  of 
\  Fillet  ' 


Nerve-cell  ofPosf.Horn , 


l:.  Horn 


ke'sCol. 


Middle  //; 


Po ssilJe  Affe rent  Paths. 


FIG.  230. — POSSIBLE  PATHS  OF  AFFERENT  IMPULSES  IN  THE  CENTRAL 
NERVOUS  SYSTEM  (SCHEMATIC). 

bility  to  pain)  is  present  in  a  region  extending  from  the  middle  line 
of  the  throat  to  the  median  border  of  the  sterno-cleido-mastoid 
muscle,  and  downwards  to  the  sterno-clavicular  articulation ;  and 
stimulation  of  the  skin  in  this  area  often  causes  reflex  coughing. 


668 


A  MANUAL  OF  PHYSIOLOGY 


Head  suggests  that  the  bond  of  connection  is  a  common  anatomical 
origin  or  a  physiological  correlation,  somewhere  or  other  in  the 
central  nervous  system,  between  the  sympathetic  sensory  fibres  of 
any  viscus  and  the  sensory  supply  of  the  corresponding  cutaneous 


Filre  for— 
Head 


Fr« 


Decussation 
of  Pyramids. 


Ft  b  rt  of  D  i  re  ct 
I  ranii  da  I  tract, 


r 

of  An  t.  Ho  rn  .  _ 
terminal  Arborisation 
tifa  Pyrami  dal  Fibre 

around  Cell  of * 

An/-  Horn 


1 1  Medulla 

li  Oblonqata 

r  sRtcrossedFilre  ?\ 

VL_ •:'.  .^Uncrossed  Fibre.     J 

\\       ''  o      •        / 

\     ,'  briincil 

Cord 


Anterior 
Root 

Fibres- 


Paf/is 


FIG.  231. — POSSIBLE  PATHS  OF  EFFERENT  IMPULSES  IN  THE  CENTRAL 
NERVOUS  SYSTEM  (SCHEMATIC). 

area.  According  to  him,  when  there  is  a  close  central  connection 
between  the  sensory  nervous  mechanism  of  a  part  of  low  sensibility 
and  that  of  a  part  of  high  sensibility,  a  painful  stimulus  applied  to 
the  former  is  felt  in  the  latter. 


THE  CENTRAL  NERVOUS  SYSTEM  669 

In  the  case  of  some  of  the  viscera  the  sensory  fibres  seem  to  arise 
from  the  same  sensory  root  or  roots  as  the  sensory  fibres  of  the 
related  cutaneous  areas,  but  in  others  this  does  not  hold. 

Recurrent  Sensibility. — Although  muscular  contraction  is 

i  the  most  conspicuous  event  that  follows  stimulation  of  the 

j  peripheral  end  of  an  anterior  nerve-root,  it  is  by  no  means 

|  the  only  one.     It  is  frequently  observed,  though  not  in  all 

|  kinds  of  animals,  that  here,  too,  pain  is  caused.     That  this 

I  pain  is  not  due  to  the  muscular  contraction  is  proved  by 

the  fact  that  it  can  still  be  elicited  when  the  nerve-trunk  is 

divided  between  the  junction  of  the  roots  and  the  periphery. 

The  real  explanation  of  the  phenomenon  seems  to  be  that 

certain   fibres  from  the  posterior  roots  bend  up  for   some 

!  distance  into  the  anterior  roots,  and  then  turn  around  again 

and  pursue  their  course  to  their  peripheral  distribution  in 

the  mixed  nerve,  or  run  on  in  the  motor  roots  to  supply  the 

sheath   surrounding  them   (nervi   nervorum),  and  even  the 

membranes  of  the  spinal  cord. 

The  afferent  impulses  that  enter  the  cord  along  the  pos- 
terior roots  have  the  choice  of  many  paths  by  which  they 
may  reach  the  brain  (Fig.  230). 

(1)  They   may  pass   directly   up    through    the    postero-median 
column.     If  they  take  this  route,  their  course  will  be  first  interrupted 
by  nerve-cells '  in   the   gracile    or   cuneate    nuclei   in   the   medulla 
oblorigata.     Thence  they  may  find  their  way  across  the  middle  line 
by   the   arcuate  fibres   of  the   upper   or   sensory  decussation,  and 
sweeping  along  the  fillet  and  the  longitudinal  fibres  of  the  reticular 
formation  of  medulla,  pons  and  crus,  and  the  sensory  path  in  the 
hinder  third  of  the  posterior  limb  of  the  internal  capsule,  finally 
arrive  at   the  cerebral  cortex.      Between   the  gracile   and  cuneate 
nuclei  and  the  cortex  they  may  pass  through  nerve-cells  in  the  optic 
thalamus  and  the  neighbouring  region. 

(2)  They  may  pass  up  by  the  direct  cerebellar  tract  and  restiform 
body.     If  they  take  this  route,  their  course  will  be  interrupted  by 
nerve-cells  very  soon  after  their  entrance  into  the  cord,  presumably 
in  Clarke's  column,  and  again  in  the  dentate  nucleus  of  the  cere- 
bellum.     The  impulses  may  then   cross   the   middle  line   by  the 
superior  peduncle  to  the  tegmental  region  of  the  crus  cerebri,  where 
they  may  again  pass  through   cells  in  the  red  nucleus.     From  the 
red  nucleus  they  may  find  their  way  by  the  tegmental  sensory  path 
to  the  cerebral  cortex. 

(3)  They  may  reach  the  cerebellum  by  the  antero-lateral  ascend- 
ing tract,  passing  through  nerve-cells  in  the  lateral  nucleus  of  the 


6;o  A  MANUAL  OF  PHYSIOLOGY 

medulla  (?),  then  by  the  formatio  reticularis  of  the  medulla  and 
pons  to  the  superior  peduncle  of  the  cerebellum,  and  thence  to  the 
grey  matter  of  the  worm  on  the  same  side. 

(4)  They  may  cross  the  middle  line  through  collaterals  (p.  654) 
which  run  in  the  posterior  grey  commissure,  enter  one  of  the  ascend- 
ing tracts  on  the  other  side,  and  continue  without  further  decussation 
up  to  their  central  destination. 

(5)  They  may  spread  in  the  tangle  of  the  grey  matter  itself  and 
pass  out  again  at  a  different  level  into  one  of  the  white  tracts  on  the 
same  or  on  the  opposite  side  of  the  cord. 

Efferent  impulses,  originating  in  the  brain,  may  travel : 

(1)  Through  the  direct  or  crossed  pyramidal  tract.     If  they  do 
so   their  course  will   not   be   interrupted   by   nerve-cells   anywhere 
between  the  cerebral  cortex  and  the  motor  cells  of  the  anterior  horn. 

(2)  From  one  side  of  the  cerebral  cortex  to  the  other,  and  then 
down  the  pyramidal  tracts  corresponding  to  that  side  (?). 

(3)  From  the  pre-frontal  part  of  the  cerebral  cortex,  through  the 
anterior  limb  of  the  internal  capsule  to  the  grey  matter  in  the  pons, 
and  thence  to  the  cerebellum  by  its  middle  peduncle. 

(4)  From  the  occipital  or  temporal  cortex  in  the  hinder  rim  of  the 
internal  capsule  to  the  pontine  grey  matter  and  through  the  middle 
peduncle  to  the  cerebellum.    From  the  cerebellum  they  may  possibly 
be  reflected  down  the  antero-lateral  descending  tract  to  the  cord,  and 
indirectly,  if  not  directly,  to  the  periphery. 

All  the  paths  enumerated,  as  well  as  others  to  which  it 
would  be  tedious  to  formally  refer,  and  which  the  ingenuity 
of  the  reader  may  be  profitably  employed  in  constructing 
for  himself,  from  the  data  already  given,  are  to  be  looked 
upon  as  possible  channels  for  the  passage  of  impulses  between 
the  brain  and  the  periphery.  But  what  is  certain  is  in 
this  case  much  more  limited  than  what  is  possible.  It 
is  certain  that  the  pyramidal  tracts  are  the  conductors  of 
voluntary  motor  impulses,  and  that  in  most  individuals  the 
great  majority  of  such  impulses  decussate  in  the  medulla 
oblongata,  only  a  small  minority  in  the  cord.  For  a  lesion 
involving  the  pyramidal  tract  above  the  decussation  of  the 
pyramids  causes  paralysis  of  the  opposite  side  of  the  body, 
a  lesion  below  the  decussation  paralysis  of  the  same  side. 
But  it  is  possible  that  when  one  pyramidal  tract  has  been 
destroyed,  in  some  animals  at  least,  the  motor  cortex  from 
which  it  leads  may  to  a  certain  extent  place  itself  again  in 
communication  with  the  paralyzed  muscles  through  its  com- 
missural  connections  with  the  opposite  hemisphere. 


THE  CENTRAL  NERVOUS  SYSTEM  671 

On  the  other  hand,  it  is  certain  that  pathological  or 
traumatic  lesions,  involving  the  destruction  of  one  lateral 
half  of  the  cord  in  man  and  experimental  hemisections  in 
animals,  are  usually  followed  by  symptoms  which  suggest 
that  the  sensory  impulses  decussate  chiefly  in  the  spinal 
cord — viz.,  increase  of  sensibility  (hyperaesthesia)  below  and 
on  the  same  side  as  the  injury,  and  diminution  of  sensibility 
on  the  opposite  side.  This  was  first  pointed  out  by  Brown- 
Sequard,  although  long  after  he  saw  cause  to  retract  this 
interpretation  of  his  experiments.  It  seems,  however,  that 
no  ascending  degeneration  is  to  be  found  on  the  opposite 
side  of  the  cord  either  after  hemisection  or  after  division  of 
posterior  roots  (Mott).  But  while  this  latter  fact  shows 
that  none  of  the  afferent  fibres  cross  the  middle  line  before 
being  interrupted  by  nerve-cells,  it  by  no  means  proves  that 
afferent  impulses  do  not  decussate  in  the  cord.  And,  indeed, 
we  know  that  some  afferent  impulses  do  decussate  far  below 
the  level  of  the  medulla.  For,  (i)  A  part  of  the  negative 
variation  (p.  622)  crosses  the  middle  line  and  ascends  in  the 
opposite  half  of  the  cord  when  the  central  end  of  one  sciatic 
is  stimulated  (Gotch  and  Horsley).  (2)  Crossed  reflex 
movements  are  possible ;  and  when  excitation  of  the  central 
end  of  the  sciatic  is  followed  by  contraction  of  the  muscles 
of  the  opposite  fore-limb,  the  afferent  impulses  must  either 
decussate  in  the  lumbar  cord,  and  then  run  up  on  the 
opposite  side  to  the  level  of  the  brachial  plexus,  or  must 
ascend  on  the  same  side  and  cross  over  somewhere  between 
the  plane  of  the  sciatic  and  the  brachial  nerve-roots.  The 
only  other  hypothesis  on  which  crossed  reflex  action  can  be 
explained — but  a  hypothesis  for  which  there  is  not  a  tittle  of 
evidence — is  that  the  afferent  impulse  always  acts  on  motor 
cells  whose  axis-cylinder  processes  pass  over  to  the  opposite 
side,  and  there  enter  anterior  nerve-roots.  But  while,  for 
these  reasons,  it  cannot  be  denied  that  some  afferent  im- 
pulses decussate  in  the  cord,  it  would  be  an  error  to  argue 
from  this  that  all,  or  even  the  majority,  do  so.  And,  indeed, 
there  is  evidence  that  many  of  the  impulses  concerned  in 
sensation  do  in  reality  remain  on  the  side  of  the  cord  which 
they  first  enter,  right  up  to  the  medulla  oblongata. 


672  A  MANUAL  OF  PHYSIOLOGY 

To  sum  up,  we  may  say  that  while  it  is  certain  that  most  of 
the  motor,  and  many  of  the  sensory,  impulses  decussate  in  the 
medulla,  unanimity  has  not  as  yet  been  reached  with  reference  to 
the  place  of  decussation  of  the  whole  of  the  sensory  impressions,  and 
it  is  possible  that  some  of  them  decussate  in  the  cord,  others  in  the 
bulb.  And  when  it  is  remembered  how  difficult  it  sometimes 
is  to  interpret  the  account  which  a  man  gives  of  his  sensa- 
tions and  to  recognise  precisely  the  degree  and  nature  of 
sensory  defects  produced  by  disease  in  the  human  subject,  it 
will  not  be  thought  surprising  that  experiments  on  animals, 
from  the  time  of  Galen  onwards,  should  have  yielded  evidence 
which,  although  perhaps  now  at  length  tending  to  a  definite 
result,  is  still  unfinished  and  in  part  conflicting.  If  this  is 
true  where  the  problem  is  merely  to  determine  the  crossing- 

I  place  of  afferent   impulses  which  are  certainly  known  to 

cross,  it  is  only  to  be  expected  that  we  should  be  still  more 

in  the  dark  as  regards  the  routes  by  which  different  kinds 

of  afferent  impulses  thread  their  way  through  the  maze  of 

conducting  paths  in  the  neural  axis  to  reach  their  planes  of 

decussation  and  gain  the  *  sensory  crossway '  in  the  internal 

capsule.     Some  authors  have  indeed  cut  the  Gordian  knot 

by  assuming  that  any  kind  of  sensory  impression  may  travel 

c,  up  any  afferent  path.     Direct  stimulation  of  a  naked  nerve- 

*    trunk,  it  has  been  argued  in  favour  of  this  view,  gives  rise 

i  to  a  sensation  of  pain ;  stimulation  of  the  skin  in  which  the 
t^JU  (end-organs  of  the  nerve  lie  gives  rise  to  a  sensation  of  touch 
or  a  sensation  of  temperature,  according  as  the  stimulus  is 
a  mild  mechanical  or  a  thermal  one,  the  contact  of  a  feather 
or  of  a  hot  test-tube.  Why,  it  has  been  asked,  should  we 
imagine  that  the  difference  in  the  result  of  stimulation 
depends  on  a  difference  in  the  nerve-fibres  excited,  and  not 
on  a  difference  in  the  kind  of  impulses  set  up  in  the  same 
nerve-fibres  ?  This  is  a  question  which  we  shall  have  again 

!  to  discuss  (p.  721).  But  apropos  of  our  present  problem, 
we  may  say  that  there  is  very  clear  proof  from  the  patho- 
logical side  that  a  limited  lesion  in  the  conducting  paths  of 
the  central  nervous  system  may  be  associated  with  defect  or 
total  loss  of  one  kind  of  sensation,  while  all  the  other  kinds 
remain  intact.  And  there  seems  no  other  tenable  hypo- 


THE  CENTRAL  NERVOUS  SYSTEM  673 

thesis  than  that  in  such  cases  the  pathological  change  has 
picked  out  a  particular  group  of  fibres,  either  collected  into 
a  single  strand  or  scattered  among  unaltered  fibres  of 
different  function.  For  example,  in  locomotor  ataxia,  a 
disease  in  which  inco-ordination  of  movement  and  derange- 
ment of  the  mechanism  of  equilibration  are  prominent 
symptoms,  degeneration  in  the  posterior  column  of  the  cord 
is  a  most  constant  lesion.  And  there  is  strong  evidence  that 
afferent  impulses  from  muscles  and  tendons,  which  give  rise 
to  impressions  belonging  to  the  group  of  tactile  sensations, 
and  which,  according  to  the  most  widely  accepted  doctrine, 
serve  as  the  basis  of  the  muscular  sense,  and  play  an  im- 
portant part  in  the  maintenance  of  equilibrium  (p.  696), 
pass  up  in  the  posterior  column.  A  case  has  been 
observed  where  a  man  received  a  stab  which  divided  the 
whole  of  one  side  of  the  cord  and  the  posterior  column  of 
the  other  side.  Sensibility  to  touch  was  lost  on  both  sides 
of  the  body  below  the  level  of  the  injury,  sensibility  to  pain 
only  on  the  side  opposite  to  the  main  lesion.  This  tactile 
path  in  the  posterior  column,  however,  is  the  only  tract 
which  has  been  associated,  on  evidence  at  all  sufficient,  with 
the  passage  of  sensory  impressions  of  a  particular  kind. 
Definite  paths  for  temperature  sensations  have,  indeed, 
been  described  in  the  lateral  column.  And  Schiff  has 
credited  the  grey  matter  of  the  cord  with  the  power  of 
conducting  the  impulses  that  give  rise  to  pain,  and  has 
asserted  that  such  impulses  can  be  propagated  along  a  cord 
in  which  hardly  a  vestige  of  white  substance  remains  uncut. 
But  these  statements  cannot  be  considered  as  resting  on 
adequate  proof,  although  it  is  certain  that  impressions  of 
pain  and  of  temperature  do  pass  up  somewhere  or  other  in 
the  antero-lateral  column,  and  Gowers  has  brought  forward 
some  facts  which  he  interprets  as  indicating  that  the 
antero-lateral  ascending  tract  is  the  path  for  sensibility  to 
pain. 

The  impulses  which  descend  the  cord  give  token  of  their 
arrival  at  the  periphery  by  causing  either  contraction  of 
voluntary  muscles,  or  contraction  of  the  smooth  muscles  of 
arteries,  or  secretion  in  glands.  They  all  pass  down  in  the 

43 


674  -4  MANUAL  OF  PHYSIOLOGY 

anterolateral  column,  but  the  path  of  the  voluntary  impulses 
in  the  pyramidal  tracts  is  the  best  known  and  most  sharply 
defined. 

2.  Modification  of  Impulses  set  up  elsewhere  (Reflex  Action). 
— The  spinal  cord,  although  it  is  a  conductor  of  nervous 
impulses  originating  elsewhere,  is  by  no  means  a  mere  con- 
ductor. Many  of  the  impulses  which  fall  into  the  cord  are 
interrupted  in  its  grey  matter.  Some  of  the  efferent  impulses 
proceeding  from  the  brain  are  perhaps  modified  in  the  cord, 
and  then  transmitted  to  the  muscles.  Some  of  the  afferent 
impulses  are  modified,  and  then  transmitted  to  the  brain  ; 
some  are  modified,  and  deflected  altogether  into  an  efferent 
path.  These  last  are  the  impulses  which  give  rise  to  reflex 
effects.  Strictly  speaking,  a  reflex  action  is  an  action  carried 
out  in  the  absence  of  consciousness ;  not  necessarily,  how- 
ever, in  the  absence  of  general  consciousness,  but  in  the 
absence  of  consciousness  of  the  particular  act  itself.  But 
the  term  is  often  used  so  as  to  embrace  all  kinds  of  actions 
which  are  not  directly  voluntary,  whether  the  individual  is 
conscious  of  them  or  not.  For  example,  when  the  sole  of 
the  foot  is  tickled,  the  leg  is  irresistibly  and  involuntarily 
drawn  up  by  reflex  contraction  of  its  muscles ;  yet  the 
person  is  perfectly  cognisant  both  of  the  movement  and  of 
the  sensation  which  accompanies  the  afferent  impulse.  Then 
there  is  a  class  of  reflex  actions  in  which  consciousness  is 
entirely  in  abeyance ;  during  sleep  most  of  the  ordinary 
reflexes  can  be  elicited. 

Normally,  it  is  believed  that  reflex  movements  are  governed 
by  impulses  descending  from  the  higher  centres,  for  (a)  it  is  a 
matter  of  common  experience  that  a  reflex  movement  may  be  to  a 
certain  extent  controlled,  or  prevented  altogether  by  an  effort  of  the 
will,  and  it  is  worthy  of  remark  that  only  movements  which  can 
be  voluntarily  produced  can  be  voluntarily  inhibited  ;  (b)  an  animal 
like  a  frog  responds  to  stimuli  by  reflex  movements  more  readily 
after  the  medulla  oblongata  has  been  divided  from  the  spinal  cord ; 
(c)  long-continued  muscular  contractions  may  be  caused  in  animals 
after  removal  of  the  cerebral  hemispheres  by  stimulation  of  sensory 
nerves,  for  example  by  scratching  the  mucous  membrane  of  the 
mouth  in  a  '  brainless '  frog  or  Menobranchus ;  (d)  by  stimulation 
of  certain  of  the  higher  centres  reflex  movements  which  would  other- 
Wise  be  elicited  may  be  suppressed  or  greatly  delayed.  If  the 


/ 


THE  CENTRAL  NERVOUS  SYSTEM  675 

cerebral  hemispheres  are  removed  from  a  frog,  and  one  leg  of  the 
animal  dipped  into  dilute  acetic  acid,  a  certain  interval,  the  (un- 
corrected)  reflex  time,  will  elapse  before  the  foot  is  drawn  up  (Tiirck's 
method,  p.  729).  If  now  a  crystal  of  common  salt  be  applied  to 
the  optic  lobes  or  the  upper  part  of  the  spinal  cord,  and  the  experi- 
ment repeated,  it  will  be  found  that  either  the  interval  is  much 
lengthened,  or  that  the  reflex  disappears  altogether.  Strong  stimula- 
tion of  any  afferent  nerve  will  also  abolish  or  delay  a  reflex  movement. 
That  the  brain,  in  man  and  the  higher  animals  at  least,  exerts 
more  than  a  merely  inhibitory  influence  on  the  production  of  reflex 
movements  is  suggested  by  many  facts.  The  knee-jerk,  for  example, 
often  disappears  in  pathological  lesions,  situated  high  up  in  the  cord 
in  man,  and  is  markedly  impaired  after  high  section  of  the  cord  in  a 
dogs.  In  hemiplegia  (paralysis  of  one  side  of  the  body,  caused  by  tw^^f* 
disease  in  the  brain)  the  cutaneous  reflexes  on  the  paralyzed  side 
may  sometimes  be  absent  for  years.  Some  observers  have  even 
gone  so  far  as  to  say  that,  under  normal  conditions,  the  so-called 
spinal  reflexes  are  really  cerebral,  in  other  words,  that  the  afferent 
impulses  run  up  to  the  cortex  of  the  brain  and  there  discharge 
efferent  impulses,  which  pass  down  to  the  motor  cells  of  the  anterior 
horn  and  cause  their  discharge.  It  may  be  admitted  that  there  is  no 
physiological  ground  for  supposing  that  the  afferent  impulses  which 
have  to  do  with  the  reflex  contraction  of  the  muscles  of  the  leg  wherr 
the  sole  is  tickled,  stop  short  at  the  motor  cells  of  those  spinal 
segments  from  which  the  efferent  nerves  come  off,  while  the  afferent 
impulses  which  have  to  do  with  the  sensation  of  tickling  pass  up  to 
the  brain.  The  probability  is  that  under  ordinary  circumstances 
such  afferent  impulses  pass  up  the  cord  in  long  afferent  paths,  as  well 
as  directly  towards  the  motor  cells,  along  those  fibres  of  the  posterior 
roots  and  their  collaterals  which  bend  forward  into  the  anterior  horn 
at  the  level  of  their  entrance  into  the  cord.  And  the  only  question 
is  whether,  as  a  matter  of  fact,  the  spinal  motor  cells  are  most  easily 
discharged  by  the  impulses  that  reach  them  directly,  or  by  the 
impulses  that  come  down  to  them  by  the  roundabout  way  of  the 
cortex  and  the  efferent  fibres  that  connect  it  with  the  motor  cells. 
It  is  evident  that  the  answer  to  this  question  need  not  be  the  same 
for  all  kinds  of  animals.  It  may  well  be  that  in  the  higher  animals, 
in  which  the  cortex  has  undergone  a  relatively  great  development, 
the  spinal  motor  mechanisms  are  more  easily  discharged  from  above 
than  from  below,  while  in  lower  animals  the  opposite  may  be  the 
case.  When  the  cord  is  cut  off  from  the  brain,  the  afferent  impulses 
may  overflow  more  easily  into  the  spinal  motor  cells  since  their 
alternative  path  is  blocked.  In  the  frog,  where  there  is  already  a 
beaten  track  between  the  posterior  root-fibres  and  the  cells  of  the 
anterior  horn,  this  overflow  may  be  established  immediately  after 
section  of  the  cord,  and  may  of  itself  lead  to  an  exaggeration  of  the 
reflexes.  In  animals  like  the  dog,  a  longer  time  may  be  necessary 
before  the  unaccustomed  route  from  the  afferent  neurons  and  their 
collaterals  to  the  dendrons  of  the  motor  cells  becomes  natural  and 
easy ;  in  man  a  still  longer  interval  may  be  required. 

43—2 


676  A  MANUAL  OF  PHYSIOLOGY 

In  order  that  a  reflex  action  may  take  place,  the  reflex 
arc — afferent  nerve,  central  mechanism,  and  efferent  nerve — 
must  be  complete;  and  in  fact  a  whole  series  of  simple  reflex 
movements  exists,  the  suppression,  diminution,  or  exaggera- 
tion of  which  can  be  used  in  diagnosis  as  tests  of  the  con- 
dition of  the  reflex  arc.  Such  are  the  plantar  reflex  (the 
drawing-up  of  the  foot  when  the  sole  is  tickled),  the  cremasteric 
reflex  (retraction  of  the  testicle  when  the  skin  on  the  inside 
of  the  thigh  just  below  Poupart's  ligament  is  stroked,  espe- 
cially in  boys),  the  knee-jerk  (a  sudden  extension  of  the  leg 
by  the  rectus  femoris  muscle  when  the  ligamentum  patellse 
is  sharply  struck),  the  gluteal,  abdominal,  epigastric,  and  inter- 
scapular  reflexes  (contraction  of  the  muscles  in  those  regions 
when  the  skin  covering  them  is  tickled).  The  jaw- jerk  (a 
movement  of  the  lower  jaw  when,  with  the  mouth  open,  the 
chin  is  smartly  tapped)  and  ankle-clonus  (a  series  of  spasmodic 
movements  of  the  foot,  brought  about  by  flexing  it  sharply 
on  the  leg)  are  phenomena  of  the  same  class,  which  can 
be  elicited  only  in  disease.  Any  condition  which  impairs 
the  conducting  power  of  the  afferent  or  efferent  fibres  of 
the  reflex  arc  necessarily  diminishes  or  abolishes  the  reflex 
movement,  even  if  the  centre  is  intact.  E.g.,  in  locomotor 
ataxia  the  disappearance  of  the  knee-jerk  is  one  of  the 
most  important  diagnostic  signs.  This  disease  involves 
the  posterior  roots  and  the  fibres  that  continue  them  in  the 
posterior  column.  The  anterior  nerve-roots  are  perfectly 
healthy.  The  grey  matter  of  the  cord — at  least,  in  the  earlier 
stages  of  the  disease — is  unaffected.  The  weak  link  in  the 
chain  is  the  afferent  path.  In  anterior  poliomyelitis  (p.  657) 
the  afferent  link  is  intact,  but  the  other  two  are  broken,  and 
the  reflexes  also  disappear.  Certain  lesions  which  cut  off 
the  spinal  cord  from  the  higher  centres  without  affecting  the 
integrity  of  the  reflex  arcs  increase  the  strength  of  reflex 
movements  and  the  facility  with  which  they  are  called  forth. 
In  paraplegia,  e.g.  (paralysis  of  the  legs  and  the  lower  portion 
of  the  body),  caused  suddenly  by  accident  to  the  cord,  or 
more  slowly  by  acute  or  chronic  transverse  myelitis,  or  in 
hemiplegia,  the  knee-jerk  can  usually  be  elicited  with  start- 
ling promptitude  and  exaggeration,  and  ankle-clonus  may 


THE  CENTRAL  NERVOUS  SYSTEM 


677 


also  be  obtained.  In  primary  spastic  paraplegia,  which  is 
associated  with  degenerative  changes  in  the  lateral  columns, 
a  similar  increase  in  the  true  and  pseudo-reflexes  may  be 
seen,  due  either  to  the  cutting  off  of  inhibitory  impulses  or 
to  an  actual  increase  of  excitability  in  the  grey  matter  of 
the  cord.  The  position  of  the 
centres  in  the  cord  for  the 
various  simple  reflex  move- 
ments is  shown  in  Fig.  232. 

Myotatic  Irritability  (Muscle 
Reflex).  —  Although  for  con- 
venience of  treatment  we  have 
included  the  knee-jerk  (with 
the  jaw-jerk  and  ankle-clonus) 
among  reflex  movements,  it 
might  more  properly  be  termed 
a  pseudo-reflex,  for  there  is 
evidence  that  the  mechanism 
by  which  it  is  produced  is 
different  from  that  concerned 
in  the  reflex  blinking  of  the 
eyelid,  or  the  reflex  retraction 
of  the  testicle,  or  the  drawing- 
up  of  the  foot  when  the  sole  is 
tickled.  The  strongest  part 
of  this  evidence  is  the  fact 
that  the  interval  which  elapses 
between  the  tap  and  the  jerk 
(TOTF  to  T^  second)  is  distinctly 
shorter  than  the  reflex  time  of 
the  extremely  rapid  lid-reflex, 

and  is  not  much   greater  than     FlG-  ^.-DIAGRAM  OF  REFLEX 
b  CENTRES  IN  CORD  (AFTER  HILL). 

the  latent  period  of  the  quadri- 
ceps muscle  for  direct  electrical  stimulation,  as  measured 
under  the  ordinary  conditions  of  its  contraction,  The  knee- 
jerk  is  obtained  in  undiminished  strength  when  the  nerves 
of  the  ligamentum  patellae  have  been  divided.  It  is  therefore 
not  a  reflex  movement  caused  by  stimulation  of  afferent 
nerves  coming  from  the  tendon,  and  the  name  *  tendon- 


678  A  MANUAL  OF  PHYSIOLOGY 

reflex  '  is  clearly  a  misnomer.  But  that  it  is  related  in  some 
way  or  other  to  afferent  impulses  is  certain,  for  division  of 
the  posterior  roots  that  enter  into  the  anterior  crural  nerve 
abolishes  the  knee-jerk.  The  phenomenon  probably  comes 
under  the  head  of  what  by  some  authors  is  called  myotatic 
irritability — that  is,  it  depends  on  mechanical  stimulation  of 
the  slightly-stretched  muscle  by  the  pull  of  the  tendon  when 
it  is  struck.  It  seems  to  be  necessary  for  this  stimulation 
that  the  muscle  should  be  to  a  certain  extent  tonically  con- 
tracted. So  that  when  the  afferent  fibres  are  interrupted, 
or  the  grey  matter  of  the  cord  disorganized,  and  the  reflex 
tone  abolished,  the  knee-jerk  disappears.  In  addition  to 
the  direct  stimulation  of  the  muscle  on  the  same  side,  the 
tendon-tap  may  cause  also  a  true  reflex  knee-jerk  on  the 
opposite  side,  the  interval  between  tap  and  contraction 
being  about  -J-  second. 

Anatomical  Basis  of  Reflex  Action. — Since  the  essence  of  reflex 
action  is  that  the  arrival  of  afferent  impulses  in  the  spinal  cord  causes 
the  discharge  of  efferent  impulses,  there  must  be  some  connection 
between  the  incoming  and  the  outgoing  nerve-fibres.  Moderate 
stimulation  of  an  afferent  nerve  causes  contraction  of  muscles  con- 
nected with  the  same  segment  of  the  cord  on  its  own  side,  and  it  has 
been  shown  that  the  sensory  nerves  of  a  skeletal  muscle  are  derived 
from  the  spinal  ganglion  corresponding  to  the  segment  of  the  cord 
containing  its  motor-cells.  Stronger  excitation,  particularly  of  the 
end-organs  of  a  nerve,  as  in  stimulation  of  the  skin,  will  be  followed 
by  more  extensive  movements  involving  higher  or  lower  segments 
of  the  cord,  or  crossing  over  to  the  opposite  side.  Sometimes  the 
reflex  movements  are  co-ordinated  to  a  high  degree,  and  even 
'purposive'  in  their  action.  This  also  is  less  true  of  movements 
caused  by  stimulation  of  naked  nerve-trunks  than  of  movements 
caused  by  stimulation  of  sensory  surfaces.  Let  a  piece  of  skin  in  a 
brainless  frog  be  severed  from  the  rest,  but  left  in  connection  with 
its  nerves.  Excitation  of  the  latter  will  produce  simple  and  com- 
paratively aimless  contractions,  while  pinching  of  the  skin  or  painting 
it  with  dilute  acid  may  cause  extensive  movements  evidently  aimed 
at  the  removal  of  the  irritation.  If  a  drop  of  dilute  acid  be  applied 
to  the  flank  of  a  '  reflex '  frog,  it  will  attempt  to  wipe  it  off  with  the 
foot  which  is  situated  most  conveniently  for  the  purpose.  If  this 
foot  be  held,  it  will  use  the  other. 

It  is  evident  that  the  connections  between  the  fibres  of  the  \  osterior 
and  anterior  roots  must  be  very  extensive.  Indeed,  the  phenomena 
of  strychnia-poisoning  seem  to  show  that  every  afferent  fibre  is 
potentially  connected  with  the  motor  mechanisms  of  the  whole  cord. 
For  in  a  frog  under  the  influence  of  this  drug,  stimulation  of  the 


THE  CENTRAL  NERVOUS  SYSTEM 


679 


FIG.  233. — DIAGRAM  OF  A  SIMPLE 
REFLEX  ARC. 

The  arrows  indicate  the  direction  of  the 
afferent  and  efferent  impulses. 


smallest  portion  of  the  skin  will  cause  violent  and  general  convulsions, 
which  are  unaffected  by  destruction  of  the  brain,  but  cease  at  once 
on  destruction  of  the  cord  (p.  729).  Our  problem,  then,  is  to  find 
connections — first,  between  the  afferent  fibres  of  each  spinal  segment 
and  its  efferent  fibres,  and,  secondly,  between  the  central  mechanisms 
of  all  the  segments  of  the  cord.  When  the  nervous  system  is  still 
only  a  process  of  an  epi- 
thelial (sensory)  cell  joining 
hands  with  a  muscular  cell, 
the  distinction  between  affer- 
ent and  efferent  fibre  does  not 
exist.  When  development  has 
gone  a  step  further,  and  the 
neuro-muscular  process  is  in- 
terrupted by  a  second  epi- 
thelial cell  transformed  into 
a  nerve-cell,  the  afferent  fibre 
enters  one  pole  and  the  effer- 
ent fibre  leaves  the  other  pole 
of  the  same  cell.  With  in- 
creasing complexity  of  organ- 
ization the  nervous  impulse  passing  up  the  afferent  fibre  is  offered  a 
choice  of  many  routes  when  it  reaches  the  nerve-cell.  This  is 
effected  by  means  of  the  feltwork  formed  by  its  branching  processes 
with  the  processes  of  other  cells. 

We  have  already  described  (p.  653)  the  course  taken  by  the  fibres 
of  the  posterior  roots  on  entering  the  spinal  cord,  and  have  seen  that 
the  fibres  or  their  collaterals  are  distributed  to  the  grey  matter  of  the 
anterior  horn,  of  the  posterior  horn,  and  of  Clarke's  column  on  the 
same  side,  while  collaterals  cross  the  middle  line  in  the  posterior 
commissure  and  run  into  the  grey  matter  of  the  opposite  side. 
Many  of  the  fibres,  too,  which  ascend  in  the  columns  of  Burdach 
and  Goll  ultimately  make  junction  with  nerve-cells  higher  up  in  the 
cord.  There  is  thus  formed  an  ample  connection  between  the 
posterior  roots  and  the  efferent  nerves  of  the  same  segment  on  both 
sides  of  the  cord,  and  also  between  any  one  posterior  root  and  the 
spinal  grey  matter  at  different  levels.  The  grey  matter  of  adjoining 
segments  is  further  united  by  the  commissural  fibres  of  the  antero- 
lateral  ground  bundle  already  spoken  of  (p.  650),  and  doubtless  also 
by  the  numerous  fibres  and  fibrils  that  interlace  in  its  own  substance. 

Under  ordinary  conditions  we  must  suppose  that  the  resistance  to 
the  passage  of  impulses  is  greater  for  certain  paths  than  for  others, 
that  it  is  easier,  e g.^  in  a  brainless  frog  for  an  impulse  travelling  up 
a  posterior  root  to  reach  the  anterior  root-fibres  of  the  same  segment 
on  the  same  side  than  to  cross  the  middle  line  and  tap  the  opposite 
efferent  tract,  or  to  extend  longitudinally  along  the  cord  and  flow  over 
into  efferent  tracts  corning  off  at  a  higher  or  lower  level.  The  action 
of  strychnia  must  be  to  diminish  the  resistance  in  the  whole  of  the 
spinal  cord,  so  that  an  impulse,  instead  of  being  confined  to  a  fairly 
definite  path,  spreads  indiscriminately  over  the  grey  matter. 


680  A  MANUAL  OF  PHYSIOLOGY 

The  transition  from  the  afferent  to  the  efferent  fibres  of  a  reflex 
arc,  so  far  as  we  know,  never  takes  place  in  highly  organized  animals 
except  through   a  nervous   plexus.     In    the   peripheral  ganglia  the 
nerve-cells  do  not  appear  to  be  junctions  through  which  impulses 
may  be  shunted  from  one  kind  of  fibre  to  another.     Thus,  the  cells 
of  a  spinal  ganglion  represent  the  original  neuroblasts  from  which 
the  posterior  root-fibres  grew  out  as  processes  towards  the  cord  on 
the  one  side   and  the  periphery  on  the    other.      A  sensory   fibre 
passing  into  the  ganglion  makes  connection  with  a  cell  by  a  T-shaped 
junction  (which  may  be  considered  as  a  stalk  formed  by  the  coales- 
cence of  a  portion  of  the  entering  and  outgoing  fibres),  and  passes 
on  its  course  again.     Here  it  is  evident  that  there  is  no  possibility  of 
a  complete  reflex  arc,  and  accordingly  no  reflex  function  has  ever 
been  associated  with  the  spinal  ganglia.     In  the  sympathetic  ganglion- 
cells,  also,  it  is  doubtful  whether  the  anatomical  foundation  for  a 
reflex  arc  exists,  and  the  most  careful  physiological  experiments  have 
failed  to  demonstrate  any  reflex  function  in  the  sympathetic  ganglia. 
Sokownin,  indeed,  observed  that  stimulation  of  the  central  end  of 
the  hypogastric  nerve  caused  contractions  of  the  bladder,  and  he 
considered  these  movements  to  be  reflex,  the  centre  being  the  in- 
ferior   mesenteric    ganglion.      Langley   and    Anderson    have    also 
found  that  when  all  the  nervous  connections  of  the  inferior  mesen- 
teric ganglion,   except  the  hypogastric  nerves,  are  cut,  stimulation 
of  the  central  end  of  one  hypogastric  causes   contraction  of  the 
bladder,  the  efferent  path  being  the  other  hypogastric.     In  addition, 
they  have  observed  an  apparent  reflex  excitation  of  the  nerves  which 
supply  the  erector  muscles  of  the  hairs  (pilo-motor  nerves)  through 
other  sympathetic  ganglia.     But  they  believe  it  likely  that  in  neither 
case  is  the  action  truly  reflex,  but  that  it  is  caused  by  stimulation  of 
the  central  ends  of  spinal  motor  fibres,  which  break  up  into  fibrils 
around  the  ganglion  cells.     These  motor  fibres,  in  the  case  of  the 
inferior  mesenteric  ganglion,  send  a  branch  to  the  sympathetic  nerve- 
cells  which  give  origin  to  the  fibres  of  the  opposite  hypogastric. 

Reflex  Time. — When  a  reflex  movement  is  called  forth,  a 
measurable  period  elapses  between  the  application  of  the 
stimulus  and  the  commencement  of  the  movement.  This 
interval  may  be  called  the  uncorrected  reflex  time.  A  pai 
of  the  interval  is  taken  up  in  the  transmission  of  the  afferent 
impulse  to  the  reflex  centre,  a  part  in  the  transmission 
the  efferent  impulse  to  the  muscles,  a  part  represents  th< 
latent  period  of  muscular  contraction,  and  the  remainder  is 
the  time  spent  in  the  centre,  or  the  true  reflex  time.  Whei 
the  conjunctiva  or  eyelid  is  stimulated  on  one  side  botl 
eyelids  blink.  This  is  a  typical  reflex  action  reduced  to  its 
simplest  expression,  and  the  true  reflex  time  is  correspond- 
ingly short — only  about  ^V  second.  An  additional  y^  secom 


THE  CENTRAL  NERVOUS  SYSTEM  68 1 

is  consumed  in  the  passage  of  the  afferent  impulse  along  the 
fifth  nerve  to  the  medulla  oblongata,  of  the  efferent  impulse 
from  the  medulla  to  the  orbicularis  palpebrarum  along  the 
seventh  nerve,  and  in  the  latent  period  of  the  muscle.  When 
a  naked  nerve,  like  the  sciatic,  is  stimulated,  the  true  reflex 
time  is  reduced  to  T^  to  -g-V  second.  As  estimated  by 
Tiirck's  method  (p.  729),  the  uncorrected  reflex  time  is 
greatly  lengthened,  it  may  be  to  several,  or  even  many, 
seconds.  For  here  it  is  evident  that  the  time  taken  by  the 
acid  to  soak  through  the  skin  and  reach  the  nerve-endings 
in  strength  sufficient  to  stimulate  them  is  included.  But 
even  when  the  peripheral  factors  remain  constant,  the 
central  factor  may  vary.  With  strong  stimulation,  e.g.,  the 
reflex  time  is  shorter  than  with  weak  stimulation.  Fatigue 
of  the  nerve  centres  delays  the  passage  of  impulses  through 
them  ;  and  strychnia,  while  it  increases  the  excitability  of 

the  cord,  also  lengthens  the  reflex  time. 

a 

3.  The  Origination  of  Impulses  in  the  Spinal  Cord. 
Automatism. — A  physiological  action  is  termed  automatic 
when  it  depends  upon  a  nervous  outburst  which  seems  to 
be  spontaneous,  in  the  sense  that  it  is  not  brought  about  by 
any  evident  reflex  mechanism,  or,  in  other  words,  is  not 
discharged  by  afferent  impulses  falling  into  the  centre  where 
it  arises.  An  action  known  to  be  caused  or  conditioned  by 
such  afferent  impulses  is  called  a  reflex  action.  Automatic 
actions  being  thus  defined  in  a  negative  manner  by  the 
defect  of  a  quality,  there  is  always  a  possibility  that  some 
day  or  other  it  may  be  demonstrated  that  any  given  action 
which  at  present  seems  automatic  in  its  origin  depends  on 
afferent  impulses  hitherto  unnoticed.  As  a  matter  of  fact, 
the  supposed  proofs  of  spinal  automatism  have  in  more  than 
one  case  vanished  with  the  advance  of  knowledge,  and  as 
the  domain  of  purely  automatic  action  has  been  narrowed, 
that  of  reflex  action  has  extended,  until  the  controversy  as 
to  the  boundaries  between  the  two  seems  not  unlikely  to  be 
ended  by  the  absorption  of  the  automatic  in  the  reflex. 
And  as  we  seem  almost  driven  to  conclude  that  from  the 
anatomical  standpoint  the  nervous  system  is  essentially  a 


682  A  MANUAL  OF  PHYSIOLOGY 

vast  collection  of  looped  conducting  paths,  each  with  an 
afferent  portion,  an  efferent  portion,  and  connections 
between  them  formed  by  cells  and  cell  networks,  so  it  may 
be  that  no  true  physiological  automatism  really  exists  either 
in  cord  or  brain,  that  every  form  of  physiological  activity — 
muscular  movement,  secretion,  intellectual  labour,  conscious- 
ness itself — would  cease  if  all  afferent  impulses  were  cut  off 
m  the  nervous  centres.  But  there  are  certain  groups  of 
flu/wactions  so  widely  separated  from  the  most  typical  reflex 
i.  actions  that,  provisionally  at  least,  they  may  be  distin- 
guished as  automatic.  Such  are  the  voluntary  movements, 
and  certain  involuntary  movements,  like  the  beat  of  the 
heart.  And  we  may  proceed  to  inquire  whether  the  spinal 
cord  has  any  power  of  originating  movements  or  other 
actions  of  this  high  degree  of  automatism. 

Muscular  Tone. — So  long  as  a  muscle  is  connected  with 
the  spinal  segment  from  which  its  nerves  arise,  it  is  never 
completely  relaxed  ;  its  fibres  are  in  a  condition  of  slight 
tonic  contraction,  and  retract  when  cut.  If  a  frog  whose 
brain  has  been  destroyed  is  suspended  so  that  the  legs  hang 
down,  and  one  sciatic  nerve  is  cut,  the  corresponding  limb 
may  be  observed  to  elongate  a  little  as  compared  with  the 
other.  At  one  time  this  tone  of  the  muscles  was  supposed 
be  due  to  the  continual  automatic  discharge  of  feeble 
impulses  from  the  grey  matter  of  the  cord  along  the  motor 
nerves.  But  it  has  been  proved  that  if  the  posterior  roots 
be  cut,  or  the  skin  removed  from  the  leg,  its  tone  is  com- 
pletely lost  although  the  anterior  roots  are  intact.  So  that 
the  tone  of  the  skeletal  muscles  depends  on  the  passage  of 
afferent  impulses  to  the  cord,  and  must  be  removed  from 
the  group  of  automatic  actions  and  included  in  the  reflexes. 
The  '  rigidity '  of  the  muscles,  often  observed  in  paralysis 
from  lesions  of  the  central  nervous  system,  and  denominated 
*  early '  or  '  late  '  according  as  it  comes  on  within  a  few  days 
or  a  few  weeks  after  the  occurrence  of  the  lesion,  is  also 
probably  in  part  a  reflex  phenomenon,  although  possessing 
some  of  the  characters  of  a  tonic  contraction  due  to  auto- 
matic discharge  from  the  spinal  centres.  For  in  such  cases 
myotatic  irritability  is  increased;  the  knee-jerk  is  exag- 


THE  CENTRAL  NERVOUS  SYSTEM  683 

gerated  ;  a  finger-jerk  may  be  elicited  by  tapping  the  wrist, 
an  arm-jerk  by  striking  the  skin  over  the  insertion  of  the 
biceps  or  triceps,  ankle-clonus  by  flexing  the  foot  (Gowers). 
Now,  myotatic  irritability  depends  on  reflex  muscular  tone 
(p.  677). 

It  is  probable  that  the  tone  of  such  visceral  muscles  as 
the  sphincters  of  the  anus  and  bladder  has  also  a  reflex 
element,  and  possible  that  the  same  is  true  of  the  tone  of 
the  smooth  muscular  fibres  of  the  bloodvessels  on  which 
the  maintenance  of  the  mean  blood -pressure  so  largely 
depends.  And  it  may  be  that  if  all  afferent  impulses  could 
be  cut  off  from  the  vaso-motor  centre,  as  by  section  of  the 
whole  of  the  posterior  spinal  roots  and  other  centripetal 
paths  to  the  medulla,  general  dilatation  of  the  arterioles 
would  take  place,  and  the  blood  -  pressure  be  greatly 
diminished.  But,  as  has  been  already  more  than  once 
pointed  out,  there  exist  peripheral  mechanisms  which,  after 
a  time,  make  good  to  some  extent  the  loss  of  tone  caused 
by  destruction  of  the  spinal  centres  (p.  664). 

Trophic  Tone. — The  degenerative  changes  that  occ  ir  in 
muscles,  nerves,  and  other  tissues  when  their  connection  with 
the  central  nervous  system  is  interrupted  have  been  already 
referred  to  (p.  584).  It  is  possible  to  explain  these  changes 
in  some  cases  without  the  assumption  that  tonic  impulses 
are  constantly  passing  out  from  the  brain  and  cord  to 
control  the  nutrition  of  the  peripheral  organs ;  and  we  have 
seen  that  there  is  no  real  evidence  of  the  existence  of 
specific  trophic  fibres.  But  the  degeneration  of  muscles] 
after  section  of  their  motor  nerves  is  difficult  to  understand  j 
except  on  the  hypothesis  that  impulses  from  the  cells  of 
the  anterior  horn  influence  their  nutrition.  The  only  ques- 
tion is  whether  these  are  the  impulses  to  which  muscular 
tone  is  due,  and  therefore  reflex,  or  different  in  nature  and 
automatically  discharged.  Now,  degeneration  of  a  muscle  is 
not  usually  caused,  or  at  least  not  for  a  long  time,  by  interrup- 
tion of  its  afferent  nerve-fibres,  as  in  locomotor  ataxia,  or 
after  section  of  the  posterior  nerve-roots  (Mott  and  Sherring- 
ton).  We  can  hardly  suppose  that  in  any  case  the  trophic 
influence  of  the  cells  of  the  spinal  or  sympathetic  ganglia 


684  A  MANUAL  OF  PHYSIOLOGY 

to  which  all  other  reflex  powers  have  been  denied,  is  of 
reflex  nature.  And  there  is,  indeed,  more  evidence  in  favour 
of  trophic  tone  being  an  automatic  action  of  the  cord  than 
for  any  of  the  other  tonic  functions  hitherto  considered. 

Respiratory  Automatism. — But  the  evidence  upon  which  the 
spinal  cord  has  been  credited  with  true  automatic  action  is 
chiefly  connected  with  the  central  respiratory  mechanism. 
It  is  known  (p.  211)  that  a  section  above  a  certain  level 
,  *,  in  the  medulla  oblongata  does  not  abolish  the  respiratory 
movements.  The  respiratory  centre,  then,  must  be  con- 
tinually sending  out  impulses  which  are  not  originated  by 
impulses  reaching  it  from  the  brain.  But  this  is  far  from 
being  a  proof  of  definite  automatic  action  by  the  spinal 
cord,  for  although  afferent  impulses  do  not,  under  the  con- 
ditions of  that  experiment,  reach  the  respiratory  centre  from 
the  brain,  they  may  and  do  reach  it  from  the  periphery; 
and  the  only  true  test  of  automatic  activity  would  be  to 
sever  the  whole  of  the  afferent  paths  leading  to  the  centre, 
and  then  to  observe  whether  or  no  the  respiratory  move- 
ments continued.  This  is  an  experiment  which  it  is  difficult, 
if  not  almost  impossible,  to  carry  out.  But  to  say  this  is 
merely  to  confess  that,  in  the  present  state  of  experimental 
physiology,  it  is  difficult  or  impossible  to  apply  a  crucial 
test  to  the  doctrine  of  respiratory  automatism. 

The  «  Centres '  of  the  Cord  and  Bulb.— We  have  frequently  used 
the  word  *  centre '  in  describing  the  functions  of  the  spinal  cord,  but 
the  term,  although  a  convenient  one,  is  apt  to  convey  the  idea  that 
our  knowledge  is  far  more  minute  and  precise  than  it  really  is.  When 
we  say  that  a  centre  for  a  given  physiological  action  exists  in  a  definite 
portion  of  the  spinal  cord,  all  that  is  meant  is  that  the  action  can  be 
called  out  experimentally,  or  can  normally  go  on,  so  long  as  this 
portion  of  the  cord  and  the  nerves  coming  to  it  and  leaving  it  are 
intact,  and  that  destruction  of  the  'centre'  abolishes  the  action. 
For  example,  a  part  of  the  medulla  oblongata  on  each  side  of  the 
middle  line  in  the  floor  of  the  fourth  ventricle  above  the  calamus 
scriptorius  is  so  related  to  the  function  of  respiration  that  when 
it  is  destroyed  the  animal  ceases  to  breathe.  But  this  respiratory 
centre,  the  '  noeud  vital '  of  Flourens,  does  not  correspond  in  position 
with  any  definite  collection  of  grey  matter,  although  it  includes  the 
nuclei  of  origin  of  several  cranial  nerves,  and  forms  an  important 
point  of  departure  for  efferent,  and  of  arrival  for  afferent,  fibres  con- 
nected with  the  respiratory  act.  Its  destruction  involves  the  cutting 
off  of  the  impulses  constantly  travelling  up  the  vagus  to  modify  the 


THE  CENTRAL  NERVOUS  SYSTEM  685 

respiratory  rhythm,  and  of  the  impulses  constantly  passing  down  the 
cord  to  the  phrenics  and  the  intercostal  nerves.  And  just  as  the 
traffic  of  a  wide  region  can  be  paralyzed  at  a  single  blow  by  severing 
the  lines  in  the  neighbourhood  of  a  great  railway  junction,  or  more 
laboriously,  though  not  less  effectually,  by  separate  section  of  the 
same  tracks  at  a  radius  of  a  hundred  miles,  so  destruction  of  the 
respiratory  centre  accomplishes  by  a  single  puncture  what  can  be 
also  performed  by  section  of  all  the  respiratory  nerves  at  a  distance 
from  the  medulla  oblongata.  But  while  nobody  speaks  of  the 
destruction  of  a  *  centre '  when  a  reflex  action  is  abolished  by 
division  of  the  peripheral  nerves  concerned  in  it,  there  is  a  tendency, 
when  the  same  effect  is  brought  about  by  a  lesion  in  the  brain  or 
cord,  to  invoke  that  mysterious  name,  and  to  forget  that  the  cerebro- 
spinal  axis  is  at  least  as  much  a  stretch  of  conducting  paths  as  a 
collection  of  discharging  nervous  mechanisms. 

It  is,  perhaps,  a  profitless  task  to  enumerate  all  the  so-called 
centres  in  the  bulb  and  cord  with  which  the  perverse  ingenuity  of 
investigators  and  systematic  writers  has  encumbered  the  archives 
and  text-books  of  physiology.  In  addition  to  the  great  vaso-motor, 
respiratory,  cardie-inhibitory  and  cardio-augmentor  centres  in  the 
bulb,  which,  perhaps,  have  more  right  than  the  rest  to  be  regarded 
as  distinct  physiological  mechanisms,  if  not  as  definitely  bounded 
anatomical  areas,  there  have  been  distinguished  ano-spinal,  vesico- 
spinal,  and  genito-spinal  centres  in  the  lumbar  cord,  a  cilio-spinal 
centre  for  dilatation  of  the  pupil  in  the  cervical  cord,  and  in  the 
medulla  centres  for  sneezing,  for  coughing,  for  sweating,  for  sucking, 
for  masticating,  for  swallowing,  for  salivating,  for  vomiting,  for  the 
production  of  general  convulsions,  for  closure  of  the  eyes.  It  would 
be  just  as  correct,  and  more  practically  useful  (for  it  would  perhaps 
encourage  the  student  who  has  lost  his  way  amidst  these  intermin- 
able distinctions),  to  say  that  the  cerebral  cortex  contains  a  centre 
for  learning  sense,  and  another  for  forgetting  nonsense,  and  that  in 
a  healthy  brain  it  is  the  latter  which  is  generally  thrown  into  activity 
in  the  study  of  this  portion  of  modern  physiology. 

j 

The  Cranial  Nerves.  O 

Unlike  the  spinal  nerves,  which  arise  at  not  very  unequal  intervals 
from  the  cord,  the  nuclei  of  origin  of  the  cranial  nerves,  with  the 
exception  of  the  olfactory  and  optic,  are  crowded  together  in  the 
inch  or  two  of  grey  matter  of  the  primitive  neural  axis  in  the 
immediate  neighbourhood  of  the  fourth  ventricle  and  the  Sylvian  * 
aqueduct.  Of  these  nuclei  some  are  sensory — sensory  nucleus  of  ^ 
fifth,  both  nuclei  of  eighth,  and  probably  the  common  nucleus  of 
ninth,  tenth,  and  eleventh.  The  motor  nuclei  lie,  upon  the  whole,  in 
two  longitudinal  rows — a  median  row,  which  consists  of  the  nuclei 
of  the_  third  and  fourth  nerves  in  the  floor  of  the  aqueduct,  and  those 
of  the  sixth  and  twelfth  nerves  in  the  floor  of  the  fourth  ventricle  ; 
and  a  lateral  row  comprising  the  motor  nuclei  of  the  fifth,  tenth,  and 
_eleventh  nerves,  and  the  nucleus  of  the  seventh.  The  clumps  of 


686  A  MANUAL  OF  PHYSIOLOGY 

grey  matter  which  make  up  these  nuclei  may  be  considered  as  homo- 
logous with  the  grey  matter  of  the  anterior  (including  the  lateral) 
horn  of  the  spinal  cord ;  and  the  motor  fibres  of  the  nerves  them- 
selves as  homologous  with  the  anterior  spinal  roots,  although  it  does 
not  follow  that  each  cranial  motor  nerve  represents  one  anterior  root 
and  one  only. 

The  first  or  olfactory  nerve  of  anatomists  is  really  a  lobe  of  the 


FIG.  234.— SCHEMATIC  TRANSPARENT  SECTION  OF  MEDULLA  OBLONGATA. 

The  numerals  V  to  XII  refer  to  the  nuclei  of  origin  of  the  respective  cranial  nerves. 
V  is  the  motor  nucleus  ;  RV,  the  roots  of  the  fifth  nerve  ;  V,  sensory  nucleus ; 
V",  sensory  nucleus  and  ascending  or  spinal  root.  RVI,  root  of  sixth  nerve  ;  RVII, 
root  of  seventh  nerve;  Py.  pyramid;  Py.  kr.,  decussation  of  the  pyramids;  O.s., 
superior  olive  ;  O,  olive  ;  G.  genu  of  the  facial. 

brain,  and  is  better  termed  the  olfactory  tract  or  bulb,  the  real 
olfactory  nerves  being  the  short  terminal  twigs  that  pierce  the  cribri- 
form plate  of  the  ethmoid  bone  to  reach  the  upper  part  of  the  nasal 
mucous  membrane.  The  olfactory  tract  can  be  traced  to  the 
uncinate  gyrus  of  the  same  side.  It  seems,  however,  to  be  also 
related  in  some  indirect  way  to  the  opposite  side  of  the  brain,  for  an 
injury  to  the  posterior  part  of  the  internal  capsule  has  been  found 
associated  with  impairment  of  smell  in  the  opposite  nostril.  Exces- 


THE  CENTRAL  NERVOUS  SYSTEM  687 

sive  stimulation  of  the  olfactory  nerve  by  exposure  to  a  strong  odour 
has  been  known  to  cause  complete  and  permanent  loss  of  smell. 

The  second  or  optic  nerve  is  connected  centrally  with  the  lateral' 
geniculate  body  and  pulvinar  (or  posterior  portion)  of  the  optic' 
thalamus,  the  anterior  corpus  quadrigeminum,  and  both  directly  and/ 
indirectly  with  the  occipital  cortex  (Fig.  14%)-  Peripherally  it  expands 
into  its  end-organ,  the  retina.  At  the  chiasma  the  fibres  of  the  optic 
nerve  decussate  partially  in  man  and  some  mammals,  as  the  dog, 
cat,  and  monkey,  completely  in  animals  whose  visual  field  is 
entirely  independent  for  the  two  eyes,  as  in  fishes  and  in  many 
mammals  (horse,  sheep,  deer).  In  man  the  fibres  for  the  nasal 
halves  of  both  retinae  cross  the  middle  line  at  the  chiasma,  those 
for  the  temporal  halves  do  not.  Since  the  field  of  vision  of  the 
nasal  side  of  the  retina  is  more  extensive  than  that  of  the  temporal 
side,  more  than  half  of  the  fibres  decussate.  A  lesion  involving 
the  whole  of  the  upper  part  of  the  occipital  cortex,  or  the  posterior 
portion  of  the  optic  thalamus,  or  the  optic  tract,  causes  hemi- 
anopia*  (blindness  of  the  corresponding  halves  of  the  two  retinae) 
on  the  side  of  the  lesion.  Thus,  a  lesion  equivalent  to  complete 
section  of  the  right  optic  tract  would  cause  blindness  of  the  nasal 
half  of  the  left,  and  of  the  temporal  half  of  the  right  eye,  and  the 
left  half  of  the  field  of  vision  would  be  blotted  out — the  patient  would 
be  unable,  with  his  eyes  directed  forwards,  to  see  an  object  at  his 
left.  A  lesion,  e.g.,  a  tumour  of  the  pituitary  body,  involving  the 
whole  of  the  optic  nerve  in  front  of  the  chiasma,  would  cause 
complete  blindness  of  the  corresponding  eye.  Sometimes  in  disease 
of  the  optic  nerve  vision  is  not  totally  destroyed  in  the  eye  to  which 
it  belongs,  but  the  field  is  narrowed  by  a  circumference  of  blindness. 
In  this  case  the  pathological  change  involves  the  circumferential 
fibres  of  the  nerve.  When  the  chiasma  is  affected  by  disease,  a  very 
frequent  symptom  is  nasal  hemianopia,  blindness  of  the  nasal  halves 
of  the  retinae,  with  loss  of  the  outer  or  temporal  half  of  each  field  of 
vision. 

It  may  be  added  that  not  only  does  a  central  lesion  lead  to 
peripheral  atrophy,  but  a  peripheral  lesion  may  cause  central  atrophy. 
Extirpation  of  the  eyeball  in  young  animals  is  followed  by  atrophy 
of  the  anterior  corpus  quadrigeminum,  lateral  geniculate  body, 
pulvinar,  and  occipital  cortex. 

The  third  nerve,  or  oculo-motor,  arises  from  a  series  of  nuclei  in 
the  floor  of  the  Sylvian  aqueduct  below  the  anterior  corpora  quadri- 
gemina.  The  root-bundles  coming  off  from  the  most  anterior  of 
the  nuclei  carry  fibres  that  have  to  do  with  the  mechanism  of 
accommodation.  The  nuclei  behind  these  are  connected  with  fibres 
that  cause  contraction  of  the  pupil  when  light  falls  on  the  retina ; 
while,  in  dogs  at  least,  the  posterior  portion  of  the  series  gives  off 
fibres  for  the  muscles  of  the  eye  in  the  following  order  from  before 

*  The  terms  'hemiopia,'  'hemianopia,'  ' hemianopsia,'  are  sometimes 
used  with  reference  to  the  blind  side  of  the  retinas,  sometimes  to  the  dark 
half  of  the  visual  field.  We  shall  always  use  the  word  '  hemianopia ' 
with  reference  to  the  retina. 


688  A  MANUAL  OF  PHYSIOLOGY 

backwards  :  internal  rectus,  superior  rectus,  levator  palpebrae 
superioris,  inferior  rectus,  inferior  oblique.  Complete  paralysis  of 
the  third  nerve  causes  loss  of  the  power  of  accommodation  of  the 
corresponding  eye,  dilatation  of  the  pupil  by  the  unopposed  action 
of  the  sympathetic  fibres,  diminution  of  the  power  of  moving  the 
eyeball,  ptosis,  or  drooping  of  the  upper  lid,  external  squint,  and 
consequent  diplopia,  or  double  vision. 

The  fourth  or  trochlear  nerve  arises  from  the  posterior  part  of 
the  same  tract  of  grey  matter  which  gives  origin  to  the  third  nerve. 
It  supplies  the  superior  oblique  muscle.  Paralysis  of  the  nerve 
causes  internal  squint  when  an  object  below  the  horizontal  plane  is 
looked  at,  owing  to  the  unopposed  action  of  the  inferior  rectus. 
There  is  also  diplopia  on  looking  down.  Unlike  the  other  cranial 
nerves,  the  two  trochlear  nerves  decussate  completely  after  they 
emerge  from  their  nuclei  of  origin. 

The  fifth  or  trigeminiis  nerve  appears  on  the  surface  of  the  pons 
as  a  large  sensory  root  and  a  smaller  motor  root.  Its  deep  origin  is 
more  extensive  than  that  of  any  of  the  other  cerebral  nerves,  stretch- 
ing as  it  does  from  the  level  of  the  anterior  corpus  quadrigeminum 
above  to  the  upper  part  of  the  spinal  cord  below.  Its  sensory  root, 
in  fact,  seems  to  include  the  sensory  divisions  of  all  the  motor  cranial 
nerves. 

The  motor  root  arises  partly  from  a  nucleus  in  the  floor  of  the 
fourth  ventricle  below  the  pons,  partly  as  the  so-called  descending 
root  from  large  nerve-cells  scattered  in  the  grey  matter  around  the 
aqueduct  of  Sylvius  all  the  way  from  the  anterior  quadrigeminate 
body  to  the  point  at  which  the  motor  root  is  given  off. 

The  sensory  root  has  likewise  two  deep  origins  :  a  nucleus  in  the 
neighbourhood  of  the  motor  nucleus  in  the  floor  of  the  fourth 
ventricle,  and  a  long  spinal  root  running  up  from  the  level  of  the 
second  cervical  nerve  through  the  medulla  oblongata  and  the 
tegmentum  of  the  pons,  where  it  lies  external  to  the  descending 
root. 

The  motor  fibres  of  the  fifth  nerve  supply  the  muscles  of  mastica- 
tion and  the  tensor  tympani.  The  sensory  fibres  confer  common 
sensation  on  the  face,  conjunctiva,  the  mucous  membranes  of  the 
mouth  and  nose,  and  the  structures  contained  in  them,  and  special 
sensation,  through  branches  given  off  to  the  facial  and  glosso- 
pharyngeal  nerves,  on  the  organs  of  taste.  Complete  paralysis  of  the 
nerve  causes  loss  of  movement  in  the  muscles  of  mastication,  some- 
times impaired  hearing,  and  loss  of  common  sensation  in  the  area 
supplied  by  it.  Loss  or  impairment  of  taste  in  the  corresponding 
half  of  the  tongue  is  also  often  seen  in  disease  involving  the  sensory 
root,  although  not  in  affections  of  the  trunk  of  the  nerve,  since  the 
taste-fibres  leave  it  near  its  origin.  Both  taste  and  touch  are  lost  in 
the  monkey  in  the  anterior  two-thirds  of  the  tongue  after  intracranial 
section  of  the  trigeminus. 

Vaso-motor  changes  are  occasionally,  and  '  trophic '  changes 
frequently,  observed  in  disease  of  the  fifth  nerve.  The  trophic 
disturbance  is  most  conspicuous  in  the  eyeball  (ulceration  of  the 


THE  CENTRAL  NERVOUS  SYSTEM  689 

cornea,  going  on,  it  may  be,  to  complete  disorganization  of  the  eye). 
These  effects  seem  to  be  partly  due  to  the  loss  of  sensation  in  the 
eye,  and  the  consequent  risk  of  damage  from  without,  and  the  un- 
regarded presence  of  foreign  bodies  and  accumulation  of  secretion 
within  the  lids. 

The  sixth  or  abducens  nerve  takes  origin  from  a  nucleus  in  the 
floor  of  the  fourth  ventricle  at  the  level  of  the  posterior  portion  of  the 
pons.  It  supplies  the  external  rectus  muscle  of  the  eyeball.  Paralysis 
of  it  causes  internal  squint. 

The  seventh  or  facial  nerve  arises  from  a  nucleus  in  the  reticular 
formation  of  the  medulla  oblongata,  and  running  up  some  distance 
into  the  pons.  It  supplies  the  muscles  of  the  face ;  and  when  these 
are  greatly  developed,  as  in  the  trunk  of  the  elephant,  the  nerve 
reaches  very  large  proportions.  Since  the  fibres  which  connect  the 
nucleus  with  the  cerebral  cortex  decussate  about  the  middle  of  the 
pons,  a  lesion  above  this  level  which  causes  hemiplegia  paralyzes 
the  face  on  the  same  side  as  the  rest  of  the  body,  i.e.,  on  the  side 
opposite  the  lesion.  But  the  paralysis  is  confined  to  the  muscles  of 
the  lower  portion  of  the  face,  and  affects  especially  the  muscles  about 
the  mouth.  Sometimes  the  pyramidal  tract  and  the  facial  nerve,  or 
nucleus,  are  involved  in  a  common  lesion.  In  this  case  paralysis  of 
the  face  is  on  the  side  of  the  lesion,  and  is  total,  while  the  rest 
of  the  body  is  paralyzed  on  the  opposite  side.  Complete  facial 
paralysis  is  often  caused  by  an  inflammatory  process  in  the  nerve 
itself  (neuritis).  The  symptoms  of  complete  facial  paralysis  are  very 
characteristic.  The  face  and  forehead  on  the  paralyzed  side  are 
smooth,  motionless,  and  devoid  of  expression.  The  eye  remains 
•open  even  in  sleep,  owing  to  paralysis  of  the  orbicularis  palpebrarum. 
A  smile  becomes  a  grimace.  An  attempt  to  wink  with  both  eyes 
results  in  a  grotesque  contortion.  The  mouth  appears  like  a  diagonal 
slit  in  the  face,  its  angle  being  drawn  up  on  the  sound  side,  and  the 
patient  cannot  bring  the  lips  sufficiently  close  together  to  be  able  to 
blow  out  a  candle  or  to  whistle  Liquids  escape  from  the  mouth, 
and  food  collects  between  the  paralyzed  buccinator  and  the  teeth. 
The  labial  consonants  are  not  properly  pronounced.  Taste  is  lost  in 
the  anterior  two-thirds  of  the  tongue  when  the  nerve  is  injured 
between  the  entrance  of  the  gustatory  fibres  from  the  trigeminus 
and  their  exit  by  the  chorda  tympani,  but  not  when  the  lesion  is  in 
the  nucleus  of  origin,  or  anywhere  above  it.  Hearing  is  sometimes 
impaired  because  the  auditory  and  facial  nerves,  lying  close  together 
for  part  of  their  course,  are  apt  to  suffer  together,  but  perhaps  also 
because  the  stapedius  muscle  is  supplied  by  the  seventh  'nerve. 

The  eighth  or  auditory  nerve  arises  from  the  medulla  oblongata 
toy  two  roots,  one  of  which  passes  in  on  each  side  of  the  restiform 
body.  The  auditory  nucleus  in  the  floor  of  the  fourth  ventricle  con- 
sists of  two  parts,  a  lateral  and  a  mesial  nucleus,  the  first  of  which  is 
connected  with  the  fibres  of  the  ventral,  and  the  second  with  those 
of  the  dorsal  root.  The  accessory  nucleus  on  the  ventral  surface  of 
the  restiform  body  forms  an  additional  nucleus  for  the  dorsal  root. 
It  is  believed  that  the  two  roots  of  the  auditory  nerve  are  physiologi- 

44 


690  A  MANUAL  OF  PHYSIOLOGY 

cally  as  well  as  anatomically  distinct,  for  the  dorsal  root  seems  to 
carry  the  fibres  which  are  distributed  in  the  cochlear  division  of  the 
auditory  nerve  to  the  cochlea,  the  ventral  root  those  which  pass  to 
the  semicircular  canals  and  the  vestibule  of  the  internal  ear.  And, 
as  we  shall  see  (p.  698),  it  is  extremely  probable  that  the  cochlea 
subserves  the  function  of  hearing,  the  semicircular  canals  and  vesti- 
bule the  function  of  equilibration.  We  must  assume,  from  clinical 
and  experimental  data,  that  the  dorsal  root  is  connected  through  its 
nuclei  with  the  first  or  first  and  second  temporo-sphenoidal  convolu- 
tions on  the  opposite  side.  Two  prominent  symptoms  may  be 
associated  with  disease  of  the  auditory  nerve — (a)  disturbance  or 
loss  of  hearing ;  (b)  loss  or  impairment  of  equilibration. 

The  ninth  or  glosso-pharyngeal  nerve  arises  from  the  upper  portion 
of  an  elongated  nucleus  in  the  medulla  oblongata,  the  lower  portion 
of  which  gives  origin  to  the  accessory  division  of  the  spinal  accessory, 
and  the  middle  to  the  vagus.  An  additional  origin  is  formed  by  a 
bundle  of  fibres,  the  ascending  root  of  the  glosso-pharyngeal,  which 
arises  from  the  grey  matter  of  the  lateral  horn  of  the  cord  and  the 
formatio  reticularis  of  the  medulla,  and  commences  as  far  down  as 
the  fourth  cervical  nerve.  The  glosso-pharyngeal  has  both  sensory 
and  motor  fibres — sensory  for  the  posterior  third  of  the  tongue  and 
the  mucous  membrane  of  the  back  of  the  mouth,  motor  for  the 
middle  constrictor  of  the  pharynx  and  the  stylo-pharyngeus.  It  also 
contains  the  nerves  of  taste  for  the  posterior  third  of  the  tongue,  but 
these  reach  it  from  the  fifth  nerve. 

The  tenth  or  vagus  or  pneumogastric  nerve  is  joined  near  its 
origin  by  the  accessory  portion  of  the  spinal  accessory,  that  is,  the 
portion  which  arises  from  the  medulla  oblongata,  and  we  shall 
describe  them  together.  The  mixed  nerve  contains  both  sensory  and 
motor  fibres,  the  latter  chiefly  derived  from  the  accessory,  the  former 
entirely  from  the  vagus.  The  distribution  of  the  nerve  is  more 
extensive  than  that  of  any  other  in  the  body.  The  oesophagus 
receives  both  motor  and  sensory  branches  from  the  cesophageal 
plexus.  The  pharyngeal  branch  of  the  vagus  is  the  chief  motor 
nerve  of  the  pharynx  and  soft  palate  (including  the  tensor  palati). 
The  superior  laryngeal  branch  is  the  nerve  of  common  sensation  for 
the  larynx  above  the  vocal  cords,  and  the  motor  nerve  of  the  crico- 
thyroid  muscle.  The  inferior  or  recurrent  laryngeal  supplies  the  rest 
of  the  laryngeal  muscles,  and  the  sensory  fibres  for  the  mucous 
membrane  of  the  trachea  and  the  larynx  below  the  glottis.  The 
superior  laryngeal  contains  afferent  fibres,  stimulation  of  which 
gives  rise  to  coughing,  slows  respiration,  or  stops  it  in  expiration. 
Reflex  movements  of  deglutition  are  also  caused.  The  vagus 
supplies  the  lung  both  with  motor  and  sensory  filaments  through  the 
pulmonary  plexus.  The  motor  fibres  when  stimulated  cause  con- 
striction of  the  bronchi ;  excitation  of  the  afferent  fibres  causes  reflex 
changes  in  the  rate  or  depth  of  respiration.  The  cardiac  branches 
contain  inhibitory  fibres  probably  derived  from  the  spinal-accessory, 
and  depressor  fibres  which  pass  up  in  the  vagus  trunk  (dog),  or  as  a 
separate  nerve  to  join  the  vagus  or  its  superior  laryngeal  branch  or 


THE  CENTRAL  NERVOUS  SYSTEM  691 

both  (rabbit).  The  gastric  and  intestinal  branches  contain  both 
motor  and  sensory  nerves  for  the  stomach  and  intestines.  The  sensory 
are  probably  large  medullated  fibres  (7  /x  to  9  /A).  The  afferent  vagus 
fibres  from  the  stomach  carry  up  impulses  which  excite  the  action  of 
vomiting.  Lesions  of  the  vagus,  its  nuclei  of  origin,  or  its  branches, 
are  associated  with  many  interesting  forms  of  paralysis  and  other 
symptoms.  Paralysis  of  the  pharynx  is  generally  caused  by  disease 
of  the  nucleus  in  the  medulla.  From  its  anatomical  relation  to 
the  nuclei  of  the  glosso  pharyngeal  and  hypoglossal,  it  will  be  easily 
understood  that  these  nerves  are  often  involved  in  localized  central 
lesions  along  with  the  vagus.  But  the  fact  that  in  glosso  labio- 
laryngeal  palsy — a  condition  characterized  by  progressive  paralysis 
and  atrophy  of  the  muscles  of  the  tongue,  lips,  larynx,  and  pharynx 
— the  orbicularis  oris  is  paralyzed,  while  the  other  muscles  supplied 
by  the  facial  remain  intact,  would  seem  to  show  that  in  system 
diseases  it  is  not  so  much  anatomical  groups  of  nerve-cells  which  are 
liable  to  simultaneous  degeneration  and  failure,  as  physiological 
groups  normally  associated  in  particular  functions.  Such  functional 
groups  of  cells,  occupied  with  the  same  kinds  of  labour  at  the  same 
times  and  under  the  same  conditions,  may  be  supposed  to  take  on  a 
similar  bias  or  tendency  to  degeneration,  a  tendency  not  indicated,  it 
may  be,  by  any  structural  peculiarity,  but  traced  deep  in  the  molecular 
activity  of  the  cells.  Difficulty  in  swallowing  is  the  chief  symptom 
of  pharyngeal  paralysis.  The  symptoms  of  laryngeal  paralysis  have 
been  already  described  under  'Voice'  (p.  270).  Tachycardia,  or  a 
permanent  increase  in  the  rate  of  the  heart,  has  been  stated  to 
occur  in  certain  cases  of  paralysis  of  the  vagus,  caused  by  disease  or 
accidental  interference ;  and  a  persistent  slowing  of  the  respiration 
has  been  occasionally  attributed  to  the  same  cause.  But  it  is  difficult 
to  reconcile  many  of  these  cases  with  experimental  results,  for  in 
most  of  them  the  lesion  only  involved  one  vagus ;  and  in  animals 
section  of  one  vagus  has  no  permanent  effect  on  the  rate  of  the  heart 
or  of  the  respiratory  movements. 

Destruction  of  the  nerve  near  its  origin  has  been  sometimes  found 
associated  with  disappearance  of  the  food-appetites,  hunger  and 
thirst,  and  it  has  been  assumed  that  this  was  due  to  loss  of  afferent 
impulses  from  the  stomach.  But  clinical  testimony  is  by  no  means 
unanimous  on  this  point,  and  experiments  on  animals  show  that  other 
factors  are  involved  in  these  sensations. 

The  eleventh  or  spinal-accessory  nerve  consists  of  two  parts  :  the 
accessory  or  internal  branch,  which  arises  from  the  medulla  oblongata, 
and  which  we  have  just  considered  in  conjunction  with  the  vagus ; 
and  the  external  or  spinal  branch,  which,  arising  from  the  lateral  rim 
of  the  anterior  horn  of  the  cord  from  the  sixth  or  seventh  cervical 
nerve  upwards,  passes  out  to  supply  the  trapezius  and  sterno-mastoid 
muscles  with  motor  fibres. 

The  twelfth  or  hypoglossal  nerve  contains  the  motor  supply  of  the 
intrinsic  and  extrinsic  muscles  of  the  tongue  and  of  the  thyro-  and 
genio-hyoid.  Paralysis  of  it  causes  deficient  movement  of  the  corre- 
sponding half  of  the  tongue.  When  the  tongue  is  put  out,  it  deviates 

44—2 


692  A  MANUAL  OF  PHYSIOLOGY 

towards  the  paralyzed  side,  being  pushed  over  by  the  unparalyzed 
genio-hyoglossus  of  the  opposite  side,  which  is  thrown  into  action  in 
protruding  the  tongue. 

The  Functions  of  the  Brain. 

The  paths  by  which  the  various  parts  of  the  central  nervous 
system  are  connected  with  each  other  and  with  the  periphery 
have  been  already  described,  and  we  have  completed  the 
examination  of  the  functions  of  the  spinal  cord  and  medulla 
oblongata.  The  events  that  take  place  in  the  upper  part  of 
the  central  nervous  stem  and  in  the  cortex  of  the  cerebellum 
and  cerebrum  now  claim  our  attention. 

From  very  early  times  the  brain  has  been  popularly  believed  to  be 
•  the  seat  of  all  that  we  mean  by  consciousness — sensation,  ideation, 
emotion,  volition.  And  he  who  loves  to  trace  the  roots  of  things 
back  into  the  past  may  see,  if  he  choose,  running  through  the  whole 
texture  of  the  older  speculations  a  belief  that  the  brain  does  not  act 
as  a  whole,  but  is  divided  into  mechanisms,  each  with  its  special 
work — a  foreshadowing,  often  in  grotesque  outlines,  of  the  doctrine 
of  localization  so  widely  held  to-day.  But  until  comparatively  recent 
times,  cerebral  physiology  remained  a  kind  of  scientific  terra  incog- 
nita ;  and  no  notable  additions  were  made  for  a  thousand  years  to 
the  doctrines  of  Galen.  Even  to-day  the  utmost  limit  of  our  know- 
ledge is  reached  when  in  certain  cases  we  have  connected  a  particular 
movement  or  sensation  with  a  more  or  less  sharply  defined  anatomical 
area.  How  the  cerebral  processes  that  lead  to  sensations  and 
movements,  to  emotions  and  intellectual  acts,  arise  and  die  out; 
what  molecular  changes  are  associated  with  them  ;  above  all,  how 
the  molecular  changes  are  translated  into  consciousness — how,  for 
example,  it  is  that  a  series  of  nerve-impulses  flickering  across  the 
labyrinth  of  the  occipital  cortex  should  light  up  there  a  visual 
sensation— these  are  questions  to  which  we  can  as  yet  give  no 
answer,  and  the  answers  to  some  of  which  must  for  ever  remain 
hidden  from  us. 

Functions  of  the  Upper  Part  of  the  Central  Stem  and  Basal 
Ganglia. — Some  of  the  transverse  fibres  of  the  pens  form  a  com- 
missure between  the  hemispheres  of  the  cerebellum,  but  many  of 
them  are  the  cerebellar  portions  of  commissural  arcs  interrupted  by 
pontine  grey  matter,  and  continued  by  fibres  of  the  corona  radiata  to 
the  pre-frontal,  temporal  and  occipital  portions  of  the  cerebral  cortex 
(p.  659). 

The  posterior  corpora  quadrigemina  (testes)  and  internal  geniculate 
bodies  are  connected  with  the  cochlear  division  of  the  auditory 
nerves,  and  therefore  have  some  relation  to  the  sense  of  hearing. 
Stimulation  of  the  testes  causes  a  peculiar  cry,  and  the  pupils  dilate. 

The  anterior  corpora  quadrigemina  (nates)  and  the  lateral  corpora 
geniculata  are  connected  with  the  optic  tracts.  Their  development 


THE  CENTRAL  NERVOUS  SYSTEM 


693 


is  arrested  after  extirpation  of  the  eyeball  in  young  animals,  and 
they  may  therefore  be  assumed  to  be  concerned  in  vision,  although 
the  size  of  their  homologues,  the  optic  lobes  or  corpora  bigemina,  in 
animals  below  the  rank  of  mammals  (birds,  reptiles,  amphibians), 
does  not  seem  to  be  related  to  the  development  of  the  organs  of 
sight.  The  Proteus  and  the  Hag-fish,  e.g.,  have  large  optic  lobes, 
rudimentary  eyes  and  optic  tracts.  The  optic  nerve,  the  nuclei  of 
the  oculo-motor  nerve  in  the  wall  of  the  Sylvian  aqueduct,  and  the 
fibres  which  it  carries  to  the  iris,  form  reflex  arcs  for  the  contraction 
of  the  pupil  to  light  and  during  accommodation. 

The  functions  of  the  optic  thalami  have  not  been  satisfactorily 
defined  either  by  experiment  or  pathological  observation.  Lying  as, 
they  do  in  the  isthmus  of  the  brain,  begirt  by  the  great  motor  and 


Corpus  striatum 

Anterior  pillar  of  the 
fornix 

Optic  thalamus 
Third  ventricle 


FIG.  235.— HORIZONTAL  SECTION  THROUGH  BRAIN  TO  SHOW  THE  BASAL 
GANGLIA  AND  THIRD  VENTRICLE  (HUMAN). 

sensory  paths,  it  is  to  be  expected  that  lesions  of  the  thalami  should 
affect  also  the  internal  capsule,  and  give  rise  to  the  symptoms  of 
motor  and  sensory  paralysis.  But  no  definite  defect  of  motor  power 
or  common  sensation  has  ever  been  unequivocally  connected  with  a 
lesion  restricted  to  the  thalami.  They  have,  however,  extensive 
connections  with  the  cerebral  cortex,  each  of  the  thalamic  nuclei 
being  connected  with  a  definite  cortical  region  in  such  a  way  that 
destruction  of  the  cortical  area  in  young  animals  or  human  beings 
ids  to  degeneration  of  the  corresponding  nucleus.  The  posterior 
>ortion  of  the  thalamus,  or  pulvinar,  forms  part  of  the  central 
visual  apparatus  ;  for  (a)  it  is  found  to  be  undeveloped  in  animals 
from  which  the  eyeballs  have  been  removed  soon  after  birth ;  (b)  a 
portion  of  the  optic  tract  is  certainly  connected  with  it ;  (c}  in  some 
cases  of  atrophy  of  the  occipital  cortex,  which,  as  we  shall  see,  is 


694 


A  MANUAL  OF  PHYSIOLOGY 


undoubtedly  a  central  area  for  visual  sensations,  atrophy  of  the 
pulvinar  has  also  been  noticed  ;  (d)  a  lesion  of  the  pulvinar  may 
apparently  give  rise  to  hemianopia  (p.  687). 

Haemorrhage  into  the  caudate  or  lenticular  nucleus  of  the  corpus 
striatum  often  causes  h^emiplegia,  but  this  is  always  due  to  implica- 
tion of  the  internal  capsule.  Experimental  lesions  in  dogs  and 
rabbits  are  followed  by  disturbances  of  the  heat-regulating  mechanism 
and  rise  of  temperature. 

Certain  structures,  belonging  to  the  primary  fore-brain,  which  have 
now  no  functional  importance,  may  nevertheless  be  mentioned  as 

milestones  in  the 
march  of  develop- 
ment. The  pineal 
body  is  made  up  of 
the  vestiges  of  the 
single  mesial  eye  of 
the  ancient  amphi- 
bians, which  re- 
sembled the  eye  of 
invertebrates  i  n 
having  the  retinal 
rods  directed  towards 
the  cavity  instead  of 
towards  the  circum- 
ference of  the  eye- 
ball. The  ganglia 
habenulce  seem  to 
represent  the  optic 
ganglia  of  this  cyclo- 
pean  eye.  The  in- 
fundibulum  is  pro- 
bably what  remains 
of  the  gullet  of  the 
ancestors  of  the  ver- 
tebrates. The  pitui- 
tary body  consists  of 
two  portions,  the  an- 
terior being  derived 

from  the  buccal  cavity,,  the  posterior  from  the  primary  fore-brain. 
It  has  been  stated  that  after  excision  of  the  thyroid  glands,  the  anterior 
division,  the  tissue  of  which  has  a  resemblance  to  thyroid  tissue,  has 
sometimes  been  found  hypertrophied  (but  see  p.  475). 

Functions  of  the  Cerebellum. — The  elaborate  pattern  of  the 
arbor  vitas,  the  appearance  given  by  the  branched  laminae  in 
a  section  of  the  cerebellum,  excited  the  speculation  of  the 
old  anatomists.  A  structure  so  marvellous  must  be  matched, 
they  thought,  with  functions  as  unique.  At  a  time  when 
the  discoveries  of  Galvani  and  Volts/ were  fresh,  and  the 


FIG.  236.— LONGITUDINAL  SECTION  OF  THE  GREY 
MATTER  OF  A  LAMELLA  OF  THE  CEREBELLUM 
(DIAGRAMMATIC,  AFTER  KOLLIKER). 

gr,  a  '  granule '  cell  with  its  neuron,  n  ;  n' ,  bifurcation 
of  n,  in  the  molecular  layer,  into  two  fine  longitudinal 
branches ;  m,  a  Purkinje's  cell ;  m',  antler  process  (Golgi's 
method). 


THE  CENTRAL  NERVOUS  SYSTEM 


695 


world  ran  mad  on  electricity,  the  hypothesis  of  Rolando, 
that  '  nerve-force  '  was  generated  by  the  lamellae  of  the 
cerebellum  as  electrical  energy  is  generated  by  the  plates 
of  the  voltaic  pile,  ridiculous  as  it  now  appears,  was  not 
unnatural.  The  speculation  of  Gall,  who  connected  the 
cerebellum  with  the  development  of  sexual  emotions  and 
the  action  of  the  generative  mechanisms,  was  based  on  no 
fact.  It  has  been  definitely  disproved  by  the  observations 
of  Luciani,  who  found  that  a  bitch  deprived  of  its  cerebellum 
showed  all  the  phenomena  of  heat  or  '  rut,'  was  impregnated, 
whelped  at  full  term  in  an  en- 
tirely normal  manner,  and  mani- 
fested the  maternal  instincts  in 
their  full  intensity.  Flourens 
put  forward  the  doctrine  that 
the  cerebellum  is  an  organ 
especially  concerned  in  the  co- 
ordination of  movements  and 
the  maintenance  of  equilibrium, 
supporting  his  conclusions  by 
an  elaborate  series  of  experi- 
ments. Notwithstanding  the 
very  large  amount  of  experi- 
mental and  clinical  study  which 
has  been  devoted  to  the  cere- 
be  Hum  since  the  time  of 

Flourens,  our  knowledge  of  its  FIG.  237.— A  PURKINJE'S  CELL  FROM 
functions  has  hardly  advanced 
beyond  the  point  then  reached. 
Indeed,  it  may  be  said  that  the  tendency  has  been  rather  to 
abridge  than  to  extend  the  field  of  current  physiological 
doctrine  on  this  subject.  For  while  it  has  been  shown  that 
the  integrity  of  the  cerebellum  is  essential  to  equilibration,  it 
is  by  no  means  certain  that  it  is  essential  for  the  co-ordination 
of  movements  other  than  those  concerned  in  the  maintenance 
of  equilibrium  and  in  locomotion.  Animals  entirely  deprived 
of  the  cerebellum  have  shown,  after  the  primary  effects  of 
the  operation  have  passed  away,  no  impairment  in  general 
co-ordinative  power ;  and  cases  are  on  record  in  which  the 


THE  CEREBELLUM  OF  A  CAT  (AFTER 
CAJAL  ;  GOLGI'S  METHOD). 


696  A  MANUAL  OF  PHYSIOLOGY 

human  cerebellum  has  been  found  at  death  to  be  utterly 
disorganized,  and  yet  in  which  many  classes  of  movements 
have  been  well  co-ordinated  during  life.  But  what  has  been 
noticed  in  such  cases  is  a  marked  inability  to  maintain  the 
upright  posture,  a  staggering  gait,  twitching  movements  of 
the  eyes  (nystagmus) — in  a  word,  a  general  disorder  of  the 
mechanism  of  equilibration.  In  cases  of  congenital  defect 
of  the  cerebellum,  the  power  of  walking,  and  even  of 
standing,  is  late  in  being  acquired,  and  usually  imperfect. 
The  connections  of  the  cerebellum  with  other  parts  of  the 
central  nervous  system  and  with  the  periphery  corroborate 
the  direct  results  of  experiment  For  the  most  important 
afferent  impulses  concerned  in  equilibration  are  those  from 
the  muscles,  the  skin,  the  semicircular  canals  and  vestibule 
of  the  internal  ear,  and  the  eyes.  And  the  cerebellum,  as 
we  have  seen  (p.  655),  is  linked  with  all  of  these,  and  has 
besides  an  extensive  crossed  connection  through  the  middle 
and  superior  peduncles  with  the  opposite  cerebral  hemi- 
sphere. 

We  do  not  as  yet  know  the  full  significance  of  this  extra- 
ordinarily free  communication  of  the  grey  matter  of  the 
cerebellum  with  every  part  of  the  central  nervous  system. 
But  it  is  evident  that  by  the  broad  highway  of  the  restiform 
body,  or  the  cross-country  routes  from  cerebral  cortex  to 
cerebellum,  impulses  may  pass  into  it  from  every  quarter; 
and  it  is  an  organ  so  connected  that  is  suited  to  take 
cognizance  of  the  multitudes  of  impressions  concerned  in 
the  maintenance  of  equilibrium.  This  is  a  convenient  place 
to  consider  a  little  more  in  detail  the  nature  and  peripheral 
sources  of  the  most  important  of  these  impressions. 

(i)  Afferent  Impressions  from  the  Muscles. — Muscles  are  richly 
supplied  with  afferent  fibres,  for  about  half  of  the  fibres  in  the  nerves 
of  skeletal  muscles  degenerate  after  section  of  the  posterior  roots 
beyond  the  ganglia  (Sherrington)  Various  kinds  of  impressions 
may  pass  up  these  muscular  nerves  :  (a)  Impressions  giving  rise  to 
pain,  as  in  muscular  cramp  and  in  experimental  excitation  of  even 
the  finest  muscular  nerve-filament ;  (b)  impulses  causing  a  rise  of 
blood-pressure  ;  (c)  impulses  which  are  not  associated  with  a  distinct 
impression  in  consciousness,  but  enable  us  to  localize  the  position 
of  the  limbs,  head,  eyes,  and  other  parts  of  the  body  ;  (d)  impulses 
which  inform  us  as  to  the  extent  and  force  of  muscular  contraction, 


THE  CENTRAL  NERVOUS  SYSTEM 


697 


and  seem  to  underlie  the  so-called  muscular  sense.  It  is  the  last 
two  kinds— if,  indeed,  they  are  distinct — which  must  be  concerned 
in  equilibration.  In  locomotor  ataxia  such  impressions  are  blocked 
by  degeneration  in  a  part  of  the  afferent  path  (p.  673),  and  disorders 
of  equilibrium  are  the  result. 

(2)  Afferent  Impressions  from  the  Skin. — Of  the  various  kinds  of 
nerve-impulses  that  arise  in  the  nerve-endings  of  the  skin,  only  those 
of  touch  and  pressure  seem  to  be  concerned  in  the  maintenance  of 
equilibrium.     When  the  soles  of  the  feet  are  anaesthetized  by  chloro- 
form or  by  cold,  and  the  person  is  directed  to  close  his  eyes,  he 
staggers  and  sways  from  side   to  side. 

The  disturbance  of  equilibrium  in 
locomotor  ataxia  must  be  partly  attri- 
buted to  the  loss  of  these  tactile 
sensations,  for  numbness  of  the  feet 
is  a  frequent  symptom,  and  the  patient 
asserts  that  he  does  not  feel  the 
ground.  An  interesting  illustration  of 
the  importance  of  afferent  impulses 
from  the  skin  in  the  maintenance  of 
equilibrium  is  afforded  by  the  behaviour 
of  a  frog  deprived  of  its  cerebral  hemi- 
spheres. Such  a  frog  will  balance  itself 
on  the  edge  of  a  board  like  a  normal 
animal,  but  if  the  skin  be  removed 
from  the  hind-legs,  it  will  fall  like  a  log 

(3)  Afferent    Impulses    from    the 
Semicircular   Canals.  —  The   semicir- 
cular canals  are  three  in  number,  and 
lie  nearly  in  three  mutually  rectangular 

planes  :  the  external  canal  in  the  horizontal  plane,  the  superior 
canal  in  a  vertical  longitudinal  plane,  and  the  posterior  canal 
in  a  vertical  transverse  plane.  Each  canal  bulges  out  at  one 
end  into  a  swelling,  or  ampulla,  which  opens  into  the  utricular 
division  of  the  vestibule  (Fig.  292).  The  other  extremities  of  the 
superior  and  posterior  canals  join  together,  and  have  a  common 
aperture  into  the  utricle,  but  the  undilated  end  of  the  external  or 
horizontal  canal  opens  separately.  The  utricle  and  the  semicircular 
canals  are  thus  connected  by  five  distinct  orifices.  The  greater  part 
of  the  internal  surface  of  the  membranous  canals,  utricle  and  saccule, 
is  lined  by  a  single  layer  of  flattened  epithelium.  But  at  one  part  of 
each  ampulla  projects  a  transverse  ridge,  the  crista  acustica,  covered 
not  with  squamous,  but  with  long  columnar  epithelium.  Hair-like 
processes  (auditory  hairs),  borne  either  by  the  columnar  cells  or  by 
spindle-shaped  cells  scattered  among  them,  project  into  the  endo- 
lymph,  which  fills  all  the  membranous  labyrinth,  and  are  covered  by 
a  thin  membrana  tectoria.  The  utricle  and  saccule  have  each  a 
somewhat  similar  but  broader  elevation,  the  macula  acustica,  covered 
with  epithelium  and  hair-cells  of  the  same  character,  and  the  hairs 
project  into  an  otolith,  or  small  mass  of  carbonate  of  lime.  The 


FIG.  238. — THE  SEMICIRCULAR 
CANALS  (DIAGRAMMATIC). 

H,    horizontal    or    external ;    S, 
superior ;  P,  posterior. 


698  A  MANUAL  OF  PHYSIOLOGY 

vestibular  branch  of  the  auditory  nerve  breaks  up  into  five  twigs  : 
one  for  each  ampulla,  one  for  the  utricle,  and  one  for  the  saccule. 
The  nerve-fibres,  on  which  lie  ganglion-cells,  lose  their  medulla  as 
they  approach  the  layer  of  hair-cells  in  which  they  terminate.  There 
is  very  strong  evidence  that  the  semicircular  canals  are  concerned, 
not  in  hearing,  but  in  equilibration.  A  pigeon  from  which  the 
membranous  canals  have  been  removed  still  hears  perfectly  well 
so  long  as  the  cochlea  is  intact,  but  exhibits  the  most  profound 
disturbance  of  equilibrium.  If  the  horizontal  canal  is  destroyed 
or  divided,  the  pigeon  moves  its  head  continually  from  side  to 
side  around  a  vertical  axis  ;  if  the  superior  canal  is  divided,  the 
head  moves  up  and  down  around  a  horizontal  axis.  The  power 
of  co-ordination  of  movements  is  diminished,  but  not  to  the  same 
extent  in  all  kinds  of  animals.  Thrown  into  the  air,  the  pigeon  is 
helpless  ;  it  cannot  fly  ;  but  a  goose  with  divided  semicircular  canals 
can  still  swim.  The  condition  is  only  temporary,  even  when  the 
injury  involves  the  three  canals  on  one  side ;  but  if  the  canals  on 
both  sides  are  destroyed,  recovery  is  tardy,  and  often  incomplete. 
In  mammals  the  loss  of  co-ordination  is  much  less  than  in  birds ; 
and  movements  of  the  eyes,  the  direction  of  which  depends  on  the 
canal  destroyed,  take  to  a  large  extent  the  place  of  movements  of 
the  head.  The  effects  of  destructive  lesions  have  their  counterpart 
in  the  phenomena  caused  by  stimulation  ;  excitation  of  a  posterior 
canal,  for  example,  in  the  pigeon  causes  movements  of  the  head  from 
side  to  side. 

Lee's  results  in  fishes  are,  on  the  whole,  of  similar  tenor.  Mechanical 
stimulation  of  the  ampullae  in  the  dogfish,  by  pressing  on  them  with 
a  blunt  needle,  calls  forth  characteristic  movements  of  the  eyes  and 
fins,  and  electrical  stimulation  of  the  auditory  nerve  causes  move- 
ments compounded  of  the  separate  movements  obtained  by  stimula- 
tion of  the  ampullae  one  by  one.  Lee  concludes  that  the  semicircular 
canals  are  the  sense-organs  for  dynamical  equilibrium  (i.e.,  equilibrium 
of  an  animal  in  motion),  and  the  utricle  and  saccule  for  statical 
equilibrium  (i.e.,  equilibrium  of  an  animal  at  rest). 

The  evidence  from  all  sources  points  strongly  to  the  conclusion 
that  afferent  impulses  are  actually  set  up  in  the  fibres  of  the  auditory 
nerve,  through  the  hair-cells,  by  alterations  of  pressure  or  by  stream- 
ing movements  of  the  endolymph  when  the  position  of  the  head  is 
changed.  Rotation  of  the  head  to  the  right  may  be  supposed  to 
cause  the  endolymph  in  the  right  external  canal,  in  virtue  of  its 
inertia,  to  lag  behind  the  movement,  and  to  press  upon  the  anterior 
surface  of  the  ampulla.  The  disorders  of  movement  after  lesions  of 
the  canals  may  be  explained  as  the  result  of  the  withdrawal  of  certain 
of  these  afferent  impulses,  and  the  consequent  overthrow  of  that 
equipoise  of  excitation  necessary  for  the  maintenance  of  equilibrium. 
Even  in  man  there  is  evidence  of  the  existence  of  some  mechanism 
not  depending  on  the  muscular  sense  or  on  impressions  passing  up 
the  channels  of  ordinary  or  special  sensation,  by  which  orientation 
(the  determination  of  the  position  of  the  body  in  space)  is  rendered 
possible.  For  a  man  lying  perfectly  still,  with  eyes  shut,  on  a  hori- 


THE  CENTRAL  NERVOUS  SYSTEM  699 

zontal  table  which  is  made  to  rotate  uniformly,  can  not  only  judge 
whether,  but  also  in  what  direction,  and  approximately  through  what 
angle,  he  is  moved  (Crum  Brown).  The  phenomena  of  pathology 
afford  weighty  additional  testimony  in  favour  of  the  equilibratory 
function  of  the  semicircular  canals.  For  many  cases  of  vertigo  are 
associated  with  changes  in  the  internal  ear  (Meniere's  disease).  And 
while  nearly  every  normal  individual  becomes  dizzy  when  rapidly 
rotated,  35  per  cent,  of  deaf-mutes  are  entirely  unaffected  (James), 
and  the  proportion  seems  to  be  much  higher  among  congenital  deaf- 
mutes.  KreidI  and  Bruck,  too,  have  found  that  abnormalities  of  loco- 
motion and  equilibration  are  much  more  common  in  deaf  and  dumb 
children  than  in  others.  Now,  in  these  cases  the  defect  is  usually 
in  the  internal  ear.  We  must  conclude,  then,  that  the  co-ordination 
of  muscular  movements  necessary  for  equilibrium  is  achieved  in 
some  centre,  to  which  afferent  impulses  pass  from  the  internal  ear 
by  the  vestibular  branch  of  the  auditory  nerve,  and  from  which 
efferent  impulses  pass  out  to  the  muscles.  If,  as  there  is  strong 
reason  to  believe,  this  centre  is  situated  in  the  cerebellum,  the 
efferent  path  is  in  all  probability  an  indirect  one  (perhaps  by  com- 
missural  fibres  to  the  Rolandic  area,  and  then  out  along  the  pyramidal 
tract) ;  for,  as  we  have  seen,  the  cerebellum  is  either  not  connected 
directly  with  the  anterior  roots  at  all,  or  only  by  a  few  fibres.  Ewald 
has  made  a  curious  observation  which  illustrates  the  peculiar  relation 
of  the  semicircular  canals  to  the  muscular  system,  namely,  that  the 
labyrinth  (in  rabbits)  influences  the  course  of  rigor  mortis  in  the 
striped  muscles.  Rigor  does  not  come  on  so  soon  on  the  side  from 
which  the  labyrinth  has  been  removed. 

It  is  the  middle  lobe  of  the  cerebellum  which  seems  to  be  concerned 
in  the  co-ordination  of  movements  and  maintenance  of  equilibrium. 
In  birds  and  lower  vertebrates  the  worm  is  alone  present.  The 
cerebellar  hemispheres  become  more  prominent  the  higher  we 
ascend,  and  it  cannot  be  doubted  that  they  have  important  functions, 
but  what  these  are  is  entirely  unknown.  The  fact  that  they  are  con- 
nected chiefly  with  those  parts  of  the  cerebral  cortex  which  are  sup- 
posed to  be  concerned  in  psychical  and  sensory  processes  suggests 
that,  at  any  rate,  the  superficial  grey  matter  of  the  cerebellum  is  not 
motor,  and  no  movements  can  be  obtained  on  stimulating  it ;  while 
stimulation  of  the  worm  may  cause  movements  of  the  eye.  Excita- 
tion of  the  line  of  junction  of  the  superior  worm  with  the  lateral  lobe 
in  animals  which  exhibit  tonic  contraction  of  extensor  muscles  after 
excision  of  the  cerebral  hemispheres  (acerebral  tonus,  as  it  is  called) 
causes  relaxation  of  the  extensors  accompanied  by  contraction  of  the 
antagonistic  flexors — for  example,  relaxation  of  the  triceps  and  con- 
traction of  the  biceps  (Horsley  and  Lowenthal). 

Forced  Movements. — We  have  incidentally  mentioned  that  in  fishes 
injuries  to  the  semicircular  canals  may  give  rise  to  movements  which 
seem  to  be  beyond  the  control  of  the  animal,  and  which  have 
consequently  received  the  name  of 'forced  movements.'  It  may  be 
added  that  when  the  internal  ear  of  a  Menobranchus  (one  of  the 
tailed  amphibia)  is  destroyed  on  one  side,  rapid  movements  of  rota- 


700  A  MANUAL  OF  PHYSIOLOGY 

tion  around  a  longitudinal  axis  are  observed.  The  animal  spins 
round  and  round  apparently  without  voluntary  control,  purpose,  or 
fatigue.  The  direction  of  rotation  is  towards  the  side  of  the  lesion, 
the  observer  being  supposed  to  look  down  upon  the  animal  as  it  lies 
in  its  normal  position.  After  a  time  it  becomes  quiescent ;  but  the 
forced  movements  can  be  again  produced  by  pinching  or  exciting  it 
in  other  ways.  In  man,  too,  during  the  passage  of  a  galvanic  current 
between  the  two  mastoid  processes,  a  tendency  to  move  the  head 
towards  the  anode  is  experienced.  The  person  may  resist  the 
tendency,  but  if  the  current  be  strong  enough  his  resistance  will  be 
overcome  :  he  will  execute  a  forced  movement.  Complex  as  such 
an  experiment  is,  involving  as  it  does  stimulation  of  so  many  struc- 
tures within  the  cranium,  there  is  reason  to  believe  that  it  is  the 
excitation  of  the  semicircular  canals  that  is  responsible  for  this  forced 
movement.  For  when  the  experiment  is  performed  on  a  pigeon, 
forced  movements  are  caused  so  long  as  the  membranous  canals  are 
intact,  but  not  after  they  have  been  destroyed  (Ewald). 

But  forced  movements  may  also  follow  injuries  (especially  uni- 
lateral) to  many  portions  of  the  brain — e.g.,  the  pons,  crus  cerebri, 
posterior  corpora  quadrigemina,  corpus  striatum,  cerebellum,  and 
even  the  cerebral  cortex.  The  movements  are  of  the  most  various 
kinds.  The  animal  may  run  round  and  round  in  a  circle  (circus 
movements)  ;  or,  with  the  tip  of  its  tail  as  centre  and  the  length  of 
its  body  as  radius,  it  may  describe  a  circle  with  its  head,  as  the  hand 
of  a  clock  does  (clock-hand  movement) ;  or  it  may  rush  forward, 
turning  endless  somersaults  as  it  goes.  Intervals  of  rest  alternate 
with  paroxysms  of  excitement,  and  the  latter  may  be  brought  on  by 
stimulation.  In  man  forced  movements  associated  with  vertigo  have 
been  sometimes  seen  in  cases  of  tumour  of  the  cerebellum — e.g., 
involuntary  rotation  of  the  body  in  tumour  of  the  middle  peduncle. 
No  entirely  satisfactory  explanation  of  these  forced  movements  has 
been  given.  They  are  evidently  connected  with  disturbance  of  the 
mechanism  of  co-ordination,  leading  to  a  loss  of  proportion  in  the 
amount  of  the  motor  discharge  to  muscles  or  groups  of  muscles 
accustomed  to  act  together  in  executing  definite  movements.  For 
instance,  in  circus  movements  the  muscles  of  the  outer  side  of  the 
body  contract  more  powerfully  than  those  of  the  inner  side,  and  the 
animal  is  therefore  constrained  to  trace  a  circle  instead  of  a  straight 
line,  the  excess  of  contraction  on  the  outer  side  being  analogous  to 
the  acceleration  along  the  radius  in  the  case  of  a  point  moving  in  a 
circle. 

Co-ordination  of  Movements. — The  capacity  of  executing  some 
co-ordinated  movements,  occasionally  of  considerable  complexity, 
seems  to  be  inborn  in  man,  and  to  a  still  greater  extent  in  many  of 
the  lower  animals.  The  new-born  child  brings  with  it  into  the  world 
a  certain  endowment  of  co-ordinative  powers  ;  it  has  inherited,  for 
example,  from  a  long  line  of  mammalian  ancestors  the  power  of 
performing  those  movements  of  the  cheeks,  lips,  and  tongue,  on 
which  sucking  depends  ;  perhaps  from  a  long,  though  somewhat 
shadowy,  race  of  arboreal  ancestors  the  power  of  clinging  with  hands 


THE  CENTRAL  NERVOUS  SYSTEM  701 

and  feet,  and  thus  suspending  itself  in  the  air.  Many  movements, 
such  as  walking  and  the  co-ordinated  muscular  contractions  involved 
in  standing,  and  even  in  sitting,  which,  once  acquired,  appear  so 
natural  and  spontaneous,  have  to  be  learnt  by  painful  effort  in  the 
hard  school  of  (infantile)  experience.  Most  people  learn,  and  are 
willing  to  confess  that  they  have  learnt,  to  execute  a  considerable 
number  of  co-ordinated  movements  with  the  arms,  and  especially 
with  the  fingers  ;  but  few  have  considered  that  the  extreme  dexterity 
of  jaws,  tongue,  and  teeth  displayed  by  a  hungry  mouse  or  school- 
boy is  the  result  of  the  much  practice  which  maketh  perfect.  The 
exquisite  co-ordination  of  the  muscles  of  the  eyeball,  which  we 
shall  afterwards  have  to  speak  of,  and  the  no  less  wonderful  balance 
of  effort  and  resistance,  of  power  put  forth  and  work  to  be  done,  of 
which  we  have  already  had  glimpses  in  studying  the  mechanism 
of  voice  and  speech,  become  to  a  great  extent  the  common  property 
of  all  fully-developed  persons.  But  the  technique  of  the  finished 
singer  or  musician,  of  the  swordsman  or  acrobat,  and  even  the 
operative  skill  of  the  surgeon,  are  in  large  part  the  outcome  of  a 
special  and  acquired  agility  of  mind  or  body,  in  virtue  of  which 
highly-complicated  co-ordinated  movements  are  promptly  determined 
on  and  immediately  executed. 

With  such  special  and  elaborate  movements  it  is  impossible  to 
occupy  ourselves  in  a  book  like  this.  Their  number  may  be  almost 
indefinitely  extended,  and  their  nature  almost  infinitely  varied,  by 
the  needs  and  training  of  special  trades  and  professions.  It  will 
be  sufficient  for  our  purpose  to  sketch  in  a  few  words  the  mechanism 
of  one  or  two  of  the  most  common  and  fundamental  co-ordinations 
of  muscular  effort,  passing  over  the  rest  with  the  general  statement 
that  the  more  refined  and  complex  movements  are  in  general  brought 
about  not  by  the  abrupt  contraction  of  crude  anatomical  groups  of 
muscles,  but  by  the  contraction  of  portions  of  muscles,  perhaps  even 
single  fibres  or  small  bundles  of  fibres,  while  the  rest  remain  relaxed. 
The  excitation  may  gradually  wax  and  wane  as  the  different  stages 
of  the  movement  require.  Antagonistic  muscles  may  be  called  into 
play  to  balance  and  tone  down  a  contraction  which  might  otherwise 
be  too  abrupt. 

A  most  interesting  illustration  of  this  process  of  *  give  and  take ' 
between  opposing  muscles  has  been  reported  by  Sherrington.  In 
the  cortex  cerebri,  as  we  shall  see  (pp.  708,  712),  there  is  an  area 
in  the  frontal  region,  and  another  in  the  occipital  region,  stimulation 
of  which  gives  rise  to  conjugate  deviation  of  the  eyes — that  is,  rotation 
of  both  eyes — to  the  opposite  side,  Sherrington  divided  the  third 
and  fourth  cranial  nerves  in  monkeys — say  on  the  left  side.  The 
external  rectus,  which  is  supplied  by  the  sixth  nerve,  caused  now  by 
its  unopposed  contraction  external  squint  of  the  left  eye.  When 
either  of  the  cortical  areas  referred  to,  or  even  the  subjacent  portion 
of  the  corona  radiata,  was  stimulated  on  the  left  side,  both  eyes 
moved  towards  the  right,  the  left  eye,  however,  only  reaching  the 
middle  line — that  is,  the  position  in  which  it  looked  straight  forward. 
The  same  thing  was  observed  when  the  animal,  after  complete  re- 


702  A  MANUAL  OF  PHYSIOLOGY 

covery  from  the  operation,  was  caused  to  voluntarily  turn  its  eyes  to 
the  right  by  the  sight  of  food.  Here  an  inhibitory  influence  must 
have  descended  the  fibres  of  the  abducens,  the  only  nervous  path 
connected  with  the  extrinsic  muscles  of  the  left  eye,  and  the  relaxa- 
tion of  the  left  external  rectus  must  have  kept  accurate  step  with  the 
contraction  of  the  right  internal  rectus.  (See  also  p.  699). 

Standing. — In  the  upright  posture  the  body  is  supported  chiefly 
by  non-muscular  structures,  the  bones  and  ligaments.  But  muscles 
also  play  an  essential  part,  for  it  is  only  peculiarly-gifted  individuals 
like  some  of  the  fishermen  of  the  North  Sea  who  can  go  to  sleep  on 
their  feet,  and  a  dead  body  cannot  be  made  to  stand  erect.  The 
condition  of  equilibrium  is  that  the  perpendicular  dropped  from  the 
centre  of  gravity  to  the  ground  should  fall  within  the  base  of  support 
— that  is,  within  the  area  enclosed  by  the  outer  borders  of  the  feet 
and  lines  joining  the  toes  and  heels  respectively.  The  centre  of 
gravity  alters  its  position  with  the  position  of  the  body,  which  tends 
to  fall  whenever  the  perpendicular  cuts  the  ground  beyond  the  base 
of  support. 

The  centre  of  gravity  of  the  head  is  a  little  in  front  of  the  vertical 
plane  passing  through  the  occipital  condyles.  A  slight  degree  of 
contraction  of  the  muscles  of  the  nape  of  the  neck  is  required  to 
balance  it.  When  these  muscles  are  relaxed,  as  in  sleep,  the  head 
must  fall  forward,  and  this  is  the  reason  why  Homer  or  any  lesser 
individual  nods.  In  animals  which  go  upon  all  fours,  none  of  the 
weight  of  the  head  bears  directly  upon  the  occipito-atloid  articula- 
tion ;  its  support  by  muscular  action  alone  would  be  an  intolerable 
fatigue,  and  the  ligamentum  nuchse  is  specially  strengthened  to  hold 
it  up 

The  vertebral  column  is  kept  erect  by  the  ligaments  and  muscles 
of  the  back.  The  centre  of  gravity  of  the  trunk  lies  between  the 
ensiform  cartilage  and  the  eighth  or  tenth  dorsal  vertebra.  The 
perpendicular  dropped  from  it  passes  a  little  behind  the  horizontal 
line  joining  the  two  acetabula ;  but  the  body  is  prevented  from  falling 
backward  by  the  tension  of  the  ileo-femoral  ligament  and  the  fascia 
lata,  and  perhaps  by  slight  contraction  of  some  of  the  muscles  on  the 
front  of  the  thigh.  The  perpendicular  let  fall  from  the  centre  of 
gravity  of  the  whole  of  the  body  above  the  knee  passes  very  slightly 
behind  the  axis  of  rotation  of  that  joint,  so  that  but  little  muscular 
action  is  required  to  keep  the  knee  joints  rigid.  The  whole  weight 
of  the  body  is  finally  transferred  to  the  astragalus  on  each  side,  the 
perpendicular  from  the  centre  of  gravity  of  the  whole,  which  is 
situated  near  the  sacral  promontory,  falling  a  little  in  front  of  these 
bones.  By  means  of  the  muscular  sense,  and  the  tactile  sensations 
set  up  by  the  pressure  of  the  soles  on  the  ground,  alterations  in  the 
position  of  the  centre  of  gravity,  and  consequent  deviations  of  the 
perpendicular  passing  through  it,  are  detected,  and  equilibrium  is 
maintained  by  adjustment  of  the  amount  of  contraction  of  this  or  the 
other  muscular  group. 

In  standing  at  'attention,'  the  heels  are  close  together,  the  legs 
and  back  straightened  to  the  utmost,  and  the  head  erect ;  the  weight 


THE  CENTRAL  NERVOUS  SYSTEM  703 

falls  equally  upon  both  legs,  but  the  advantage  is  much  more  than 
counterbalanced  by  the  considerable  muscular  exertion  required  to 
maintain  this  more  ornamental  than  useful  position.  In  'standing 
at  ease,'  practically  the  whole  weight  is  supported  by  one  leg,  the 
perpendicular  from  the  centre  of  gravity  passing  through  the  knee 
and  ankle-joints.  The  centre  of  gravity  is  brought  over  the  support- 
ing leg  by  flexure  of  the  body  to  the  corresponding  side,  and  com- 
paratively little  muscular  effort  is  required.  The  other  foot  rests 
lightly  on  the  ground,  the  weight  of  the  leg  itself  being  almost 
balanced  by  the  atmospheric  pressure  acting  upon  the  air-tight  and 
air-free  cavity  of  the  hip-joint.  The  light  touch  of  this  foot  varies 
slightly  from  time  to  time,  so  as  to  maintain  equilibrium. 

When  the  arms  or  head  are  moved,  or  the  body  swayed,  the 
centre  of  gravity  is  correspondingly  displaced,  and  it  is  by  such 
movements  that  tight-rope  dancers  continue  to  keep  the  perpen- 
dicular passing  through  it  always  within  the  narrow  base  of  support. 

In  sitting,  the  base  of  support  is  larger  than  in  standing,  and  the 
equilibrium  therefore  more  stable.  The  easiest  posture  in  sitting 
without  support  to  the  back  or  feet  is  that  in  which  the  perpendicular 
from  the  centre  of  gravity  passes  through  the  horizontal  line  joining 
the  two  tubera  ischii. 

Locomotion. — In  walking,  the  legs  are  alternately  swung  forward 
and  rested  on  the  ground.  In  military  marching,  it  is  directed  that 
toe  and  heel  be  simultaneously  set  down.  But  with  most  persons 
the  swinging  foot  first  strikes  the  ground  by  the  heel ;  then  the  sole 
comes  down,  the  heel  rises,  the  leg  is  extended,  and,  with  a  parting 
push  from  the  toe,  the  leg  again  swings  free.  By  this  manoeuvre  the 
body  is  raised  venically,  tilted  to  the  opposite  side,  and  also  pushed 
in  advance. 

The  forward  swing  of  the  leg  is  only  slightly,  if  at  all,  due  to 
muscular  action ;  it  is  more  like  the  oscillation  of  a  pendulum  dis- 
placed behind  its  position  of  equilibrium,  and  swinging  through  that 
position,  and  in  front  of  it,  under  the  influence  of  gravity.  For  this 
reason  the  natural  pace  of  a  tall  man  is  longer  and  slower  than  that 
of  a  short  man ;  but  it  may  be  modified  by  voluntary  effort,  as  when 
a  rank  of  soldiers  of  different  height  keeps  step. 

The  lateral  swing  of  the  body  is  illustrated  by  the  everyday 
experience  that  two  persons  knock  against  each  other  when  they 
try  to  walk  close  together  without  keeping  step.  In  step,  both  swing 
their  bodies  to  the  same  side  at  the  same  moment,  and  there  is  no 
jarring. 

Even  in  the  fastest  walking  there  is  a  short  time  during  which 
both  feet  are  on  the  ground  together,  the  one  leg  not  beginning  its 
swing  until  the  other  foot  has  been  set  down.  In  running,  on  the 
other  hand,  there  is  an  interval  during  which  the  body  is  completely 
in  the  air. 

Functions  of  the  Cerebral  Cortex. — When  an  animal,  like  a 
frog,  is  deprived  of  its  cerebral  hemispheres,  the  power  of 


704  A  MANUAL  OF  PHYSIOLOGY 

automatic  voluntary  movement  appears  to  be  definitively 
and  entirely  lost.  The  animal,  as  soon  as  the  effects  of  the 
anaesthetic  and  the  shock  of  the  operation  have  passed  away, 
draws  up  its  legs,  erects  its  head,  and  assumes  the  charac- 
teristic position  of  a  normal  frog  at  rest.  So  close  may  be 
the  resemblance,  that  if  all  external  signs  of  the  operation 
have  been  concealed,  it  may  not  be  possible  to  tell  merely 
by  inspection  which  is  the  intact  and  which  the  *  brainless ' 
frog.  The  latter  will  jump  if  it  be  touched  or  otherwise 
stimulated.  It  will  croak  if  its  flanks  be  stroked  or  gently 
squeezed  together.  It  will  swim  if  thrown  into  water.  If 
placed  on  its  back,  it  will  promptly  recover  its  normal 
position.  But  it  will  do  all  these  things  as  a  machine  would 
do  them,  without  purpose,  without  regard  to  its  environ- 
ment, with  a  kind  of  '  fatal '  regularity.  Every  time  it  is 
stimulated  it  will  jump,  every  time  its  flanks  are  squeezed 
it  will  croak,  and,  in  the  absence  of  all  stimulation,  it  will 
sit  still  till  it  withers  to  a  mummy,  even  by  the  side  of  the 
water  that  might  for  a  while  preserve  it. 

A  Menobranchus,  without  its  cerebral  hemispheres,  will, 
like  the  frog,  refuse  to  lie  on  its  back.  On  stimulation  it 
moves  its  feet  or  tail,  or  its  whole  body  ;  but  if  not  interfered 
with,  it  lies  for  an  indefinite  time  in  the  same  position.  Its 
gills  are  seen  to  execute  rhythmic  movements,  which  never 
stop,  and  rarely  slacken,  except  for  an  instant,  when  some 
part  of  the  skin,  particularly  in  the  region  of  the  head,  is 
mechanically  or  electrically  stimulated.  The  normal  Meno- 
branchus, on  the  other  hand,  lies  for  long  periods  with  its 
gills  at  perfect  rest,  and  when  stimulated  moves  for  a  con- 
siderable distance.  After  a  time,  two  months  or  more,  it  is 
true  the  '  brainless  frog,'  if  it  be  kept  alive,  as  may  be  done 
by  careful  attention,  will  recover  a  certain  portion  of  the 
powers  which  it  has  lost  by  removal  of  the  cerebral  hemi- 
spheres ;  and,  indeed,  the  longer  it  lives,  the  nearer  it 
approximates  to  the  condition  of  a  normal  frog.  A  brain- 
less frog  has  been  seen  to  catch  flies  and  to  bury  itself  as 
winter  drew  on.  A  fish  even  three  days  after  the  destruction 
of  its  cerebrum  has  been  seen  to  dart  upon  a  worm,  seize 
it  before  it  had  time  to  sink  to  the  bottom  of  the  aquarium, 


THE  CENTRAL  NERVOUS  SYSTEM  705 

and  swallow  it.  Even  in  the  pigeon  the  loss  of  the  hemi- 
spheres, which  at  first  induces  a  state  of  profound  and 
seemingly  permanent  lethargy,  is  to  a  great  extent  com- 
pensated for,  as  time  passes  on,  by  the  unfolding  in  the 
lower  centres  of  capabilities  previously  dormant  or  sup- 
pressed. A  brainless  pigeon  has  been  known  to  come  at 
the  whistle  of  the  attendant  and  follow  him  through  the 
whole  house.  In  the  dog,  as  might  be  expected  from  its 
greater  intellectual  development,  recovery  is  more  imperfect 
than  in  the  bird,  much  more  imperfect  than  in  the  frog. 
But  even  in  the  dog  wonderful  resources  lie  hidden  in  the 
grey  matter  of  the  central  neural  axis,  and  are  called  forth 
by  degrees  to  replace  the  lost  powers  of  the  cerebral  cortex. 
It  is  true  that  a  brainless  dog  is  a  less  efficient  animal  than 
a  brainless  fish,  or  even  than  a  brainless  frog;  but  in  favour- 
able cases  even  in  the  dog,  the  movements  of  walking  may 
still  be  carried  out  with  tolerable  precision  in  the  absence 
of  the  cerebral  hemispheres.  The  animal  can  swallow  food 
pushed  well  back  into  the  mouth,  although  it  cannot  feed 
itself.  Stupid  and  listless  as  it  is  compared  with  the  normal 
dog,  it  seems  to  be  by  no  means  devoid  of  the  power  of 
experiencing  sensations  as  the  result  of  impressions  from 
without,  nor  of  carrying  on  many  mental  operations  of  a 
low  intellectual  grade. 

Goltz  had  a  dog  which  lived  more  than  a  year  and  a  half  without 
its  cerebral  hemispheres,  and  another  which  lived  thirteen  weeks. 
He  believes  that  they  had  lost  understanding,  reflection,  and  memory, 
but  not  sensation,  special  or  general,  nor  emotions  and  voluntary 
power.  Their  condition  may  be  best  described  as  one  of  general 
imbecility.  Hunger  and  thirst  are  present.  They  experience  satis- 
faction when  fed,  become  angry  when  attacked,  see  a  very  bright 
light,  avoid  obstacles,  hear  loud  sounds,  such  as  those  produced  by  a 
fog-horn,  and  can  be  awakened  by  them.  They  are  not  completely 
deprived  of  sensations  of  taste  and  touch.  But  it  ought  to  be  re- 
membered that  the  interpretation  of  the  objective  signs  of  sensation 
in  animals  is  beset  with  difficulties ;  and  although  everybody  admits 
the  accuracy  of  Goltz's  description  of  what  is  to  be  seen,  his  inter- 
pretation of  the  facts  has  been  severely  criticised,  particularly  by 
H.  Munk. 

To  the  monkey  it  is  probable  that  the  loss  of  the  cerebral 
hemispheres  is  a  heavier  and  more  irremediable  blow  than 
to  the  dog. 

45 


706 


A  MANUAL  OF  PHYSIOLOGY 


We  see,  then,  that  homologous  organs  are  not  necessarily, 
nor  indeed  usually,  of  the  same  physiological  value  in  different 
kinds  of  animals.  A  loss  which  perhaps  hardly  narrows  the 
range  of  the  psychical,  and  certainly  restricts  only  to  a  slight 
extent  the  physical  powers  of  a  fish,  cuts  off  from  the  dog 
a  great  part,  from  the  monkey  almost  all,  of  its  intellectual 
life,  and  is  in  man  incompatible  with  life  altogether. 

The  results  of  the  removal  of  the  entire  cerebral  hemi- 
spheres help  us  to  fix  their  position  as  a  whole  in  the 
physiological  hierarchy.  A  more  minute  analysis  shows  us 
that  the  cerebral  cortex  itself  is  not  homogeneous  in  function, 
that  certain  regions  of  it  have  been  set  aside  for  special 
labours.  Our  knowledge  of  this  localization  of  function  in 
the  cerebral  cortex  has  been  derived  partly  from  clinical, 
coupled  with  pathological  observations  on  man,  and  partly 

from  the  results  of  the 
removal  or  stimulation 
of  definite  areas  in 
animals.  And  so  varied 
and  extensive  have  been 
the  contributions  from 
both  of  these  sources, 
that  it  is  difficult  to 
decide  to  which  we  owe 
most. 

It  is  a  fact  which  might 
appear  strange  and  almost 
inexplicable  did  the  history 
of  science  not  constantly 
present  us  with  the  like, 
that  thirty  years  ago  the 
universal  opinion  among 
FIG.  239.— MOTOR  AREAS  OF  DOG'S  BRAIN,  physiologists,  pathologists, 
n,  neck  ;/./.,  fore-limb  ;  h.L,  hind-limb  ;  /,  tail ;  and  physicians  was  that  the 
/,  face;  c.s.,  crucial  sulcus  ;  e.m.,  eye  movements;  rf>r~hr*}  rnrrpy  i<s  inpvrir- 
p,  dilatation  of  the  pupil  in  both  eyes,  but  especially  Cf  ^CDral  CO] 
in  the  opposite  eye.  All  the  areas  are  marked  in  able  to  artificial  Stimuli, 
the  figure  only  on  the  left  side  except  the  eye  that  no  visible  response 
areas,  whose  position,  to  avoid  confusion,  is  in-  ,  ^  «Uf«;.  ,~i  A.^™  in- 

dicated on  the  right  hemisphere.  can   be    obtained    from    it. 

The     great      names    of 

ilourens  and  Magendie  stood  sponsors  for  this  error,  and  re- 
pressed research.  In  1870,  however,  Hitzig  had  occasion  to  pass 
a  voltaic  current  through  the  brain  of  a  soldier  wounded  in 
the  Franco-German  war,  and  observed  that  movements  of  the  eyes 


THE  CENTRAL  NERVOUS  SYSTEM 


707 


were  produced,  and,  along  with  Fritsch,  he  entered  on  a  series  of 

experiments.     These  observers  were  rewarded  by  finding  that  not 

only  was  it  possible  to  elicit  muscular  contractions  by  stimulation  of 

the  cortex  of  the  brain  in  the  dog  with  voltaic  currents,  but  that  the 

excitable  area  occupied  a  definite  region  in  the  neighbourhood  of 

the  crucial  sulcus,  which 

lies  over  the  convexity 

of  the    hemispheres 

nearly  at  right  angles  to 

the  longitudinal  fissure. 

In  this  region  they  were 

further  able    to    isolate 

several     distinct    areas, 

stimulation  of  which  was 

followed  by  movements 

respectively  of  the  head, 

face,  neck,  hind-leg,  and 

fore-leg.      This  was  the 

starting-point  of  a  long 

series  of  researches  by 

Ferrier,  Munk,  Horsley, 

Schafer,       Heidenhain, 

and  many  others,  on  the 

brains    of    monkeys   as 

well  as  dogs — researches 

which  have  formed  the 


FIG.  240. — DOG'S  BRAIN  WITH  LESION. 


A  portion  of  the  cortex  indicated  by  the  shaded  area 
basis  of  an  exact  cortical    was  destroyed  by  cauterization.    The  symptoms  were 
localization  in  the  brain    complete  blindness  of  the  opposite  eye  (in  this  case  the 
,    ,  right)  ;  weakness  of  the  muscles  of  the  limbs  and  of  the 

01  man,  and  have  en-  neck  on  the  right  side  ;  slight  weakness  of  the  limbs  on 
riched  surgery  with  a  tne  lfift  side.  When  the  animal  walked  there  was  a 
Tn  thp<;p  tendency  to  turn  to  the  left  in  a  circle.  In  eating  or 
"  drinking  the  head  was  turned  to  the  left,  so  that  the 
mouth  was  oblique,  and  the  right  angle  of  the  mouth 
was  lower  than  the  left.  The  tail  movements  were 
normal,  and  there  was  no  deviation  of  the  tail  to  one 
machine  side 


new  province. 

later     experiments     the 

interrupted  current  from 

an    induction 

has  been  found  the  most 

suitable  form  of  stimulus  (see  Practical  Exercises,  p.  730). 


Motor  Areas. — Lying  around  the  fissure  of  Rolando,  and 
lapping  over  on  the  mesial  surface  of  the  hemisphere  in  this 
region,  are  the  so-called  motor  areas  (Figs.  241,  242,  243). 
They  occupy  the  whole  of  the  ascending  frontal  and  parietal 
convolutions,  running  forward  a  little  into  the  horizontal 
frontal  convolutions,  backward  a  little  into  the  superior 
parietal  convolution,  and  turning  over  on  the  mesial  surface 
into  the  marginal  convolution.  Highest  of  all  on  the  con- 
vexity of  the  hemisphere  lies  the  area  of  the  leg ;  below  this, 
in  order,  the  areas  for  the  arm,  face,  mouth,  pharynx,  and 

45—2 


7o8 


A  MANUAL  OF  PHYSIOLOGY 


larynx.  In  front  of  the  leg  and  arm  areas  lies  the  area  of 
the  head,  neck,  and  eyes,  passing  out  into  the  posterior 
portions  of  the  first  and  second  frontal  convolutions.  On 
the  mesial  surface  in  the  marginal  convolution  lie  areas  for 


FISSURE  OF  ROLANDO 


SYLVIA  W 
FISSURE 


FIG.  241. — LATERAL  VIEW  OF  LEFT  HEMISPHERE  (MAN),  WITH  MOTOR  ANI> 

SENSORY  AREAS. 

The  front  of  the  brain  is  towards  the  left. 

the  head,  arm,  trunk,  and  leg  in  order  from  before  back- 
wards. 

It  is  to  be  particularly  noted  (i)  that  within  the  larger 
areas,  such  as  those  of  the  arm  and  leg,  smaller  foci  can  be 
mapped  off  which  are  related  to  movements  of  the  separate 
joints — thus,  in  the  leg  area,  the  hip,  knee,  and  ankle  joints, 


THE  CENTRAL  NERVOUS  SYSTEM 


709 


and  the  great  toe,  are  represented  by  separate  and  special 
centres ;  (2)  that  stimulation  of  any  one  of  these  areas  leads, 
not  to  contraction  of  individual  muscles,  but  to  contraction 


FIG.  242. — CEREBRAL  CORTEX  (MAN)  SEEN  FROM  ABOVE. 

The  front  of  the  brain  is  towards  the  right.     The  dotted  line  shows  the  position  of 
the  fissure  of  Rolando,  as  fixed  by  Thane's  rule  (p.  711). 

of  muscular  groups  which  have  to  do  with  the  execution  of 
definite  movements. 


~' 


^ 


FIG.  243. — MOTOR  AND  SENSORY  AREAS  OF  MESIAL  SURFACE  OF  HUMAN 

BRAIN. 

The  front  of  the  brain  is  towards  the  right. 

Removal  of  the  whole  of  the  motor  cortex  of  one  hemi- 
sphere causes  paralysis  of  movement  on  the  opposite  side 


710  A  MANUAL  OF  PHYSIOLOGY 

of  the  body.  The  paralysis  is  less  marked  in  the  case  of 
bilateral  muscles  that  habitually  act  together  than  in  the 
case  of  those  which  ordinarily  act  alone.  Thus  the  muscles 
of  respiration  and  the  muscles  of  the  trunk  in  general  are, 
although  perhaps  weakened,  never  completely  paralyzed. 
This  is  an  indication  that  each  member  of  such  functional 
pairs  of  muscles  is  innervated  from  both  hemispheres ;  and 
this  physiological  deduction  is  supported  by  the  anatomical 
fact  already  referred  to,  that  after  removal  of  the  motor 
cortex,  or  injury  to  the  pyramidal  tracts  in  the  internal 
capsule  or  crus,  some  degeneration  is  found  in  the  crossed 
pyramidal  tract  on  the  side  of  the  lesion,  as  well  as  in  the 
anterior  pyramidal  tract  on  that  side  and  the  opposite 
crossed  pyramidal  tract  (p.  658).  It  was  supposed  by  some 
that  these  fibres  are  really  recrossed,  i.e.,  have  decussated 
twice — once,  perhaps,  in  the  medulla  oblongata,  and  again 
at  a  lower  level  in  the  cord ;  but  this  view  has  since  been 
modified. 

Removal  of  a  single  motor  region  leads  to  paralysis  only 
of  the  corresponding  limb,  or  part  of  a  limb,  on  the  opposite 
side.  In  the  dog  after  a  time  the  paralysis  may  more  or 
less  completely  disappear,  the  loss  of  the  cortical  centres  on 
one  side  being  perhaps  compensated  by  increased  activity 
of  those  that  are  left.  In  the  monkey  restoration  is  less 
complete ;  in  man  it  is  more  imperfect  still. 

The  movements  with  which  the  motor  areas  are  con- 
cerned are  essentially  skilled  movements,  and  we  may  sup- 
pose that  it  is  more  difficult  for  a  monkey  to  educate  again 
a  centre  for  such  complex  and  elaborate  manoeuvres  as  are 
performed  by  its  hand  than  for  a  dog  to  regain  cortical 
control  of  the  comparatively  simple  movements  of  its  paw. 
In  man  in  cases  of  hemiplegia,  when  the  patient  lives  for 
some  time,  a  certain  amount  of  recovery  usually  takes  place, 
especially  in  young  persons,  in  the  paralyzed  leg,  but  much 
less  in  the  paralyzed  arm. 

It  is  in  the  light  of  the  results  obtained  in  monkeys,  and  by  the 
aid  of  clinical  and  pathological  observations,  that  the  motor  areas  in 
man  have  to  a  great  extent  been  mapped  out  .  An  extensive 
haemorrhage  involving  the  cerebral  cortex  on  both  sides  of  the  fissure 
of  Rolando,  or  an  embolus  blocking  the  middle  cerebral  artery, 


THE  CENTRAL  NERVOUS  SYSTEM  711 

causes  paralysis  of  the  opposite  side  of  the  body.  An  embolus  of 
a  branch  of  the  middle  cerebral  artery  causes  paralysis  of  the  muscles, 
or  rather  movements,  represented  in  the  area  supplied  by  it.  A 
tumour  causes  symptoms  of  irritation,  motor  or  sensory — con- 
vulsions beginning  in,  or  an  aura  referred  to,  the  parts  represented 
in  the  regions  on  which  it  presses.  In  connection  with  the  localiza- 
tion of  lesions  in  the  motor  area  of  the  cortex,  and  operative  inter- 
ference for  their  cure,  the  exact  position  of  the  fissure  of  Rolando 
becomes  important ;  and  Thane  has  given  the  following  simple 
method  for  fixing  it :  The  point  midway  between  the  root  of  the  nose 
and  the  occipital  protuberance  is  fixed  by  measuring  the  distance  with 
a  tape-  The  upper  end  of  the  fissure  of  Rolando  lies  half  an  inch 
behind  this  middle  point.  The  fissure  makes  an  angle  of  67°  with  the 
longitudinal  fissure  (Fig.  242). 

When  we  have  deducted  from  the  cortex  of  the  hemi- 
sphere the  whole  Rolandic  area,  there  still  remains  a  large 
portion  unaccounted  for.  The  greater  part  of  the  frontal 
lobe  anterior  to  the  ascending  frontal  convolution  responds 
to  stimulation  by  neither  motor  nor  sensory  sign ;  and  by  a 
process  of  exclusion  it  has  been  supposed  that  it  is  the  seat 
of  intellectual  processes.  Extensive  destruction  and  loss  of 
substance  of  this  pre-frontal  region  may  occur  without  any 
marked  symptoms,  except  some  restriction  of  mental  power 
or  loss  of  moral  restraint.  Thus  in  the  famous  *  American 
crowbar  case,'  an  iron  bar  completely  transfixed  the  left 
frontal  lobe  of  a  man  engaged  in  blasting.  Although 
stunned  for  the  moment,  he  was  able  in  an  hour  to  climb  a 
long  flight  of  stairs,  and  to  answer  the  inquiries  of  the 
surgeon.  Finally,  he  recovered,  and  lived  for  nearly  thirteen 
years  without  either  sensory  or  motor  deficiency,  except  that 
he  suffered  occasionally  from  epileptic  convulsions.  But  his 
intellect  was  impaired  ;  he  became  fitful  and  vacillating, 
profane  in  his  language  and  inefficient  in  his  work,  although 
previously  decent  in  conversation  and  a  diligent  and  capable 
workman. 

Sensory  Areas — Visual  Centres. —  In  the  occipital  lobe  an 
area  of  considerable  extent  has  been  found,  destruction  of 
which  causes  hemianopia,  i.e.,  loss  of  vision  in  the  corre- 
sponding halves  of  the  retinae.  Thus,  if  the  right  occipital 
cortex  is  destroyed,  the  right  halves  of  the  two  retinae  are 
paralyzed,  and  the  left  half  of  the  field  of  vision  is  a  blank. 
Destruction  of  this  region  on  both  sides  causes,  according 


712 


A  MANUAL  OF  PHYSIOLOGY 


to  Munk,  complete  blindness.  Ferrier  believes  that  for  this 
it  is  necessary  that  the  angular  gyrus  should  also  be  de- 
stroyed. When  the  same  region  is  stimulated,  the  eyes 
and  head  are  turned  to  the  left — that  is,  to  the  opposite 
side.  The  movements  differ  from  those  produced  by  stimu- 
lation of  the  Ro- 
landic  area.  They 
are  not  so  certain, 
their  latent  period  is 
longer,  and  they  are 
considered  to  be  not 
direct,  but  reflex 
movements.  It  can- 
not be  doubted  that 
the  occipital  region 
is  concerned  in 
vision,  and  it  is  a 
very  natural  sugges- 
tion that  the  move- 
ments are  the  result 
of  visual  sensations 
in  the  excited  occi- 
pital cortex.  The 
right  occipital  lobe  is 
concerned  with  vision 
in  the  right  halves  of 
the  two  retinae.  Now, 
under  normal  con- 
ditions a  visual  image 
would  be  cast  on  the 
two  right  retinal 
halves  by  an  object  placed  towards  the  left  of  the  field. 
The  movements  of  the  head  and  eyes  to  the  left  may  there- 
fore be  plausibly  explained  as  an  attempt  to  look  at,  and  a 
rotation  towards,  the  supposed  object. 

The  pathological  evidence  is  very  clear  that  disease  of  the  occipital 
lobe,  especially  of  the  cuneus,  causes  hemianopia  in  man.  A  limited 
lesion  may  even  be  associated  with  an  incomplete  hemianopia,  and 
cases  have  been  recorded  in  which  colour  hemianopia  (blindness 
of  the  corresponding  halves  of  the  two  retinae  for  coloured  objects) 


FIG.  244. — DIAGRAM  OF  RELATIONS  OF  OCCI- 
PITAL CORTEX  TO  THE  RETIN/E. 

RO,  LO,  right  and  left  occipital  cortex;  RE, 
LE,  right  and  left  retina  ;  C,  optic  chiasma  ;  RF, 
LF,  right  and  left  visual  fields.  The  continuous 
lines  passing  back  from  the  retinae  to  the  occipital 
cortex  represent  the  crossed,  the  broken  lines  the 
uncrossed,  fibres  of  the  optic  nerves  and  tracts. 


THE  CENTRAL  NERVOUS  SYSTEM  713 

existed  with  normal  vision  for  white  light.  Sometimes  dimness  of 
vision  in  the  opposite  eye  (crossed  amblyopia),  and  not  hemianopia, 
is  caused  by  a  lesion  of  the  occipital  cortex.  It  seems  impossible  to 
explain  this  and  other  facts  without  postulating  the  existence  of  more 
than  one  visual  centre  in  the  occipital  lobe ;  and  it  has  been  supposed 
that  in  the  angular  gyrus  a  higher  visual  centre  exists  which  is  con- 
nected with  the  lower  occipital  centres  for  the  two  halves  of  the 
opposite  eye.  Thus,  the  right  angular  gyrus  would  be  in  connection 
with  the  part  of  the  right  occipital  cortex  which  has  to  do  with 
vision  in  the  nasal  half  of  the  left  eye,  and  with  the  part  of  the  left 
occipital  cortex  which  has  to  do  with  vision  in  the  temporal  half  of 
that  eye.  It  has  been  stated  that  after  complete  removal  of  the 
occipital  lobes  in  young  monkeys,  the  power  of  vision,  lost  for  a 
time,  is  gradually  regained,  the  growth  of  new  nerve-cells  and  nerve- 
fibres  having  made  good  the  deficiency  (Vitzou). 

Auditory  Centre. — On  the  outer  surface  of  the  temporo- 
sphenoidal  lobe,  in  the  hinder  portion  of  the  first  and  second 
temporal  convolutions,  lies  an  area  associated  with  the 
sense  of  hearing.  Stimulation  in  the  region  of  the  first 
temporal  convolution  may  cause  the  animal  to  prick  up  its 
ear  on  the  opposite  side.  Destruction  of  this  area  on  both 
sides  is  followed  by  complete  and  irremediable  loss  of  hear- 
ing. If  it  is  destroyed  only  on  one  side  there  is  deafness  of 
the  opposite  ear,  which,  however,  is  gradually  recovered 
from.  In  deaf-mutes  the  first  temporal  convolution  may  be 
atrophied.  There  is  evidence  that  the  posterior  corpora 
quadrigemina  and  the  mesial  geniculate  body  form  an 
inferior  relay  on  the  route  between  the  fibres  of  the  auditory 
nerve  and  the  temporal  cortex. 

Centre  for  Smell. — As  to  the  position  of  the  centre  for 
smell,  direct  experiment  on  animals  cannot  teach  us  much, 
for  if  the  outward  tokens  of  visual  and  auditory  sensations 
are  dubious  and  fluctuating,  still  more  is  this  the  case  with 
the  signs  of  sensations  of  smell.  A  further  source  of  fallacy 
is  the  fact  that  other  sensations  than  those  of  smell  are 
caused  by  stimulation  of  the  mucous  membrane  of  the  nose. 
Substances  like  ammonia,  for  example,  affect  entirely  the 
endings  of  the  trigeminus,  which  is  the  nerve  of  common 
sensation  for  the  nostrils.  Pathological  and  clinical  evidence 
would  be  of  great  value,  but  it  is  as  yet  scanty,  and  of  itself 
indecisive.  So  far  as  it  goes,  however,  it  undoubtedly 
supports  the  view  derived  from  the  anatomical  connections 


714  A  MANUAL  OF  PHYSIOLOGY 

of  the  olfactory  tracts,  that  the  centre  for  smell  is  situated 
in  the  uncinate  gyrus  on  the  mesial  aspect  of  the  temporal 
lobe,  for  the  olfactory  tract  may  be  traced  into  this  region. 
In  animals  with  a  very  acute  sense  of  smell,  this  gyrus 
is  magnified  into  a  veritable  lobe,  called  from  its  shape 
the  pyriform  lobe ;  from  its  supposed  function,  the  rhin- 
encephalon. 

Ordinary  sensation  and  in  part  tactile  sensation  are  located 
on  the  mesial  surfaces  of  the  hemispheres — by  Ferrier  in  the 
hippocampal  convolution,  by  Schafer  and  Horsley  in  the 
^  gyrus  fornicatus.  But  whatever  may  be  the  truth  in  this 
matter,  it  would  appear  that  this  is  not  the  only  region 
where  ordinary  sensation  is  represented.  For  example,  it 
is  certain  that  the  Rolandic  area  has  sensory  as  well  as 
motor  functions. 

Pathological  evidence  in  man  agrees,  upon  the  whole,  with 
wonderful  precision  with  the  results  of  experiments  on 
animals ;  and,  indeed,  before  any  experimental  proof  of  the 
minute  and  elaborate  subdivision  of  the  cortex  had  been 
obtained,  Broca  had  already,  from  the  phenomena  of  the 
sick-bed  and  the  post-mortem  room,  located  a  centre  for 
speech  in  the  left  inferior  frontal  convolution,  and  Hughlings 
Jackson  had  associated  pathological  lesions  of  the  Rolandic 
area  with  certain  cases  of  epileptiform  convulsions. 

Aphasia. — In  most  persons  the  inferior  frontal  convolution 
on  the  left  side  is  concerned  in  the  expression  of  ideas  in 
spoken  or  written  language.  It  is  even  said  that  oratorical 
powers  have  been  found  associated  with  marked  development 
of  this  convolution  (as  in  the  case  of  Gambetta,  the  French 
statesman).  Words  are,  at  bottom,  arbitrary  signs  by 
which  certain  ideas  are  expressed.  The  power  of  intelligent 
communication  by  spoken  or  written  language  may  be  lost : 
(i)  by  paralysis  of  the  muscles  of  articulation  or  the  muscles 
which  guide  the  pen  ;  (2)  by  inability  to  hear  or  see  the 
spoken  or  written  word,  i.e.,  by  deafness  or  blindness  ;  (3)  by 
inability  to  comprehend  the  meaning  of  spoken  or  written 
language,  although  sensations  of  hearing  and  sight  may  not 
be  abolished — that  is  to  say,  by  inability  to  interpret  the 
auditory  or  visual  symbols  by  which  ideas  are  conveyed  : 


THE  CENTRAL  NERVOUS  SYSTEM  715 

(4)  by  inability  to  clothe  ideas  in  words,  although  the  ideas 
conveyed  by  speech  or  writing  may  be  perfectly  compre- 
hended. Neither  (i)  nor  (2)  is  considered  to  constitute  the 
condition  of  aphasia ;  (3)  represents  what  is  called  amnesia, 
or  sensory  aphasia ;  (4)  is  aphasia  in  the  ordinary  restricted 
sense,  or  motor  aphasia.  In  motor  aphasia  the  patient 
understands  quite  well  what  is  said  to  him,  and  also 
knows  quite  well  what  to  reply,  but  the  words  necessary  to 
express  his  meaning  do  not  come  to  him.  He  makes  no 
answer  whatever,  or  strings  together  a  series  of  words  each 
correctly  articulated  but  having  no  meaning,  or  utters  a 
jargon  not  composed  of  known  words  at  all.  The  failure 
does  not  lie  in  the  articulatory  mechanism.  The  patient 
uses  the  same  muscles  of  articulation,  without  any  sign  of 
impairment  of  function,  for  chewing  and  swallowing  his 
food.  He  may  sometimes  sing  a  song  without  a  single  slip 
in  words  or  measure,  and  yet  be  unable  to  speak  or  write  it. 
In  certain  cases  the  change  is  confined  to  loss  of  the  power 
of  spontaneous  speech,  and  the  patient  may  be  able  to  read 
intelligently.  Sometimes  he  can  express  his  ideas  in  speech 
but  not  in  writing  (agraphia).  Sometimes  the  loss  is  re- 
stricted to  certain  sets  of  ideas.  For  example,  a  boy  was 
injured  by  falling  on  his  head.  Typical  symptoms  of  motor 
aphasia  developed,  but  the  power  of  dealing  with  ideas  of 
number  was  not  interfered  with,  and  the  boy  continued  to 
learn  arithmetic  as  if  nothing  had  happened.  Proper  names 
and  nouns  are  more  easily  lost  than  adjectives  and  verbs. 
Motor  aphasia  is  generally  accompanied  by  paralysis,  fre- 
quently transient,  of  voluntary  movement  on  the  right  side, 
sometimes  amounting  to  complete  hemiplegia,  but  more 
often  involving  the  arm  or  the  head  and  face  alone.  This 
association  is  explained  by  the  proximity  of  the  inferior 
frontal  convolution  to  the  motor  areas  of  the  arm  and  head, 
and  their  common  blood-supply. 

Why,  now,  is  it  that  motor  aphasia  is  commonly  due  to 
a  lesion  in  the  left  hemisphere  alone  ?  The  answer  to  this 
question  is  partly  supplied  by  the  important  and  curious 
observation  that  in  left-handed  individuals  damage  to  the 
right  inferior  frontal  convolution  may  cause  aphasia.  In 


716  A  MANUAL  OF  PHYSIOLOGY 

the  right-handed  man  the  motor  areas  of  the  left  hemisphere 
may  be  supposed  to  be  more  highly  educated  than  those  of 
the  right  hemisphere.  The  movements  of  the  right  side 
which  they  initiate  or  control  are  stronger  and  more  delicate 
and  precise  than  those  of  the  left  side.  It  is  only  necessary 
to  assume  that  this  process  of  specialization,  of  selective 
training,  has  been  carried  on  to  a  still  greater  extent  in  the 
left  frontal  convolution,  that  in  most  men  the  speech-centre 
there  has  taken  upon  itself  the  whole  of  the  labour  of 
clothing  ideas  in  words,  leaving  to  the  right  centre  only  its 
primitive  but  undeveloped  powers.  In  left-handed  persons 
the  speech-centre  on  the  right  side  may  be  supposed  to 
share  in  the  general  functional  development  of  the  right 
hemisphere.  That  great  capabilities  are  lying  dormant 
in  the  right  speech-centre  of  the  ordinary  right-handed 
individual  is  indicated  by  the  fact  that  after  complete  de- 
struction of  the  left  inferior  frontal  convolution  the  power 
of  speech  may  be  to  a  considerable  extent,  though  slowly 
and  laboriously,  regained  ;  and  it  is  said  that  this  second 
accumulation  may  be  swept  away,  and  without  remedy,  by 
a  second  lesion  in  the  right  inferior  frontal  convolution. 
But  frail  is  the  tenure  of  life  in  a  person  who  has  twice 
suffered  from  such  a  lesion ;  and  it  is  possible  that  recovery 
might  take  place  to  some  extent  even  after  destruction  of 
both  speech  centres,  if  the  patient  only  lived  long  enough. 

Temporary  aphasia  may  occur  without  any  structural 
change  in  the  speech-centre — for  example,  during  an  attack 
of  migraine.  In  children  it  may  even  be  caused  by  some 
comparatively  slight  irritation  in  the  digestive  tract,  such  as 
that  due  to  the  presence  of  a  tape-worm. 

Sensory  Aphasia. — In  typical  motor  aphasia  spoken  and 
written  words  convey  to  the  patient  their  ordinary  meaning. 
They  call  up  in  his  mind  the  usual  sequence  of  ideas,  but 
the  chain  is  broken  at  the  speech-centre,  and  the  outgoing 
ideas  cannot  be  clothed  in  words.  In  another  class  of  cases 
the  patient  may  be  perfectly  capable  of  rational  speech  ;  he 
may  talk  to  himself  or  on  a  set  topic  with  fluency  and  sense, 
but  he  may  be  unable  to  respond  to  a  question  or  read  a 
single  line  of  print.  Damage  to  two  regions  of  the  brain 


THE  CENTRAL  NERVOUS  SYSTEM  717 

has  been  found  associated  with  this  strange  condition,  (i) 
the  occipital,  (2)  the  temporal  cortex.  When  the  lesion  is 
confined  to  the  occipital  region,  spoken  language  is  perfectly 
understood,  written  language  not  at  all  (word-blindness). 
When  the  temporal  region  is  alone  affected,  it  is  the  spoken 
word  that  is  missed,  the  written  that  is  understood  (word- 
deafness).  Sensory,  like  motor  aphasia  may  exist  in  any 
degree  of  completeness,  from  absolute  word-deafness  or 
word-blindness,  in  which  no  spoken  or  printed  word  calls 
up  any  mental  image,  to  a  condition  not  amounting  to  much 
more  than  a  marked  absence  of  mind  or  unusual  obtuseness. 
Motor  and  sensory  aphasia  may  be  present  together.  In 
well-marked  word -deafness  speech  is  always  interfered  with 
to  some  extent. 

Cortical  Epilepsy. — While  it  was  still  believed  that  the 
cortex  was  inexcitable,  epilepsy  was  supposed  to  be  ex- 
clusively due  to  morbid  conditions,  structural  or  functional, 
of  the  medulla  oblongata  (Kussmaul  and  Tenner).  Some 
more  recent  writers  have  put  forward  precisely  the  opposite 
opinion,  that  the  disease  is  always  cortical  in  origin  (Unver- 
richt,  etc.).  What  we  know  for  certain  is  that  some  cases, 
but  only  a  minority,  are  associated  with  irritative  lesions  in 
or  near  the  Rolandic  area  (cortical  or  Jacksonian  epilepsy). 
It  has  even  been  found  possible  to  localize  the  position 
of  the  lesion  from  the  part  of  the  body  in  which  the  fit,  or 
the  aura  (the  sensation  or  group  of  sensations  peculiar  to 
each  case,  which  precedes  and  announces  it),  begins.  For 
example,  if  the  convulsions  commence  with  a  twitching  of 
the  right  thumb  and  extend  over  the  arm,  or  if  the  aura 
consists  of  sensations  beginning  in  the  thumb,  there  is  a 
strong  presumption  that  the  seat  of  the  lesion  is  the  part  of 
the  arm-area  known  as  the  'thumb-centre*  in  the  left 
cerebral  hemisphere.  It  is  the  seat  of  the  convulsion  at  its 
commencement,  not  the  regions  to  which  it  may  afterwards 
spread,  that  is  important  in  diagnosing  the  position  of  the 
lesion.  For  just  as  strong  or  long-continued  stimulation  of 
a  given  '  centre '  of  the  motor  cortex  may  give  rise  to  con- 
tractions of  muscles  associated  with  other  '  centres,'  so  the 
excitation  set  up  by  localized  disease  may  spread  far  and 


7i8  A  MANUAL  OF  PHYSIOLOGY 

wide  from  its  original  focus,  involving  area  after  area  of  the 
Rolandic  region  first  in  the  one  hemisphere  and  then  in  the 
other.  The  part  of  the  body  to  which  a  sensory  aura  is 
referred  is  as  significant  an  indication  of  the  seat  of  the 
discharging  lesion  as  is  the  part  of  the  body  which  first 
begins  to  twitch. 

This  is  one  of  the  proofs  that  the  Rolandic  region  is  not  a  purely 
motor,  but  a  sensori-motor  area.  From  the  field  of  experiment 
further  evidence  is  forthcoming. 

(1)  It  has  been  found  that  if  the  posterior  roots  of  the  nerves 
supplying  one  of  the  limbs  be  cut  in  a  monkey,  all  the  most  delicate 
and  skilled  movements  of  the  limb  are  either  greatly  impaired  or 
totally  abolished  (Mott  and  Sherrington).     The  limb  is  not  used  for 
progression  or  for  climbing,  but  hangs  limp,  and  apparently  helpless, 
by  the  side  of  the  animal.     That  this  condition  is  not  due  to  any 
loss  of  functional  power  by  the  peripheral  portion  of  the  motor  path 
may  be  assumed,  since  the  anterior  roots  remain  intact.     That  it  is 
not  due  to  any  want  of  capacity  on  the  part  of  the  motor  centres  to 
discharge  impulses  when  stimulated  may  be  shown  by  exciting  the 
cortical  area  of  the  limb — either  electrically  or  by  inducing  epileptic 
convulsions  by  intravenous  injection  of  absinthe — when  movements 
of  the  affected  limb  take  place  just  as  readily  as  movements  of  the 
sound  limbs.     The  cause  of  the  impairment  of  voluntary  motion, 
then,  can  only  be  the  loss  of  the  afferent  impulses  which  normally 
pass  up  to  the  brain,  and  presumably  to  the  motor  cortex.     When 
only  one  sensory  nerve-root  is  cut,  no  defect  of  movement  can  be 
seen ;  and  this  is  evidently  in  accordance  with  the  fact  already  men- 
tioned (p.  666),  that  complete  anaesthesia  of  even  the  smallest  patch 
of  skin  is  never  caused  by  section  of  a  single  posterior  root.     And 
that  it  is  the  loss  of  impulses  from  the  skin  which  plays  the  chief 
part  is  shown  by  the  fact  that  after  division  of  the  posterior  roots 
supplying  the  muscles  of  the  hand  or  foot,  which  only  partially  inter- 
feres with  the  sensory  supply  of  the  skin,  joints,  sheaths  of  tendons, 
etc.,  movement  is  unimpaired ;  while  section  of  the  nerve-roots  sup- 
plying the  skin,  those  of  the  muscles  being  left  intact,  causes  extreme 
loss  of  motor  power. 

(2)  If  a  strength  of  stimulus  be  sought  which  will  just  fail  to  cause 
contraction  of  the  muscular  group  related  to  a  given  motor  area,  and 
a  sensory  nerve,  or,  better,  a  sensory  surface  (best  of  all,  the  skin 
over  the  corresponding  muscles),  be  now  stimulated,  contraction  will 
occur — that  is  to  say,  the  excitability  of  the  motor  centres  will  be 
increased.     This  shows  that  the  motor  region  is  en  rapport  not  only 
with  efferent,  but  also  with  afferent  fibres,  that  it  receives  impulses  as 
well  as  discharges  them. 

The  same  experiment  is  a  proof  that  the  results  of  excitation  of 
the  motor  cortex  are  due  to  stimulation  of  the  grey  matter,  and  not, 
as  has  been  asserted,  of  the  white  fibres  of  the  corona  radiata.  It  is 
undoubtedly  possible  to  excite  these  fibres  by  electrodes  directly 


THE  CENTRAL  NERVOUS  SYSTEM  719 

applied  to  the  motor  cortex,  but  in  the  latter  case  the  current  has 
to  be  made  stronger  than  is  sufficient  to  excite  the  grey  matter 
alone.  Further  evidence  is  afforded  by  the  following  facts  :  (a)  The 
'period  of  delay,'  that  is,  the  period  which  elapses  between  stimula- 
tion and  contraction,  is  greater  by  nearly  50  per  cent,  when  the 
cortex  is  stimulated  than  when  the  white  fibres  are  directly  excited. 
(ti)  Morphia  greatly  increases  the  period  of  delay  for  stimulation  of 
the  cortex,  and  at  the  same  time  renders  the  resulting  contractions 
more  prolonged  than  normal,  while  the  results  of  direct  stimulation 
of  the  white  fibres  are  much  less,  if  at  all,  affected,  (c)  Mechanical 
stimulation  of  the  motor  areas  also  causes  appropriate  movements. 
(d)  Stimulation  of  the  grey  matter,  when  separated  from  the  sub- 
jacent white  matter  by  the  knife  but  left  in  position,  is  without 
effect  unless  the  strength  of  stimulus  be  increased,  although  twigs  of 
the  current  ought,  of  course,  to  pass  into  the  corona  radiata  as  easily 
as  before. 

Evidence  that  the  phenomena  are  not  due  to  accidental  excitation 
of  the  corona  radiata  is  a  fortiori  evidence  that  they  are  not  caused 
by  escape  of  current  to  the  basal  ganglia,  for  the  distance  of  the 
baual  ganglia  from  the  larger  part  of  the  motor  cortex  is  much 
greater  than  the  thickness  of  the  grey  matter ;  and,  indeed,  that  portion 
of  the  grey  matter  at  the  bottom  of  the  Sylvian  fissure  which  lies 
nearest  to  the  basal  ganglia  does  not  respond  to  stimulation  by  motor 
effects. 

Localization  of  Function  in  the  Central  Nervous  System. — Let 
us  now  consider  a  little  more  closely  the  real  meaning  of  this 
localization  of  function.  Scattered  all  over  the  grey  matter  of  the 
primitive  neural  axis,  and,  as  we  have  seen,  over  the  grey  mantle  of 
the  brain  as  well,  are  numerous  '  centres '  which  seem  to  be  related 
in  a  special  way  to  special  mechanisms,  sensory,  secretory  or  motor. 
The  question  may  fitly  be  asked  whether  those  centres  are  really  dis- 
tinct from  each  other  io  quality  of  structure  or  action,  or  whether 
they  owe  their  peculiar  properties  solely  to  differences  in  situation 
and  anatomical  connection.  It  is  clear  at  the  outset  that  the  nature 
of  the  work  in  which  a  centre  is  engaged  must  be  largely  determined 
by  its  connections.  The  kind  of  activity  which  goes  on  in  the  vaso- 
motor  centre  in  the  bulb,  for  example,  may  in  no  essential  respect 
differ  from  that  which  goes  on  in  the  respiratory  centre.  The  calibre 
of  the  bloodvessels  will  alter  in  response  to  a  change  of  activity  in 
the  one  because  it  is  anatomically  connected  with  the  muscular  coat 
of  the  bloodvessels.  The  rate  or  depth  of  the  respiratory  movements 
will  alter  in  response  to  a  change  of  activity  in  the  other  because  it 
is  connected  with  muscles  which  can  act  upon  the  chest-walls. 

The  localization  of  function  in  the  cerebral  cortex  has  been  likened 
to  the  localization  of  industries  in  the  multiplex  commercial  life  of 
the  modern  world.  The  barbarian  household  in  which  cloth  is 
woven  and  worked  into  garments,  sandals  or  moccasins  cobbled 
together,  rough  pottery  baked  in  the  kitchen  fire,  and  all  the  rude 
furniture  of  the  lodge  fashioned  by  the  hands  which  built  it,  and 
which  rest  beneath  its  roof  at  night — this  state  of  things  where  centrali- 


720  A  MANUAL  OF  PHYSIOLOGY 

zation  has  not  yet  begun,  it  has  been  said,  is  a  picture  of  what  goes 
on  in  the  undeveloped  brains  of  the  frog,  the  pigeon,  and  the  rabbit. 
The  '  diffusion '  of  industries  which  is  characteristic  of  a  primitive 
state  has  given  place  among  the  most  highly  civilized  men  to  extreme 
centralization  and  concentration.  Manchester  spins  cotton  and 
Liverpool  ships  it.  Chicago  handles  wheat  and  pork  that  have  been 
produced  on  the  prairies  of  Minnesota  and  Illinois.  Amsterdam 
cuts  diamonds.  Munich  brews  beer.  Lyons  weaves  silk.  New 
York  and  London  are  centres  of  finance.  This,  it  is  said,  is  the 
picture  of  the  highly  specialized  brain  of  a  monkey  or  a  man.  But 
ingenious  and  alluring  though  such  analogies  are,  they  do  not  rest 
upon  a  sufficient  basis  of  fact. 

It  has  never  been  shown — nor  is  it  likely  that  the  proof  will  soon 
be  forthcoming — that  there  is  any  difference  whatever  in  the  physical, 
chemical  or  psychical  processes  which  go  on  in  the  various  centres 
of  the  Rolandic  cortex.  It  may  be  supposed,  indeed,  that  the  so- 
called  sensory  areas  of  the  cortex  differ  more  widely  in  their  internal 
activity  from  the  motor  areas  than  the  latter  do  among  themselves, 
and  that  the  activity  of  the  anterior  portion  of  the  brain,  the  portion 
which  has  been  credited  par  excellence  with  psychical  functions, 
differs  in  kind,  not  merely  in  degree,  from  that  of  all  the  rest.  But, 
as  we  have  just  seen,  even  the  motor  areas  have  sensory  functions ; 
and  although  a  cast-iron  physiology  may  explain  this  by  the  assump- 
tion of  '  sensory '  as  well  as  *  motor'  cells  in  the  Rolandic  area,  there 
is  absolutely  nothing  to  contradict  the  supposition  that  the  discharge 
of  energy  from  the  most  circumscribed  motor  area  or  element  (be  it 
cell,  or  nervous  network,  or  both)  may  be  accompanied  not  only  with 
consciousness,  but  with  a  high  degree  of  psychical  activity.  And, 
indeed,  some  writers  have  supposed  that  such  a  consciousness  of,  or 
even  conscious  measurement  of,  the  discharge  from  the  motor  areas 
is  the  basis  of  the  muscular  sense  (Bain,  Wundt). 

So  far,  at  least,  as  the  Rolandic  region  and  the  grey  matter  imme- 
diately around  the  neural  canal  is  concerned,  the  analogy  of  an 
electrical  switch-board  connected  with  machines  of  various  kinds 
might  be  more  correct.  Touch  one  key  or  another,  and  an  engine 
is  set  in  motion  to  grind  corn,  or  to  saw  wood,  or  to  light  a  town. 
The  difference  in  result  lies  not  in  any  difference  of  material  or 
workmanship  in  the  switches,  but  solely  in  the  difference  in  their 
connections,  j 

Grey  matter  in  the  upper  part  of  the  Rolandic  cortex  is  excited, 
and  the  muscles  of  the  leg  contract.  Grey  matter  around  the  lower 
part  of  the  fissure  is  excited,  and  there  are  movements  of  the  face 
and  mouth.  Grey  matter  in  the  medulla  oblongata  is  excited, 
and  the  salivary  glands  pour  forth  a  thin,  watery  fluid,  poor  in 
proteids,  and  containing  an  amylolytic  ferment.  Another  portion  of 
grey  (?)  matter  in  the  medulla  is  thrown  into  activity,  and  the  pan- 
creatic ducts  become  flushed  with  a  thick  secretion,  rich  in  proteids 
and  in  ferments  which  act  on  proteids,  starch,  and  fat.  Here,  too, 
there  is  a  variety  in  result  according  as  one  or  another  nervous 
switch  is  closed;  here,  too,  the  variety  is  due,  not  to  essential 


THE  CENTRAL  NERVOUS  SYSTEM  721 

differences  in  the  structure  or  the  activity  of  the  nervous  centres,  but 
to  their  connection,  by  nervous  paths,  with  peripheral  organs  of 
different  kinds.  There  is,  indeed,  a  specialization,  a  localization,  of 
function,  but  the  localization  is  at  the  periphery,  the  specialization  is 
in  the  peripheral  organs. 

It  may  be  asked  whether,  if  this  is  the  case  for  the  peripheral 
organs  of  efferent  nerves,  the  converse  does  not  hold  true  for  the 
afferent  nerves — in  other  words,  whether  the  localization  here  is  not 
at  the  centre.  And  that  there  is  in  some  degree  a  central  localization 
of  sensation  may  be  considered  proved  by  the  well-known  clinical  * 
fact,  already  referred  to,  that  sensations  of  various  kinds  may  be  pro-P 
duced_by_pathological  changes  in  the  cortex.  For  example,  a  tumour/  r' 
involving  the  upper  part  of  the  temporal  lobe  may  give  rise  to 
epileptiform  convulsions  preceded  by  an  auditory  aura,  a  sound,  it 
may  be,  resembling  the  ringing  of  bells ;  a  tumour  involving  the 
occipital  region  may  cause  a  visual  aura,  and  so  on.  Central  sensory 
localization  is,  indeed,  inevitable  if  we  accept  the  old  doctrine  of 
'  specific  energy.'  If  the  impulses  set  up  in  the  auditory  nerve 
when  sound  impinges  on  the  tympanic  membrane  do  not  differ 
essentially  from  those  set  up  in  the  optic  nerve  when  a  ray  of  light 
falls  upon  the  retina,  or  from  those  set  up  in  the  trigeminal  nerve  by 
the  irritation  of  a  carious  tooth,  or  from  those  set  up  in  certain  fibres 
of  all  cutaneous  nerves  when  a  warm  body  comes  in  contact  with  the 
skin  ;  then,  since  the  results  in  consciousness  are  very  different,  we 
must  assume  that  somewhere  or  other  in  the  central  nervous  system 
there  exist  organs  that  are  differently  affected  by  the  same  kinds  of 
afferent  impulses — in  other  words,  that  sensory  localization  is  at  the 
centre.  On  this  view,  the  visual  areas  in  the  cortex  respond  to  all 
kinds  of  stimuli  by  visual  sensations  ;  the  auditory  areas  by  sensations 
of  sound ;  and  possibly  the  whole  or  part  of  the  limbic  lobe  (the 
convolutions  lying  around  the  corpus  callosum  on  the  mesial  surface 
of  the  hemisphere)  by  sensations  of  touch  and  pain. 

But  while  it  cannot  be  doubted  that  special  sensory  regions  exist  in 
the  grey  matter  of  the  brain,  there  is  no  reason  to  suppose  that  the 
nerve-impulses  which  travel  up  the  optic  and  up  the  auditory  nerve 
are  absolutely  similar  until  they  have  reached  the  visual  and  auditory 
centres,  and  that  there  they  suddenly  become,  or  produce,  sensations 
absolutely  different.  And  it  would  seem  that  the  tendency  of  research 
is  at  present  to  increase  the  evidence  in  favour  of  a  certain  amount 
of  sensory  specialization  at  the  periphery,  and  therefore  to  diminish 
the  scope,  if  not  the  necessity,  of  such  a  specialization  in  the  brain. 
For  example,  when  an  ordinary  nerve-trunk  is  touched,  the  resultant 
sensation  is  not  one  of  touch.  If  there  is  any  sensation  at  all,  it  is 
one  of  pain.  Heating  or  cooling  a  naked  nerve-trunk  gives  rise  to 
no  sensations  of  temperature.  When  the  ulnar  nerve  is  artificially 
cooled  at  the  elbow,  the  first  effect  is  severe  pain  in  the  parts  of  the 
hand  supplied  by  the  nerve.  The  pain  disappears  somewhat  abruptly 
as  cooling  goes  on,  and  is  succeeded  by  gradual  loss  of  all  sensation, 
the  sensations  of  touch,  pain  and  temperature  disappearing  in  the  ulnai 
area  of  the  hand  in  the  order  named ;  but  the  cooling  of  the  nerve-trunk 

46 


722  A  MANUAL  OF  PHYSIOLOGY 

does  not  give  rise  to  any  sensation  of  cold  (Weir  Mitchell).  Stimu- 
lation of  the  end  organs  is  essential  in  order  that  sensations  of  touch 
and  temperature  should  be  experienced.  The  tradition  which  has 
come  down  from  the  older  surgery  before  the  days  of  anaesthetics, 
that  when  the  optic  nerve  was  cut  in  removing  the  eyeball  the  patient 
experienced  the  sensation  of  a  flash  of  light,  was  long  looked  upon 
as  the  strongest  prop  of  the  law  of  specific  energy.  But  neither  the 
evidence  of  the  alleged  fact  nor  the  consequences  deduced  from  it 
have  escaped  modern  criticism.  And  it  is  possible  that  in  some 
cases,  at  least,  the  retina  was  excited — directly  by  mechanical  stimu- 
lation, or  by  means  of  fibres  carrying  impulses  peripherally  (?)  in  the 
optic  nerve — at  the  moment  when  the  knife  entered  it,  and  that 
sufficient  time  elapsed  before  the  section  was  completed  for  the  ex- 
citation to  pass  up  across  an  isthmus  of  uncut  fibres.  Ewald  has 
indeed  stated  that  even  after  extirpation  of  the  end  organs  of  the 
auditory  nerve  in  the  pigeon,  sounds  too  feeble  to  excite  ordinary 
tactile  nerves  are  still  heard  so  long  as  the  nerve-trunk  is  intact. 
But  the  explanation  of  this  might  be  either  that  the  impulses  set  up 
in  this  nerve  by  the  mechanical  stimulation  of  aerial  waves  are  of  a 
special  kind,  and  therefore  result  in  a  special  sensation,  or  that,  the 
impulses  being  alike  in  the  auditory  and  other  nerves,  the  former  is 
peculiarly  susceptible  to  sound-waves.  In  the  first  case  a  certain 
amount  of  specialization  in  the  afferent  impulses  would  be  proved  to 
be  accomplished  before  they  reach  their  centres.  One  reason,  then, 
why  excitation  of  the  temporal  cortex  by  impulses  falling  into  it  along 
the  auditory  nerve-fibres  causes  a  sensation  different  from  that  caused 
by  impulses  reaching  the  occipital  cortex  through  the  fibres  of  the 
optic  nerve  may  be  a  difference  in  the  nature  of  the  impulses.  If 
this  were  the  only  reason,  it  would  follow  that  were  it  possible 
to  physiologically  connect  the  fibres  of  the  optic  radiation  with  the 
temporal  cortex,  and  those  of  the  temporal  radiation  with  the 
occipital  cortex,  sights  and  sounds  would  still  be  perceived  and  dis- 
criminated in  a  normal  manner,  although  now  the  integrity  of  the 
occipital  lobe  would  be  bound  up  with  the  perception  of  sound,  the 
integrity  of  the  temporal  lobe  with  visual  sensation.  This  state  of 
affairs  would  correspond  to  complete  specialization  for  sensation  in 
the  peripheral  organs,  complete  absence  of  specialization  in  the 
centres.  On  the  other  hand,  it  is  conceivable  that,  after  such  an 
ideal  experiment,  sound-waves  falling  on  the  auditory  apparatus 
might  cause  visual  sensations,  and  luminous  impressions  falling  on 
the  retina  sensations  of  sound.  This  would  correspond  to  complete 
specialization  of  sensation  in  the  centres,  complete  absence  of 
specialization  at  the  periphery.  A  third  possibility  would  be  that 
the  *  transposed '  centres,  responding  at  first  feebly  or  not  at  all  to 
the  new  impulses,  might,  by  slow  degrees,  become  more  and  more 
excitable  to  them.  This  would  correspond  to  a  peripheral  specializa- 
tion, combined  with  a  tendency  to  development  of  central  specializa- 
tion. And,  indeed,  it  is  not  easy  to  conceive  in  what  way,  except 
as  the  result  of  differences  in  the  nature  of  impulses  coming  from 


THE  CENTRAL  NERVOUS  SYSTEM  723 

the  periphery,  specialization  of  sensory  areas  in  the  central  nervous 
system  could  have  at  first  arisen.  <£ 

Reaction  Time. — Just  a's  in  a  reflex  act  a  certain  measure- 
able  time  (reflex  time)  is  taken  up  by  the  changes  that  occur 
in  the  lower  nervous  centres,  so  we  may  assume  that  in  all 
psychical  processes  the  element  of  time  is  involved.  And, 
indeed,  when  the  interval  that  elapses  between  the  applica- 
tion of  a  stimulus  and  the  signal  which  announces  that  it 
has  been  felt  (reaction  time)  is  measured,  it  is  found  that  the 
cerebral  processes  associated  with  the  perception  of  the 
simplest  sensation  and  the  production  of  the  simplest 
voluntary  contraction  is  longer  than  the  time  which 
the  spinal  centres  require  for  the  elaboration  of  even  com- 
plex and  co-ordinated  reflex  movements.  Suppose,  e.g., 
that  the  stimulus  is  an  induction  shock  applied  to  a  given 
point  of  the  skin,  and  that  the  signal  is  the  closing  of 
the  circuit  of  an  electro-magnet,  then,  if  both  events  are 
automatically  recorded  on  a  revolving  drum,  the  interval 
can  be  readily  determined.  It  is  evident  that  this  includes, 
not  only  the  time  actually  consumed  in  the  central  pro- 
cesses, but  also  the  time  required  for  the  afferent  impulse 
to  reach  the  brain,  and  the  efferent  impulse  the  hand, 
along  with  the  latent  period  of  the  muscles.  The  time 
taken  up  in  these  three  events  can  be  approximately  cal- 
culated, and  when  it  is  subtracted,  the  remainder  repre- 
sents the  reduced  or  corrected  reaction  time  ;  that  is,  the 
interval  actually  spent  in  the  centres  themselves.  This  is 
by  no  means  a  constant.  It  is  influenced  not  only  by  the 
degree  of  complexity  of  the  psychical  acts  involved,  and  the 
mental  attitude  of  the  person  (whether  he  expects  the 
stimulus  or  is  taken  by  surprise,  whether  he  has  to  choose 
between  several  possible  kinds  of  stimuli  and  respond  to 
only  one,  etc.),  but  it  varies  also  for  different  kinds  of  sensa- 
tion, for  the  same  sensation  at  different  times,  and  as  is 
recognised  in  the  personal  equation  of  astronomers,  in  different 
individuals.  For  sensations  of  touch  and  pain  it  may  be 
taken  as  one-ninth  to  one-fifth,  for  hearing  one-eighth  to 
one-sixth,  and  for  sight  one-eighth  to  one-fifth  of  a  second.  ' 
So  that  the  proverbial  quickness  of  thought  is  by  no  means 

46—2 


724  A  MANUAL  OF  PHYSIOLOGY 

great,  even  in  comparison  with  that  of  such  a  gross  process 
as  the  contraction  of  a  muscle  (one-tenth  of  a  second).  Nor 
is  it  the  case  that  the  man  '  of  quick  apprehension '  has 
always  a  short  reaction  time,  or  the  dullard  always  a  long 
one,  although  in  all  kinds  of  persons  practice  will  reduce  it. 
Sleep. — Certain  gland-cells,  certain  muscular  fibres,  and 
the  epithelial  cells  of  ciliated  membranes,  never  rest,  and 
perhaps  hardly  ever  even  slacken  their  activity.  But  in  most 
organs  periods  of  action  alternate  at  more  or  less  frequent 
intervals  with  periods  of  relative  repose.  In  all  the  higher 
animals  the  central  nervous  system  enters  once  at  least  in 
the  twenty-four  hours  into  the  condition  of  rest  which  we 
call  sleep.  What  the  cause  of  this  regular  periodicity  is 
we  do  not  know.  Some  have  suggested  that  sleep  is  in- 
duced by  the  action  of  the  waste  products  of  the  tissues,  and 
especially  lactic  acid,  when  they  accumulate  beyond  a  certain 
amount  in  the  blood,  or  in  the  nervous  elements  themselves. 
And  actual  histological  changes  have  been  described  in 
nerve-cells  as  the  result  of  physiological  fatigue  or  of  fatigue 
induced  by  artificial  stimulation  of  nerves  (Hodge).  Others 
have  looked  for  an  explanation  to  vascular  changes  in  the 
brain,  but  so  far  are  the  possible  causes  of  such  changes 
from  being  understood,  that  it  is  even  yet  a  question 
whether  in  sleep  the  brain  is  congested  or  anaemic.  In 
coma,  a  pathological  condition  which  in  some  respects  has 
analogies  to  profound  and  long-continued  sleep,  the  brain  is 
congested,  and  the  proper  elements  of  the  nervous  tissue 
presumably  compressed.  And  artificial  pressure  (applied  by 
means  of  a  distensible  bag  introduced  through  a  trephine 
hole  into  the  cranial  cavity)  may  cause  not  only  unconscious- 
ness, but  absolute  anaesthesia.  But  it  is  possible  that  this 
artificial  increase  of  intracranial  pressure  may  produce  its 
effects  by  rendering  the  brain  anaemic,  and  it  has  been 
actually  observed  that  the  retinal  vessels,  as  seen  with  the 
ophthalmoscope  and  the  vessels  of  the  pia  mater  exposed 
to  direct  observation  in  man  by  disease  of  the  bones  of  the 
skull,  or  in  animals  by  operation,  shrink  during  sleep. 
Further,  a  condition  closely  resembling,  if  not  identical  with, 
natural  sleep  can  be  induced  by  tying  the  cerebral  arteries. 


THE  CENTRAL  NERVOUS  SYSTEM  725 

So  that  the  balance  of  evidence  is  decidedly  in  favour  of  the 
view  that  sleep  is  associated  with  anaemia,  although  it  is  not 
a  good  argument  to  say,  as  some  writers  have  done,  that 
when  the  brain  rests  the  quantity  of  blood  in  it  must  be 
supposed,  as  in  other  resting  organs,  to  be  diminished. 
For  when  the  whole  body  rests,  as  it  does  in  sleep,  it  has  as 
much  blood  in  it  as  when  it  works ;  in  sleep,  therefore,  if 
some  resting  organs  have  less  blood  than  in  waking  life, 
other  resting  organs  must  have  more ;  and  it  is  the  province 
of  experiment  to  decide  which  are  congested  and  which 
anaemic.  < 

In  general,  the  depth  of  sleep,  as  measured  by  the  intensity  of 
sound  needed  to  awaken  the  sleeper,  increases  rapidly  in  the  first 
hour,  falls  abruptly  in  the  second,  and  then  slowly  creeps  down  to 
its  minimum,  which  it  reaches  just  before  the  person  awakens.  As 
to  the  amount  of  sleep  required,  no  precise  rules  can  be  laid  down. 
It  varies  with  age,  occupation,  and  perhaps  climate.  An  infant, 
whose  main  business  is  to  grow,  spends,  or  ought  to  spend,  if  mothers 
were  wise  and  feeding-bottles  clean,  the  greater  part  of  its  time  in 
sleep.  The  man,  whose  main  business  it  is  to  work  with  his  hands 
or  brain,  requires  his  full  tale  of  eight  hours'  sleep,  but  not  usually 
more.  The  dry  and  exhilarating  air  of  some  of  the  inland  portions 
of  North  America,  and  perhaps  the  plains  of  Victoria  and  New 
South  Wales,  incites,  and  possibly  enables  a  new-comer  to  live  for  a 
considerable  period  with  less  than  his  ordinary  amount  of  sleep. 
Idiosyncrasy,  and  perhaps  to  a  still  greater  extent  habit,  have  also  a 
marked  influence.  The  great  Napoleon,  in  his  heyday,  never  slept 
more  than  four  or  five  hours  in  the  twenty-four.  Five  or  six  hours 
or  less  was  the  usual  allowance  of  Frederick  of  Prussia  throughout 
the  greater  part  of  his  long  and  active  life. 

Hypnosis  is  a  condition  in  some  respects  allied  to  natural  slumber ; 
but  instead  of  the  activity  of  the  whole  brain — or  perhaps  we  should 
rather  say,  the  whole  activity  of  the  brain — being  in  abeyance,  the 
susceptibility  to  external  impressions  remains  as  great  as  in  waking 
life,  or  may  be  even  increased,  while  the  critical  faculty,  which 
normally  sits  in  judgment  on  them,  is  lulled  to  sleep.  The  condi- 
tion can  be  induced  in  many  ways — by  asking  the  subject  to  look 
fixedly  at  a  bright  object,  by  closing  his  eyes,  by  occupying  his  atten- 
tion, by  a  sudden  loud  sound  or  a  flash  of  light,  etc.  The  essential 
condition  is  that  the  person  should  have  the  idea  of  going  to  sleep, 
and  that  he  should  surrender  his  will  to  the  operator.  In  the  hypnotic 
condition  the  subject  is  extremely  open  to  suggestions  made  by  the 
operator  with  whom  he  is  en  rapport.  He  adopts  and  acts  upon 
them  without  criticism.  If,  for  example,  the  hypnotizer  raises  the 
subject's  arm  above  his  head,  and  suggests  that  he  cannot  bring  it 
down  again,  it  stays  fixed  in  that  position  for  a  long  time  without  any 


726  A  MANUAL  OF  PHYSIOLOGY 

appearance  of  fatigue ;  or  the  whole  body  may  be  thrown,  on  a  mere 
hint,  into  some  unnatural  pose  in  which  it  remains  rigid  as  a  statue. 
Suggested  hemiplegia  or  hemianaesthesia,  or  paralysis  of  motion 
and  sensation  together  or  apart  in  limited  areas,  can  also  be  realized  ; 
and  surgical  operations  have  been  actually  performed  on  hypnotized 
persons  without  any  appearance  of  suffering.  If,  on  the  other 
hand,  the  operator  suggests  that  the  subject  is  undergoing  intense 
pain,  he  will  instantly  take  his  cue,  writhing  his  body,  pressing 
his  hands  upon  his  head  or  breast,  and  in  all  respects  behaving 
as  if  the  suggestion  were  in  accord  with  the  facts.  If  he  is  told  that 
he  is  blind  or  deaf,  he  will  act  as  if  this  were  the  case.  If  it  is  sug- 
gested that  a  person  actually  present  is  in  Timbuctoo,  the  subject 
will  entirely  ignore  him,  will  leave  him  out  if  told  to  count  the 
persons  in  the  room,  or  try  to  walk  through  him  if  asked  to  move  in 
that  direction.  What  is  even  more  curious  is  that  the  organic 
functions  of  the  body  are  also  liable  to  be  influenced  by  suggestion. 
A  postage-stamp  was  placed  on  the  skin  of  a  hypnotized  person,  and 
it  was  suggested  that  it  would  raise  a  blister.  Next  day  a  blister  was 
actually  found  beneath  it.  The  letter  K,  embroidered  on  a  piece  of 
cloth,  was  suggested  to  be  red-hot.  The  left  shoulder  was  then 
'  branded  '  with  it,  and  on  the  right  shoulder  appeared  a  facsimile  of 
the  K  as  if  burnt  with  a  hot  iron.  The  secretions  can  be  increased 
or  diminished,  subcutaneous  haemorrhages,  veritable  stigmata,  can  be 
caused,  and  many  of  the  *  miracles '  of  Lourdes  and  other  shrines, 
ancient  and  modern,  repeated  or  surpassed  by  the  aid  of  hypnotic 
suggestion.  Hypnotism  has  also  been  practically  employed  in  the 
treatment  of  various  diseases,  and  particularly  in  functional  derange- 
ments of  the  nervous  system.  But  care  and  judgment  are  necessary 
on  the  part  of  the  operator,  and  although  as  a  rule  there  is  no  diffi- 
culty in  putting  an  end  to  the  condition  by  a  suitable  suggestion,  it 
is  said  that  in  rare  instances  grave  mischances  have  occurred.  There 
seems  to  be  no  ground  for  the  opinion  that  women  are  more  easily 
hypnotized  than  men.  Out  of  more  than  a  thousand  persons,  Liebault 
found  only  seventeen  absolutely  refractory. 

Relation  of  Size  of  Brain  to  Intelligence. — While  it  is  the  case 
that  some  men  of  great  ability  have  had  remarkably  heavy  and  richly 
convoluted  brains,  it  would  seem  that  in  general  neither  great  size 
nor  any  other  anatomical  peculiarity  of  the  cerebrum  is  constantly 
associated  with  exceptional  intellectual  power.  In  the  animal 
kingdom  as  a  whole,  there  is  undoubtedly  some  relation  between 
the  status  of  a  group  and  the  average  brain  development  within  the 
group.  But  that  this  is  a  relation  which  is  complicated  by  other 
circumstances  than  the  mere  degree  of  intelligence  is  sufficiently 
shown  by  the  fact  that  a  mouse  has  more  brain,  in  proportion 
to  its  size,  than  a  man,  and  thirteen  times  more  than  a  horse ;  while 
both  in  the  rabbit  and  sheep  the  ratio  of  brain-weight  to  body- 
weight  is  nearly  twice  as  great  as  in  the  horse,  in  the  dog  only  half 
as  great  as  in  the  cat,  and  not  very  much  more  than  in  the  donkey. 
The  following  tables,  too,  which  illustrate  the  weight  of  the  brain  in 
man  at  different  ages,  show  that,  although  we  might  give  '  the  infant 


THE  CENTRAL  NERVOUS  SYSTEM 


727 


Age. 

Brain-weight. 

i  year. 

885  grm. 

2  years. 

9°9     » 

3     , 

1071     „ 

4     , 

1099     „ 

5           > 

1033     ,, 

6     , 

H47          „ 

7           5 

1201        „ 

Age. 
10  —  19 

20  29 

Men. 
1411  grm. 

1419  ,5 

Women. 

1219  grm. 

1260   „ 

Age. 

5°—  59 
60  —  69 

Men. 

1389  grm. 
1292  „ 

3°—  39 
40—49 

1424  „ 
1406  „ 

1272   „ 
1272   „ 

70—79 

80  —  90 

1254  „ 
1303  » 

phenomenon'  an  anatomical  basis,  we  should  greatly  overrate  the 
intellectual  acuteness  of  the  average  baby  if  we  were  to  measure  it 
by  the  ratio  of  brain  to  body-weight  alone. 

Age.  Brain-weight. 

8  years.  1045  grm- 

10     „          1315     5, 

11  „    1168  „ 

12  „      1286   „ 

13  55          I5°5     >* 

14  „   1336  „ 

15  „    1414  ,, 

(Bischoff.) 

Women. 

1239  grm. 

I2I9   „ 

II29   „ 

898   „ 

(Huschke.) 

In  some  small  birds  the  ratio  is  as  high  as  i  :  12,  in  large  birds  as 
low  as  i  :  1,200  ;  in  certain  fishes  a  gramme  of  brain  has  to  serve  for 
over  5  kilos  of  body.  As  a  rule,  especially  within  a  given  species, 
the  brain  is  proportionally  of  greater  size  in  small  than  in  large 
animals. 

The  Circulation  in  the  Central  Nervous  System. — The  arrange- 
ment of  the  cerebral  bloodvessels  has  certain  peculiarities  which  it  is 
of  great  importance  to  remember  in  connection  with  the  study  of 
the  diseases  of  the  brain,  many  of  which  are  caused  by  lesions  in 
the  vascular  system — haemorrhage  or  embolism.  Four  great  arterial 
trunks  carry  blood  to  the  brain,  two  internal  carotids  and  two  verte- 
brals  (Plate  V?74).  The  vertebrals  unite  at  the  base  of  the  skull 
to  form  the  single  mesial  basilar  artery,  which,  running  forward  in  a 
groove  in  the  occipital  bone,  splits  into  the  two  posterior  cerebral 
arteries.  Each  carotid,  passing  in  through  the  carotid  foramen, 
divides  into  a  middle  and  an  anterior  cerebral  artery ;  the  latter 
runs  forward  in  the  great  longitudinal  fissure,  the  former  lies  in 
the  fissure  of  Sylvius.  A  communicating  branch  joins  the  middle 
and  posterior  cerebrals  on  each  side,  and  a  short  loop  connects  the 
two  anterior  cerebrals  in  front.  In  this  way  a  hexagon  is  formed  at 
the  base  of  the  brain,  the  so-called  circle  of  Willis.  While  the  anas- 
tomosis between  the  large  arteries  is  thus  very  free,  the  opposite  is 
true  of  their  branches.  All  the  arteries  in  the  substance  of  the  brain 
and  cord  are  '  end-arteries  ';  that  is  to  say,  each  terminates  within  its 
area  of  distribution  without  sending  any  communicating  branches  to 
make  junction  with  its  neighbours.  The  consequence  of  these  two 
anatomical  facts  is:  (i)  that  interference  with  the  blood-supply  of 
the  brain  between  the  heart  and  the  circle  of  Willis  does  not  readily 
produce  symptoms  of  cerebral  anaemia — e.g.,  both  common  carotids 
may  be  tied,  in  a  dog,  without  any  harmful  effect ;  (2)  that  the  block- 
ing of  any  of  the  arteries  which  arise  from  the  circle  or  any  of  their 


728  A  MANUAL  OF  PHYSIOLOGY 

branches  leads  to  destruction  of  the  area  supplied  by  it.  The  basal 
ganglia  are  fed  by  twigs  from  the  circle  of  Willis  and  the  beginning 
of  the  posterior,  middle,  and  anterior  cerebral  arteries.  Of  these 
the  most  important  are  the  lenticulo-striate  and  lenticulo-optic 
branches  of  the  middle  cerebral,  which  are  given  off  near  its  origin, 
and  run  through  the  lenticular  nucleus  into  the  internal  capsule,  and 
thence  to  the  caudate  nucleus  and  optic  thalamus  respectively.  The 
chief  part  of  the  blood  from  the  circle  of  Willis  is  carried  by  the 
three  great  cerebral  arteries  over  the  cortex  of  the  brain.  The  white 
matter,  with  the  exception  of  that  in  the  im mediate  neighbourhood 
of  the  basal  ganglia,  is  nourished  by  straight  arteries  which  penetrate 
the  cortex.  The  middle  cerebral  supplies  the  whole  of  the  parietal 
as  well  as  that  portion  of  the  frontal  lobe  which  lies  immediately  in 
front  of  the  fissure  of  Rolando  and  the  upper  part  of  the  temporal 
lobe.  The  rest  of  the  frontal  lobe  is  supplied  by  the  anterior  cere- 
bral, and  the  occipital  lobe,  with  the  lower  part  of  the  temporal  lobe, 
by  the  posterior  cerebral.  The  medulla  oblongata,  cerebellum,  and 
pons  are  fed  from  the  vertebrals  and  the  basilar  artery  before  the 
circle  of  Willis  has  been  formed. 


PRACTICAL  EXERCISES  ON  CHAPTER  XII. 

i.  Hemisection  of  the  Spinal  Cord.* — Put  a  small  dog  under 
morphia  (p.  58),  and  fasten  it  on  a  holder  in  the  prone  position. 
Clip  and  shave  the  skin  over  the  three  lower  dorsal  vertebrae.  Wash 
with  soap  and  water,  then  with  corrosive  sublimate  solution.  Then, 
giving  ether  if  necessary,  make  a  longitudinal  incision  under  anti- 
septic precautions  down  to  the  spines  of  the  vertebrae.  Dissect  the 
muscles  away  from  the  spines  and  vertebral  laminae ;  with  bone 
forceps  or  strong  scissors  cut  through  the  laminae  on  each  side  of  one 
of  the  lower  dorsal  vertebrae,  and  remove  the  posterior  portion  of  the 
arch  with  the  spinous  process.  The  spinal  cord  will  now  come  into 
view,  covered  by  the  dura  mater.  Seize  the  dura  with  fine-pointed 
forceps,  and  divide  it  freely  in  the  mesial  line.  Then  with  a  narrow- 
bladed,  sharp  knife  (a  cataract-knife,  e.g.)  divide  one  half  of  the 
cord.  If  there  is  not  room  enough  to  work  satisfactorily  in  the 
spinal  canal,  remove  another  vertebral  arch.  Sponge  the  wound 
with  iodoform  gauze  wrung  out  of  normal  saline  solution  previously 
boiled  and  still  as  hot  as  the  hand  can  bear  ;  then  put  in  a  row  of 
deep  sutures,  bring  the  skin  together  by  stitches,  and  paint  the  surface 
with  collodion.  Place  the  dog  in  its  cage,  and  study  the  loss  of 
motion  and  sensation  in  the  two  hind-legs  during  '  the  stage  of  shock ' 
(first  few  days),  and  then  later  on  when  a  certain  degree  of  recovery 
has  taken  place.  Test  the  sensibility  for  pain  by  pinching  the  legs 
or  toes  ;  for  temperature  by  placing  them  in  hot  or  cold  water,  and 
comparing  the  promptitude  with  which  they  are  withdrawn  with 

*  This  experiment  is  difficult,  and  is  only  to  be  attempted  by  advanced 
students  selected  by  the  demonstrator. 


PRACTICAL  EXERCISES  729 

what  happens  in  the  case  of  the  fore-limbs  ;  for  slight  tactile  sensation 
by  blowing  through  a  tube  on  the  legs.  Note  the  rectal  tempera- 
ture from  day  to  day,  and  observe  whether  the  faeces  and  urine  are 
normally  under  control.  After  five  or  six  weeks,  or  a  longer  or 
shorter  time  according  to  whether  the  symptoms  are  stationary  or 
not,  kill  the  animal  by  chloroform.  Take  out  the  brain  and  cord, 
noting  particularly  the  state  of  matters  at  the  site  of  the  hemi- 
section.  Harden  first  in  Miiller's  fluid  (essentially  potassium  bichro- 
mate, with  a  little  sodic  sulphate)  for  ten  days,  then  put  portions  into 
Marchi's  fluid  (a  mixture  of  one  part  of  a  i  per  cent,  solution  of 
osmic  acid  with  two  parts  of  Miiller's  fluid),  cut  in  celloidin,  and 
examine  the  degenerated  tracts  (p.  649). 

2.  Section  and  Stimulation  of  the  Spinal  Nerve-roots  in  the  Frog. 
— Select  a  large  frog  (a  bull-frog,  if  possible).     Pith  the  brain.    Fasten 
the  frog,  belly  down,  on  a  plate  of  cork.     Make  an  incision  in  the 
middle  line  over  the  spinous  processes  of  the  lowest  three  or  four 
vertebrae,  separate  the  muscles  from  the  vertebral  arches,  and  with 
strong  scissors  open  the  spinal  canal,  taking  care  not  to  injure  the 
cord  by  passing  the  blade  of  the  scissors  too  deeply.     Extend  the 
opening  upwards  till  two  or  three  posterior  roots  come  into  view. 
Pass  fine  silk  ligatures  under  two  of  them,  tie,  and  divide  one  root 
central  to  the  ligature,  the  other  peripheral  to  it.    Stimulate  the  central 
end,  and  reflex  movements  will  occur.    Stimulate  the  peripheral  end  : 
no  effect  is  produced.     Now  cut  away  the  exposed  posterior  roots 
and  isolate  and  ligature  two  of  the  anterior  roots,  which  are  smaller 
than  the  posterior.     Stimulate  the  central  end  of  one  :  there  is  no 
effect.     Stimulation  of  the  peripheral  end  of  the  other  causes  con- 
tractions of  the  corresponding  muscles. 

3.  Reflex  Action:  Inhibition  of  the  Reflexes. — Pith  a  frog  (brain 
only).    Pass  a  hook  through  the  jaws.    Holding  the  frog  by  the  hook, 
dip  one  leg  into  a  dilute  solution  of  sulphuric  acid  ('2  to  -5  per  cent.), 
and  note  with  the  stop-watch  the  interval  which  elapses  before  the 
frog  draws  up  its  leg  (Tiirck's  method  of  determining  the  reflex  time). 
Wash  the  acid  off  with  water.     Now  touch  the  skin  of  one  thigh  with 
blotting-paper  soaked  in  strong  acetic  acid.     The  leg  is  drawn  up, 
and  the  foot  moved  as  if  to  get  rid  of  the  irritant.    If  the  leg  is  held, 
the  other  is  brought  into  action.     Immerse  the  frog  in  water  to  wash 
away  the  acid.     Again  dip  one  leg  into  the  dilute  acetic  acid,  and 
estimate  the  reflex  time.     Then  apply  a  crystal  of  common  salt  to 
the  upper  part  of  the  spinal  cord.     If  the  opening  made  for  pithing 
the  frog  is  not  large  enough  to  enable  the  cord  to  be  clearly  seen, 
enlarge  it.    Again  dip  the  leg  in  the  dilute  acid.    It  will  either  not  be 
drawn  up  at  all,  or  the  interval  will  be  distinctly  longer  than  before. 

4.  Action  of  Strychnia. — Pith  a  frog  (brain  only).     Inject  into 
one  of  the  lymph-sacs  three  or  four  drops  of  a  o'i  per  cent,  solution 
of  strychnia.     In  a  few  minutes  general  spasms  come  on,  which  have 
intermissions,  but  are  excited  by  the  slightest  stimulus.    The  extensor 
muscles  of  the  trunk  and  limbs  overcome  the  flexors.     Destroy  the 
spinal  cord ;  the  spasms  at  once  cease,  and  cannot  again  be  excited. 

5.  Excision  of  Cerebral  Hemispheres  in  the  Frog  (Fig.  245). — Put 


730  A  MANUAL  OF  PHYSIOLOGY 

a  frog  under  a  bell-jar  with  a  small  piece  of  cotton-wool  soaked  in  ether. 
In  a  few  minutes  it  will  be  anaesthetized.  Then,  holding  it  in  a  cloth, 
make  an  incision  through  the  skin  over  the  skull  in  the  mesial  line. 
With  scissors  open  the  cranium  about  the  position  of  a  line  drawn  at 
a  tangent  to  the  posterior  borders  of  the  two  tympanic  membranes. 
Remove  the  roof  of  the  skull  in  front  of  this  line  with  forceps,  scoop 
out  the  cerebral  hemispheres,  and  sew  up  the  wound.  As  soon  as 
the  animal  has  recovered  from  the  ether,  the  phenomena  described 
at  p.  704  should  be  verified.  The  frog  will  still  swim  when  thrown  into 
water,  will  refuse  to  lie  on  its  back,  and  will  not  fall  if  the  board  on 
which  it  lies  be  gradually  slanted.  Let  the  frog  live  for  a  day,  keeping 
it  in  a  moist  atmosphere ;  then  expose  the  brain  again,  determine  the 
reflex  time  by  Tiirck's  method ;  apply  a  crystal  of  common  salt  to 
the  optic- lobes,  and  repeat  the  observation.  The  reflex  movements 
will  be  completely  inhibited  or  delayed.  Remove  the  salt,  wash  with 
normal  saline,  excise  the  optic  lobes,  and  see  whether  the  frog  will 
now  swim. 

6.  Excision  of  the  Cerebral  Hemispheres  in  a  Pigeon. — Feed  a 
pigeon  for  two  or  three  days  on  dry  food,  etherize  it  by  holding  a 
piece  of  cotton-wool  sprinkled  with  ether  over  its  beak,  or  inject  into 
the  rectum  J  gramme  chloral  hydrate.     The  pigeon  being  wrapped 
up  in  a  cloth,  and  the  head  held  steady  by  an  assistant,  the  feathers 
are  clipped  off  the  head,  an  excision  made  in  the  middle  line  through 
the  skin,  and  the  flaps  reflected  so  as  to  expose  the  skull.     Cut 
through  the  bones  with  scissors,  and  make  a  sufficiently  large  opening 
to  bring  the  cerebral  hemispheres  into  view.     They  are  now  rapidly 
divided  from  the  corpora  bigemina  and  lifted  out  with  the  handle  of 
a  scalpel.     The  bleeding  is  very  free,  but  may  be  partially  controlled 
by  stuffing  the  cavity  with  pengawahr  yambi,  which  should  be  re- 
moved in  a  few  minutes,  the  wound  cleansed  with  iodoform  gauze 
wrung  out  of  normal  salt  solution  at  50°  C.,  and  sewed  up.     Study 
the  phenomena  described  on  p.  704. 

7.  Stimulation  of  the  Motor  Areas  in  the  Dog. — (a)  Study  a 
hardened  brain  of  a  dog,  noting  especially  the  crucial  sulcus  (Fig.  239), 
the  convolutions  in  relation  to  it,  and  the  areas  mapped  out  around  it 
by  Hitzig  and  Fritsch  and  others,    (b)  Inject  morphia  under  the  skin 
of  a  dog.    Set  up  an  induction-coil  arranged  for  tetanus,  with  a  single 
Daniell  in  the  primary  circuit.     Connect  a  pair  of  fine  but  not  sharp- 
pointed  electrodes  through  a  short-circuiting  key  with  the  secondary. 
Fasten  the  dog  on  the  holder,  belly  down,  and  put  a  large  pad  under 
the  neck  to  support  the  head.     Clip  the  hair  over  the  scalp.     Feel 
for  the  condyles  of  the  lower  jaw,  and  join  them  by  a  string  across 
the  top  of  the   head.     Connect  the  outer  canthi  of  the  eyes  by 
another  thread.     The  crucial  sulcus  lies  a  little  behind  the  mid-point 
between  these  two  lines.     Now  give  the  dog  ether  if  necessary,  make 
a  mesial  incision  through  the  skin  down  to  the  bone,  and  reflect  the 
flaps  on  either  side.     Detach  as  much  of  the  temporal  muscle  from 
the  bone  as  is  necessary  to  get  room  for  two  trephine  holes,  the 
internal  borders  of  which  must  be  not  less  than  J  inch  from  the 
middle  line,  so  as  to  avoid  wounding  the  longitudinal  sinus.     Care- 


PRACTICAL  EXERCISES 


fully  work  the  trephine  through  the  skull,  taking  care  not  to  press 
heavily  on  it  at  the  last.  Raise  up  the  two  pieces  of  bone  with 
forceps,  connect  the  holes  with  bone  forceps,  and  enlarge  the  opening 
as  much  as  may  be  necessary  to  reach  all  the  motor  areas.  At  this 
stage  only  enough  ether  should  be  given  to  prevent  suffering.  Now 
unbind  the  hind  and  fore  limbs  on  the  side  opposite  to  that  on  which 
the  brain  has  been  exposed,  apply  blunt  electrodes  successively  to 
the  areas  for  the  fore  and  hind  limbs,  and  stimu- 
late.* Contraction  of  the  corresponding  groups 
of  muscles  will  be  seen  if  the  narcosis  is  not 
too  deep.  Movements  of  the  head,  neck,  and 
eyelids  may  also  be  called  forth  by  stimulating 
the  motor  areas  for  these  regions.  Stimulation 
in  front  of  the  crucial  sulcus  may  also  cause 
great  dilatation  of  the  pupil,  the  iris  almost 
disappearing.  The  dilatation  takes  place  most 
promptly,  and  is  greatest  on  the  opposite  side, 
but  the  pupil  on  the  same  side  is  also  widened. 
Even  after  section  of  both  vago-sympathetic 
nerves  in  the  neck,  a  slow  and  slight  dilatation 
may  be  caused  by  cortical  stimulation,  greatest 
perhaps  on  the  same  side.  Repeat  the  whole 
experiment  on  the  opposite  side  of  the  brain. 
In  the  course  of  his  observations  the  student 
will  perhaps  have  the  opportunity  of  seeing 
general  epileptiform  convulsions  set  up  by  a 
localized  excitation.  They  begin  in  the  group 
of  muscles  represented  in  the  portion  of  the 
cortex  directly  stimulated.  After  the  convulsions 
have  been  sufficiently  studied,  they  should  be 
again  induced,  and  the  stimulated  motor  area 
rapidly  excised  during  their  course.  In  some 
cases  this  will  be  followed  by  immediate  cessa- 
tion of  the  spasms. 

8.  Removal  of  the  Motor  Areas  on  One  Side 
in  the  Dog.-Proceedasin  7 ,  but  use  antiseptic 

precautions,  and  instead  of  stimulating,  destroy  A,  upper  end  of  spinal 
with  the  actual  cautery  or  remove  with  the  cord- 
knife  all  the  grey  matter  around  the  crucial 

sulcus  on  one  side.  Stop  bleeding  by  iodoform  gauze  wrung  out 
of  hot  normal  saline  solution.  Sew  up  the  muscles  by  one  set  of 
sutures,  the  skin  by  another,  and  cover  the  wound  with  collodion. 
When  the  dog  has  recovered  from  the  operation,  study  the  deficiency 
of  motor  and  sensory  power  on  the  opposite  side  (p.  710).  (Fig.  240, 
p.  707.) 


FIG.  245. — BRAIN  OF 
FROG.  (AFTER 
STEINER.) 

a,  cerebral  hemispheres ; 
ft,  position  of  optic  thalami ; 


*  It  is  not  necessary  to  remove  the  dura  mater. 

*  AT 


CHAPTER  XIII. 
THE  SENSES. 

HITHERTO  we  have  been  considering  from  a  purely  objective  stand- 
point the  organs  that  compose  the  body,  and  their  work.  The 
student  has  been  assumed  to  be  in  the  little  world — 'the  microcosm  ' 
— of  organization  which  he  has  been  studying,  but  not  of  it.  He 
has  listened  to  the  sounds  of  the  heart,  seen  its  contraction,  felt 
it  hardening  under  his  fingers ;  but  we  have  not  inquired  as  to  the 
meaning  or  the  mechanism  of  this  hearing,  seeing,  and  feeling.  We 
have  now  to  recognise  that  all  our  knowledge  of  external  things 
comes  to  us  by  the  channels  of  the  senses,  and,  like  the  light  that 
falls  through  coloured  windows  on  the  floor  of  a  church,  is  tinged, 
and  perhaps  distorted,  in  the  act  of  reaching  us. 

The  Senses  in  General. — The  old  and  orthodox  enumeration 
of  '  the  five  senses '  of  sight,  hearing,  touch,  taste  and  smell 
must  be  augmented  by  at  least  two  more,  the  senses  of 
pressure  and  temperature.  The  power  of  appreciating  the 
amount  of  a  muscular  effort ;  the  power  of  localizing  the 
various  portions  of  the  body  in  space  ;  the  sensations  of 
pain,  tickling,  itching,  hunger,  and  thirst ;  the  sensations 
accompanying  the  generative  act,  etc.,  have  also  been  looked 
upon  by  some  as  separate  senses  subserved  by  special  nerves 
and  connected  with  definite  centres.  In  the  development 
of  a  simple  sensation  we  may  distinguish  three  stages  :  the 
stimulation  of  a  peripheral  end-organ,  the  propagation  of 
the  impulses  thus  set  up  along  an  afferent  nerve,  and  their 
reception  and  elaboration  in  a  central  organ. 

We  do  not  know  in  what  manner  a  series  of  transverse  vibrations 
in  the  ether  when  it  falls  upon  the  eye,  or  a  series  of  longitudinal 
vibrations  in  the  air  when  it  strikes  the  ear,  excites  a  sensation  of 
light  or  sound.  We  can  trace  the  ray  of  light  through  the  refractive 


THE  SENSES  733 

media  of  the  eyeball,  see  it  focussed  on  the  retina,  lead  off  the 
current  of  action  set  up  in  that  membrane,  which,  doubtless,  gives 
token  of  the  passage  of  nervous  impulses  into  and  up  the  optic  nerve. 
We  can  even  follow  the  nervous  impulses  to  a  definite  portion  of  the 
cortex  of  the  occipital  lobe,  and  determine  that  if  this  is  removed 
no  sensation  of  sight  will  result  from  any  excitation  of  retina  or  optic 
nerve.  And  it  is  fair  to  conclude  that  in  some  manner  this  part  of 
the  cerebral  cortex  is  essential  to  the  production  of  visual  sensations. 
But  in  what  way  the  chemical  or  physical  processes  in  the  axis 
cylinders  or  nerve-cells  are  related  to  the  psychical  change,  the  inter- 
ruption of  the  smooth  and  unregarded  flow  of  consciousness  which 
we  call  a  sensation  of  light,  we  do  not  know.  To  our  reasoning,  and 
even  to  our  imagination,  there  is  a  great  gulf  fixed  between  the 
physical  stimulus  and  its  psychical  consequence ;  they  seem  incom- 
mensurable quantities ;  the  transition  from  light  to  sensation  of  light 
is  certain,  but  unthinkable. 

Each  kind  of  peripheral  end-organ  is  peculiarly  suited  to 
respond  to  a  certain  kind  of  stimulus.  The  law  of  '  adequate ' 
or  '  homologous '  stimuli  is  an  expression  of  this  fact.  The 
*  adequate '  stimuli  of  the  organs  of  special  sense  may  be 
divided  into  :  (i)  vibrations  set  up  at  a  distance  without  the 
actual  contact  of  the  object,  e.g.,  light,  sound,  radiant  heat ; 
(2)  changes  produced  by  the  contact  of  the  object,  e.g.,  in 
the  production  of  sensations  of  taste,  touch,  pressure,  altera- 
tion of  temperature  (by  conduction).  Midway  between  (i) 
and  (2)  lies  the  adequate  stimulus  of  the  olfactory  end-organs, 
which  are  excited  by  material  particles  given  off  from  the 
odoriferous  body  and  borne  by  the  air  into  the  upper  part 
of  the  nostrils. 

The  end-organs  of  the  special  senses  all  agree  in  consisting  essen- 
tially of  modified  epiblastic  cells,  but  they  occupy  areas  by  no  means 
proportioned  to  their  importance  and  to  the  amount  of  information 
we  acquire  through  them.  The  extent  of  surface  which  can  be 
affected  by  light  in  a  man  is  not  more  than  20  sq.  cm. ;  the  endings 
of  both  nerves  of  hearing  taken  together  do  not  at  most  expand  to 
more  than  5  sq.  cm. ;  the  olfactory  portion  of  the  mucous  mem- 
brane of  the  nose  has  an  area  of  not  more  than  10  sq.  cm. ;  the 
sensations  of  taste  are  ministered  to  by  an  area  of  less  than 
50  sq.  cm. ;  the  end-organs  of  the  senses  of  pressure,  touch,  and 
temperature  are  distributed  over  a  surface  reckoned  by  square 
metres.  As  the  physiological  status  of  the  sensory  end- organs 
rises,  their  anatomical  distribution  tends  to  shrink.  The  organs  of 
comparatively  coarse  and  common  sensations  are  widely  spread, 
intermingled  with  each  other,  and  seated  in  tissues  whose  primary 
function  may  not  be  sensory  at  all.  Even  the  nerve-endings  of  the 
sense  of  taste  are  not  confined  to  one  definite  and  circumscribed 


734  A  MANUAL  OF  PHYSIOLOGY 

patch,  but  scattered  over  the  tongue  and  palate ;  and  both  tongue 
and  palate  are  at  least  as  much  concerned  in  mastication  and 
deglutition  as  in  taste.  The  olfactory  portion  of  the  nasal  mucous 
membrane,  although  a  continuous  area  with  fairly  distinct  boun- 
daries, is  still  a  part  of  the  general  lining  of  the  nostril.  The 
epithelial  surfaces  which  minister  to  the  supreme  sensations  of  sight 
and  hearing — the  retina  and  the  sensitive  structures  of  the  cochlea — 
are  the  most  sequestered  of  all  the  sensory  areas,  as  the  organs  of 
which  they  form  a  part  are,  of  all  the  organs  of  sense,  the  most  highly 
specialized  in  function,  and  anatomically  the  most  limited.  But 
although  hidden  in  protected  hollows,  they  are  endowed,  either  in 
virtue  of  their  own  movements  or  of  those  of  the  head,  with  the 
power  of  receiving  impressions  from  every  side,  and  their  actual  size 
is  thus  indefinitely  multiplied. 

VISION. 

Physical  Introduction. — Physically  a  ray  of  light  is  a  series  of 
disturbances  or  vibrations  in  the  luminiferous  ether,  which  radiates 
out  from  a  luminous  body  in  what  is  practically  a  straight  line.  The 
ether  is  supposed  to  fill  all  space,  including  the  interstices  between 
the  molecules  of  matter  and  the  atoms  of  which  those  molecules  are 
composed.  Suppose  a  bar  of  iron  to  be  gradually  heated  in  a  dark 
room.  In  the  cold  iron  the  molecules  are  moving  on  the  average 
at  a  relatively  slow  rate,  and  the  waves  set  up  in  the  ether  by  their 
.vibrations  are  comparatively  long.  Now,  the  long  ethereal  vibrations 
do  not  excite  the  retina,  because  it  is  only  fitted  to  respond  to  the 
impact  of  the  shorter  waves ;  and,  indeed,  the  long  waves  are  largely 
absorbed  by  the  watery  media  of  the  eye.  As  the  temperature  of  the 
iron  bar  is  increased,  the  molecules  begin  to  move  more  quickly,  and 
waves  of  smaller  and  smaller  length,  of  greater  and  greater  frequency, 
are  set  up,  until  at  last  some  of  them  are  just  able  to  stimulate  the 
retina,  and  the  iron  begins  to  glow  a  dull  red.  As  the  heating  goes 
on  the  molecules  move  more  quickly  still,  and,  in  addition  to  waves 
which  cause  the  sensation  of  red,  shorter  waves  that  give  the  sensa- 
tion of  yellow  appear.  Finally,  when  a  high  temperature  has  been 
reached,  the  very  shortest  vibrations  which  can  affect  the  eye  at  all 
mingle  with  the  medium  and  long  waves,  and  the  sensation  is  one 
of  intense  white  light. 

We  have  said  that  a  ray  of  light  travels  in  a  straight  line,  and  the 
direction  of  the  straight  line  does  not  change  so  long  as  the  medium 
is  homogeneous.  But  when  a  ray  reaches  the  boundary  of  the 
medium  through  which  it  is  passing,  a  part  of  it  is  in  general  turned 
back  or  reflected.  If  the  second  medium  is  transparent  (water  or 
glass,  e.g.),  the  greater  part  of  the  ray  passes  on  through  it,  a  smaller 
portion  is  reflected.  If  the  second  medium  is  opaque,  the  ray  does 
not  penetrate  it  for  any  great  distance  ;  if  it  is  a  piece  of  polished 
metal,  e.g.,  nearly  the  whole  of  the  light  is  reflected ;  if  it  is  a  layer  of 
lampblack,  very  little  of  the  light  is  reflected,  most  of  it  is  absorbed. 

Reflection. — The  first  law  of  reflection  is  that  the  reflected  ray\  the 


THE  SENSES 


735 


ray  which  falls  upon  the  reflecting  surface  (incident  ray),  and  the 
normal  to  the  surface,  are  in  one  plane.  The  second  law  is  that  the 
reflected  ray  makes,  with  the  perpendicular  (normal}  to  the  reflecting 
surface,  the  same  angle  as  the  incident  ray.  A  corollary  to  this  is  that 
a  ray  perpendicular  to  the  surface  is  reflected  along  its  own  path. 

Reflection  from  a  Plane  Mirror. — Let  a  ray  of  light  coming  from 
the  point  P  meet  the  surface  DE  at  B,  making  an  angle  PBA  with 
the  normal  to  the  surface.  The  re- 
flected ray  BC  will  make  an  equal 
angle  ABC  with  the  normal ;  and  the 
eye  at  C  will  see  the  image  of  P  as  if 
it  were  placed  at  P',  the  point  where 
the  prolongation  of  BC  cuts  the 
straight  line  drawn  from  P  perpendicu- 
lar to  DE.  This  is  the  position  of  an 
ordinary  looking-glass  image. 

Reflection  from  a  Concave  Spherical 
Mirror. — A  spherical  surface  may  be 
supposed  to  be  made  up  of  an  infinite 
number  of  infinitely  small  plane  surfaces. 
The  normal  to  each  of  these  plane 
surfaces  is  the  radius  of  the  sphere,  and  the  reflected  ray  makes  with 
the  radius  at  the  point  of  incidence  the  same  angle  as  the  incident 
ray.  Let  D  (Fig.  247)  be  the  middle  point  of  the  mirror,  and  C  its 
centre  of  curvature,  /.*.,  the  centre  of  the  sphere  of  which  it  is  a 


FIG. 


246.— REFLECTION   FROM 
A  PLANE  MIRROR. 


FIG.  247.— REFLECTION  FROM  A  CONCAVE 
SPHERICAL  MIRROR. 


FIG.  248. — FORMATION  OF  REAL  IN- 
VERTED IMAGE  BY  A  CONCAVE 
SPHERICAL  MIRROR. 


segment.  Then  CD  is  the  principal  axis,  and  any  other  line  through 
C  which  cuts  the  mirror  is  a  secondary  axis.  When  the  mirror  is  a 
small  portion  of  a  sphere,  rays  parallel  to  the  principal  axis  are 
focussed  at  the  principal  focus  F  midway  between  C  and  D ;  rays 
parallel  to  any  secondary  axis  are  focussed  in  a  point  lying  on  that 
axis  •  and  rays  diverging  from  a  point  on  any  axis  are  focussed  in  a 
point  on  the  same  axis. 

These  facts  afford  a  simple  construction  for  finding  the  position  of 
the  image  of  an  object  formed  by  a  concave  mirror.     Let  AB  be  the 


736  A  MANUAL  OF  PHYSIOLOGY 

fa 

object  (Fig.  248).  Then  the  image  of  A  is  the  point  in  which  all 
rays  proceeding  from  A  and  falling"  on  the  mirror,  including  rays 
parallel  to  the  principal  axis,  are  focussed.  But  the  ray  AE,  parallel 
to  the  principal  axis,  passes  after  reflection  through  the  principal 
focus  F,  therefore  the  image  of  A  must  lie  on  the  straight  line  EF. 
If  any  secondary  axis  ACD  be  drawn,  the  image  of  A  must  lie  on 
ACD.  It  must  therefore  be  the  point  of  intersection,  a,  of  EF  and 
ACD.  Similarly,  the  image  of  B  must  be  the  point  of  intersection, 
bt  of  GF  and  BCH.  The  image  ab  of  an  object  AB  farther  from 
the  mirror  than  the  principal  focus  is  real  and  inverted.  The 
Purkinje-Sanson  image  reflected  from  the  concave  anterior  surface  of 
the  vitreous  humour  (Fig.  263)  is  an  example. 

After  reflection  from  a  convex  mirror^  rays  of  light  always  diverge, 

and  only  erect,  virtual 
images  are  formed,  i.e., 
images  which  do  not 
really  exist  in  space,  but 
which,  from  the  direc- 
tion of  the  rays  of 
light,  we  judge  to  exist. 
The  position  of  the 
image  of  an  object  AB 
(Fig.  249)  may  be 
found  by  a  construc- 
tion similar  to  that  for 
reflection  from  a  con- 
cave mirror.  The 
FIG.  249. — FORMATION  OF  IMAGE  BY  A  CONVEX  image  of  "*  flame 

reflected  from  the 

anterior  surface  of  the  cornea  or  lens  is  erect  and  virtual.  It 
diminishes  in  size  with  increase  in  the  curvature  or  convexity  of  the 
reflecting  surface  (Fig.  263). 

Refraction. — A  ray  of  light  passing  from  one  medium  into  another 
has  its  velocity,  and  consequently  its  direction,  altered.  It  is  said  to 
be  refracted.  The  first  law  of  refraction  is  that  the  refracted  ray  is 
in  the  same  plane  as  the  incident  ray  and  the  normal  to  the  surface. 
The  second  law  is  that  the  sine  of  the  angle  of  incidence  has  a  coristant 
ratio  (for  any  given  pair  of  media)  to  the  sine  of  the  angle  of  refraction. 
The  angle  of  incidence  is  the  angle  which  the  ray  makes  with  the 
normal  to  the  surface,  separating  the  two  media ;  the  angle  of  refrac- 
tion is  the  angle  made  with  the  normal  in  the  second  medium.  This 
ratio  is  called  the  index  of  refraction  between  the  two  media.  For 
purposes  of  comparison,  the  refractive  index  of  a  substance  is  usually 
taken  as  the  ratio  of  the  sine  of  the  angle  of  incidence  to  the  sine  of 
the  angle  of  refraction  of  a  ray  passing  from  air  into  the  substance. 

When  a  ray  strikes  a  surface  at  right  angles,  it  passes  through 
without  suffering  refraction.  When  a  ray  passes  from  a  less  dense 
to  a  denser  medium  (e.g.,  from  air  to  water),  it  is  bent  towards  the 
perpendicular.  When  it  passes  from  a  more  dense  to  a  less  dense 
medium  (as  from  water  to  air),  it  is  bent  away  from  the  perpendicular. 


THE  SENSES 


737 


When  a  ray  passes  across  a  medium  bounded  by  parallel  planes,  it 
issues  parallel  to  itself;  in  other  words,  it  undergoes  no  refraction 
(Fig.  251). 

Refraction  and  Dispersion  by  a  Prism. — The  beam  of  light  is  bent 
towards  the  normal  N  as  it  passes  across  BA  and  away  from  the 


FIG.  250. — REFRACTION  AT   A   PLANE 
SURFACE. 

AB  is  the  incident ;  BD,  the  refracted 
ray  ;  CB,  the  normal  to  the  surface.  When 
the  ray  passes  from  air  into  another  medium, 
the  refractive  index  of  the  latter  is  the  fraction 
sin  a 
sin  /s* 

normal  N'  as  it  passes  across  BC  (Fig.  252) ;  at  both  surfaces  it  is 
bent  towards  the  base  of  the  prism  AC.  At  the  same  time  the  light 
suffers  dispersion  ;  that  is,  the  rays  of  shorter  wave-length  are  more 
refracted  than  those  of  greater  wave-length.  The  deviation  of  any 


FIG.  251.  —  REFRACTION  BY  A 
MEDIUM  BOUNDED  BY  PARALLEL 
PLANES,  P  AND  P'. 

The  ray  ABDE  issues  parallel  to  its 
original  direction  ;  CB,  FD,  normals  to 
P  and  P' ;  a,  angle  of  incidence ;  /8,  7, 
angles  of  refraction. 


FIG.  252. — REFRACTION  AND  DISPERSION  BY  A  PRISM. 

given  ray  is  measured  by  the  angle  which  the  refracted  ray  makes 
with  its  original  direction.  The  amount  of  dispersion  produced  by 
a  prism  is  measured  by  the  difference  in  the  deviation  of  the  extreme 
rays  of  the  spectrum.  The  dispersion  produced  by  any  given  sub- 

47 


738 


A  MANUAL  OF  PHYSIOLOGY 


stance  is  proportional  to  the  difference  of  its  refractive  index  for  the 
extreme  rays. 

Refraction  by  a  Biconvex  Lens. — A  straight  line  ACB  passing 
through  the  centres  of  curvature  of  the  two  surfaces  of  the  lens  is 
called  the  principal  axis.  A  point  C  lying  on  the  principal  axis 
between  the  two  centres  of  curvature,  and  possessing  the  property 


FIG.  253. — REFRACTION  BY  A  BICONVEX  LENS. 

that  rays  passing  through  it  do  not  suffer  refraction,  is  called  the 
optical  centre  of  the  lens.  Any  straight  line,  DCE,  passing  through 
the  optical  centre  is  a  secondary  axis.  Rays  of  light  proceeding 
from  a  point  in  the  principal  axis  are  focussed  in  a  point  on  that 
axis.  When  the  rays  proceed  from  an  infinitely  distant  point  in  the 
principal  axis,  /.&,  when  they  are  parallel  to  it,  they  are  focussed  in  F, 


FIG.  254 — FORMATION  OF  IMAGE  BY  BICONVEX  LENS. 

the  principal  focus.  Similarly,  rays  parallel  to,  or  proceeding  from,  a 
point  in  a  secondary  axis  are  focussed  in  a  point  on  that  axis ;  but  if 
the  focus  is  to  be  sharp,  the  angle  between  the  secondary  and  the 
principal  axis  must  not  be  so  large  as  is  indicated  in  Fig.  253. 

"Formation  of  Image  by  Biconvex  Lens  (Fig.  254). — Let  AB  be  the 
object ;  then  if  AHD  be  the  path  of  a  ray  from  A  parallel   to  the 


THE  SENSES 


739 


FIG.  255. — REFRACTION  BY  A  BICONCAVE  LENS. 


principal  axis,  the  image  of  A  will  be  the  intersection  of  the  straight 
line  DF  -and  the  secondary  axis  passing  through  A.  Similarly,  the 
image  of  B  will  be  the  intersection  of  GF  and  the  secondary  axis  BC. 
Where  AB  is  farther  from  the  lens  than  the  principal  focus,  the  image 
ab  is  real  and  inverted  This  is  the  case  with  the  image  of  an  external 
object  formed  on  the  retina.  When  the  object  is  nearer  than  the 
principal  focus,  the  image  is  virtual  and  erect.  The  image  formed  by 
the  objective  of  a 
microscope  when  the 
object  is  in  focus  is 
real  and  inverted ;  the 
ocular  forms  a  virtual 
erect  image  of  this 
real  image. 

Refraction  by  a  Bi- 
concave Lens  (Fig. 
255).  —  Parallel  rays 
are  rendered  diver- 
gent by  the  lens ; 
there  is  no  real  focus  ;  but  if  the  rays  are  prolonged  backwards  they 
meet  in  the  virtual  focus  F,  from  which  they  appear  to  come  when 
received  by  the  eye  through  the  lens. 

Formation  of  Image  by  Biconcave  Lens  (Fig.  256). — Let  AB  be 
the  object.  Let  AHDI  be  the  path  of  a  ray  from  any  point  A  of 
the  object  parallel  to 
the  principal  axis. 
Produce  DI  back- 
wards (dotted  line)  ; 
it  will  pass  through 
the  principal  focus  F. 
Through  A  draw  the 
secondary  axis  AC. 
The  image  of  A  must 
lie  both  on  AC  and 
on  IDF  ;  /.<?.,  it  must 
be  the  intersection,  a,  of  these  straight  lines.  Similarly,  the  image 
of  B  is  £,  the  intersection  of  KGF  and  BC.  The  image  is  virtual 
and  erect. 

Absorption. — No  substance  is  perfectly  transparent ;  in  addition 
to  what  is  reflected,  some  light  is  always  absorbed.  In  other  words, 
in  passing  through  a  body  some  of  the  light  is  transformed  into  heat, 
a  portion  of  the  energy  of  the  short,  luminous  waves  going  to  in- 
crease the  vibrations  of  the  molecules  of  the  medium,  just  as  a  wave 
passing  under  a  row  of  barges  or  fishing-boats  sets  them  swinging 
and  pitching,  and  so  imparts  to  them  a  certain  amount  of  energy, 
which  is  ultimately  changed  into  heat  by  friction  against  the  water, 
and  against  each  other,  and  by  the  straining  and  rubbing  of  the 
chains  at  their  points  of  attachment.  Some  bodies  absoib  all  the 
rays  in  the  proportion  in  which  they  occur  in  white  light ;  whether 
looked  at  or  looked  through,  they  appear  colourless  or  white.  Other 


FIG.  256. — FORMATION  OF  IMAGE  BY  BICONCAVE 
LENS. 


740 


A  MANUAL  OF  PHYSIOLOGY 


substances  absorb  certain  rays  by  preference,  and  the  amount  of 
absorption  is  proportional  to  the  thickness  of  the  layer.  The  colours 
of  most  natural  bodies  are  due  to  this  selective  absorption.  Even 
when  looked  at  in  reflected  light,  they  are  seen  by  rays  that  have 
penetrated  a  certain  way  into  the  substance  and  have  then  been 
reflected ;  and,  of  course,  a  smaller  number  of  the  rays  which  the 
body  specially  absorbs  are  reflected  than  of  the  rays  which  it  readily 
transmits,  for  more  of  the  latter  than  of  the  former  reach  any  given 
depth.  This  is  called  '  body  colour' ;  and  such  substances  have  the 
same  colour  when  seen  by  reflected  and  by  transmitted  light.  The 
colour  of  haemoglobin  is  due  to  the  absorption  of  the  violet  and  many 
of  the  yellow  and  green  rays,  as  is  shown  by  the  position  of  the 
absorption  bands  in  its  spectrum  (p.  48).  In  Fig.  257  the  violet  rays 
are  represented  as  being  totally  absorbed  before  passing  through  the 

substance.  Some  of 
the  green  rays  are  re- 
flected, some  trans- 
mitted, some  ab- 
sorbed. The  red  rays 
are  supposed  to  be 
mostly  reflected  and 
transmitted,  only  to 
a  slight  extent  ab- 
sorbed. The  colour 
of  such  a  substance,, 
both  when  looked  at 
and  when  looked 
through,  would  there- 
fore be  that  due  to  a 
mixture  of  red  light 
with  a  smaller 
quantity  of  green. 
Then  there  is  another 
class  of  substances 
Certain  rays  only  are 


FIG.  257. — DIAGRAM  TO  SHOW  CONNECTION   OF 
BODY  COLOUR  WITH  SELECTIVE  ABSORPTION. 


which  owe  their  colour  to  selective  reflection. 

reflected  from  their  surface,  and  the  light  transmitted  through  a  thin 
layer  is  complementary  to  the  reflected  light ;  that  is,  the  reflected 
and  transmitted  rays  together  would  make  up  white  light.  These 
bodies  have  what  is  called  ^surface  colour,'  and  include  metals,  various 
aniline  dyes,  and  other  substances. 

Comparative. — Many  invertebrate  animals  possess  rudimentary 
sense-organs,  by  means  of  which  they  may  receive  certain  luminous 
impressions.  It  is  true  that  the  mere  sensation  of  light  is  not  in 
itself  sufficient  for  the  exact  appreciation  of  the  form  and  situation  of 
surrounding  objects.  But  even  the  closure  of  the  eyelids  does  not 
prevent  a  person  of  normal  eyesight  from  distinguishing  differences 
in  the  intensity  of  illumination.  And  it  is  possible  that  many  of  the 
humbler  animals  may,  through  the  pigment  spots  which  are  often 
called  eyes,  or  perhaps,  as  in  the  earthworm,  by  means  of  end-organs 
more  generally  diffused  in  the  skin,  attain  to  some  such  dim  con- 


THE  SENSES 


741 


sciousness  of  light  and  shadow  as  will  enable  them  to  avoid  an 
obstacle  or  an  enemy,  to  seek  the  sunny  side  of  a  boulder  or  the 
obscurity  of  an  overhanging  ledge  of  rock.  But  the  indispensable 
condition  of  distinct  vision  is  that  an  image  of  each  part  of  an  object 
should  be  formed  upon  a  separate  portion  of  the  receiving  or  sensitive 
surface.  This  condition  is,  to  a  certain  extent,  fulfilled  by  the  com- 
pound eyes  of  some  of  the  higher  invertebrates  (insects,  e.g.].  Here 
rays  from  one  point  of  the  object  pass  through  one  of  the  funnel- 
shaped  elements  of  the  compound  eye,  and  rays  from  another  point 
through  another.  Rays  striking  obliquely  on  the  facets  are  stopped 
by  the  opaque  partitions  between  them.  In  the  Cephalopods  we 


FIG.  258.— DIAGRAMMATIC  HORIZONTAL  SECTION  OF  THE  LEFT  EYE. 

find  that  this  compound  type  of  eye  has  already  been  abandoned ; 
the  single  system  of  curved  refracting  surfaces  so  characteristic  of  the 
vertebrate  eye  has  made  its  appearance;  and  the  formation  of  a 
clean-cut  image  of  the  object  on  the  retina,  with  the  excitation  of  a 
sharply-bounded  area  of  that  membrane,  follows  as  a  geometrical 
consequence  from  the  theory  of  lenses. 

We  have  to  consider  (i)  the  mechanism  by  which  an 
image  is  formed  on  the  retina,  and  (2)  the  events  that  follow 
the  formation  of  such  an  image  and  their  relations  to  the 
stimulus  that  calls  them  forth. 


742 


A  MANUAL  OF  PHYSIOLOGY 


Structure  of  the  Eye.— The  eye  may  be  described  with  sufficient 
accuracy  as  a  spherical  shell,  transparent  in  front,  but  opaque  over  the 
posterior  five-sixths  of  its  surface,  and  filled  up  with  a  series  of  trans- 
parent liquids  and  solids.  The  shell  consists  of  three  layers  concen- 
trically arranged,  like  the  coats  of  an  onion  :  (i)  An  external  tough, 
fibrous  coat,  the  sclerotic,  the  anterior  portion  of  which  appears  as  the 
white  of  the  eye.  In  front  this  external  layer  is  completed  by  the 


Rods. 


Cones. 


FIG.  260. 


FIG. 


FIG.  259. 


259. — THE    RETINA    (AFTER    HELM- 

HOLTZ). 

FIG.  260.— DIAGRAM    OF    STRUCTURE    OF 
RETINA  (BOWDITCH,  AFTER  CAJAL). 

i,  internal  limiting  membrane  ;  2,  If,  layer  of 
nerve-fibres  ;  3,  G,  layer  of  ganglion  cells ;  4,  F, 
internal  molecular  layer  ;  5,  E,  internal  nuclear 
layer ;  6,  C,  external  molecular  layer ;  7,  B, 
external  nuclear  layer  ;  8,  external  limiting  mem- 
brane ;  g,  A,  layer  of  rods  and  cones  ;  10,  pig- 
mented  epithelium. 


transparent  cornea.  (2)  A  vascular  and  pigmented  layer,  the  choroid, 
which,  in  the  restricted  sense  of  the  term,  ends  in  front  in  a  series  of 
folds  or  plaits,  the  ciliary  processes.  These  abut  on  the  outer 
boundary  of  the  iris,  which  may  be  looked  upon  as  an  anterior  con- 
tinuation of  the  choroidal  or  middle  coat  of  the  eyeball.  Between 
the  corneo-sclerotic  junction  and  the  anterior  portion  of  the  choroid 
is  interposed  a  ring  of  unstriped  muscular  fibres,  the  ciliary  muscle. 


THE  SENSES  743 

(3)  The  inner  or  sensitive  coat,  termed  the  retina  (Figs.  259,  260). 
This  covers  the  choroid  as  a  delicate  membrane,  extending  to  the 
ciliary  processes,  where  it  ends  in  a  toothed  margin,  the  ora  serrata. 
The  optic  nerve  forms  a  kind  of  stalk  to  which  the  eyeball  is  attached. 
Its  point  of  entrance  at  the  optic  disc  is  a  little  nearer  the  median  line 
than  the  antero-postenoraxis,  which  nearly  passes  through  the  centre 
of  a  small  depression,  the  fovea  centralis,  situated  in  the  middle  of 
the  macula  lutea,  or  yellow  spot.  From  the  optic  disc  (sometimes 
called  the  optic  papilla,  but  inappropriately,  since  it  does  not  project 
beyond  the  general  surface),  the  optic  nerve  spreads  over  the  retina 
as  a  layer  of  non-medullated  fibres,  separated  from  the  interior  of 
the  eyeball  only  by  the  internal  limiting  membrane.  This  so- 
called  membrane  is  formed  by  the  expanded  feet  of  the  fibres  of 
Miiller,  which  run  like  a  scaffolding  or  framework  through  nearly  the 
whole  thickness  of  the  retina,  terminating  at  the  outer  limiting  mem- 
brane. External  to  the  layer  of  nerve-fibres  is  the  stratum  of  large 
ganglion  cells,  whose  neurons  they  are ;  next  to  this  the  inner 
molecular  layer,  made  up  largely  of  the  branching  dendrons  of  these 
cells.  The  fifth  layer  is  the  inner  granular  or  nuclear  layer,  containing 
many  fusiform  'granule '  cells  which  send  out  neurons  into  the  fourth, 
and  dendrons  into  the  sixth,  or  outer  molecular  layer,  and  are  thus 
connected  with  the  ganglion  cells  of  the  third  layer  on  the  one  hand, 
and  with  the  seventh  or  outer  nuclear  layer  on  the  other.  The  seventh 
stratum  receives  its  name  from  the  large  number  of  nuclei  which  it 
contains.  These  are  connected  with  the  rods  and  cones  of  the  ninth 
layer,  which  is  divided  from  the  seventh  by  the  external  limiting 
membrane.  At  the  fovea  centralis  the  rods  are  entirely  absent,  and 
the  other  layers  of  the  retina  greatly  thinned ;  over  the  optic  disc 
neither  rods  nor  cones  are  present. 

External  to  the  rods  and  cones  is  a  sheet  of  pigmented  epithelial 
cells  of  hexagonal  shape,  belonging  to  the  choroid,  but  remaining 
attached  to  the  retina  when  the  latter  is  separated,  and  therefore  often 
reckoned  as  its  most  external  layer. 

A  little  behind  the  cornea  and  anterior  to  the  retina  is  the  lens, 
enclosed  in  a  capsule,  and  attached  to  the  choroid  by  the  suspensory 
ligament,  or  zonule  of  Zinn.  The  iris  hangs  down  in  front  of  the  lens 
like  a  diaphragm,  with  a  central  hole,  the  pupil.  Between  the  iris 
and  the  posterior  surface  of  the  cornea  is  the  anterior  chamber  of 
the  eye,  filled  with  the  aqueous  humour.  Between  the  iris  and  the 
anterior  surface  of  the  lens  lies  the  posterior  chamber,  which  is  rather 
a  potential  than  an  actual  cavity.  The  space  between  the  lens  and 
the  retina  is  accurately  occupied  by  an  almost  structureless  semi-fluid 
mass,  the  vitreous  humour,  enclosed  by  the  delicate  hyaloid  membrane, 
which  in  front  is  reflected  over  the  folds  of  the  ciliary  processes,  and 
blends  with  the  suspensory  ligament  of  the  lens. 

Refraction  in  the  Eye — Formation  of  the  Retinal  Image. — The 
amount  of  refraction  which  a  ray  of  light  undergoes  at  a 
curved  surface  depends  upon  two  factors,  the  radius  of 


744 


A  MANUAL  OF  PHYSIOLOGY 


curvature  of  the  surface,  and  the  difference  between  the  re- 
fractive indices  of  the  media  from  which  the  ray  comes  and 
into  which  it  passes.  The  smaller  the  radius  of  curvature, 
and  the  greater  the  difference  of  refractive  index,  the  more 
is  the  ray  bent  from  its  original  direction.  A  ray  of  light 
passing  into  the  eye  meets  first  the  approximately  spherical 
anterior  surface  of  the  cornea,  covered  with  a  thin  layer  of 
tears.  Since  the  refractive  index  of  the  tears  and  of  the 
cornea  is  greater  than  that  of  air,  refraction  must  occur 
here.  At  the  parallel  posterior  surface  of  the  cornea,  how- 
ever, the  ray  is  but  slightly  bent,  for  the  refractive  indices 
of  aqueous  humour  and  corneal  substance  are  nearly  equal. 
At  the  anterior  and  posterior  surface  of  the  lens  the  ray  is 
again  refracted,  since  the  refractive  index  of  the  aqueous  and 
vitreous  humour  is  less  than  that  of  the  lens.  The  following 
tables  show  the  radii  of  curvature  of  the  refracting  surfaces 
and  the  refractive  indices  of  the  dioptric  media,  as  well  as 
some  other  data  which  are  of  use  in  studying  the  problems 
of  refraction  in  the  eye  : 

In  accommodation  for 


{Cornea 
Anterior  surface  of  lens 
Posterior  surface  of  lens 
Anterior  surface  of  cornea  and  an- 
terior surface  of  lens    -                  -  3  '6 
Distance  Anterior  surface  of  cornea  and  pos- 
between        terior  surface  of  lens    -                 -  7  -2 
Anterior  and  posterior  surface  of  lens  3  -6 
Posterior  surface  of  lens  and  retina  -  14-6 
Antero-posterior  diameter  of  eye  along  the  axis  21-8 

Refractive  Indices — 

Air  

Cornea  ----»- 

Aqueous  humour 

Vitreous  humour    -  -         - 

Lens  (mean  for  all  its  layers)  - 

Water 


Far  Vision.  Near  Vision. 

7 '8  mm.     7*8  mm. 
io-o     „        6-0     „ 
6-0     „        5-5     „ 


7-2 
4*0 

14*6 
21-8 


•ooo 

•337 

•3365 

•3365 

•437 

•335 


It  will  be  seen  that  the  refractive  indices  of  the  cornea  and 
the  aqueous  and  vitreous  humours  are  all  nearly  the  same  as 
that  of  water.  That  of  the  lens  differs  for  its  various  layers, 
the  central  core  having  a  higher  refractive  index  than  the 


THE  SENSES  745 

more  superficial  portions  ;  but  a  mean  may  be  struck,  and, 
although  such  calculations  are  open  to  error,  it  has  been 
computed  that  the  lens  acts  as  a  homogeneous  lens  of  the 
same  curvatures,  and  with  a  refractive  index  of  1*437, 
would  do. 

The  optical  problems  connected  with  the  formation  of  the 
retinal  image  are  complicated  by  the  existence  in  the  eye  of 
several  media,  with  different  refractive  indices,  bounded  by 
surfaces  of  different  and,  in  certain  cases,  of  variable  curva- 
ture. For  many  purposes,  however,  the  matter  can  be 
greatly  simplified,  and  a  close  enough  approximation  yet 
arrived  at,  by  considering  a  single  homogeneous  medium,  of 
definite  refractive  index,  and  bounded  in  front  by  a  spherical 
surface  of  definite  curvature,  to  replace  the  transparent 
solids  and  liquids  of  the  eye.  The  position  of  the  principal 
focus  and  nodal  point  (i.e.,  the  point  through  which  rays 
pass  without  refraction)  of  such  a  '  reduced  '  or  *  schematic  ' 
eye,  and  other  constants,  are  shown  in  the  following  table  : 

Reduced  Eye — 

Radius  of  curvature  of  the  single  refracting  surface     -       5-1       mm. 
Index  of  refraction  of  the  single  refracting  medium     -       1*35*     „ 
Antero-posterior  diameter  of  reduced  eye  (distance  of 

principal  focus  from  the  single  refracting  surface)    -       20.0       „ 
Distance  of  the  single  refracting  surface  behind  the 

anterior  surface  of  the  cornea  i  -8       „ 

Distance  of  the  nodal  point  of  the  reduced  eye  from 

its  anterior  surface  5-0       ,, 

Distance  of  the  nodal  point  from  the  principal  focus 

(retina)-  •  15-0       „ 

Knowing  the  position  of  the  centre  of  curvature  of  the 
single  ideal  refracting  surface,  i.e.,  the  nodal  point  of  the 
reduced  eye,  all  that  is  necessary  in  order  to  determine  the 
position  of  the  image  of  an  object  on  the  retina  is  to  draw 
straight  lines  from  its  circumference  through  the  nodal 
point.  Each  of  these  lines  cuts  the  refracting  surface  at 
right  angles,  and  therefore  passes  through  without  any 
deviation.  The  retinal  image  is  accordingly  inverted,  and 
its  size  is  proportional  to  the  solid  angle  contained  between 
the  lines  drawn  from  the  boundary  of  the  object  to  the 
*  Or  about  the  same  as  that  of  the  aqueous  humour. 


746 


A  MANUAL  OF  PHYSIOLOGY 


nodal  point,  or  the  equal  angle  contained  by  the  prolonga- 
tions of  the  same  lines  towards  the  retina.  This  angle  is 

called  the  visual  angle,  and  evi- 
dently varies  directly  as  the  size 
of  the  object,  and  inversely  as  its 
distance.  Thus  the  visual  angle 
under  which  the  moon  is  seen  is 
much  larger  than  that  under  which 
we  view  any  of  the  fixed  stars, 
because  the  comparative  nearness 
of  the  earth's  satellite  more  than 
makes  up  for  its  relatively  small 
FIG.  261. — THE  REDUCED  EYE.  size. 
S,  the  single  spherical  refracting 

surface,  i'8  ram.  behind  the  an-        The  dimensions  of  the  retinal  image 

thenodSairfaoinr0f  mm  Tehmd  S  '      °f  *"  °b)QCt  ^  6aSily  Calculated  when 

F,6  the  Vindpaf  "fbcus  Vn  the    the  size  of  the  object  and  its  distance 
retina),  20  mm.  behind  s.    The    are  known.     For  let  AB  in  Fig.  262 
^r^posur'lSch^fy    ^present  one  diameter  of  an  object 
occupy  in  the  normal  eye.  A  B   the  image  of  this  diameter,  and 

let  AB',  BA',  be  straight  lines  passing 

through  the  nodal  point.  Then  AB  and  A'B'  may  be  considered 
as  parallel  lines,  and  the  triangles  of  which  they  form  the  bases, 
and  the  nodal  point  the  common  apex,  as  similar  triangles. 


FIG.  262.— FIGURE  TO  snow  HOW  THE  VISUAL  ANGLE  AND  SIZE  OF  RETINAL 
IMAGE  VARIES  WITH  THE  DISTANCE  OF  AN  OBJECT  OF  GIVEN  SIZE. 
For  the  distant  position  of  AB  the  visual  angle  is  a,  for  the  near  position  (dotted 
lines)  p. 


Accordingly,  if  D  is  the  distance  of  the  nodal  point  from  A, 

AT>  A'TV 

and  d  its  distance  from  B',  we  have  1±^  =  1±^..  Now,  d  may 

D  a 

approximately  be  taken  as  15  mm.  Suppose,  then,  that  the  size  of 
the  moon's  image  on  the  retina  is  required.  Here  D  =  238,000  miles, 
and  AB  (the  diameter  of  the  moon)  =  2,1 60  miles.  Thus  we  get 


THE  SENSES 


747 


2160    ,Ag;or(      )JL 
238,000       15 


A'B' 


no       15 
of  the  retinal  image)  =  -^-,  or  about  -J-  rnm. 


,  from  which  A'B'  (the  diameter 


no 


A  ship's  mast  120  feet  high,  seen  at  a  distance  of  25  miles,  will 


throw  on  the  retina  an  image  whose   height  is 


i.e., 


120  feet 


120  feet 
25  miles 


x  15  mm. 


x  15  mm.,  or 


x  15  mm.,  equal  to  -013  mm., 


5, 280x25  feet  1,100 

or  13  p  in  size.  This  is  not  much  larger  than  a  red  blood-corpuscle, 
and  only  four  times  the  diameter  of  a  cone  in  the  fovea  centralis, 
where  the  cones  are  most  slender. 

Accommodation. — A  lens  adjusted  to  focus  upon  a  screen 
the  rays  coming  from  a  luminous  point  at  a  given  distance 
will  not  be  in  the  proper 
position  for  focussing  rays 
from  a  point  which  is 
nearer  or  more  remote. 
Now,  it  is  evident  that  a 
normal  eye  possesses  a 
great  range  of  vision.  The 
image  of  a  mountain  at  a 
distance  of  30  miles,  and 
of  a  printed  page  at  a 
distance  of  30  cm.,  can 
be  focussed  with  equal 
sharpness  upon  the  retina. 
In  an  opera-glass  or  a 
telescope  accommodation 

FIG.  263.— PURKINJE-SANSON    IMAGES. 


A,  in  the  absence  of  accommodation ;  B, 
during  accommodation  for  a  near  object. 
The  upper  pair  of  circles  enclose  the  images 
as  seen  when  the  light  falls  on  the  eye 
through  a  double  slit  or  a  pair  of  prisms  ; 
the  lower  pair  show  the  images  seen  when 
the  slit  is  single  and  triangular  in  shape. 


is  brought  about  by  alter- 
ing the  relative  position  of 
the  lenses ;  in  a  photo- 
graphic camera  and  in  the 
eyes  of  fishes  and  cepha- 
Ippods  (Beer),  by  altering 
the  distance  between  lens  and  sensitive  surface ;  in  the 
eye  of  man,  by  altering  the  curvature,  and  therefore  the 
refractive  power  of  the  lens.  That  the  cornea  is  not  alone 
concerned  in  accommodation,  as  was  at  one  time  widely 
held,  is  shown  by  the  fact  that  under  water  the  power  of 
accommodation  is  not  wholly  lost.  Now,  the  refractive 


748  A  MANUAL  OF  PHYSIOLOGY 

index  of  the  cornea  being  practically  the  same  as  that  of 
water,  no  changes  of  curvature  in  it  could  affect  refraction 
under  these  circumstances.  That  the  sole  effective  change 
is  in  the  lens  can  be  most  easily  and  decisively  shown  by 
studying  the  behaviour  of  the  mirror  images  of  a  luminous 
object  reflected  from  the  bounding  surfaces  of  the  various 
refractive  media  when  the  degree  of  accommodation  of  the 
eye  is  altered.  Three  images  are  clearly  recognised :  the 
brightest  an  erect  virtual  image,  from  the  anterior  (convex) 
surface  of  the  cornea  ;  an  erect  virtual  image,  larger,  but 
less  bright,  from  the  anterior  (convex)  surface  of  the  lens ; 
and  a  small  inverted  real  image  from  the  (concave)  posterior 
boundary  of  the  lens  (Purkinje-Sanson  images).  The  second 
image  is  intermediate  in  position  between  the  other  two. 
It  is  possible  with  special  care  to  make  out  a  fourth  image, 
and  even  a  fifth ;  but  since  these  are  reflected  from  surfaces 
(the  posterior  surface  of  the  cornea,  e.g.)  at  which  only  a 
slight  change  in  the  refractive  index  occurs,  they  are  much 
less  brilliant  than  the  first  three.  When  the  eye  is  accom- 
modated for  near  vision,  as  in  focussing  the  ivory  point  of 
the  phakoscope  (Fig.  294),  the  corneal  image  is  entirely 
unchanged  in  size,  brightness,  and  position.  The  middle 
image  diminishes  in  size,  comes  forward,  and  moves  nearer 
to  the  corneal  image.  This  shows  that  the  curvature  of  the 
anterior  surface  of  the  lens  has  been  increased — that  is  to 
say,  its  radius  of  curvature  diminished — for  the  size  of  the 
image  of  an  object  reflected  from  a  convex  mirror  varies 
directly  as  the  radius  of  curvature.  A  slight  change  takes 
place  in  the  image  from  the  posterior  surface  of  the  lens, 
indicating  a  small  increase  of  its  curvature  too.  By  means 
of  a  method  founded  on  the  observation  of  the  changes  in 
these  images,  and  a  special  instrument  called  an  ophthalmo- 
meter  which  allows  of  their  measurement,  Helmholtz  has 
calculated  that,  during  maximum  accommodation,  the  radius 
of  curvature  of  the  anterior  surface  of  the  lens  is  only  6  mm., 
as  compared  with  10  mm.  when  the  eye  is  directed  to  a 
distant  object  and  there  is  no  accommodation.  When  the 
lens  has  been  removed  for  cataract,  fairly  distinct  vision  may 
still  be  obtained  by  compensating  for  its  loss  by  convex 


THE  SENSES  749 

spectacles  of  suitable  refractive  power  (10  diopters*  for 
distant  vision,  and  15  diopters  for  the  distance  at  which  a 
book  is  usually  held),  but  no  power  of  accommodation 
remains.  The  person  does  indeed  contract  the  pupil  in 
regarding  a  near  object,  just  as  happens  in  the  intact  eye  ; 
the  most  divergent  rays  are  thus  cut  off  and  the  image  made 
somewhat  sharper,  and  there  may  appear  to  be  some  faculty 
of  accommodation  left.  But  the  loss  of  the  whole  iris  by 
operation  does  not  affect  accommodation  in  the  least ;  the 
iris,  therefore,  takes  no  part  in  it.  That  no  change  in  the 
antero-posterior  diameter  of  the  eyeball,  caused  by  its 
deformation  by  the  contraction  of  the  extrinsic  muscles, 
can  have  any  share  in  accommodation,  as  has  been  suggested, 
is  clearly  proved  by  the  fact  that  atropia,  which  does  not 
affect  the  action  of  these  muscles,  paralyzes  the  mechanism 
of  accommodation.  To  the  consideration  of  that  mechanism 
we  now  turn. 

The  Mechanism  of  Accommodation. — While  everybody  is 
agreed  that  the  main  factor  in  accommodation  is  the  altera- 
tion in  the  curvature  of  the  lens,  there  is  by  no  means  the 
same  unanimity  as  to  the  manner  in  which  this  is  brought 
about.  Helmholtz's  explanation,  which  has  long  been  the 
most  popular,  is  as  follows :  In  the  unaccommodated  eye 
the  suspensory  ligament  and  the  capsule  of  the  lens  are 
tense  and  taut,  the  anterior  surface  of  the  lens  is  flattened 
by  their  pressure,  and  parallel  rays  (or,  what  is  the  same 
thing,  rays  from  a  distant  object)  are  focussed  on  the  retina 
without  any  sense  of  effort.  In  accommodation  for  a  near 
object,  the  meridional  or  antero-posterior  fibres  of  the 
ciliary  muscle  by  their  contraction  pull  forward  the  choroid 
and  relax  the  suspensory  ligament.  The  elasticity  of  the 
lens  at  once  causes  it  to  bulge  forwards  till  it  is  again 
checked  by  the  tension  of  the  capsule. 

*  A  diopter  (i  D)  is  the  unit  of  refractive  power  generally  adopted  in 
measuring  the  strength  of  lenses,  and  corresponds  to  a  Ien3  of  i  metre 
focal  length.  A  lens  of  2  diopters  (2  D)  has  a  focal  length  of  \  metre, 
a  lens  of  4  diopters  (4  D)  a  focal  length  of  J  metre,  and  so  on.  The 
diverging  power  of  concave  lenses  is  similarly  expressed  in  diopters,  with 
the  negative  sign  prefixed.  Thus,  a  concave  lens  of  i  metre  focal  length 
has  a  strength  of  —  i  D  and  will  just  neutralize  a  convex  lens  of  i  D. 


750  A  MANUAL  OF  PHYSIOLOGY 

The  explanation  of  Helmholtz,  although  widely  adopted  in  the 
text-books,  is  being  more  and  more  called  in  question  in  the  archives. 
Tscherning,  for  example,  has  put  forward  the  view  that  when  the 
ciliary  muscle  (which  consists  of  a  superficial  layer  of  meridional, 
and  a  deep  layer  of  radial,  fibres)  contracts,  the  ciliary  processes  are 
drawn  back,  and  pull  the  zonule  of  Zinn  backwards  and  outwards. 
The  tension  of  the  zonule  is  thus  increased,  and  the  curvature  of 
the  lens  altered,  the  region  around  its  anterior  pole  in  particular 
becoming  more  convex.  At  the  same  time  the  contraction  of  the 
posterior  portion  of  both  layers  of  the  ciliary  muscle  pulls  the 
choroid  forward,  and  so  causes  the  vitreous  body  to  press  against  the 
posterior  surface  of  the  lens,  and  prevent  its  displacement  backwards 
by  the  pull  of  the  anterior  portion  of  the  muscle.  And  Schoen, 
reviving  a  similar  theory  originated  forty  years  ago  by  Mannhardt, 
believes  that  the  contraction  of  the  ciliary  muscle  exerts  pressure  on 
the  anterior  portion  of  the  lens,  and  so  increases  its  curvature.  He 
likens  the  increase  of  curvature  to  the  bulging  of  an  indiarubber 
ball  when  it  is  held  in  both  hands  and  compressed  by  the  fingers  a 
little  behind  one  of  the  poles.  It  will  be  observed  that  in  both  of 
these  theories  the  suspensory  ligament  is  supposed  to  be  stretched 
during  accommodation,  not  relaxed  as  in  Helmholtz's  theory. 

It  has  been  already  mentioned  that  along  with  the  altera- 
tion in  the  curvature  of  the  lens  a  change  in  the  diameter 
of  the  pupil  takes  place  in  accommodation.  When  a  distant 
object  is  looked  at,  the  pupil  becomes  larger ;  when  a  near 
object  is  looked  at,  it  becomes  smaller.  Narrowing  of  the 
pupil  is  thus  associated  with  contraction  of  the  ciliary 
muscle,  and  widening  of  the  pupil  with  its  relaxation. 

This  physiological  correlation  has  its  anatomical  counterpart ;  for 
the  third  nerve  supplies  both  the  iris  and  the  ciliary  muscle.  Stimu- 
lation of  the  nerve  within  the  cranium  causes  contraction  of  the  pupil, 
while  stimulation  of  certain  portions  of  its  nuclei  in  the  floor  of  the 
third  ventricle  and  the  Sylvian  aqueduct  or  of  the  short  ciliary  nerves 
coming  off  from  the  ophthalmic  ganglion  (Fig.  264),  which  receives 
branches  from  the  third  nerve,  or  of  the  ganglion  itself,  is  followed  by 
that  change  in  the  anterior  surface  of  the  lens  which  constitutes  ac- 
commodation (Hensen  and  Voelckers).  This  can  be  observed  either 
through  a  window  in  the  sclerotic  in  a  dog  or  by  following  the  move- 
ments of  a  needle  thrust  into  the  eyeball.  By  carefully  localized 
stimulation  near  the  junction  of  the  aqueduct  with  the  third  ventricle, 
it  is  possible  to  bring  about  the  forward  bulging  of  the  lens  without 
any  change  in  the  iris  ;  but  the  normal  and  voluntary  act  of  accom- 
modation cannot  be  disjoined  from  the  corresponding  alterations  in 
the  size  of  the  pupil. 

It  is  not  only  by  accommodation  that  the  size  of  the  pupil 
may  be  affected.  In  the  dark  it  dilates ;  when  light  falls 


THE  SENSES  751 

upon  the  retina  it  contracts,  and  the  amount  of  contraction 
is  roughly  proportional  to  the  intensity  of  the  light.  Con- 
traction of  the  pupil  to  light  is  brought  about  by  a  reflex 
mechanism,  of  which  the  optic  nerve  forms  the  afferent  and 
the  oculo-motor  the  efferent  path,  while  the  centre  is  situated 
in  the  floor  of  the  aqueduct  of  Sylvius.  The  relation  of  this 
centre  to  that  which  controls  the  changes  in  the  pupil  during 
accommodation  has  not  as  yet  been  sufficiently  elucidated ; 
but  this  we  do  know,  that  one  of  the  paths  may  be  inter- 
rupted by  disease,  while  the  other  is  intact.  For  in  loco- 


FIG.  264.— NERVES  OF  THE  EYE. 

,111,  third  or  oculo-motor  nerve  ;  IV,  fourth  or  trochlear  nerve ;  V,  ophthalmic  branch 
of  fifth  nerve  ;  VI,  sixth  or  abducens  ;  C,  carotid  artery  with  its  plexus  of  sympathetic 
fibres  ;  i,  ophthalmic  ganglion,  with  its  motor  root  2,  its  sympathetic  root  3,  and  its 
sensory  root  4  ;  5,  direct  ciliary  filament ;  6,  ciliary  muscle  ;  7,  iris  ;  8,  cornea  ;  9,  con- 
junctiva ;  10,  lachrymal  gland  ;  n,  frontal  nerve  ;  12,  nasal  nerve ;  13,  recurrent  branch 
of  ophthalmic  division  of  fifth.  The  thick  white  lines  represent  the  motor  nerves  ;  the 
thin  continuous  lines  the  sympathetic  fibres  ;  the  dotted  lines  the  sensory  nerves. 

motor  ataxia  the  light-reflex  sometimes  disappears,  while  the 
constriction  of  the  pupil  in  accommodation  still  takes  place 
(Argyll- Robertson  pupil).  Artificial  stimulation  of  the  optic 
nerve  has  the  same  effect  on  the  pupil  as  the  '  adequate ' 
stimulus  of  light ;  and  in  many  animals  (including  man), 
though  not  in  those  whose  optic  nerves  completely  decus- 
sate, both  pupils  contract  when  one  retina  or  optic 
nerve  is  excited.  This  should  be  remembered  in  using 


752  A  MANUAL  OF  PHYSIOLOGY 

the  pupil-reaction  as  a  test  of  the  condition  of  the  retina. 
For  although  the  absence  of  contraction  may  show  that  the 
retina  of  the  eye  on  which  the  light  is  allowed  to  fall  is 
insensible  (unless  there  is  some  physical  hindrance  to  its 
passage,  such  as  opacity  of  the  lens  or  cataract),  the  occur- 
rence of  contraction  does  not  exclude  insensibility  of  the 
retina  unless  the  other  eye  has  been  protected  from  the 
light. 

But  not  only  is  the  iris  under  the  control  of  constrictor 
nerve-fibres,  it  is  also  governed  by  dilator  nerves  ;  and  the 
size  of  the  pupil  at  any  given  moment  depends  on  the  play 
of  two  nicely-balanced  forces. 

The  dilator  fibres  pass  out  by  the  anterior  roots  of  the  first  three 
thoracic  nerves  (dog,  cat,  rabbit),  accompanied  apparently  by  vaso- 
constrictor fibres  for  the  iris.  Reaching  the  sympathetic  chain 
through  the  corresponding  rami  communicantes,  they  traverse  the 
first  thoracic  ganglion,  the  annulus  of  Vieussens,  the  inferior  cervical 
ganglion  and  the  cervical  sympathetic.  After  making  junction  with 
some  of  the  cells  of  the  superior  cervical  ganglion  (Langley),  they 
eventually  arrive  at  the  Gasserian  ganglion,  and  running  along  the 
ophthalmic  division  of  the  trigeminal  to  the  eye,  reach  the  iris  by  its 
ciliary  branches. 

Stimulation  of  the  cervical  sympathetic  causes  marked 
dilatation  of  the  pupil  (Practical  Exercises,  p.  820),  even 
when  the  third  nerve  is  excited  at  the  same  time.  All  the 
evidence  at  our  command  goes  to  show  that  the  pupillo- 
dilator  fibres  do  not  act  by  constricting  the  bloodvessels  of 
the  iris.  For  dilatation  of  the  pupil  can  be  caused  in  a 
bloodless  animal  by  stimulating  the  sympathetic.  And  even 
when  the  circulation  is  going  on,  a  short  stimulation  of  the 
sympathetic  causes  dilatation  of  the  pupil  without  vaso-con- 
striction,  while  with  longer  excitation  the  dilatation  of  the 
pupil  begins  before  the  narrowing  of  the  bloodvessels.  Nor 
does  it  seem  possible  to  accept  the  view  that  the  sympa- 
thetic fibres  are  inhibitory  for  the  sphincter  muscle  of  the 
iris.  In  all  probability  they  act  directly  upon  dilator 
muscular  fibres.  It  has,  indeed,  long  been  known  that  in 
the  iris  of  the  otter  and  of  birds  a  radial  dilator  muscle 
exists  ;  and  it  has  been  shown  by  the  recent  experiments  of 
Langley  and  Anderson  that  in  the  iris  of  the  rabbit,  cat, 


THE  SENSES  753 

and  dog,  the  presence  of  radially  arranged  contractile  sub- 
stance, different  it  may  be  in  some  respects  from  ordinary 
smooth  muscle,  must  be  assumed.  Reflex  dilatation  of  the 
pupil  through  the  sympathetic  fibres  is  caused  in  man  by 
painful  stimulation  of  the  skin,  by  dyspnoea,  by  muscular 
exertion,  and  in  some  individuals  even  by  tickling  of  the 
palms.  In  animals  the  stimulation  of  naked  sensory  nerves 
has  the  same  effect.  The  '  starting  of  the  eyeballs  from 
their  sockets,'  which  the  records  of  torture  so  often  note, 
is  probably  due  to  a  similar  reflex  excitation  of  the  sympa- 
thetic fibres  supplying  the  smooth  muscle  of  the  orbits  and 
eyelids. 

The  statement  has  been  made  that  in  addition  to  the  sympathetic 
dilators  of  the  pupil,  dilating  fibres  pass  out  directly  from  the  brain 
along  the  fifth  nerve ;  and  it  has  been  said  that  after  section  of  the 
cervical  sympathetic  or  excision  of  the  superior  cervical  ganglion, 
reflex  dilatation  can  still  be  caused.  Stimulation  of  certain  cortical 
areas  causes  slight  dilatation  even  after  the  sympathetic  has  been 
divided.  But  it  is  not  known  whether  this  is  due  to  inhibition  of 
the  pupillo-constrictor  fibres  in  the  third  nerve  or  to  excitation  of 
cerebral  pupillo-dilator  fibres.  The  reflex  centre  for  dilatation  of  the 
pupil  is  in  the  medulla  oblongata.  The  lower  cervical  and  upper 
thoracic  portion  of  the  spinal  cord  has  received  the  name  of  the 
cilio-spinal  region  from  its  relation  to  the  pupillo-dilator  fibres.  It 
must  not  be  looked  upon  as  a  centre  in  any  proper  sense  of  the 
term,  but  rather  as  the  pathway  by  which  these  fibres  pass  down 
from  the  bulb,  and  where  they  may  accordingly  be  tapped  by  stimu- 
lation. 

That,  in  addition  to  the  cerebral  centre  for  the  constrictor 
and  the  bulbar  centre  for  the  dilator  fibres,  there  exists 
within  the  eye  some  local  mechanism  which  controls  the 
muscles  of  the  iris  and  regulates  the  size  of  the  pupil  is 
rendered  certain  by  many  facts.  The  excised  eye  of  a  frog 
or  an  eel  constricts  its  pupil  on  exposure  to  light,  and  dilates 
it  in  the  dark.  It  is  said  that  even  the  isolated  iris  of  the 
eel  contracts  to  light ;  and  it  is  known,  although  here  the 
explanation  is  less  difficult,  that  the  iris  both  of  cold-  and 
warm-blooded  animals  contracts  in  warm,  and  dilates  in 
cold  normal  saline  solution.  The  local  application  of  atropia 
causes  temporary  paralysis  of  accommodation  and  dilatation 
of  the  pupil.  When  the  third  nerve  is  divided,  the  pupil 
dilates;  it  dilates  still  more  when  atropia  is  administered 


754  A  MANUAL  OF  PHYSIOLOGY 

after  the  operation.  Dropped  into  one  eye  in  small 
quantity,  atropia  only  produces  a  local  effect ;  the  pupil 
of  the  other  eye  remains  of  normal  size,  or  somewhat  con- 
stricted on  account  of  the  greater  reflex  stimulation  of  its 
third  nerve  by  the  greater  quantity  of  light  now  entering  the 
widely-dilated  pupil  of  the  atropinized  eye.  Even  in  an 
excised  eye  the  effect  of  the  drug  is  the  same.  Introduced 
into  the  blood,  atropia  causes  both  pupils  to  dilate.  Other 
mydriatic,  or  pupil-dilating  drugs,  are  cocaine,  daturine,  and 
hyoscyamine.  Eserine,  pilocarpine,  and  morphia  are  the  chief 
myotics,  or  pupil-constricting  substances.  They  also  cause 
spasm  of  the  ciliary  muscle,  and  inability  to  accommodate 
for  distant  objects.  The  work  of  the  mydriatics  can  be 
undone  by  the  myotics.  Thus  the  dilatation  produced  by 
atropia  is  removed  by  pilocarpine.  The  most  plausible  ex- 
planation of  the  action  of  these  drugs  is  that  the  mydriatics 
paralyze  the  third  nerve,  and  stimulate  the  dilator  nerve- 
fibres  of  the  iris,  while  the  myotics  paralyze  the  dilators  and 
stimulate  the  third.  Nicotine,  which  ultimately  causes  con- 
striction of  the  pupil,  does  so  by  paralyzing  the  cells  on 
the  course  of  the  dilating  fibres  in  the  superior  cervical 
ganglion. 

Inward  rotation  of  the  eyes  is  associated  with  contraction  of  the 
pupil,  and  the  contraction  that  occurs  during  sleep  is  probably  to  be 
thus  explained.  When  the  pressure  in  the  anterior  chamber  of  the 
eye  is  diminished,  as  by  tapping  the  aqueous  humour  through  the 
cornea,  contraction  of  the  pupil  occurs  ;  and  stimulation  of  the 
sympathetic  has  now  a  far  smaller  dilating  effect  than  usual.  Re- 
moval of  the  cornea  narrows  the  pupil,  partly  by  occasioning  direct 
stimulation  of  the  sphincter  pupillse,  partly  by  abolishing  the  pressure 
of  the  aqueous  humour.  The  attached  (ciliary)  border  of  the  iris 
then  bulges  forward,  and  the  pupil  becomes  smaller.  On  the  other 
hand,  an  increased  pressure  in  the  anterior  chamber  forces  back  the 
ciliary  border  of  the  iris,  and  causes  mechanical  dilatation  of  the 
pupil. 

Functions  of  the  Iris. — In  vision,  the  iris  performs  two 
chief  functions  :  (i)  It  regulates  the  quantity  of  light  allowed 
to  fall  upon  the  retina.  The  larger  the  aperture  of  a  lens, 
the  greater  is  its  collecting  power,  the  more  light  does  il 
gather  in  its  focus.  In  the  eye,  the  area  of  the  pupil 
determines  the  breadth  of  the  pencil  of  light  that  falls  upoi 


THE  SENSES  755 

the  lens.  If  this  area  was  invariable,  the  retina  would  either 
be  '  dark  from  excess  of  light '  in  bright  sunshine,  or  dark 
from  defect  of  light  in  dull  weather  or  at  dusk.  In  order 
that  the  iris  may  act  as  an  efficient  diaphragm  it  must  be 
pigmented,  and  it  is  the  pigment  in  it  which  gives  the  colour 
to  the  normal  eye.  The  vision  of  albinos,  in  whose  eyes 
this  pigment  is  wanting,  is  often,  though  not  invariably, 
deficient  in  sharpness.  There  is  always  intolerance  of  bright 
light ;  and  the  same  is  true  in  the  condition  known  as 
irideremia,  or  congenital  absence  or  defect  of  the  iris. 

(2)  Another,  and  perhaps  equally  important,  function  of 
the  iris  is  to  cut  off  the  more  divergent  rays  of  a  pencil  of 
light  falling  upon  the  eye,  and  thus  to  increase  the  sharpness 
of  the  image.  This  leads  us  to  the  consideration  of  certain 
defects  in  the  dioptric  arrangements  of  the  eye. 

Defects  of  the  Eye  as  an  Optical  Instrument,  (i)  Spherical 
Aberration. — It  is  a  property  of  a  spherical  refracting  surface  that 
rays  of  light  passing 
through  the  peri- 
pheral portions  are 
more  strongly  re- 
fracted than  rays 
passing  near  the  prin- 
cipal axis.  Hence  a 
luminous  point  is  not 
focussed  accurately 
in  a  single  point  by 
a  spherical  lens  ;  the 
image  is  surrounded  FlG-  265.— SPHERICAL  ABERRATION. 

by  circles  of  diffusion.  Rays  passing  through  the  more  peripheral  parts  of  a 
T«  fKo  we*  tVii'c  cr^V.^  biconvex  lens  L  are  brought  to  a  focus  F  nearer  the 
in  me  eye  cms  spn<  leng  than  F/i  the  focus  Qf  fays  passing  through  the  central 

rical     aberration    is     portions  of  the  lens, 
partly   corrected    by 

the  interposition  of  the  iris,  which  cuts  off  the  more  peripheral  rays, 
especially  in  accommodation  for  a  near  object,  when  they  are  most 
divergent.  In  addition,  the  anterior  surfaces  of  the  cornea  and  lens 
are  not  segments  of  spheres,  but  of  ellipsoids,  so  that  the  curvature 
diminishes  somewhat  with  the  distance  from  the  optic  axis,  and, 
therefore,  the  refracting  power  as  we  pass  away  from  the  axis  does  not 
increase  so  rapidly  as  it  would  do  if  the  surfaces  were  truly  spherical. 
Further,  the  refractive  index  of  the  peripheral  parts  of  the  lens  is 
less  than  that  of  its  central  portions. 

(2)  Chromatic  Aberration. — All  the  rays  of  the  spectrum  do  not. 
travel  with  the  same  velocity  through  a  lens,  and  are,  therefore, 
unequally  refracted  by  it,  the  short  violet  rays  being  focussed  nearer 

48—2 


756 


A  MANUAL  OF  PHYSIOLOGY 


the  lens  than  the  long  red  rays.  It  was  at  one  time  supposed  that 
this  chromatic  aberration,  as  it  is  called,  is  compensated  in  the  eye  ; 
and  it  is  said  that  this  mistake  gave  the  first  hint  that  Newton's 
dictum  as  to  the  proportionality  between  deviation  and  dispersion 
was  erroneous,  and  led  to  the  discovery  of  achromatic  lenses.  But  in 
reality  the  eye  is  not  an  achromatic  combination  ;  and  the  violet  rays 
are  focussed  about  \  mm.  in  front  of  the  red.  Thus,  in  Fig.  266 
the  white  light  passing  through  the  lens  is  broken  up  into  its  con- 
stituents :  the  violet  focus  is  at  V,  and  the  red  at  R,  behind  it.  A 
screen  placed  at  R  would  show  not  a  point  image,  but  a  central 
point  surrounded  by  concentric  circles  of  the  spectral  colours,  with 
violet  outside.  If  the  screen  was  placed  at  V,  the  centre  would  be 
violet  and  the  red  would  be  external.  For  this  reason  it  is  impossible 


FIG.  266. — CHROMATIC  ABERRATION. 

The  violet  rays  are  brought  to  a  focus  V  nearer 
the  lens  than  R,  the  focus  of  the  red  rays. 


FIG.  267.— To  SHOW  DISPER- 
SION IN  EYE. 

View  the  figure  from  a  distance 
too  small  for  accommodation. 
Approach  the  eye  towards  it ;  the 
white  rings  appear  bluish  owing 
to  circles  of  dispersion  falling  on 
them.  A  little  closer,  and  the  black 
rings  become  white  or  yellowish- 
white,  being  covered  by  circles  of 
dispersion  and  diffusion. 


to  focus  at  the  same  time  and  with  perfect  sharpness  objects  of 
different  colours  :  a  red  light  on  a  railway  track  appears  nearer  than  a 
blue  light,  partly  perhaps  for  the  reason  that  it  is  necessary  to  accom- 
modate more  strongly  for  the  red  than  for  the  blue,  and  we  associate 
stronger  accommodation  with  shorter  distance  of  the  object,  although 
other  data  are  also  involved  in  such  a  visual  judgment.  When  we 
look  at  a  white  gas-flame  through  a  cobalt  glass,  which  allows  only 
red  and  violet  to  pass,  we  see  either  a  red  flame  surrounded  by  a 
violet  ring,  or  a  violet  flame  surrounded  by  a  red  ring,  according  as  we 
focus  for  the  red  or  for  the  violet  rays.  The  dispersive  power  of  the 
eye,  however,  is  so  small,  and  the  capacity  of  rapidly  altering  its 
accommodation  so  great,  that  no  practical  inconvenience  results  from 
the  lack  of  achromatism,  which,  however,  may  be  easily  demonstrated 
by  looking  at  a  pattern  such  as  that  in  Fig.  267  at  a  distance  too 
small  for  exact  accommodation. 

It  is  also  reckoned  among  the  optical  imperfections  of  the  eye 
(3)  that  the  curved  surfaces  of  the  cornea  and  lens  do  not  form  a 
*  centred '  system — that  is  to  say,  their  apices  and  their  centres  of 
curvature  do  not  all  lie  in  the  same  straight  line  ;  (4)  that  the  pupil 
is  eccentric,  being  situated  not  exactly  opposite  the  middle  of  the 
lens  and  cornea,  but  nearer  the  nasal  side,  and  that  in  consequence 


THE  SENSES  757 

the  optic  axis,  or  straight  line  joining  the  centre  of  curvature  of  the 
lens  and  cornea,  does  not  coincide  with  the  visual  axis,  or  straight 
line  joining  the  fovea  centralis  with  the  centre  of  the  pupil,  which  is 
also  the  straight  line  joining  the  centre  of  the  pupil  and  any  point  to 
which  the  eye  is  directed  in  vision.  The  angle  between  the  optic 
and  visual  axis  is  about  5°  (Fig.  258).  (5)  Muscat  volitantes,  the 
curious  bead-like  or  fibrillar  forms  that  so  often  flit  in  the  visual  field 
when  one  is  looking  through  a  microscope,  are  the  token  that  the 
refractive  media  of  the  eye  are  not  perfectly  transparent  at  all  parts  ; 
they  seem  to  be  due  to  floating  opacities  in  the  vitreous  humour, 
probably  the  remains  of  the  embryonic  cells  from  which  the  vitreous 
body  was  developed.  (6)  Lastly,  it  may  be  mentioned  that  slight 
irregularities  in  the  curvature  of  the  lens  exist  in  all  eyes,  so  that  a 
point  of  light,  like  a  star  or  a  distant  street-lamp,  is  not  seen  as  a 
point,  but  as  a  point  surrounded  by  rays  (irregular  astigmatism).  In 
bringing  this  review  of  the  imperfections  of  the  dioptric  media  of  the 
normal  eye  to  a  close,  it  may  be  well  to  explain  that  what  are  defects 


FIG.  268.— REFRACTION  IN  THE  (NORMAL)  EMMETROPIC  EYE. 
The  image  P'  of  a  distant  point  P  falls  on  the  retina  when  the  eye  is  not  accommodated. 

from  the  point  of  view  of  the  student  of  pure  optics  are  not 
necessarily  defects  from  the  freer  standpoint  of  the  physiologist,  who 
surveys  the  mechanism  of  vision  as  a  whole,  the  relations  of  its 
various  parts  to  one  another  and  to  the  needs  of  the  organism  it  has 
to  serve,  the  long  series  of  developmental  changes  through  which  it 
has  come  to  be  what  it  is,  and  the  possibilities,  so  far  as  we  can  limit 
them,  that  were  open  to  evolution  in  the  making  of  an  eye.  The 
optician  may  perhaps  assert,  and  with  justice,  that  he  could  easily 
have  made  a  better  lens  than  Nature  has  furnished,  but  the  physio- 
logist will  not  readily  admit  that  he  could  have  made  as  good  an  eye. 

While  the  defects  hitherto  mentioned  are  shared  in 
greater  or  less  degree  by  every  normal  eye,  there  are  certain 
other  defects  which  either  occur  in  such  a  comparatively 
small  number  of  eyes,  or  lead  to  such  grave  disturbances 
of  vision  when  they  do  occur,  that  they  must  be  reckoned 


758  ,          A  MANUAL  OF  PHYSIOLOGY 

as  abnormal  conditions.  In  the  normal  or  emmetropic  eye, 
parallel  rays — and  for  this  purpose  all  rays  coming  from  an 
object  at  a  distance  greater  than  65  metres  may  be  con- 
sidered parallel  —  are  brought  to  a  focus  on  the  retina 
without  any  effort  of  accommodation.  The  distance  at 
which  objects  can  be  distinctly  seen  is  only  limited  by  their 
size,  the  clearness  of  the  atmosphere,  and  the  curvature 
of  the  earth ;  in  other  words,  the  punctum  remotum,  or  far 
point  of  vision,  the  most  distant  point  at  which  it  is  pos- 
sible to  see  with  distinctness,  is  practically  at  an  infinite 
distance.  When  accommodation  is  .paralyzed  by  atropia, 
only  remote  objects  can  be  clearly  seen.  On  the  other  hand, 
the  normal  eye,  or,  to  be  more  precise,  the  normal  eye  of 


•  FIG.  269.— MYOPIC  EYE. 

The  image  P'of  a  distant  point  P  falls  in  front  of  the  retina  even  without  accommo- 
dation. By  means  of  a  concave  lens  L  the  image  may  be  made  to  fall  on  the  retina 
(dotted  lines).  To  save  space,  P  is  placed  much  too  near  the  eye  in  Figs.  268-270. 

a  middle-aged  adult,  can  be  adjusted  for  an  object  at  a  dis- 
tance of  not  more  than  12  cm.  (or  5  inches).  Nearer  than 
this  it  is  not  possible  to  see  distinctly ;  this  point  is  accord- 
ingly called  the  punctum  proximum,  or  near  point.  The  range 
of  accommodation  for  distinct  vision  in  the  emmetropic  eye 

12  cm.  to  infinity. 

Myopia,  or  short-sightedness,  is  generally  due  to  the 
excessive  length  of  the  antero-posterior  diameter  of  the  eye- 
ball in  relation  to  the  converging  power  of  the  cornea  and 
the  lens.  Even  in  the  absence  of  accommodation,  parallel 
rays  are  not  focussed  on  the  retina,  but  in  front  of  it ;  and 
in  order  that  a  sharp  image  may  be  formed  on  the  retiha 


THE  SENSES  759 

the  object  must  be  so  near  that  the  rays  proceeding  from  it 
to  the  eye  are  sensibly  divergent — that  is  to  say,  it  must  be 
at  least  nearer  than  65  metres ;  but  as  a  rule  an  object  at 
a  distance  of  more  than  2  to  3  metres  cannot  be  distinctly 
seen.  With  the  strongest  accommodation  the  near  point 
may  be  as  little  as  5  cm.  from  the  eye.  The  range  of  vision 
in  the  myopic  eye  is  therefore  very  small.  The  defect  may 
be  corrected  by  concave  glasses,  which  render  the  rays  more 
divergent.  It  is  to  be  noted  that  many  cases  of  internal 
squint  in  children  are  connected  with  myopia,  the  eyes 
necessarily  rotating  inwards  as  they  are  made  to  fix  an 
abnormally  near  object.  The  treatment  both  of  the  squint 
and  the  myopia  in  these  cases  is  the  use  of  concave  spec- 


FIG.  270. — HYPERMETROPIC  EYE. 

The  image  P'  of  a  point  P  falls  behind  the  retina  in  the  unaccommodated  eye.  By 
means  of  a  convex  lens  it  may  be  focussed  on  the  retina  without  accommodation  (dotted 
lines). 

tacles  (Fig.  269).  Myopia,  although  a  condition  that  shows 
a  distinct  hereditary  tendency,  is  rarely  present  at  birth; 
the  elongation  of  the  antero-posterior  diameter  of  the  eye- 
ball develops  gradually  as  the  child  grows. 

In  hypermetropia,  or  long-sightedness,  the  eye  is,  as  a  rule, 
too  short  in  relation  to  its  converging  power;  and  with  the 
lens  in  the  position  of  rest,  parallel  rays  would  be  focussqd 
behind  the  retina.  Accordingly  the  hypermetropic  eye  must 
accommodate  even  for  distant  objects,  while  even  with 
maximum  accommodation  an  object  cannot  be  distinctly 
seen  unless  it  is  farther  away  than  the  near  point  of  the 
emmetropic  eye.  The  far  point  of  distinct  vision  is  at  the 
same  distance  as  in  the  emmetropic  eye,  viz.,  at,  infinity; 


76o  A  MANUAL  OF  PHYSIOLOGY 

the  near  point  is  farther  from  the  eye.  The  defect  is  cor- 
rected by  convex  glasses  (Fig.  270).  Hypermetropia,  unlike 
myopia,  is  present  at  birth. 

Presbyopia,  or  the  long-sightedness  of  old  age,  is  not  to 
be  confounded  with  hypermetropia.  It  is  essentially  due 
to  failure  in  the  power  of  accommodation,  chiefly  through 
weakness  of  the  ciliary  muscle,  but  partly  owing  to  increased 
rigidity  and  loss  of  elasticity  of  the  lens.  Images  of  distant 
objects  are  still  formed  on  the  retina  of  the  unaccommodated 
eye  with  perfect  sharpness ;  i.e.,  the  far  point  of  vision  is  not 
affected.  But  the  eye  is  unable  to  accommodate  sufficiently 
for  the  rays  diverging  from  an  object  at  the  ordinary  near 
point ;  in  other  words,  the  near  point  is  farther  away  than 
normal.  Convex  glasses  are  again  the  remedy. 

The  near  point  of  distinct  vision  can  be  fixed  in  various 
ways — among  others,  by  means  of  Scheiner's  experiment 
(Practical  Exercises,  p.  816).  Two  pin-holes  are  pricked  in 
a  card  at  a  distance  less  than  the  diameter  of  the  pupil. 
A  needle  viewed  through  the  holes  appears  single  when  it  is 
accommodated  for,  double  if  it  is  out  of  focus.  The  near 
point  of  vision  is  the  nearest  point  at  which  the  needle 
can  still,  by  the  strongest  effort  of  accommodation,  be  seen 
single. 

Astigmatism. — It  has  been  mentioned  that  slight  differences 
of  curvature  along  different  meridians  of  the  refracting 
surfaces  exist  in  all  eyes.  But  in  some  cases  the  difference 
in  two  meridians  at  right  angles  to  each  other  is  so  great  as 
to  amount  to  a  serious  defect  of  vision.  To  this  condition 
the  name  of  'astigmatism'  or  'regular  astigmatism'  has 
been  given.  It  is  usually  due  to  an  excess  of  curvature  in 
the  vertical  meridians  of  the  cornea,  less  frequently  in  the 
horizontal  meridians  ;  occasionally  the  defect  is  in  the  lens. 
Rays  proceeding  from  a  point  are  not  focussed  in  a  point, 
but  along  two  lines,  a  horizontal  and  a  vertical,  the  hori- 
zontal linear  focus  being  in  front  of  the  other  when  the 
vertical  curvature  is  too  great,  behind  it  when  the  horizontal 
curvature  is  excessive.  The  two  limbs  of  a  cross  or  the  two 
hands  of  a  clock  when  they  are  at  right  angles  to  each  other 
cannot  be  seen  distinctly  at  the  same  time,  although  they 


THE  SENSES  761 

can  be  successively  focussed.  The  condition  may  be  cor- 
rected by  glasses  which  are  segments  of  cylinders  cut 
parallel  to  the  axis. 

The  Ophthalmoscope. — The  pupil  of  the  normal  eye  is  dark, 
and  the  interior  of  the  eye  invisible,  without  special  means 
of  illuminating  it.  But  this  is  not  because  all  the  light  that 
falls  upon  the  fundus  is  absorbed  by  the  pigment  of  the 
choroid,  for  even  the  pupil  of  an  albino  appears  dark  when 
the  eye  is  covered  by  a  piece  of  black  cloth  with  a  hole  in 
front  of  the  pupil. 

Let  the  rays  from  a  luminous  point  P  be  focussed  by  the 
lens  L  at  P'  (Fig.  271).  It  is  plain  that  rays  proceeding  from 
P'  will  exactly  retrace 
the  path  of  those  from 
P  and  be  focussed  at  P. 
Now,  the  eye  receives 
rays  from  all  directions, 
and,  when  it  is  suf- 
ficiently well  illumi- 
nated, sends  rays  out 
in  all  directions.  The  FIG.  271. 

moment,  however,  that  the  observing  eye  is  placed  in  front 
of  the  observed  eye,  the  latter  ceases  to  receive  light  from 
the  part  of  the  field  occupied  by  the  pupil  of  the  former,  and 
therefore  ceases  to  reflect  light  into  it. 

This  difficulty  is  avoided  by  the  use  of  an  ophthalmo- 
scopic  mirror.  The  original  and  theoretically  the  most 
perfect  form  of  such  a  mirror  is  a  plate,  or  several  superposed 
plates,  of  glass,  from  which  a  beam  of  light  from  a  laterally 
placed  candle  or  lamp  is  reflected  into  the  observed  eye,  and 
through  which  the  eye  of  the  observer  looks  (Fig.  272).  But 
the  illumination  thus  obtained  is  comparatively  faint ;  and 
a  concave  mirror,  with  a  small  hole  in  the  centre  for  the 
pupil  of  the  observer's  eye,  is  now  generally  used.  In  the 
direct  method  of  examination  (Fig.  273),  the  mirror  is  held 
close  to  the  observed  eye,  and  an  erect  virtual  image  of  the 
fundus  is  seen.  When  the  eye  of  the  observer  and  of  the 
patient  are  both  emmetropic,  and  both  eyes  are  unaccommo- 
dated, the  rays  of  light  proceeding  from  a  point  of  the  retina 


762 


A  MANUAL  OF  PHYSIOLOGY 


of  the  observed  eye  are  rendered  parallel  by  its  dioptric  media, 
and  are  again  brought  to  a  focus  on  the  observer's  retina. 
If  the  observed  eye  is  myopic,  the  rays  of  light  coming 


FIG.  272. — FIGURE  TO  ILLUSTRATE  THE  PRINCIPLE  OF  THE  OPHTHALMOSCOPE. 

Rays  of  light  from  a  point  P  are  reflected  by  a  glass  plate  M  (several  plates  together 
in  Helmholtz's  original  form)  into  the  observed  eye  E'.  Their  focus  would  fall,  as  shown 
in  the  figure,  at  P',  a  little  behind  the  retina  of  E'.  The  portion  of  the  retina  AB  is  there- 
fore illuminated  by  diffusion  circles ;  and  the  rays  from  a  point  of  it  F  will,  if  E'  is 
emmetropic  and  unaccommodated,  issue  parallel  from  E'  and  be  brought  to  a  focus  at 
F'  on  the  retina  of  the  (emmetropic  uad  unaccommodated)  observing  eye  E. 


FIG.  273. — DIRECT  METHOD  OF  USING  THE  OPHTHALMOSCOPE. 

Light  falling  on  the  perforated  concave  mirror  M  passes  into  the  observed  eye  E'; 
and,  both  E'  and  the  observing  eye  E  being  supposed  emmetropic  and  unaccommodated, 
an  erect  virtual  image  of  the  illuminated  retina  of  E'  is  seen  by  E. 

from  a  point  of  the  retina  leave  the  eye,  even  when  it  is 
unaccommodated,  as  a  convergent  pencil;  and  the  emme- 


THE  SENSES  763 

tropic  non-accommodated  eye  of  the  observer  must  have  a 
concave  lens  placed  before  it  in  order  that  the  fundus  may 
be  distinctly  seen. 


FIG.  274.— USE  OF  THE  OPHTHALMOSCOPE  (DIRECT  METHOD)  FOR  TESTING 
ERRORS  OF  REFRACTION  IN  MYOPIC  EYE. 

Rays  issuing  from  a  point  of  the  retina  of  E',  the  observed  (myopic  and  unaccom- 
modated) eye,  pass  out,  not  parallel,  but  convergent.  They  will  therefore  be  focussed 
in  front  of  the  retina  of  the  observing  (unaccommodated)  eye  E  if  the  latter  is  emme- 
tropic.  By  introducing  a  concave  lens  L  of  suitable  strength,  however,  a  clear  view 
of  the  retina  of  E'  will  be  obtained,  and  the  strength  of  this  lens  is  the  measure  of  the 
amount  of  myopia. 


FIG.  275.— TESTING  ERRORS  OF  REFRACTION  IN  HYPERMETROPIC  EYE. 

Rays  from  a  point  of  the  retina  of  E',  the  observed  eye,  issue  divergent,  and  are 
focussed  behind  the  retina  of  the  observing  (unaccommodated  and  emmetropic)  eye  E. 
The  strength  of  the  convex  lens  L,  which  must  be  introduced  in  front  of  E  to  give  cleat 
vision  of  the  retina  of  E',  measures  the  degree  of  hypermetropia. 

When  the  observed  eye  is  hypermetropic,  the  rays  emerg- 
ing from  the  unaccommodated  eye  are  divergent,  and  a 
convex  lens,  the  strength  of  which  is  proportional  to  the 


764  A  MANUAL  OF  PHYSIOLOGY 

amount  of  hypermetropia,  must  be  placed  before  the  ob- 
server's unaccommodated  eye  if  he  is  to  see  the  fundus 
distinctly.  By  accommodating,  the  observer  can  see  the 
fundus  clearly  without  a  convex  lens. 

By  this  method  errors  of  refraction  in  the  eye  may  be 
detected  and  measured.*  The  observer  must  always  keep 
his  eye  unaccommodated,  and  if  it  is  not  emmetropic,  he 
must  know  the  amount  of  his  short-  or  long-sightedness, 
i.e.,  the  strength  and  sign  of  the  lens  needed  to  correct  his 
defect  of  refraction,  and  must  allow  for  this  in  calculating 


FIG.  276.— INDIRECT  METHOD  OF  USING  THE  OPHTHALMOSCOPE. 

The  rays  of  light  issuing  from  E',  the  observed  eye,  are  focussed  by  the  biconvex  lens 
L,  and  a  real  inverted  image  of  a  portion  of  the  retina  of  E',  magnified  four  or  five 
times,  is  formed  in  the  air  between  the  lens  and  the  observing  eye  E.  This  image  is 
viewed  by  E  at  the  ordinary  distance  of  distinct  vision  (10  or  12  inches).  (The  exaggera- 
tion of  the  size  of  the  mirror  makes  it  appear  as  if  some  of  the  rays  from  the  lamp 
passed  through  the  lens  before  being  reflected  from  the  mirror.  This  would  not  be  the 
case  in  an  actual  observation.) 

the  defect  of  his  patient.     Non-accommodation  of  the  eye 
of  the  latter  can  always  be  secured  by  the  use  of  atropia. 

By  the  direct  method  of  ophthalmoscopic  examination, 
only  a  small  portion  of  the  retina  can  be  seen  at  a  time,  and 
this  is  highly  magnified.  A  larger,  though  less  magnified, 
view  can  be  got  by  the  indirect  method.  The  observed  eye 
is  illuminated  as  before,  but  the  mirror  and  the  observer's 

*  To  a  great  extent  the  opthalmoscopic  method  of  measuring  errors  of 
refraction  has  been  replaced  by  the  more  modern  method  of  skiascopy 
(shadow  test),  which,  however,  it  would  be  out  of  place  to  describe  here. 


THE  SENSES  765 

eye  are  at  a  greater  distance  (Fig.  276).  Here  the  rays 
from  a  considerable  portion  of  the  retina,  emerging  in 
parallel  pencils  if  the  observed  eye  is  emmetropic  and  not 
accommodated,  are  brought  to  a  focus  by  a  convex  lens  held 
near  the  eye  of  the  patient,  so  as  to  form  a  real  and  inverted 
aerial  image  of  the  retina.  This  image  is  viewed  by  the 
observer  at  his  ordinary  visual  distance. 

Single  Vision  with  Both  Eyes — Diplopia. — Scheiner's  experi- 
ment shows  that  it  is  possible  to  have  double  vision,  or 
diplopia,  with  a  single  eye  when  two  separate  images  of  the 
same  object  fall  upon  different  parts  of  the  retina.  In  vision 
with  both  eyes,  or  binocular  vision,  an  image  of  every 
object  looked  at  is,  of  course,  formed  on  each  retina,  and  we 
have  to  inquire  how  it  is  that  as  a  rule  these  images  are 
blended  in  consciousness  so  as  to  produce  the  perception  of 
a  single  object ;  and  how  it  is  that  under  certain  conditions 
this  blending  does  not  take  place,  and  diplopia  results.  Two 
chief  theories  have  been  invoked  in  the  attempt  to  answer 
these  questions  :  (i)  the  theory  of  identical  points,  (2)  the 
theory  of  projection. 

In  regard  to  the  second  theory,  we  shall  merely  say  that  it 
assumes  that  in  some  way  or  other  the  retina,  or,  rather,  the 
retino-cerebral  apparatus,  has  the  power  of  appreciating  not 
only  the  shape  and  size  of  an  image,  but  also  the  direction 
of  the  rays  of  light  which  form  it,  and  that  the  position  of 
the  object  is  arrived  at  by  a  process  of  mental  projection  of 
the  image  into  space  along  these  directive  lines.  The  first 
theory  we  shall  examine  in  some  detail. 

The  Theory  of  Identical  Points. — This  theory  assumes  that 
every  point  of  one  retina  '  corresponds  '  to  a  definite  point  of 
the  other  retina,  and  that  in  virtue  of  this  correspondence, 
either  by  an  inborn  necessity  or  from  experience,  the  mind 
refers  simultaneous  impressions  upon  two  corresponding  or 
identical  points  to  a  single  point  in  external  space.  If  we 
imagine  the  two  retinas  in  the  position  which  the  eyes 
occupy  when  fixing  an  infinitely  distant  object  (that  is,  with 
the  visual  axes  parallel)  to  be  superposed,  with  fovea  over 
fovea,  every  point  of  the  one  retina  will  be  covered  by  the 
corresponding  point  of  the  other  retina,  so  that  identical 


766  A  MANUAL  OF  PHY.SIOLOGY 

points  could  be  pricked  through  with  a  needle.  But  since 
the  actual  centre  of  the  retina  does  not  correspond  with  the 
fovea  centralis  (Fig.  256),  but  lies  nearer  the  nasal  side,  the 
nasal  edge  of  the  left  retina  will  overlap  the  temporal  edge 
of  the  right,  and  the  nasal  edge  of  the  right  will  overlap  the 
temporal  edge  of  the  left ;  so  that  a  part  of  each  retina  has 
no  corresponding  points  in  the  other. 

When  the  eyes  are  directed  to  two  distant  objects  at  the  same 
height  as  themselves — when,  in  other  words,  the  visual  axes  are 
parallel  and  horizontal — neither  the  middle  vertical  meridians  nor 
the  middle  horizontal  meridians  of  the  two  retinae,  as  a  rule,  exactly 
correspond,  although  the  correspondence  is  much  nearer  for  the 
horizontal  than  for  the  vertical  meridians.  A  meridian  of  the  left 
retina,  the  upper  end  of  which  is  slightly  inclined  towards  the  left, 
contains  the  points  corresponding  to  a  meridian  of  the  right  eye 
whose  upper  end  is  slightly  inclined  to  the  right.  When  this  physio- 
logical incongruence  of  the  retina  is  taken  into  account  in  determining 
the  points  which  are  to  be  considered  as  identical,  the  adherents  of 
this  theory  claim,  and  with  justice,  that  a  small  object  so  situated 
that  its  image  must  be  formed  on  corresponding  points  of  the  two 
retinae  does,  as  a  rule,  appear  single,  and,  what  is  even  more  striking, 
that  a  phosphene,  or  luminous  circle  produced  by  pressing  the  blunt 
end  of  a  pencil  or  the  finger-nail  on  a  point  of  the  globe  of  one  eye, 
is  not  doubled  by  pressure  over  the  corresponding  point  of  the  other 
eye,  although  two  circles  are  seen  when  pressure  is  made  upon  points 
which  do  not  correspond. 

But  too  much  weight  must  not  be  allowed  to  such  evi- 
dence, for  it  is  also  a  fact  that  images  situated  on  corre- 
sponding points  may  not,  and  that  images  not  situated  on 
corresponding  points  may,  give  rise  to  a  single  impression. 
For  example,  if  one  of  the  closed  eyes  be  held  slightly  out 
of  its  ordinary  position  by  the  finger,  pressure  on  identical 
points  of  the  two  eyes  gives  rise  to  two  separate  phosphenes. 
And  some  of  the  phenomena  of  stereoscopic  vision  (p.  767) 
show  clearly  that  images  falling  on  non-corresponding  points 
may  give  a  single  impression ;  while  we  do  not  habitually 
see  double,  although  it  is  certain  that  the  images  of  multi- 
tudes of  objects  are  constantly  falling  on  points  of  the  retinae 
not  anatomically  identical.* 

*  In  every  fixed  position  of  the  eyes,  the  objects  whose  images  fall  on 
corresponding  points  will  be  arranged  on  certain  definite  lines  or  surfaces, 
which  vary  with  the  direction  of  the  visual  axis,  and  to  which  the  name 
of  horopter,  or  point-horopter,  has  been  given.  For  most  eyes  when 


THE  SENSES  767 

The  question  therefore  arises,  How  is  it  that  we  do  not 
see  these  double  images  ?  This  is  one  of  the  difficulties  of 
the  theory  of  identical  points.  The  following  is  a  partial 
explanation  :  (i)  The  images  of  objects  in  the  portion  of 
the  field  most  distinctly  seen,  that  is,  the  portion  in  the 
immediate  neighbourhood  of  the  intersection  of  the  visual 
lines,  or  the  part  to  which  the  gaze  is  directed,  are  formed 
on  identical  points ;  and  by  rapid  movements  the  eyes  fix 
successively  different  parts  of  the  field  of  view.  (2)  Vision 
grows  less  distinct  as  we  pass  out  from  the  centre  of  the 
retina,  and  we  are  accustomed  to  neglect  the  blurred  peri- 
pheral images  in  comparison  with  those  formed  on  the 
fovea.  (3)  When  the  images  of  an  object  do  not  fall  on 
identical  points,  one  of  the  points  on  which  they  do  fall  may 
be  occupied  with  the  images  of  other  objects,  some  of  which 
may  be  so  boldly  marked  as  to  enter  into  conflict  with  the 
extra  image  and  to  suppress  it.  (4)  And  lastly,  the  physio- 
logical '  identical  point '  is  not  a  geometrical  point,  but  an 
area  which  increases  in  size  in  the  more  peripheral  zones  of 
the  retina,  so  that  images  which  lie  wholly  or  in  chief  part 
within  two  corresponding  areas  practically  coincide. 

Stereoscopic  Vision. — Although  the  retinal  image  is  a  projection 
of  external  objects  on  a  surface,  we  perceive  not  only  the  length  and 
breadth,  but  also  the  depth  or  solidity  of  the  things  we  look  at. 
When  we  look  directly  at  the  front  of  a  building,  the  impression  as 
to  its  form  is  the  same  whether  one  or  both  eyes  be  used,  although 
with  a  single  eye  its  distance  cannot  be  judged  so  accurately.  But 
when  we  view  the  building  from  such  a  :positipn  that  one  of  the 
corners  is  visible,  we  obtain  a  more  correct  impression  of  its  depth 
with  the  two  eyes.  This  is  partly  due  to  the  fact  that  to  fix  points  at 
different  distances  from  the  eyes  the  visual  lines  must  be  made  to 
converge  more  or  less,  and  of  the  amount  of  this  convergence  we  are 
conscious  through  the  contraction  of  the  muscles  which  regulate  it. 
But  there  is  another  element  involved.  When  the  two  eyes  look  at 

directed  to  the  horizon,  that  is,  with  the  visual  axes  parallel,  the  horopter 
is  practically  the  horizontal  plane  of  the  ground,  so  that  all  objects 
within  the  field  of  vision,  and  resting  on  the  ground,  fall  upon  corre- 
sponding points,  and  are  seen  single.  When  the  eyes  are  directed  to  a 
point  at  such  a  distance  that  the  lines  of  vision  are  sensibly  convergent, 
the  horopter  consists  (i)  of  a  straight  line  drawn  through  the  fixing-point 
and  at  right  angles  to  the  plane  passing  through  the  fixing-point  and  the 
two  visual  lines  (visual  plane)  ;  (2)  of  a  circle  passing  through  the  fixing- 
point  and  the  nodal  points  of  the  two  eyes  (the  famous  horopteric  circle 
of  Miiller). 


768 


1  MANUAL  OF  PHYSIOLOGY 


a  uniformly-coloured  plane  surface,  the  retinal  image  is  precisely  the 
same  in  both.  But  when  the  two  eyes  are  directed  to  a  solid  object, 
say  a  book:  lying  on  a  table,  the  picture  formed  on  the  left  retina 
differs  slightly  from  that  formed  on  the  right,  for  the  left  eye  sees 
more  of  the  left  side  of  the  book,  and  the  right  eye  more  of  the  right 
side. 

That  there  is  a  close  connection  between  uniformity  of  retinal  images 
and  impression  of  a  plane  surface  on  the  one  hand,  and  difference  of 
retinal  images  and  impression  of  solidity  on  the  other,  is  proved  by  the 
facts  of  stereoscopy.  It  is  evident  that  if  an  exact  picture  of  the 
solid  object  as  it  is  seen  by  each  eye  can  be  thrown  on  the  retina,  the 
impression  produced  will  be  the  same,  whether  these  images  are  really 
formed  by  the  object  or  not.  Now,  two  such  pictures  can  be  pro- 
duced with  a  near  approach  to  accuracy  by  photographing  the  object 
from  the  point  of  view  of  each  eye.  It  only  remains  to  cast  the 

image  of  each  picture  on  the  cor- 
responding retina,  while  the  eyes 
are  converged  to  the  same  extent 
as  would  be  the  case  if  they  were 
viewing  the  actual  object.  This  is 
accomplished  by  means  of  a  stereo- 
scope (Fig.  277). 

It  is  found  that  the  resultant  im- 
pression is  that  of  the  solid  object. 
It  is  impossible  to  reconcile  this 
with  the  doctrine  of  strictly  identical 
points.  A  pair  of  identical  pictures 
gives  with  the  stereoscope  not  the 
impression  of  a. solid,  but  of  a  plane 
surface.  If  the  relative  position  of 
any  two  points  differs  in  the  two 
pictures,  the  blended  picture  has  a 
corresponding  point  in  high  or  low 
relief.  So  great  is  the  delicacy  of 
this  test  that  a  good  and  a  bad 
banknote  will  not  blend  under  the 
stereoscope  to  a  flat  surface,  and  the 
method  may  be  actually  used  for 
the  detection  of  forgery. 

When  the  pictures  are  inter- 
changed in  the  stereoscope  so  that 
the  image  which  ought  to  be  formed 
on  the  right  retina  falls  on  the  left, 

and  that  which  is  intended  for  the  left  eye  falls  on  the  right,  what 
were  projections  before  become  hollows,  and  what  were  hollows  stand 
out  in  relief.  The  pseudoscope  of  Wheatstone  is  an  arrangement  by 
which  each  eye  sees  an  object  by  reflection,  so  that  the  images  which 
would  be  formed  on  the  two  retinae,  if  the  object  were  looked  at 
directly,  are  interchanged,  with  the  same  reversal  of  our  judgments  of 
relief. 


FIG.   277.— BREWSTER'S   STEREO- 
SCOPE. 

P  and  ""  are  prisms,  with  their  re- 
fracting angles  turned  towards  each 
other.  The  prisms  refract  the  rays 
coming  from  the  points  c,  -j  of  the 
pictures  ab  and  ud  so  that  they 
appear  to  come  from  a  single  point  q. 
Similarly,  the  points  a  and  a  appear 
to  be  situated  at  /,  and  the  points  b 
and  0  at  <t>. 


THE  SENSES  769 

^ 

Visual  Judgments. — We  say  judgments  of  relief;  for  what  we  call 
seeing  is  essentially  an  act  that  involves  intellectual  processes.  As 
the  retina  is  anatomically  and  developmentally  a  projection  of  the 
brain  pushed  out  to  catch  the  waves  of  light  which  beat  in  upon  the 
organism  from  every  side,  so  physiologically  retina,  optic  nerve  and 
visual  nervous  centre  are  bound  together  in  an  indissoluble  chain. 
We  cannot  say  that  the  retina  sees,  we  cannot  say  that  the  optic 
nerve  sees — the  optic  nerve  in  itself  is  blind — we  cannot  say  that  the 
visual  centre  sees.  The  ethereal  waves  falling  on  the  retina  set  up 
impulses  in  it  which  ascend  the  optic  nerve ;  certain  portions  of  the 
brain  are  stirred  to  action,  and  the  resulting  sensations  of  light 
springing  up,  we  know  not  where,  are  elaborated,  we  know  not  how 
(by  processes  of  which  we  have  not  the  faintest  guess),  into  the  per- 
ception of  what  we  call  external  objects — trees,  houses,  men,  parts  of 
our  own  bodies,  and  into  judgments  of  the  relations  of  these  things 
among  themselves,  of  their  distance  and  movements. 

A  child  learns  to  see,  as  it  learns  to  speak,  by  a  process,  often  un- 
conscious or  subconscious,  of  '  putting  two  and  two  together.'  The 
musical  sounds  united  and  terminated  by  noises  which  make  up  the 
spoken  word  '  apple '  are  gradually  associated  in  its  mind  with  the 
visual  sensation  of  a  red  or  green  object,  the  tactile  sensation  of  a 
smooth  and  round  object,  and  the  gustatory  and  olfactory  sensations 
which  we  call  the  taste  or  flavour  of  an  apple.  And  as  it  is  by 
experience  that  the  child  learns  to  label  this  bundle  of  sensations 
with  a  spoken,  and  afterwards  with  a  written  name,  so  it  is  by  experience 
that  it  learns  to  group  the  single  sensations  together,  and  to  make  the 
induction  that  if  the  hand  be  stretched  out  to  a  certain  distance  and 
in  a  certain  direction  (i.e.,  if  various  muscular  movements,  also 
associated  with  sensations,  be  made),  the  tactile  sensation  of  grasping 
a  smooth,  round  body  will  be  felt,  and  that  if  the  further  muscular 
movements  involved  in  conveying  it  to  the  mouth  be  carried  out,  a 
sensation  agreeable  to  the  youthful  palate  will  follow.  At  length  the 
child  comes  to  believe,  and,  unless  he  happens  to  be  specially  in- 
structed, carries  his  belief  with  him  to  his  grave,  that  when  he  looks 
at  an  apple  he  sees  a  round,  smooth,  tolerably  hard  body,  of  definite 
size  and  colour ;  while  in  reality  all  that  the  sense  of  sight  can  inform 
him  of  is  the  difference  in  the  intensity  and  colour  of  the  light  falling 
on  his  retina  when  he  turns  his  head  in  a  particular  direction. 

An  interesting  illustration  of  the  role  of  experience  in  shaping  our 
visual  judgments  is  found  in  the  sensations  of  persons  born  blind  and 
relieved  in  after-life  by  operation.  A  boy  between  thirteen  and  four- 
teen years  of  age,  operated  on  by  Cheselden,  thought  all  the  objects 
he  looked  at  touched  his  eyes.  '  He  forgot  which  was  the  dog  and 
which  the  cat,  but  catching  the  cat  (which  he  knew  by  feeling),  he 
looked  at  her  steadfastly  and  said,  "  So,  Puss,  I  shall  know  you  another 
time."  Pictures  seemed  to' him  only  parti-coloured  planes;  but  all 
at  once,  two  months  after  the  operation,  he  discovered  they  repre- 
sented solids.'  Nunnely,  perhaps  remembering  the  dictum  of 
Diderot,  true  as  it  is  in  the  main,  though  tinged  with  the  exaggera- 
tion of  the  Encyclopedic,  that  '  to  prepare  and  interrogate  a  person 

49 


770  A  MANUAL  OF  PHYSIOLOGY 

born  blind  would  not  have  been  an  occupation  unworthy  of  the 
united  talents  of  Newton,  Des  Cartes,  Locke  and  Leibnitz,'  made  an 
elaborate  investigation  in  the  case  of  a  boy  nine  years  old,  on  whom 
he  operated  for  congenital  cataract  of  both  eyes,  and,  what  is  of 
special  importance,  instituted  a  set  of  careful  experiments  and 
interrogations  before  the  operation  so  as  to  gain  data  for  comparison. 
Objects  (cubes  and  spheres)  which  before  the  operation  he  could 
easily  recognise  by  touch  were  shown  him  afterwards,  but  although 
'  he  could  at  once  perceive  a  difference  in  their  shapes,  he  could  not 

In  A  the  opaque  body  o 
is  in  the  plane  of  the  pupil. 
The  position  of  the  shadow 
relatively  to  the  bright  field 
is  not  altered  when  the 
illuminating  pencil  is 
focussed  at  F  instead  of 
P.  In  B  the  opaque  body 
is  in  front  of  the  plane 
of  the  pupil.  When  P  is 
lowered  to  P',  the  shadow 
moves  towards  the  upper 
edge  of  the  bright  field, 
and  appears  to  move  down- 
wards in  the  visual  field. 
When  P  is  raised,  the 
shadow  moves  towards  the 
lower  edge  of  the  bright 
field,  and  appears  to  move 
upwards.  In  C  the  opaque 
body  is  behind  the  plane 
of  the  pupil.  When  P  is 
moved  downwards  to  P', 
the  shadow  moves  towards 
the  lower  edge  of  the  bright 
field,  and  appears  to  the 
person  under  observation 
to  move  upwards,  and  vice- 
versa  when  P  is  moved 
upwards.  The  farther  the 
opaque  body  is  from  the 
pupil,  the  greater  is  the 
apparent  movement,  or 
parallax,  of  its  shadow  for 
a  given  movement  of  the 
source  of  light. 
•• 

FIG.  278. 

in  the  least  say  which  was  the  cube  and  which  the  sphere.'  It  took 
several  days,  and  the  objects  had  to  be  placed  many  times  in  his 
hands  before  he  could  tell  them  by  the  eye.  '  He  said  everything 
touched  his  eyes,  and  walked  most  carefully  about,  with  his  hands 
held  out  before  him  to  prevent  things  hurting  his  eyes  by  touching 
them.' 

The  apparent  size  and  form  of  an  object  is  intimately 
related  to  the  size,  form,  and  sharpness  of  its  image  on  the 
retina.  We  are,  therefore,  able  to  discriminate  with  great 
precision  the  unstimuiated  from  the  excited  portions  of  that 


THE  SENSES  771 

membrane,  especially  in  the  fovea  centralis,  and  also  the 
degree  of  excitation  of  neighbouring  excited  parts.  But 
instead  of  localizing  the  image  on  the  retina  as  we  localize 
on  the  skin  the  pressure  of  an  object  in  contact  with  it, 
we  project  the  retinal  image  into  space,  and  see  everything 
outside  the  eye.  In  vision,  in  fact,  we  have  no  conception 
of  the  existence  of  either  retina  or  retinal  image ;  and  even 
the  shadows  of  objects  within  the  eye  are  referred  to  points 
outside  it.  Thus,  for  instance,  an  opacity  or  a  foreign  body 
in  any  of  the  refractive  media — and  no  eye  is  entirely  free 
from  relatively  opaque  spots — can  be  detected,  and  its 
position  determined  by  the  shadow  which  it  casts  on  the 
retina  when  the  eye  is  examined  by  a  pencil  of  light  pro- 
ceeding from  a  very  small  point.  Let  a  diaphragm  with  a 
small  hole  in  it  be  placed  in  front  of  the  eye  at  such  a 
distance  that  a  pencil  diverging  from  the  hole  will  pass 
through  the  vitreous  humour  as  a  parallel  beam,  equal  in 
cross-section  to  the  pupil  (Fig.  278),  and  let  the  aperture 
be  illuminated  by  focussing  on  it  the  light  of  a  lamp  placed 
behind  a  screen.  Opaque  bodies  in  the  vitreous  humour  will 
cast  shadows  equal  in  area  to  themselves.  The  shadows  of 
opacities  in  the  lens  and  in  front  of  it  will  be  somewhat 
larger  than  the  bodies  themselves,  since  the  latter  intercept 
rays  which  are  still  diverging  ;  but  since  the  greater  part  of 
the  refraction  of  the  eye  occurs  at  the  anterior  surface  of 
the  cornea,  it  is  only  the  shadows  of  objects  on  the  front  of 
the  cornea,  such  as  drops  of  mucus,  which  will  be  much 
magnified.  Fig.  278  shows  diagrammatically  how  the  shadows 
shift  their  position  within  the  bright  field  when  the  direction 
of  the  illuminating  beam  is  altered.  Generally  opacities  in 
the  vitreous  humour  are  movable,  in  the  lens  not. 

Purkinje's  Figures. — As  was  first  pointed  out  by  Purkinje, 
the  shadows  of  the  bloodvessels  in  the  retina  itself,  and  even 
of  the  corpuscles  circulating  in  them,  although  neglected  in 
ordinary  vision,  may  be  recognised  under  suitable  conditions, 
a  conclusive  proof  that  the  sensitive  layer  must  lie  behind 
the  vessels  (p.  773). 

If  a  beam  of  sunlight  is  concentrated  on  the  sclerotic  as  far  as 
possible  from  the  margin  of  the  cornea,  and  the  eye  directed  to  a 

49—2 


772 


A  MANUAL  OF  PHYSIOLOGY 


dark  ground,  the  network  of  retinal  bloodvessels  will  stand  out  on  it 
Another  method  is  to  look  at  a  dark  ground  while  a  lighted  candle, 

held  at  one  side  of 
the  eye  at  a  distance 
from  the  visual  line,  is 
moved  slightly  to  and 
fro.  In  the  first 
method,  a  point  of  the 
sclerotic  behind  the 
lens  is  illuminated, 
and  rays  passing  from 
it  across  the  interior 
of  the  eyeball  in  every 
direction  cast  shadows 
of  the  vessels  of  the 
on  its  sensitive 
In  the  second 

FIG.  279. -METHOD  OF  RENDERING  TITE  RETINAL  *"w"1"d'  the,  ima%e  of 

BLOODVESSELS  VISIBLE  BY  CONCENTRATING  A  tne  name  termed  on 

BEAM  OF  LIGHT  ON  THE  SCLEROTIC.  the  retina  by  rays  fall- 

From  the  brightly  illuminated  point  of  the  sclerotic,  ing  obliquely  through 

<z,  rays  issue,  and  a  shadow  of  a  vessel,  v,  is  cast  at  a'. 


retina 
layer. 


It  is  referred  to  an  external  point  a"  in  the  direction  of 
the  straight  line  joining  a  with  the  nodal  point.  When 
the  light  is  shifted  so  as  to  be  focussed  at  b,  the  shadow 
cast  at  b'  is  referred  to  b",  i.e.,  it  appears  to  move  in  the 
same  direction  as  the  illuminated  point  of  the  sclerotic. 


the  pupil  becomes  in 
the  general  darkness 
itself  a  source  of  light, 
by  interrupting  the 
rays  from  which  the 
retinal  vessels  form  shadows. 
The  distance  of  the  sensitive 
from  the  vascular  layer  may 
be  approximately  calculated 
by  measuring  the  amount  by 
which  the  shadows  change 
their  position,  when  the  posi- 
tion of  the  illuminated  point 
of  the  sclerotic  is  altered. 
The  nearer  a  vessel  lies  to 
the  sensitive  layer,  the  smaller 
must  be  the  angle  through 
which  the  apparent  position 
of  its  shadow  moves  for  a 
given  movement  of  the  spot 
of  light.  In  this  way  it  has 
been  calculated  that  the  sensi- 
tive layer  is  about  0-2  to 
0-3  mm.  behind  the  stratum 
which  contains  the  blood- 
vessels. This  corresponds 
sufficiently  well  with  the  posi- 
tion of  the  layer  of  rods  and  cones,  which  all  otber  evidence  shows  to 
be  the  portion  of  the  retina  actually  stimulated  by  light.  The  shadows 


FIG.  280. — METHOD  OF  RENDERING  THE 
BLOODVESSELS  OF  THE  RETINA  VISIBLE 
BY  OBLIQUE  ILLUMINATION  THROUGH 
THE  CORNEA. 

Light  from  a  candle  at  a  illuminates  a',  and 
rays  proceeding  from  a'  cast  a  shadow  of  the 
bloodvessel  v  at  a",  which  is  referred  to  a"'. 
When  a  is  moved  to  b,  the  shadow  on  the 
retina  moves  to  b",  and  the  shadow  in  the 
visual  field  of  the  illuminated  eye.  to  b'". 


THE  SENSES  773 

of  the  blood-corpuscles  in  the  retinal  vessels  may  be  rendered  visible 
by  looking  at  a  bright  and  uniformly  illuminated  ground,  like  the  milk 
glass  shade  of  a  lamp  or  the  blue  sky,  and  moving  the  slightly  separated 
fingers  or  a  perforated  card  rapidly  before  the  eye.  From  the  rate 
of  their  apparent  movement,  Vierordt  calculated  the  velocity  of  the 
blood  in  the  retinal  capillaries  at  0-5  to  0-9  mm.  per  second.  One 
reason  why  the  shadows  of  these  intra-retinal  structures  do  not 
appear  in  ordinary  vision  seems  to  be  their  small  size.  The  retinal 
vessels  are  in  reality  only  vascular  threads ;  the  thickest  branch  of 
the  central  vein  is  not  -^  mm.  in  diameter.  The  apex  of  the  cone 
of  complete  shadow  (umbra)  cast  by  a  disc  of  this  size,  at  a  distance 
of  20  mm.  from  a  pupil  4  mm.  wide,  would  lie  only  i  mm.  behind 
the  disc — that  is  to  say,  the  umbra  of  the  retinal  vessels  would  not 
reach  the  layer  of  the  rods  and  cones  at  all,  and  only  the  penumbra, 
or  region  of  relative  darkness,  would  fall  upon  it. 

When  the  eyes,  after  being  closed  for  some  time,  are  suddenly 
opened,  the  branches  of  the  retinal  vessels  may  be  seen  for  a 
moment  This  is  especially  the  case  after  sleep  ;  and  a  good  view 
of  the  phenomenon  may  be  obtained  by  looking  at  a  white  pillow  or 
the  ceiling  immediately  on  awaking.  If  the  eyes  are  kept  open  for 
a  few  seconds,  the  branching  pattern  fades  away ;  if  they  are  only 
allowed  to  remain  open  for  an  instant,  it  may  be  seen  many  times  in 
succession. 

Relation  of  the  Rods  and  Cones  to  Vision. — We  have  more 
than  once  referred  to  the  rods  and  cones  as  the  sensitive 
layer  of  the  retina.  It  is  now  necessary  to  develop  a  little 
more  the  evidence  in  favour  of  this  statement.  And  at 
the  outset,  since  the  sensitive  layer  has  been  shown  to  lie 
behind  the  plane  of  the  retinal  bloodvessels,  the  only  com- 
petitors of  the  rods  and  cones  are  the  external  nuclear 
layer  and  the  pigmented  epithelium.  The  nuclear  layer 
may  be  at  once  excluded,  because  in  the  fovea  centralis, 
where  vision  is  most  distinct,  it  becomes  very  thin  and 
inconspicuous. 

The  layer  of  pigmented  hexagonal  cells,  or  at  least  their 
pigment,  cannot  be  essential  to  vision,  for  albino  rats, 
rabbits  and  men,  in  whose  eyes  pigment  is  absent,  can  see. 
In  man  and  most  mammals  there  are  cones,  but  no  rods  in 
the  yellow  spot  and  fovea  centralis  ;  the  relative  proportion 
of  rods  increases  as  we  pass  out  from  the  fovea  towards 
the  ora  serrata.  But  this  does  not  enable  us  to  analyze 
the  bacillary  layer  into  sensitive  cones  and  non-sensitive 
rods,  for  on  the  rim  of  the  retina,  which  is  still  sensitive  to 
light,  there  are  only  rods ;  in  the  bat  and  mole  there  are  no 


774  A  MANUAL  OF  PHYSIOLOGY 

cones  in  the  yellow  spot,  in  the  rabbit  very  few.  Reptiles 
possess  only  cones  over  the  whole  retinal  surface,  and  birds, 
true  to  their  reptilian  affinities,  have  everywhere  more  cones 
than  rods,  as  have  also  fishes. 

One  of  the  most  serious  difficulties  in  the  way  of  under- 
standing how  a  ray  of  light  can  set  up  an  excitation  in  a  rod 
or  cone  is  the  transparency  of  these  structures.  An  absolutely 
transparent  substance — that  is,  a  substance  which  would 
allow  light  to  traverse  it  without  the  least  absorption — 
would,  after  the  passage  of  a  ray,  remain  in  precisely  the 
same  state  as  before  ;  its  condition  could  not  be  altered  by 
the  passage  of  the  light  unless  some  of  the  energy  of  the 
ethereal  vibrations  was  transferred  to  it.  But  an  absolutely 
transparent  body  does  not  exist  in  Nature  ;  and  it  is  not 
necessary  to  suppose  that  all  the  energy  required  to  stimulate 
the  end-organs  of  the  optic  nerve  comes  from  the  luminous 
vibrations.  These  may,  and  probably  do,  act  by  setting 
free  energy  stored  up  in  the  retina,  just  as  the  touch  of  a 
child's  hand  could  be  made  to  fire  a  mine,  or  launch  a  ship, 
or  flood  a  province.  Some  have  looked  upon  the  transverse 
lamellae  into  which  the  outer  members  of  the  rods  and  cones 
can  be  made  to  split  as  an  arrangement  for  reflecting  back 
the  light  to  the  inner  members,  and  have  compared  them  to 
^—  a  pile  of  plates  of  glass,  which,  transparent  as  it  is,  is  a  most 
efficient  reflector.  It  is  even  possible,  although  here  we  are 
already  treading  the  thin  air  of  pure  speculation,  that  the 
light  may  be  polarized  in  the  process  of  reflection,  and  that 
the  rods  and  cones  may  be  less  transparent  to  light  polarized 
in  certain  planes  than  to  unpolarized  light. 

As  to  the  nature  of  the  transformation  undergone  by  the 
ethereal  vibrations  in  the  rods  and  cones,  various  theories 
have  been  formed.  Some  have  supposed  that  the  absorbed 
light-waves  are  transformed  into  long  heat-waves,  and  that 
Jl^  the  endings  of  the  optic  nerve  are  thus  excited  by  thermal 
stimuli.  This  hypothesis  has  so  little  evidence  in  its  favour 
that  it  is  perhaps  an  unjustifiable  waste  of  time  even  to 
mention  it.  It  is  ruled  out  of  court  by  the  mere  fact  that 
the  long  radiations  of  the  ultra  red,  filtered  from  luminous 
rays  by  being  passed  through  a  solution  of  iodine,  and 


THE  SENSES  775 

focussed  on  the  eye  by  a  lens  of  rock-salt,  produce  not  the 
slightest  sensation  of  light,  although  they  are  by  no  means 
all  absorbed  in  their  passage  through  the  dioptric  media. 
Again,  it  has  been  suggested  that  the  energy  of  the  waves  of 
light  is  first  transformed  into  electrical  energy,  and  that  the 
visual  stimulus  is  really  electrical.  In  support  of  this  view  it 
has  been  urged  that  light  undoubtedly  causes  (p.  624)  an 
electrical  change  in  the  retina  and  optic  nerve.  But,  as  has 
more  than  once  been  pointed  out,  an  electrical  change  is  the 
token  and  accompaniment  of  the  activity  of  the  excitable 
tissues  in  general ;  and  all  that  the  currents  of  action  of  the 
retina  show  is  that  light  excites  the  retina — a  proposition 
which  nobody  who  can  see  requires  an  objective  proof  of, 
and  which  does  not  carry  us  very  far  towards  the  solution  of 
the  problem  how  that  excitation  is  brought  about.  Lastly, 
there  is  the  photo-chemical  theory,  which  owes  its  origin  to 
the  discovery,  or  rather  re-discovery,  of  the  famous  visual 
purple  or  rhodopsin  by  Boll,  and  its  present  form  to  the 
investigations  and  arguments  of  Kiihne.  Though  it  has  not 
fulfilled  all  the  hopes  excited  in  sanguine  minds,  and  has 
not  explained,  or  even  lessened,  the  mystery  of  vision,  the 
discovery  of  the  visual  purple  is  in  itself  so  interesting  and 
so  suggestive  as  a  basis  for  future  work,  that  a  short  account 
of  the  properties  of  the  substance  cannot  be  omitted  here.  ?vi 

Visual  Purple. — If  the  eye  of  a  frog  or 
rabbit,  which  has  been  kept  in  the  dark,  be 
cut  out  in  a  dimly-lighted  chamber  or  in  a 
chamber  illuminated  only  by  red  light,  and 
the  retina  removed,  it  is  seen,  when  viewed 
in  ordinary  light,  to  be  of  a  beautiful  red  or 
purple  colour.     Exposed  to  bright  light,  the 
colour  soon  fades,  passing  through  red  and 
orange    to    yellow,  and   then    disappearing 
altogether.     The  yellow  colour  is  due  to  the 
formation  of  another  pigment,  visual  yellow ; 
the   preceding  stages  are  due  to  the  inter-     FIG.  281.— OPTOGRAM. 
mixture  of   this  visual  yellow  with  the  un-      part  Of  retina  of  rabbit, 
changed  visual  purple   in   different  proper-   the  eye  of  which  had  been  ^_    ^^ 
tions.     With  the  microscope  it  may  be  seen  ~}  %J?J%$*&  M 
that  the  pigment  is  entirely  confined  to  the  strips  of  black  paper, 
outer  segment  of  the  rods,  where  it  exists  in 

most  vertebrate  animals.  It  may  be  extracted  by  a  watery  solution 
of  bile-salts,  and  the  properties  of  the  pigment  in  solution  are  very 


776  A  MANUAL  OF  PHYSIOLOGY 

much  the  same  as  its  properties  in  situ;  light  bleaches  the  solution 
as  it  does  the  retina.  Examined  with  the  spectroscope,  the  solution 
shows  no  definite  bands,  but  only  a  general  absorption,  which  is  very 
slight  in  the  red,  and  reaches  its  maximum  in  the  yellowish-green. 
In  accordance  with  this,  it  is  found  that  of  all  kinds  of  monochro- 
matic light  the  yellowish  green  rays  bleach  the  purple  most  rapidly, 
the  red  rays  most  slowly. 

If  a  portion  of  the  retina  is  kept  dark  while  the  rest  is  exposed  to 
light,  only  the  latter  portion  is  bleached.  And  when  the  image  of  an 
object  possessing  well-marked  contrasts  of  light  and  shadow  (e.g.,  a 
glass  plate  with  strips  of  black  paper  pasted  on  it  at  intervals,  or  a 
window  with  dark  bars)  is  allowed  to  fall  on  an  eye  otherwise  pro 
tected  from  light,  the  pattern  of  the  object  is  picked  out  on  the  retina 
in  purple  and  white  A  veritable  photograph  or  '  optogram '  may  thus 
be  formed  even  on  the  retina  of  a  living  rabbit ;  and  if  the  eye  be 
rapidly  excised,  the  picture  may  be  '  fixed '  by  a  solution  of  alum, 
and  thus  rendered  permanent. 

These  facts  certainly  suggest  that  light  falling  on  the 
retina  may  cause  in  some  sensitive  substance  or  substances 
chemical  changes,  the  products  of  which  stimulate  the  end- 
ings of  the  optic  nerve,  and  set  up  the  impulses  that  result 
in  visual  sensations. 

The  visual  purple  cannot  itself  be  such  a  substance,  for  it  is 
absent  from  the  cones  of  all  animals  and  the  rods  of  some. 
Frogs  and  rabbits  can  undoubtedly  see  at  a  time  when, 
by  continued  exposure  to  bright  sunlight,  the  purple  must 
have  been  completely  bleached.  And  although  the  absence 
of  the  pigment  in  the  eye  of  the  bat  might  seem  to  afford 
a  ready  explanation  of  the  proverbial  '  blindness '  of  that 
animal,  such  a  hasty  deduction  would  be  at  once  corrected 
by  the  fact  that  birds  with  as  sharp  vision  as  the  pigeon  are 
equally  devoid  of  visual  purple.  The  pigmented  retinal 
epithelium  is  undoubtedly  sensitive  to  light,  and  has  im- 
portant relations  to  the  formation  of  the  visual  purple. 
When  the  eye  is  exposed  to  light,  the  pigmented  cells  push 
down  processes  between  the  rods.  In  the  dark  they  draw 
them  back  again,  so  that  while  it  is  easy  to  separate  the 
retina  without  the  pigmented  layer  from  the  eye  of  an 
animal  kept  in  the  dark,  the  hexagonal  epithelium  always 
adheres  to  a  retina  which  has  shortly  before  death  been  acted 
upon  by  light.  The  precise  meaning  of  these  changes  of 
form  in  the  pigmented  cells  is  unknown.  Some  have  sup- 


THE  SENSES  777 

posed  that  they  alone  contain  the  essential  visual  substance, 
and  that,  altering  their  volume  under  the  stimulus  of  light, 
they  press  upon  the  cones,  and  in  this  way  set  up  impulses 
in  the  optic  nerve.     By  others  it  has  been  plausibly  urged 
that  in  bright  light  the  processes  that  stretch  in  among  the 
rods  serve  as  insulators  to  confine  the  excitation  by  pre- 
venting the  lateral  passage   of  scattered  light  from    one 
element  to  another.     But  it  may  be  that  the  movements  are 
related  rather  to  the  formation  of  photo-chemical  substances 
to  act  as  stimuli  to  the  end-organs  of  the  optic  nerve.     And 
the  pigmented  epithelium  is  known  to  be  concerned  in  the 
regeneration  of  the  visual  purple.    When  a  frog  is  curarized, 
oedema  occurs  between  the  retina  and  the  choroid,  so  that 
the   former  membrane  is  separated  from    the   hexagonal 
epithelium.     If  the  frog  is  now  exposed  to  sunlight  till  the 
visual  purple  is  bleached,  and  the  retina  then  taken  out  and 
placed  in  the  dark,  no  regeneration  of  the  pigment  takes 
place.     When  the  same  experiment  is  repeated  on  a  non- 
curarized  frog,  the  visual  purple  is  restored  in  the  dark,  and 
may  be  seen  under  the  microscope  in  the  rods.     The  only 
difference  in  the  two  experiments  is  that  in  the  latter  the 
pigmented   epithelium   adheres  to  the  retina,  and  it  must 
therefore  have  a  hand  in  the  regeneration  of  the  pigment. 
Even  the  visual  purple  of  a  retina  from  which  the  epithelium 
has  been  detached  will,  after  being  bleached,  be  restored  if 
the  retina  is  simply  laid   again   on  the   epithelial  surface. 
And  it  does  not  seem  to  be  the  black  pigment  of  the  hex- 
agonal cells  which  is  the  agent  in  this  restoration,  for  it  takes 
place  in  the  pigment-free  retinae  of  albino  rabbits  or  rats. 
Even  a  retina  isolated  from  the  pigmented  epithelium,  and 
then  bleached,  may,  to  a  certain  extent,  develop  new  visual 
purple  in  the  dark.     This  is  even  true  when  it  has  been  kept 
in  the  dark  in  a  saturated  solution  of  sodium  chloride,  and 
is  then,  after  washing  with  normal  saline,  bleached  by  light. 
Here  the  regeneration  of  the  pigment  cannot  be  the  result 
of  vital  processes,  but  must  be  due  to  chemical  changes  in 
products  formed  from  the  original  pigment  by  the  action  of 
light.     No  such  regeneration  takes  place  in  a  retina  which, 
after  having  been  bleached  in  situ,  is  removed  without  the 


778  A  MANUAL  OF  PHYSIOLOGY 

pigmented  epithelium  and  placed  in  the  dark  ;  and  the  only 
probable  explanation  of  the  difference  is  that  in  this  case 
the  photo-chemical  substances  from  which  visual  purple  can 
be  formed  have  been  absorbed  into  the  circulation,  and  have 
so  escaped. 

The  inner  segments  of  the  cones  of  certain  animals  (birds,  reptiles, 
and  some  fishes)  contain  globules  of  various  colours,  ranging  over 
almost  the  whole  spectrum,  and  including,  besides,  the  non-spectral 
colour,  purple.  The  globules  are  composed  chiefly  of  fat  with  the 
pigments  (chromophanes,  as  they  have  been  called)  dissolved  in  it. 
The  function  of  these  globules  is  unknown.  They  cannot  be  con- 
cerned in  colour  vision,  or,  at  least,  they  cannot  be  essential  to  it, 
for  in  the  human  retina  they  do  not  exist. 

The  yellow  pigment  of  the  macula  lutea  does  not  belong  to  the 
layer  of  rods  and  cones  ;  it  only  exists  in  the  external  molecular 
layer  and  the  layers  in  front  of  it ;  in  the  fovea  centralis  it  is  absent. 

The  Blind  Spot. — The  fibres  of  the  optic  nerve  are  insensible 
to  light ;  light  only  stimulates  them  through  their  end-organs. 
This  can  be  proved  by  directing  by  means  of  an  ophthalmo- 
scope a  beam  of  light  upon  the  optic  disc,  where  the  true 
retinal  layers  do  not  exist.  The  person  experimented  on 
has  no  sensation  of  light  when  the  beam  falls  entirely  upon 
the  disc ;  when  its  direction  is  shifted  so  that  it  impinges 
upon  any  other  portion  of  the  retina,  a  sensation  of  light  is 
at  once  experienced.  The  blind  spot  is  not  recognised  in 
ordinary  vision,  for  (i)  the  two  optic  discs  do  not  corre- 
spond. The  left  disc  has  its  corresponding  points  on  a 
sensitive  part  of  the  right  retina,  and  the  right  disc  on  a 
sensitive  part  of  the  left  retina ;  and  the  consequence  is  that 
in  binocular  vision  the  objects  whose  images  are  formed  on 
the  corresponding  points  fill  up  the  blind  spots.  (2)  The 
optic  disc  does  not  lie  in  the  line  of  direct,  and  therefore 
distinct,  vision.  The  eye  is  constantly  moving  so  as  to  bring 
the  surrounding  objects  successively  on  the  fovea  centralis ; 
and  the  gap  which  the  blind  spot  makes  in  the  visual  field 
of  a  single  eye  is  thus  more  easily  neglected.  In  any  case 
we  ought  not  to  see  it  as  a  dark  spot,  for  darkness  is  only 
associated  with  the  absence  of  excitation  in  parts  of  the 
retina  capable  of  being  excited  by  light.  There  is  no  more 
reason  why  the  optic  discs  should  appear  dark  than  there  is 
for  our  having  a  sensation  of  darkness  behind  us  when  we 


THE  SENSES  779 

are  looking  straight  in  front.  And  since  the  experience  of 
our  other  senses,  the  sense  of  touch,  for  example,  tells  us 
that  the  objects  we  look  at  do  not  in  general  have  a  gap  in 
the  position  corresponding  to  the  part  of  the  image  that 
falls  on  the  blind  spot,  we  see,  so  to  speak,  across  the  spot. 

By  Marietta's  experiment,  however,  the  existence  of  the  blind 
spot  can  not  only  be  demonstrated,  but  its  size  determined  and  its 
boundaries  mapped  out.  Let  the  left  eye  be  closed,  and  fix  with  the 
right  the  small  cross ;  then,  if  the  eye  be  moved  towards  or  away 
from  the  paper,  keeping  the  cross  fixed  all  the  time,  a  position  will 


FIG.  282. — MARIOTTE'S  EXPERIMENT. 

be  found  in  which  the  white  disc  disappears  altogether.  In  this 
position  its  image  falls  on  the  blind  spot.  (See  Practical  Exercises, 
Figs.  296,  297.) 

Time  necessary  for  Excitation  of  the  Retina  by  Light — Fusion 
of  Stimuli. — Whatever  the  exact  nature  of  retinal  excitation  may  be, 
it  is  called  forth  by  exceedingly  slight  stimuli.  A  lightning  flash, 

although  it  may  last  only th  of  a  second,  lasts  long  enough 

1,000,000 

to  be  seen.     A  beam  of  light  thrown  from  a  rotating  mirror  on  the 

eye  stimulates  when  it  only  acts  for  5 th  of  a  second.     The 

8,000,000 

minimum  stimulus  in  the  form  of  green  light  corresponds,  as  we  have 
already  seen  (p.  573),  to  a  quantity  of  work  equivalent  to  no  more 

than  -7-  x  — 15  gramme-degree,  i.e.  — ^  gramme-millimetre,  or  — 7 

milligramme-millimetre,  which  is  the  work   done   by  -  — th 

'   10,000,000 

of  a  milligramme  in  falling  through  a  millimetre ;  and  it  cannot  be 
doubted  that  a  portion  even  of  this  Lilliputian  bombardment  is 
wasted  as  heat.  So  quickly,  too,  is  the  stimulus  followed  by  the 
response  that  no  latent  period  has  as  yet  ever  been  measured.  It  is 
certain,  however,  that  there  is  a  latent  period,  as  surely  as  there  is  a 
latent  period  in  the  excitation  of  a  naked  nerve-trunk,  although  this 
also  has  never  been  experimentally  detected.  The  analogies,  in  fact, 
between  a  muscular  contraction  and  a  retinal  excitation  are  numerous 
and  close.  Like  the  muscle,  the  retina  seems  to  possess  a  store  of 
explosive  material  which  the  stimulus  serves  only  to  fire  off.  The 
retina,  like  the  muscle,  is  exhausted  by  its  activity,  and  recovers 


780  A  MANUAL  OF  PHYSIOLOGY 

during  rest.  Like  the  muscle  curve,  the  curve  of  retinal  excitation 
rises  not  abruptly,  but  with  a  measurable  slowness  to  its  height,  and 
when  stimulation  is  stopped,  takes  a  sensible  time  to  fall  again. 
With  comparatively  slow  intermittent  stimuli  the  retinal,  like  the 
muscle  curve,  flickers  up  and  down.  When  the  rate  of  stimulation 
is  increased,  the  steady  contraction  of  the  tetanized  muscle  is 
analogous  to  the  fusion  of  the  individual  stimuli  by  the  tetanized 
retina  (or  retino- cerebral  apparatus)  into  a  continuous  sensation  of 
light.  But  the  maximum  retinal  excitation  which  a  stimulus  of  given 
strength  can  call  forth  depends  much  more  closely  upon  the  time 
during  which  the  stimulus  acts  than  the  maximum  contraction  does 
upon  the  length  of  the  muscular  stimulus. 

As  the  strength  of  the  light  increases  in  geometrical  progression, 
the  time  during  which  it  must  act  in  order  to  produce  its  maximum 
effect  decreases  approximately  in  arithmetical  progression  (Exner). 
For  light  of  moderate  intensity  this  time  is  about  J  second.  As 
soon  as  the  stimulus  of  light  is  withdrawn  the  retinal  excitation 
begins  to  sink  ;  while  a  stimulated  muscle  need  not  even  commence 
its  contraction  till  the  stimulus  has  ceased  to  act.  The  result  is,  that 
while  a  muscle  in  complete  tetanus  reaches  a  degree  of  contraction 
as  great  as,  or  greater  than,  that  produced  by  any  one  of  a  series  of 
stimuli  acting  alone,  the  retinal  excitation,  as  measured  by  the 
resultant  sensation,  is  always  less  when  a  succession  of  similar  stimuli 
are  fused  than  when  any  one  of  the  stimuli  is  allowed  to  produce  its 
maximum  effect. 

If  the  time  of  each  stimulus  is  equal  to  the  interval  during  which 
there  is  no  stimulation,  the  sensation,  when  complete  fusion  has  been 
reached,  is  the  same  as  would  be  produced  by  a  constant  light  of 
half  the  strength  employed.  And,  in  general,  if  m  be  the  pro- 
portion of  the  time  during  which  the  eye  is  stimulated  by  a  light  of 
intensity  /,  and  n  the  proportion  of  the  time  during  which  it  is  not 
stimulated,  the  resultant  impression  is  the  same  as  that  which  would 

be  produced  by  an  uninterrupted  light  of  intensity  I \  L    This 

is  Talbot's  law,  which  may  be  expressed  without  the  aid  of  symbols 
thus :  When  a  light  of  given  intensity  is 
allowed  to  act  on  the  eye  at  intervals  so  short 
that  the  impressions  are  completely  fused,  the 
resultant  sensation  is  independent  of  the  abso- 
lute length  of  each  flash,  and  is  proportional 
only  to  the  fraction  of  the  whole  time  which  is 
occupied  by  flashes  and  to  the  intensity  of  the 
light.  Talbot's  law  may  be  readily  demon- 
strated by  means  of  a  rotating  disc  with 
alternate  white  and  black  sectors  (Fig.  283), 

FIG.  283  —Disc  FOR  DE-  so  arranaed  that  the  same  proportion  of  the 
MONSTRATING  TALBOT'S  circumference  of  each  of  the  three  concentric 
LAW.  zones  is  black. 

When  the  rotation  is  sufficiently  rapid  to 

give  complete  fusion  (say  20  to  30  times  a  second),  the  whole  disc 


THE  SENSES  781 

appears  equally  bright.  However  much  the  rate  of  rotation  is  now  in- 
creased, no  further  change  occurs.  It  has  been  shown  that  even  for 
stimuli  as  short  as  the  -girethnroth  of  a  second,  repeated  at  intervals 
of  -y^g-th  second,  Talbot's  law  holds  good.  So  that  not  only  does  a 
flash  so  inconceivably  brief  affect  the  retina,  but  it  sets  up  changes 
which  last  for  a  measurable  time. 

Colour  Vision. — Besides  differences  in  the  distance,  size, 
shape,  and  brightness  of  objects,  the  eye  recognises  differ- 
ences in  their  colour;  and  we  have  now  to  consider  the 
physical  and  physiological  differences  on  which  these  depend. 

Colours  may  differ  from  each  other — (i)  In  tone  or  hue,  e.g.,  red, 
yellow,  green.  (2)  In  degree  of  saturation  or  fulness  or  purity ',  i.e., 
in  the  degree  in  which  they  are  free  from  admixture  with  white  light ; 
e.g.,  a  '  pale '  or  '  light '  blue  is  a  blue  mixed  with  much  white  light, 
a  'deep'  or  'full*  blue  with  little  or  none.  (3)  In  brightness  or  in- 
tensity, i.e.,  in  the  amount  of  the  light  coming  from  unit  area  of  the 
coloured  object.  Thus,  a  '  dark '  red  cloth  sends  comparatively  little 
light  to  the  eye,  a  '  bright '  red  cloth  sends  a  great  deal. 

When  a  beam  of  sunlight  falls  into  the  eye,  a  sensation  of 
'  white  light '  results.  When  a  prism  is  placed  before  the  eye, 
the  sensation  is  entirely  different ;  we  see  a  spectrum  running 
up  from  red  through  green  to  violet,  with  a  multitude  of 
intermediate  shades.  What,  then,  has  happened  ?  Physi- 
cally, nothing  more  has  taken  place  than  a  rearrangement 
of  the  rays  in  the  beam  of  white  light.  A  few  of  them  may 
have  been  lost  by  reflection,  but  upon  the  whole  the  beam 
is  made  up  of  exactly  the  same  constituents  as  before ;  only 
the  rays  are  now  arranged  in  the  precise  order  of  their 
refrangibility,  the  more  refrangible,  which  are  also  those 
of  shortest  wave-length,  being  displaced  more  towards  the 
base  of  the  prism  than  the  longer  and  less  refrangible  rays. 
Instead  of  the  long  and  short  rays  falling  together  on  the 
same  elements  of  the  retina,  as  they  did  in  the  absence  of 
the  prism,  they  now  fall,  if  proper  precautions  have  been 
taken  to  secure  a  pure  spectrum,  in  regular  order  from 
one  side  to  the  other  of  the  portion  of  retina  on  which 
the  image  is  formed.  The  physical  condition,  then,  of  our 
sensations  of  the  prismatic  colours  is,  that  rays  of  approxi- 
mately the  same  wave-length  should  fall  unmixed  with  other 
rays  upon  the  retinal  elements.  Rays  of  a  wave-length  of 
to  650,-^  give  the  sensation  of  red ;  from 


782  A  MANUAL  OF  PHYSIOLOGY 

to  59°TinnP  the  sensation  of  orange;  from  43OdW to 
the  sensation  of  violet,  and  so  on.  When  rays  of  all  these 
wave-lengths  fall  together,  in  the  proportions  in  which  they 
are  present  in  sunlight,  upon  the  same  part  of  the  retina, 
the  resultant  physiological  effect  is  very  different ;  we  are 
no  longer  able  to  distinguish  red,  blue,  green,  etc. ;  we 
receive  the  single  sensation  of  white  light.  The  sensation 
is  a  simple  one  ;  in  consciousness  we  have  no  hint  that  it 
has  a  multiple  physical  cause. 

But  we  find  further  that  it  is  not  necessary  for  the 
sensation  of  white  light  that  waves  of  every  length  present 
in  the  solar  spectrum  should  be  mixed.  If  rays  of  wave- 
length 675T^  (which  acting  alone  produce  the  sensation 
of  red)  be  mixed  in  certain  proportions,  i.e.,  be  allowed  to 
fall  on  the  same  part  of  the  retina,  with  rays  of  wave-length 
4g6TTj^nr  which  give  the  sensation  of  bluish-green),  the  re- 
sultant sensation  is  also  that  of  white  light.  And  an  indefi- 
nite number  of  sets  can  be  combined,  two  and  two,  so  as  to 
give  the  same  sensation  of  white.  Such  colours  are  called 
complementary.  The  following  are  pairs  of  complementary 
colours  : 

Red  and  bluish-green.  Yellow  and  indigo-blue. 

Orange  and  cyan-blue.  Greenish-yellow  and  violet. 

The  green  of  the  spectrum  has  no  simple  complementary 
colour ;  purple,  a  mixture  of  red  and  violet,  may  be  considered 
complementary  to  it.  Suppose  now  that  one  of  a  pair  of 
complementary  colours  is  added  to  the  other  in  greater 
intensity  than  is  required  to  give  white,  the  resultant  sensa- 
tion is  a  colour  which  has  a  certain  amount  of  resemblance 
both  to  white  and  to  the  colour  present  in  excess.  Thus,  it 
the  two  colours  are  orange  and  blue,  and  the  blue  is  present 
in  greater  intensity  than  is  necessary  to  give  white,  the 
resultant  colour  is  a  whitish  or  pale  blue,  or,  to  use  the 
technical  phrase,  an  unsaturated  blue.  The  more  nearly 
the  intensity  of  the  blue  rays  in  the  mixed  light  approaches 
the  proportion  necessary  to  give  white,  the  less  saturated  is 
the  resultant  colour ;  the  greater  the  excess  of  blue,  the  more 
nearly  does  the  resultant  sensation  approach  that  of  the 
saturated  blue  of  the  spectrum.  But  any  non-saturated 


THE  SENSES 


783 


spectral  colour  produced  by  the  mixture  of  two  comple- 
mentary  colours  may  be  equally  well  produced  by  the 
mixture  of  the  corresponding  spectral  colour  with  a  certain 
quantity  of  ordinary  white  light.  And  it  is  found  that  when 
two  spectral  colours  which  are  not  complementary  are  mixed 
together  the  resultant  is  not  white,  but  a  colour  which  may 
be  matched  by  some  spectral  colour  lying  between  the  two, 
plus  a  larger  or  smaller  quantity  of  ordinary  white  light 
From  all  this  it  follows  that  the  retina  may  be  excited 
an  infinite  number  of  different  physical  stimuli,  and  yet  the 
resultant  sensation  may  be  the  same.  This  leads  straight 
to  the  conclusion  that  somewhere  or  other  in  the  retino- 

The  '  colour  triangle '  is 
a  graphic  method  of  re- 
presenting various  facts  in 
colour  mixture :  (i)  On  the 
curve  the  spectral  colours 
are  arranged  at  such  dis- 
tances that  the  angle  con- 
tained between  straight 
lines  drawn  from  the  point 
W  and  intersecting  the 
curve  at  the  positions  cor- 
responding to  any  two 
colours  is  proportional  to 
their  difference  in  tone. 
FIG.  284. — COLOUR  TRIANGLE.  (2)  The  distance  of  any 

(In  the  description  the  point  marked   '  White '  is       point  on  the  curve  from 
referred  to  as  W. )  W  is  proportional  to  the 

stimulation  intensity  of  the 

colour  corresponding  to  it.  (If  the  stimulation  intensities  of  all  the  colours  be  represented 
by  proportional  weights  lying  at  the  corresponding  points  on  the  curve,  W  will  be  the 
centre  of  gravity  of  the  system.)  (3)  The  position  of  a  colour  produced  by  the  mixture 
of  any  pair  of  spectral  colours  is  found  by  joining  the  corresponding  points  by  a 
straight  line.  The  mixed  colour  lies  on  this  line  at  distances  from  the  two  points 
inversely  proportional  to  the  stimulation  intensity  of  the  two  colours,  i.e.,  it  lies  in  the 
centre  of  gravity  of  the  weights  representing  the  two  colours.  (4)  It  is  a  particular 
case  of  (3)  that  the  complementary  colours  are  situated  at  the  points  where  straight 
lines  drawn  through  W  intersect  the  curve,  since  W  is  the  centre  of  gravity  correspond- 
ing to  a  pair  of  colours  only  when  it  lies  on  the  straight  line  joining  them.  The  non- 
spectral purple  is  represented  by  a  broken  line. 

cerebral  apparatus  simplification,  or  synthesis,  of  impressions 
must  take  place ;  and  we  have  to  inquire  what  the  simplest 
assumptions  are  which  will  explain  all  the  phenomena. 
Now,  it  is  not  possible,  from  two  spectral  colours  alone,  to 
produce  a  sensation  corresponding  to  any  of  the  others. 
By  mixing  three  standard  spectral  colours,  however,  in 
various  proportions,  we  can  produce  not  only  the  sensation 
of  white  light,  but  that  of  every  colour  of  the  spectrum. 
The  simplest  assumption  we  can  make,  then,  is  that  there 


784  A  MANUAL  OF  PHYSIOLOGY 

are  three  standard  sensations,  and  that  either  the  retina 
itself  can  respond  by  no  more  than  three  distinct  modes  of 
excitation  to  the  multiplex  stimuli  of  the  luminous  vibra- 
tions, or  that  complex  impulses  set  up  in  the  retina  are 
reduced  to  simplicity  because  the  central  apparatus  is 
capable  of  responding  by  only  three  distinct  kinds  of  sensa- 
tion. Which  three  sensations  we  select  as  fundamental  or 
primary  is,  to  a  certain  extent,  arbitrary.  Pick  chooses  red, 
green,  and  blue ;  most  commonly  red,  green,  and  violet  are 
accepted  as  the  primary  colours.  The  theory  which  best 
explains  the  facts,  and  has  been  most  widely  accepted,  is 
that  of  Young,  generally  called,  on  account  of  its  adoption 
and  extension  by  Helmholtz,  the  Young-Helmlioltz  theory. 
It  assumes  that  in  the  retina,  or  in  the  retino-cerebral 


nge,  Green. 


FIG.  285.— DIAGRAM  OF  CURVES  OF  EXCITABILITY  OF  THE  THREE  FIBRE- 
GROUPS. 

apparatus,  there  are  three  kinds  of  elements — (i)  'red 
fibres/  which  are  chiefly  excited  by  light  of  comparatively 
long  wave-length  (red),  to  a  less  extent  by  light  of  medium 
wave-length  (green),  and  to  a  still  less  extent  by  the  shortest 
visible  waves  (violet) ;  (2)  '  green  fibres,'  mainly  excited  by 
medium,  but  also  to  a  certain  extent  by  long  and  short 
waves;  (3)  'violet  fibres,'  chiefly  affected  by  the  short 
vibrations,  less  by  the  medium,  and  still  less  by  the  long 
waves.  The  curves  in  Figs.  285  and  286  illustrate  these 
relations.  It  must  be  carefully  remembered  that  here  the 
word  'fibre'  is  merely  a  convenient  term  to  avoid  some 
such  cumbrous  phrase  as  '  physiological  unit.'  There  is  no 
ground  for  believing  that  an  anatomical  distinction  of  three 
*  fibre '  groups  can  be  made  in  retina,  optic  nerve,  or  brain. 

This   assumption    explains    the    phenomena    of    colour- 
mixture  to  which  we  have  referred  above.     When  all  the 


THE  SENSES 


785 


rays  of  the  spectrum  act  upon  the  retina  together,  the  three 
groups  of  fibres  are  about  equally  excited,  and  this  equal 
excitation  may  be  supposed  to  be  the  condition  of  the  sensa- 
tion of  white  light.  When  the  green  of  the  spectrum  alone 
falls  on  the  retina,  the  green  fibres  are  strongly  excited,  the 
other  two  groups  only  slightly ;  this  is  the  relation  between 
the  amount  of  excitation  in  the  three  groups  which  is 
associated  with  a  sensation  of  spectral  green.  When  two 
complementary  colours,  such  as  red  and  bluish-green,  fall 
together  on  the  same  portion  of  the  retina,  the  three  fibre 
groups  are  excited  in  the  relative  proportions  associated 
with  the  sensation  of  white  light. 


FIG.  286. — CURVES   OF   EXCITABILITY   OF    PRIMARY    SENSATION'S   FROM 

OBSERVATIONS  ON  COLOUR  MIXTURES  (KoNio). 
The  numbers  give  wave-lengths  of  the  spectrum  in  millionths  of  a  mm. 

'  When  the  retina  is  stimulated  by  a  succession  of  short  flashes  of 
white  light,  that  are  not  completely  fused  (as  when  the  image  of  a 
flame  is  looked  at  in  a  small  revolving  mirror,  or  the  flame  directly 
viewed  through  a  slit  in  a  revolving  disc),  the  proportion  between 
the  amount  of  excitation  in  the  three  hypothetical  groups  of  fibres  is 
not  constant,  and  the  resultant  sensation  is  not  that  of  white  light. 
For  any  given  intensity  of  light,  violet  preponderates  with  a  certain 
duration  of  each  stimulus;  with  a  shorter  duration,  green;  with  a  still 
shorter  duration,  red.'*  These  phenomena  are  especially  seen  at  the 
edges  of  the  image,  which  is  surrounded  by  coloured  fringes.  The 
explanation  is  that  the  sensation  does  not  reach  its  maximum  at  the 
same  time  for  different  colours,  the  excitation  in  the  red  fibres  in- 
creasing at  first  more  rapidly  than  in  the  green,  and  in  the  green  more 
rapidly  than  in  the  violet.  When  the  flashes  are  completely  fused, 
*  Stewart,  *  Proc.  Roy.  Soc.  Edin.,'  1888,  p.  441. 

50 


786  A  MANUAL  OF  PHYSIOLOGY 

the  colour  phenomena  disappear,  and  the  resultant  impression  is 
white,  because  now  the  maximum  excitation  for  the  given  intensity 
of  light  and  duration  of  each  stimulus  is  steadily  maintained. 

It  is  a  point  of  great  theoretical  interest  that  on  the  Young-Helm- 
holtz  theory  the  pure  spectral  colours,  although  physically  saturated, 
ought  not  to  be  physiologically  saturated,  since  they  all  excite  the 
three  fibre  groups,  although  in  different  degrees.  Now,  it  is  found 
that  this  is  really  the  case.  If,  for  example,  we  look  first  at  the  bluish- 
green  and  then  at  the  red  of  the  spectrum,  the  sensation  of  red  is 
fuller  or  more  saturated  than  if  we  had  looked  at  the  red  directly. 
Similarly,  if  we  look  first  at  a  small  bluish-green  square  on  a  black 
ground,  and  then  at  a  red  ground,  we  see  a  more  fully  saturated 
square  in  the  middle  of  the  latter.  The  explanation,  on  the  Young- 
Helmholtz  theory,  is  that  the  'green'  fibres  being  tired  before  the 
eye  is  turned  upon  the  red,  the  latter  colour  no  longer  affects  them, 
or  affects  them  less  than  it  would  otherwise  do,  and  therefore  the 
excitation  is  almost  entirely  confined  to  the  red  fibres  in  the  area 
fatigued  for  green.  This  brings  us  to  the  subject  of  retinal  fatigue, 
and  the  related  phenomena  of  after-images  and  contrast. 

After-images. — We  have  seen  that  the  retinal  excitation 
always  takes  time  to  die  away  after  the  stimulus  is  removed. 
If  a  white  object  is  looked  at,  especially  when  the  eye  is 
fresh,  for  a  time  not  long  enough  to  cause  fatigue,  and  the 
eye  is  then  closed,  an  image  of  the  object  remains  for  a  short 
time,  diminishing  in  brightness  at  first  rapidly,  then  more 
slowly.  This  is  a  positive  after-image,  and  by  careful  ob- 
servation it  may,  under  certain  conditions,  be  seen  that  the 
positive  after-image  of  a  white  object,  of  a  slit  illuminated 
by  sunlight,  for  example,  undergoes  changes  of  colour  as  it 
fades,  passing  through  greenish-blue,  indigo,  violet,  or  rose, 
to  dirty  orange.  On  the  Young- Helmholtz  theory  this  is 
explained  by  the  supposition  that  the  excitation  does  not 
decline  with  the  same  rapidity  in  the  three  hypothetical  fibre 
groups.  If  the  object  is  looked  at  for  a  longer  time,  or  if 
the  eye  is  fatigued,  a  dark  or  negative  image  may  be  seen 
upon  the  faintly-illuminated  ground  of  the  closed  eyes ;  but 
negative  after-images  may  be  more  easily  obtained  when  the 
eye,  after  being  made  to  fix  a  small  white  object  on  a  black 
ground,  is  suddenly  turned  upon  a  white  or  neutral  tint 
surface. 

Here  the  portion  of  the  retina  on  which  the  image  of  the  object 
is  formed  may  be  assumed  to  be  more  or  less  fatigued.  And  this 
fatigue  will  extend  to  all  three  kinds  of  fibres ;  so  that  white  light  of 


THE  SENSES  787 

a  given  intensity  will  now  cause  less  excitation  in  this  part  than  in 
the  rest  of  the  retina.  It  is  easy  to  understand  that  the  negative 
after-image  of  a  coloured  object  will  be  seen,  upon  a  white  ground, 
in  the  complementary  colour,  for  the  fibres  chiefly  excited  by  the 
latter  will  have  been  least  fatigued.  The  negative  after-images  seen 
when  the  eye,  after  receiving  the  positive  impression,  is  turned  upon 
a  coloured  ground,  vary  with  the  colour  of  the  object  and  ground  in 
a  manner  which  can  be  readily  explained  as  due  to  fatigue  of  one  or 
other  fibre  group. 

The  phenomena  of  negative  after-images  are  often  included 
together  as  examples  of  successive  contrast,  the  name  implying 
mutual  influence  of  the  portions  of  the  retina  successively  stimu- 
lated. We  have  now  to  consider  simultaneous  contrast,  often  spoken 
of  simply  as  contrast. 

Contrast. — A  small  white  disc  in  a  black  field  appears  whiter, 
and  a  small  black  disc  in  a  white  field  darker,  than  a  large  surface 
of  exactly  the  same  objective  brightness.  A  disc  with  alternate 
sectors  of  white  and  black,  so  arranged  that  the  proportion  of  white 
to  black  increases  in  each  zone  from  centre  to  circumference,  when 
set  in  rotation,  ought,  by  Talbot's  law,  to  show  sharply  marked  and 
uniform  rings,  of  which  each  is  brighter  than  that  internal  to  it. 
But  each  zone  appears  brightest  at  its  inner  edge,  where  it  borders 
on  a  zone  darker  than  itself,  and  darkest  at  its  outer  edge,  where  it 
borders  on  a  brighter  zone.  The  most  natural  explanation  of  this  is 
that  in  the  neighbourhood  of  an  excited  area  of  the  retina,  as  well  as 
within  the  area  itself,  the  excitability  is  diminished ;  and  the  same 
explanation  holds  for  the  contrast  phenomena  of  coloured  objects. 
A  small  piece  of  grey  paper,  e.g.,  is  placed  on  a  green  sheet,  and 
the  whole  covered  with  translucent  tracing-paper.  The  grey  patch 
appears  in  the  complementary  colour  of  the  ground,  viz.,  rose-red 
(Meyer).  Here  we  may  suppose  that  the  fatigue  of  the  group  of 
fibres  chiefly  excited  by  the  ground  colour  spreads  into  the  portion 
of  the  retina  occupied  by  the  image  of  the  grey  paper ;  the  white 
light  coming  from  the  latter,  therefore,  excites  mainly  the  fibres  which 
give  the  sensation  of  the  complementary  colour. 

The  curious  phenomenon  of  coloured  shadows  is  also  an  illus- 
tration of  contrast.  They  may  be  produced  in  various  ways.  For 
example,  when  a  lamp  is  lit  in  a  room  in  the  twilight,  before  it  has 
yet  grown  too  dark,  the  shadows  cast  by  opaque  objects  on  a  white 
window-blind  are  coloured  blue.  The  yellow  light  of  the  lamp 
overpowers  the  feeble  daylight  which  passes  through  the  blind,  and 
the  general  ground  is  yellowish :  but  wherever  a  shadow  is  thrown 
it  appears  of  a  bluish  tint  in  contrast  to  the  yellow  ground.  Here 
the  only  illumination  the  eye  receives  from  the  region  occupied  by 
the  shadow  is  the  feeble  daylight.  Falling  upon  an  area  in  which 
the  fibres  chiefly  excited  by  yellow  rays  are  more  or  less  fatigued,  it 
causes  a  sensation  of  the  complementary  colour.  As  darkness  comes 
on,  the  shadows  become  black,  for  now  practically  no  light  at  all 
comes  from  them. 

Helmholtz  looked  upon  simultaneous  contrast  as  a  result  of  false 

50 — 2 


788  A  MANUAL  OF  PHYSIOLOGY 

judgment,  and  not  a  change  of  excitability  in  parts  of  the  retina 
bordering  on  the  actually  excited  parts.  For  the  sake  of  perspective, 
it  will  be  worth  while  to  apply  this  theory  by  way  of  illustrating  it,  to 
the  explanation  of  the  case  of  contrast  we  have  just  been  consider- 
ing, from  the  other  point  of  view  in  Meyer's  experiment.  Helm 
holtz's  explanation  of  this  experiment  is  as  follows  :  When  a  coloured 
surface  is  covered  with  translucent  paper,  the  latter  appears  as  a 
coloured  covering  spread  over  the  field.  The  mind  does  not  recog- 
nise that  at  the  grey  patch  there  is  any  breach  of  continuity  in  this 
covering ;  it  is  therefore  assumed  that  the  greenish  veil  extends  over 
this  spot  too.  Now,  the  grey  seen  through  the  translucent  white 
paper  is  objectively  white  —  i.e.,  sends  to  the  eye  the  vibrations 
which  together  would  give  the  sensation  of  white  light.  But  with  a 
green  veil  in  front  of  it,  this  could  only  happen  if  the  really  grey 
patch  was  of  the  colour  complementary  to  green  —  that  is,  rose- 
red.  The  mind,  therefore,  judges  falsely  that  the  patch  is  red. 
Hering  has  severely  criticised  this  theory  of  Helmholtz  as  to  false 
judgments;  and  the  weight  of  evidence  certainly  seems  to  be  in 
favour  of  the  view  that  simultaneous,  like  successive,  contrast  is  due 
to  the  influence  of  one  portion  of  the  retina,  or  retino-cerebral 
apparatus,  on  another. 

The  Young-Helmholtz  theory  of  colour  vision  has  not 
met  with  universal  acceptance.  The  most  important  rival 
theory  is  that  of  Hering,  who  takes  his  stand  upon  the  fact 
that  certain  sensations  of  light  (red,  yellow,  green,  blue, 
white,  black)  do  appear  to  us  to  be  fundamentally  distinct 
from  each  other,  while  all  the  rest  are  obviously  mixtures 
of  these.  Accepting  these  six  as  primary  sensations,  he 
assumes  the  existence  in  the  visual  nervous  apparatus  of 
substances  of  three  different  kinds,  which  may  be  called  the 
black-white,  the  green-red,  and  the  blue-yellow.  Like  all 
other  constituents  of  the  body,  these  substances  are  broken 
down  and  built  up  again — in  other  words,  undergo  disassi- 
milation  and  assimilation,  destructive  and  constructive 
metabolism.  The  sensations  of  black,  of  green,  and  of  blue 
he  supposes  to  be  associated  with  the  constructive,  and  the 
sensations  of  white,  of  red,  and  of  yellow  with  the  destruc- 
tive, processes  in  the  three  substances.  The  black-white 
substance  is  used  up  under  the  influence  of  all  the  rays  of 
the  spectrum,  but  in  different  degrees ;  the  smaller  the 
quantity  of  light  falling  on  the  retina,  the  more  rapidly  is  it 
restored,  and  the  more  intense  is  the  sensation  of  black. 
The  green-red  substance  is  built  up  by  green  rays,  broken 


THE  SENSES  789 

down  by  red.  The  blue-yellow  substance  is  destroyed  by 
yellow  rays,  restored  by  blue.  When  any  of  the  visual 
substances  are  consumed  at  one  part  of  the  retina,  they  are 
supposed  to  be  more  rapidly  built  up  in  the  surrounding 
parts,  and  in  this  way  many  of  the  phenomena  of  contrast 
receive  an  easy  and  natural  explanation. 

Sensibility  of  Different  Parts  of  the  Retina. — The  perception  of 
colours,  like  the  perception  of  white  light,  is  not  equally  distinct 
over  the  whole  retina.  We  have  repeatedly  had  occasion  to  refer  to 
the  fovea  centralis  as  the  region  of  most  distinct  vision  ;  but  it 
would  be  a  mistake  to  suppose  that  it  is  therefore  necessarily  more 
sensitive  than  the  rest  of  the  retina.  As  a  matter  of  fact,  when  the 
minimum  intensity  of  white  light  which  will  cause  an  impression  at  all 
is  determined  for  each  portion  of  the  retina,  it  is  found  that  the  fovea 
centralis  requires  a  somewhat  stronger  stimulus  than  the  zone  im- 
mediately surrounding  it.  But,  with  this  exception,  the  sensibility 
of  the  retina  diminishes  steadily  from  centre  to  periphery,  both  for 
white  and  for  coloured  light.  Konig  has,  indeed,  upheld  the  para- 
doxical view  that  the  fovea  is  absolutely  blind  for  blue  rays,  support- 
ing this  assertion  by  two  main  experiments  :  (a)  that  when  a  number 
of  feebly  illuminated  blue  points  are  looked  at,  those  that  fall  on  the 
fovea  disappear ;  (b}  that  when  the  moon  is  examined  through  a 
blue  glass,  her  image  is  blotted  out  as  soon  as  it  falls  on  the  fovea. 
But,  as  Gad  has  pointed  out,  the  moon's  image  is  of  such  dimen- 
sions that  it  would  lie  well  within  the  fovea,  and  there  ought,  there- 
fore, to  be  no  difficulty  in  getting  it  to  disappear  if  Konig's  theory 
were  true.  Yet  Konig  himself  admits  that  his  second  experiment  is 
difficult,  and  succeeds  only  under  special  conditions.  Hering,  too, 
seems  to  have  shattered  Konig's  first  argument  by  showing  that  the 
disappearance  of  the  weakly  illuminated  blue  points  is  only  an  illus- 
tration of  the  phenomenon  known  as  Maxwell's  spot,  a  dark-blue  or 
almost  black  blot,  seen  in  the  visual  field  when  the  eye,  after  being 
kept  closed  for  a  short  time,  is  directed  to  a  surface  illuminated 
by  a  weak  blue  light.  It  is  due  to  the  absorption  of  blue  light  by 
the  pigment  of  the  yellow  spot,  and  stands  out  as  a  rose-coloured 
disc  when  a  source  of  white  light  is  looked  at  through  a  solution  of 
chrome  alum,  since  all  the  light  which  the  chrome  alum  permits  to 
pass  is  absorbed  by  the  macula  lutea,  except  the  red  rays.  Hering, 
indeed,  asserts  that  the  fovea  is  the  most  sensitive  part  of  the  retina 
for  colours,  in  opposition  to  Charpentier,  who  finds  it  slightly 
less  sensitive  for  blue  than  the  zone  immediately  external  to  it. 
When  the  eye  is  fixed  and  the  visual  field — that  is,  the  whole  space 
from  which  light  can  reach  the  retina  in  the  given  position — or,  what 
comes  to  the  same  thing,  the  projection  of  the  visual  field  on  the 
retina  by  straight  lines  passing  through  the  nodal  point,  explored  by 
means  of  a  perimeter  (Fig.  287),  it  is  found  that,  under  ordinary 
conditions,  a  white  object  is  seen  over  a  wider  field  than  any  coloured 
object,  a  blue  object  over  a  wider  field  than  a  red,  and  a  red  over  a 


790 


A  MANUAL  OF  PHYSIOLOGY 


wider  field  than  a  green  object.  The  exact  shape,  as  well  as  size,  of 
the  visual  field  also  differs  somewhat  for  different  colours.  And 
although  it  has  been  shown  by  Aubert  and  others  that  monochro- 
matic light  of  sufficient 
intensity  can  be  per- 
ceived over  the  whole 
retina,  yet  it  may  be 
said  that  the  retinal  rim 
is  even  then  relatively 
and,  under  ordinary 
conditions,  absolutely 
colour-blind.  This  and 
other  facts  have  given 
rise  to  the  theory  that 
the  rods,  which  are 
alone  present  at  the  ora 
serrata,  have  for  their 
function  the  mere  per- 
ception of  luminous  im- 
pressions as  such,  with- 
out any  distinction  of 
quality  or  of  colour. 
The  cones  are  supposed 
on  this  theory  to  be 
PERIMETER  more  highly  developed 
than  the  rods,  their 
function  being  con- 
nected especially  with 
the  perception  of  colour. 
And  there  are,  indeed,  certain  histological  facts  that  favour  the  view 
that  the  cones  are  a  more  highly  developed  form  of  the  rods. 


FIG.    287.  —  PRIESTLEY    SMITH'S 
(JUNG,  HEIDELBERG). 

K,  rest  for  chin  ;  O,  position  of  eye  ;  Ob,  object, 
white  or  coloured,  which  slides  on  the  graduated  arc 
B  ;  f,  point  fixed  by  the  eye. 


This  brings  us  to  the  subject  of  colour-blindness  proper, 
a  phenomenon  of  the  greatest  interest  in  its  theoretical  as 
well  as  in  its  practical  bearings. 

Colour-blindness.  —  A  considerable  number  of  persons 
(about  4  per  cent  of  all  males,  but  only  one-tenth  of  this 
proportion  of  females)  are  deficient  in  the  power  of  distin- 
guishing between  certain  colours.  They  are  said  to  be 
colour-blind  ;  but  the  term  must  not  be  taken  to  signify  that 
they  are  absolutely  devoid  of  colour-sensations.  A  very 
small  minority  of  the  colour-blind  appear  to  have  but  one 
sensation  of  colour ;  a  few  confuse  green  with  blue  ;  the 
great  majority  are  unable  to  distinguish  between  red  and 
green.  The  condition  will  be  most  easily  understood  by 
considering  some  of  the  extraordinary  mistakes  which  may 


THE  SENSES 


79 1 


be  made  by  the  colour-blind  without  necessarily  leading 
them  to  suspect  that  there  is  anything  abnormal  in  their 
vision.  Thus,  to  quote  the  words  of  a  distinguished  writer 
on  this  subject,  himself  a  sufferer  from  the  deficiency: 
'  A  naval  officer  purchases  red  breeches  to  match  his  blue 
uniform ;  a  tailor  repairs  a  black  article  of  dress  with 
crimson  cloth  ;  a  painter  colours  trees  red,  the  sky  pink, 
and  human  cheeks  blue.'  The  shoemaker,  Harris,  the  dis- 


FIG.  288.— PERIMETRIC  CHART. 

Obtained  with  the  perimeter  shown  in  Fig.  287.    The  numbers  represent  degrees 
of  the  visual  field  measured  on  the  graduated  arc  of  the  perimeter. 

coverer  of  colour-blindness,  picked  up  a  stocking,  and  was 
surprised  to  hear  other  people  describe  it  as  a  red  stocking ; 
it  seemed  to  him  only  a  stocking.  The  celebrated  Dalton 
was  twenty-six  years  of  age  before  he  knew  that  he  was 
colour-blind.  He  matched  samples  of  red,  pink,  orange, 
and  brown  silk  with  green  of  different  shades ;  blue  both 
with  pink  and  with  violet ;  lilac  with  grey. 


792  A  MANUAL  OF  PHYSIOLOGY 


When  the  condition  of  vision  in  the  great  majority  of  the  colour- 
blind is  tested  by  means  of  the  spectrum,  it  is  found  that  they  fall 
into  two  classes  :  (i)  A  class  (of  green-blind)  by  whom  the  whole  of 
the  spectrum  from  red  to  yellow  is  described  as  yellow  of  different 
degrees  of  brightness  (intensity)  ;  the  green  appears  as  a  pale  yellow 
with  a  grey  or  white  band  in  its  midst  ;  while  the  violet  end  is  seen 
as  different  shades  of  blue.  (2)  A  class  (of  red-blind)  whose  whole 
spectrum,  from  red  to  green,  is  seen  as  green  of  different  intensities, 
the  extreme  red  being  entirely  invisible.  The  violet  end  is  blue,  as 
in  (i),  and  there  is  a  band  of  white  or  grey  near  the  blue  end  of  the 
green. 

The  brightest  part  of  the  spectrum  to  a  normal  eye,  and  also  to  a 
green-blind  eye,  is  the  yellow  ;  to  a  red-blind  person  it  is  the  green. 

This  may  perhaps  explain  the  terms  which  the  colour-blind  employ 
in  describing  their  less  refrangible  spectral  colours.  '  To  the  green- 
blind  red  and  yellow  are  the  same  colour,  but  the  yellow  being  the 
brighter,  he  looks  on  red  as  degraded  or  darkened  yellow.  On  the 
other  hand,  to  the  red-blind  green  is  brighter  than  yellow  or  orange, 
and  these  appear  as  degraded  green.'* 

Sir  John  Herschell  explained  Dalton's  peculiarity  of  vision  on  the 
hypothesis  that  he  only  possessed  two,  instead  of  three,  primary 
sensations. 

On  the  Young-Helmholtz  theory,  the  missing  sensation  is  supposed 
to  be  either  red  or  green.  At  the  intersection  of  the  curves  that 
represent  the  violet  and  green  sensations  (Figs.  285,  286),  the  red- 
blind  individual  will  see  what  he  describes  as  white  —  viz.,  the  sensa- 
tion produced  by  the  stimulation  of  the  only  two  fibre-groups  he 
possesses.  Similarly,  at  the  intersection  of  the  red  and  violet  curves, 
the  green-blind  person  will  see  what  is  white  to  him. 

On  Hering's  theory  the  colour-blind  possess  the  blue-yellow,  but 
lack  the  green-red,  visual  substance.  So  that  on  this  theory  there 
should  be  no  difference  between  red-blindness  and  green-blindness. 
But  v.  Kries,  in  a  study  of  twenty  cases  of  congenital  partial  colour- 
blindness, brings  forward  strong  evidence  that  the  red-green  blind 
can  be  divided,  as  regards  the  comparison  of  red  (lithium)  and 
orange  (sodium)  light,  into  two  sharply-separated  groups  —  a  result 
which  is  emphatically  in  favour  of  the  Young-Helmholtz  theory,  and 
against  the  theory  of  Hering.  It  is,  however,  equally  difficult  to 
reconcile  some  of  the  phenomena  of  colour-blindness  produced  by 
disease  (atrophy  of  the  optic  nerve)  or  by  abuse  of  tobacco  with  the 
Young-Helmholtz  theory,  for  in  some  of  these  cases  the  only  colour 
seen  in  the  spectrum  is  blue,  the  rest  is  white  ;  and  the  theory  does 
not  provide  for  the  production  of  the  sensation  of  white  by  excitation 
of  a  single  group  of  fibres  with  ordinary  intensity  of  stimulation. 
Colour-blindness,  in  its  true  sense,  is  always  congenital,  often 
hereditary  ;  the  colour-blind  are  '  born,  not  made.'  And  although 
the  condition  cannot  be  cured,  it  is  of  great  importance  that  it  should 
be  recognised  in  the  case  of  persons  occupying  positions  such  as 
those  of  engine-drivers,  railway-guards,  and  sailors,  in  which  coloured 
*  Rep.  Roy.  Soc.  Com.  on  Colour-  Blindness. 


THE  SENSES 


793 


lights  have  to  be  distinguished.  For,  while  it  is  true  that  the  sensa- 
tions which  red  and  green  lights  give  the  colour-blind  are  far  from 
being  identical  (Pole)  under  favourable  conditions,  it  is  precisely 
when  the  conditions  are  unfavourable,  as  in  a  fog  or  a  snow-storm, 
that  the  capacity  of  distinguishing  them  becomes  invaluable. 

Irradiation  was  first  described  by  Kepler,  who  gave  as  an  example 
the  appearance  known  as  the  '  new  moon  in  the  old  moon's  arms,' 
where  the  crescent  of  the  new  moon  seems  to  overlap  and  embrace 
the  unilluminated  portion  of  the  lunar  disc.  A  white  circle  on  a 
black  ground  (Fig.  289)  appears,  in  a  good  light,  to  be  larger  than 
an  exactly  equal  black  circle 
on  a  white  ground.  The  ex- 
planation seems  to  be  as  fol- 
lows :  Owing  to  the  aberration 
of  the  refractive  media  of  the 
eye,  all  the  rays  proceeding 
from  the  luminous  object  are 
not  brought  accurately  to  a 
focus  on  the  retina,  and  the  FIG.  289. 

image  is  surrounded  by  diffu- 
sion circles  which  encroach  upon  the  unilluminated  boundary. 
Physically  these  represent  a  weaker  illumination  than  that  of  the 
image  proper,  and  therefore  the  latter  ought  to  stand  out  in  its 
real  size  as  a  brighter  area  surrounded  by  weaker  haloes.  That 
this  is  not  the  case,  and  that  the  image  is  projected  in  its  full 
brightness  for  a  certain  distance  over  its  dark  boundary,  is  due  to 
two  things:  (i)  That  the  eye  does  not  recognise  very  small  differ- 
ences of  brightness,  and  (2)  that  not  only  is  the  neighbourhood  of 
the  directly  illuminated  field  stimulated  by  the  light  which  falls  on 
it  in  diffusion  circles,  but  the  excitation  set  up  in  a  given  area  of  the 
retina  is  propagated  for  a  short  distance  into  the  surrounding  parts 
(Descartes). 

When  the  accommodation  is  not  perfect,  the  diffusion  circles  are, 
of  course,  much  wider,  and  irradiation  is  better  marked  when  the 
object  is  a  little  out  of  focus.  When  it  is  too  much  out  of  focus, 
however,  the  diffusion  circles  are  no  longer  blended  with  the  rest  of 
the  image ;  and  since  their  formation  weakens  the  illumination  at 
the  edge  of  the  true  image  as  much  as  it  strengthens  the  illumina- 
tion beyond  the  edge,  the  effect  when  the  light  is  very  weak  is  a 
negative  irradiation.  Under  these  conditions,  a  white  disc  on  a 
black  ground  seems  smaller  than  a  black  disc  on  a  white  ground 
(Volkmann). 

The  Movements  of  the  Eyes. — That  the  eyes  may  be  efficient 
instruments  of  vision,  it  is  necessary  that  they  should  have 
the  power  of  moving  independently  of  the  head.  An  eye 
which  could  not  move,  though  certainly  better  than  an  eye 
which  could  not  see,  would  yet  be  as  imperfect  after  its 
kind  as  a  ship  which  could  run  before  the  wind,  but  could 


794  A  MANUAL  OF  PHYSIOLOGY 

not  tack.  The  mere  fact  that  the  angle  between  the  visual 
axes  must  be  adapted  to  the  distance  of  the  object  looked 
at  renders  this  obvious  ;  and  the  beauty  of  the  intrinsic 
mechanism  of  the  eyeball  has  its  fitting  complement  in  the 
precision,  delicacy,  and  range  of  movement  conferred  upon 
it  by  its  extrinsic  muscles. 

Not  only  are  movements  of  convergence  and  divergence 
of  the  eyeballs  necessary  in  accommodating  for  objects  at 
different  distances,  but  without  compensatory  movements 
of  the  eyes  it  would  be  impossible  to  avoid  diplopia  with 
every  movement  of  the  head  ;  for  the  images  of  an  object 
fixed  in  one  position  of  the  head  would  not  continue  to  fall 
on  corresponding  points  of  the  retinae  in  another  position. 

All  the  complicated  movements  of  the  eyeball  may  be 
looked  upon  as  rotations  round  axes  passing  through  a 
single  point,  which  to  a  near  approximation  always  remains 
fixed,  and  is  situated  about  1*77  mm.  behind  the  centre  of 
the  eye. 

The  position  which  the  eyeballs  take  up  when  the  gaze  is  directed 
to  the  horizon,  or  to  any  distant  point  at  the  level  of  the  eyes,  is 
called  the  primary  position.  Here  the  visual  axes  are  parallel,  and 
the  plane  passing  through  them  horizontal.  While  the  head  remains 
fixed  in  this  position,  the  eyeballs  can  rotate  up  or  down  around  a 
horizontal  axis,  or  from  side  to  side  around  a  vertical  axis;  or  upwards 
and  inwards,  downwards  and  outwards,  downwards  and  inwards,  and 
upwards  and  outwards  around  oblique  axes,  which  always  lie  in  the 
same  plane  as  the  vertical  and  horizontal  axes  of  rotation,  i.e.,  in  the 
vertical  plane  passing  through  the  fixed  centre  of  rotation.  These 
facts,  spoken  of  collectively  as  Listing's  law,  and  first  deduced  by 
him  from  theoretical  considerations,  were  afterwards  proved  experi- 
mentally by  Helmholtz  and  Bonders.  It  necessarily  follows  from 
Listing's  law  (and  this  is,  indeed,  another  way  of  stating  it)  that 
in  moving  from  the  primary  position  into  any  other,  there  is  no 
rotation  of  the  eyeball  round  the  visual  axis — no  wheel-movement, 
as  it  is  called. 

A  true  rotation  of  the  eye  round  the  visual  axis  does,  however, 
occur  when  the  eyes  are  converged  as  in  accommodation  for  a  near 
object,  each  eyeball  rotating  towards  the  temporal  side.  This  is 
especially  the  case  when  the  eyes  are  at  the  same  time  converged 
and  directed  downwards ;  and  the  rotation  may  amount  to  as  much 
as  5°.  When  the  head  is  rolled  from  side  to  side,  while  the  eyes  are 
kept  fixed  on  an  object,  a  slight  compensatory  rotation  of  the  eyeballs 
takes  place  against  the  direction  of  rotation  of  the  head.  The  amount 
of  rotation  of  the  eyes  is  relatively  greater  for  small  than  for  large 


THE  SENSES  795 

movements  of  the  head  (eye  5°  for  head  20° ;  eye  10°  for  head  80° — 
Kiister). 

The  Extrinsic  Muscles  of  the  Eye. — The  eyeball  is  acted 
upon  by  six  muscles  arranged  in  three  pairs,  which  may  be 
considered,  roughly  speaking,  as  antagonistic  sets.  These 
are  the  internal  and  external  recti,  the  superior  and  inferior 
recti,  and  the  superior  and  inferior  obliqui. 

Although  the  movements  of  the  eye  have  been  very  fully 
studied,  and  are,  upon  the  whole,  well  understood,  our 
knowledge  of  the  manner  in  which  any  given  movement  is 
brought  about,  and  the  exact  action  of  the  muscles  which 


FIG.  290.— HORIZONTAL  SECTION  OF  LEFT  EYE. 

Arrows  show  direction  of  pull  of  the  muscles.  The  axis  of  rotation  of  the  external 
and  internal  recti  would  pass  through  the  intersection  of  a  and  /3  at  right  angles  to  the 
plane  of  the  paper. 

take  part  in  it,  is  by  no  means  as  copious  and  precise.  And 
from  the  nature  of  the  case,  the  greater  part  of  what  we  do 
know  has  been  inferred  from  the  anatomical  relations  of  the 
muscles  as  revealed  by  dissection  in  the  dead  body  rather 
than  gained  from  actual  observation  of  the  living  eye.  A 
plane,  called  the  plane  of  traction,  is  supposed  to  pass  through 
the  middle  points  of  the  origin  and  insertion  of  the  muscle 
whose  action  is  to  be  investigated,  and  through  the  centre 
of  rotation  of  the  eyeball.  A  straight  line  drawn  at  right 
angles  to  this  plane  through  the  centre  of  rotation  is  evidently 
the  axis  round  which  the  muscle  when  it  contracts  will  cause 
the  eye  to  rotate,  provided  that  the  fibres  of  the  muscle  are 


796  A  MANUAL  OF  PHYSIOLOGY 

symmetrically  distributed  on  each  side  of  the  plane  of 
traction.  The  axes  of  rotation  of  the  antagonistic  pairs 
almost,  but  not  completely,  coincide  with  each  other.  The 
common  axis  of  the  external  and  internal  recti  practically 
coincides  with  the  vertical  axis  of  the  eyeball  (Fig.  290)  in  the 
primary  position.  The  eye  is  turned  towards  the  temple 
when  the  external  rectus  alone  contracts,  towards  the  nose 
when  the  internal  rectus  alone  contracts.  The  common 
axis  of  the  superior  and  inferior  recti,  j3,  lies  in  the  horizontal 
visual  plane  in  the  primary  position,  but  makes  an  angle  of 
about  20°  with  the  transverse  axis,  its  inner  end  being  tilted 
forwards.  The  consequence  is  that  contraction  of  the 
superior  rectus  turns  the  eye  up,  and  contraction  of  the 
inferior  rectus  turns  it  down,  but  both  movements  are  also 
combined  with  a  slight  inward  rotation.  The  common  axis 
of  the  oblique  muscles,  a,  makes  an  angle  of  60°  with  the 
transverse  axis,  the  outer  end  of  it  being  the  most  anterior. 
The  direction  of  traction  of  the  superior  oblique  is,  of  course, 
given  not  by  the  line  joining  its  bony  origin  and  its  insertion, 
but  by  the  direction  of  the  portion  reflected  over  the  pulley. 
When  the  superior  oblique  contracts  alone,  the  eyeball  is 
rotated  outwards  and  downwards;  the  inferior  oblique 
causes  an  outward  and  upward  rotation.  None  of  the 
common  axes  of  rotation  of  the  pairs  of  muscles,  except 
that  of  the  external  and  internal  recti,  lies  in  Listing's  plane. 
Now,  as  we  have  seen  that  every  movement  which  the  eye, 
supposed  to  be  originally  in  the  primary  position,  can 
execute  may  be  considered  as  a  rotation  round  an  axis  in 
this  plane,  it  is  clear  that  every  movement,  except  truly 
transverse  rotation,  must  be  brought  about  by  more  than 
one  pair  of  muscles.  For  vertical  rotation,  the  inward  pull 
of  the  superior  rectus  is  antagonized  by  a  simultaneous  out- 
ward pull  of  the  inferior  oblique ;  for  downward  rotation, 
the  inferior  rectus  and  superior  oblique  act  together.  In 
oblique  movements,  a  muscle  of  each  of  the  three  pairs  is 
concerned. 


THE  SENSES 


797 


HEARING. 

The  transverse  vibrations  of  the  ether  fall  upon  all  parts  of  the 
surface  of  the  body,  but  only  find  nerve-endings  capable  of  giving 
the  sensation  of  light  in  the  little  discs  which  we  call  the  retinae.  So 
the  much  longer  and  slower  longitudinal  waves  of  condensation  and 
rarefaction  which  are  being  constantly  originated  in  the  air  or  im- 
parted to  it  by  solid  or  liquid  bodies  that  have  been  themselves  set 
vibrating  fall  upon  all  parts  of  the  surface,  but  only  produce  the 
sensation  of  sound  when  they  strike  upon  the  tiny  mechanism  of  the 
internal  ear. 

But  just  as  the  ethereal  vibrations,  and  especially  those  of  greater 
wave-length,  are  able  to  excite  certain  end-organs  in  the  skin  which 
have  to  do  with  the  sensation  of  temperature,  so  the  sound-waves, 


m,  external  meatus ; 
/,  bead  of  malleus 

0,  short  process  of  malleus  ; 
g,  handle  of  malleus  ; , 

h,  incus  ; 

1,  foot  of  stapes  in  oval  foramen 
e,  tympanic  membrane. 


FIG.  291.— THE  EAR. 

when  sufficiently  large,  are  also  capable  of  stimulating  certain 
cutaneous  nerves  and  of  giving  rise  to  a  sensation  of  intermittent 
pressure  or  thrill.  This  is  readily  perceived  when  the  finger  is 
immersed  in  a  vessel  of  water  into  which  dips  a  tube  connected 
with  a  source  of  sound,  or  when  a  vibrating  bell  or  tuning-fork  is 
touched.  So  far  as  we  know,  what  takes  place  in  the  ear  is  essen- 
tially similar — that  is  to  say,  a  mechanical  stimulation  of  the  ends  of 
the  auditory  nerve,  but  a  stimulation  which  acts  through,  and  is 
graduated  and  controlled  by,  a  special  intermediate  mechanism. 

As  the  visual  apparatus  consists  of  a  sensitive  surface,  the 
retina,  which  contains  the  end-organs  of  the  optic  nerve  and 
of  dioptric  arrangements  which  receive  and  focus  the  rays  of 
light,  the  auditory  apparatus  consists  of  the  sensitive  end- 


798  A  MANUAL  OF  PHYSIOLOGY 

organs   of  the   eighth    nerve  and   of  a   mechanism   which 
receives  the  sound-waves  and  communicates  them  to  these. 

Physiological  Anatomy  of  the  Ear. — At  the  bottom  of  the  external 
auditory  ineatus  lies  the  membrana  tympani,  a  nearly  circular  mem- 
brane set  like  a  drum-skin  in  a  ring  of  bone,  and  separating  the 
meatus  from  the  tympanum  or  middle  ear.  Its  external  surface  looks 
obliquely  downwards,  and  at  the  same  time  somewhat  forwards,  so 
that  if  prolonged  the  membranes  of  the  two  ears  would  cut  each 
other  in  front  of,  and  also  below,  the  horizontal  line  passing  through 
the  centre  of  each  (Figs.  291,  292). 

The  tympanum  contains  a  chain  of  little  bones  stretching  right 
across  it  from  outer  to  inner  wall.  Of  these  the  malleus,  or  hammer, 
is  the  most  external.  Its  manubrium,  or  handle,  is  inserted  into 
the  membrana  tympani,  which  is  not  stretched  taut  within  its  bony 
ring,  but  bulges  inwards  at  the  centre,  where  the  handle  of  the 
malleus  is  attached.  The  stapes,  or  stirrup,  is  the  most  internal  of 
the  chain  of  ossicles,  and  is  inserted  by  its  foot-plate  into  a  small 
oval  opening — the  foramen  ovale — on  the  inner  wall  of  the  tympanic 
cavity.  A  membranous  ring — the  orbicular  membrane — surrounds 
the  foot  of  the  stapes,  helping  to  fill  up  the  foramen  and  attaching 
the  bone  to  its  edges.  The  incus,  or  anvil,  forms  a  link  between  the 
malleus  and  the  stapes.  The  auditory  ossicles,  as  well  as  the  whole 
cavity  of  the  tympanum,  are  covered  by  pavement  epithelium.  The 
tympanum  is  not  an  absolutely  closed  chamber ;  it  has  one  channel 
of  communication  with  the  external  air — the  Eustachian  tube.  By  the 
action  of  the  cilia  which  line  this  tube  the  scanty  secretion  of  the 
middle  ear  is  moved  towards  its  pharyngeal  opening.  The  loosely- 
jointed  chain  of  ossicles  is  steadied  and  its  movements  directed  by 
ligaments  and  by  the  tension  of  its  terminal  membranes.  It  forms  a 
kind  of  bent  lever,  by  which  the  oscillations  of  the  membrana 
tympani  are  transferred  to  the  membrane  covering  the  oval  foramen, 
and  at  the  same  time  reduced  in  size.  Two  slender  muscles,  the 
tensor  tympani  and  stapedius,  contained  in  the  tympanic  cavity,  are 
also  connected  with  and  may  act  upon  the  ossicles.  The  former  lies 
in  a  groove  above  the  Eustachian  tube,  and  its  tendon,  passing  round 
a  kind  of  osseous  pulley  (processus  cochleariformis),  is  inserted  into 
the  handle  of  the  malleus ;  the  stapedius  is  lodged  in  a  hollow  of  the 
inner  bony  wall  of  the  tympanum.  Its  tendon  is  attached  to  the  neck 
of  the  stapes  near  its  articulation  with  the  incus.  This  inner  wall  is 
pierced  not  only  by  the  oval  foramen,  but  also  by  a  round  opening, 
the  fenestra  rotunda,  which  is  closed  by  a  membrane  to  which  the 
name  of  secondary  membrana  tympani  is  sometimes  given. 

The  internal  ear  consists  of  the  bony  labyrinth,  a  series  of  curiously 
excavated  and  communicating  spaces  in  the  substance  of  the  petrous 
portion  of  the  temporal  bone,  filled  with  a  liquid  called  the  peri- 
lymph,  in  which,  anchored  by  strands  of  connective  tissue,  floats  a 
corresponding  series  of  membranous  canals  (the  membranous  laby- 
rinth), filled  with  a  liquid  called  endolymph.  The  labyrinth  of  the 
internal  ear  is  divided  into  three  well-marked  parts  :  the  cochlea,  the 


THE  SENSES 


799 


vestibule,  and  the  semicircular  canals  (Fig.  292).  The  cochlea,  the 
most  anterior  of  the  three,  consists  of  a  convoluted  tube  which  coils 
round  a  central  pillar  or  modiolus  like  a  spiral  staircase.  The 
lamina  spiralis,  which,  except  that  it  forms  a  continuous  surface,  may 
be  taken  as  representing  the  steps,  projects  from  the  modiolus  and 


FIG.  292.— MIDDLE  AND  INTERNAL  EAR  (DIAGRAMMATIC). 

divides  the  tube  into  an  upper  compartment,  the  scala  vestibuli,  and 
a  lower,  the  scala  tympani  (Fig.  293).  The  part  of  the  lamina  next 
the  modiolus  is  of  bone,  but  it  is  completed  at  its  outer  edge  by  a 
membrane,  the  lamina  spiralis  membranacea.  The  scala  tympani 
abuts  on  the  fenestra  rotunda,  and  its  perilymph  ia  only  separated 


J&eissntrs  membrane 


l  Scala  VestibuliJ/^^Canahs  cochleae 


FIG.  293. — TRANSVERSE  SECTION  OF  A  TURN  OF  THE  COCHLEA  (DIAGRAM- 
MATIC). 

from  the  air  of  the  tympanic  cavity  by  the  membrane  which  closes 
that  opening.  At  the  apex  of  the  cochlea  the  lamina  spiralis  is 
incomplete,  ending  in  a  crescentic  border,  so  that  the  scala  tympani 
and  the  scala  vestibuli  here  communicate  by  a  small  opening,  the 
helicotrema.  The  scala  vestibuli  communicates  with  the  vestibule, 


8oo  A  MANUAL  OF  PHYSIOLOGY 

and  the  vestibule  with  the  semicircular  canals,  so  that  the  peri- 
lymph  of  the  entire  labyrinth  forms  a  continuous  sheet,  separated 
from  the  cavity  of  the  middle  ear  by  the  structures  that  fill  up 
the  round  and  oval  foramina.  In  the  membranous  labyrinth,  and  in 
it  alone,  are  contained  the  end-organs  of  the  auditory  nerve.  The 
membranous  portion  of  the  cochlea  is  a  small  canal  of  triangular 
section,  cut  off  from  the  scala  vestibuli  by  the  membrane  of  Reissner, 
which  stretches  from  near  the  edge  of  the  bony  spiral  lamina  to  the 
outer  wall  (Fig.  293).  It  has  received  the  name  of  the  scala  media, 
or  canal  of  the  cochlea.  Below  it  ends  blindly,  but  communicates 
by  a  side-channel  with  the  portion  of  the  membranous  vestibule  called 
the  saccule,  which  in  its  turn  communicates  with  the  utricle  by  a 
Y-shaped  sac,  the  saccus  endolymphaticus.  Into  the  utricle  open 
the  three  semicircular  canals,  the  endolymph  of  which  has,  there- 
fore, free  communication  with  that  of  the  vestibule  and  cochlea. 
But  although  the  semicircular  canals  and  vestibule  belong  anatomi- 
cally to  the  internal  ear,  and  are  supplied  by  branches  of  the  auditory 
nerve,  we  have  no  positive  proof  that  in  the  higher  animals,  at  least, 
they  are  in  any  way  concerned  in  hearing ;  and  since  experiment  has 
assigned  them,  with  a  great  degree  of  probability,  a  definite  function 
of  another  kind  (p.  698),  we  shall  not  consider  them  further  in  this 
connection.  The  scala  media  contains  the  organ  of  Corti,  which 
(Fig.  293)  consists  of  a  series  of  modified  epithelial  cells  planted 
upon  the  membranous  spiral  lamina  or  basilar  membrane.  The 
most  conspicuous  constituent  of  the  latter  is  a  layer  of  parallel  trans- 
parent fibrils.  The  epithelial  cells  are  of  two  kinds  :  (i)  the  pillars 
or  rods  of  Corti,  sloped  against  each  other  like  the  rafters  of  a  roof, 
and  covering  in  a  vault  or  tunnel  which  runs  along  the  whole  of  the 
scala  media  from  the  base  to  the  apex  of  the  cochlea ;  (2)  the  hair- 
cells,  which  are  columnar  epithelial  cells  running  out  below  into 
processes  connected  with  the  terminal  fibres  of  the  auditory  nerve, 
and  surmounted  by  hairs.  They  are  arranged  in  several  rows,  one 
row  lying  just  internal  to  the  inner  line  of  pillars,  and  four  or  five 
rows  external  to  the  outer  line  of  pillars.  A  thin  membrane,  the 
membrana  reticularis,  covers  the  pillars  and  hair-cells  of  Corti,  and 
is  pierced  by  the  hairs ;  while  a  thicker  membrane,  the  membrana 
tectoria,  springing  from  the  edge  of  the  osseous  spiral  lamina  near 
the  attachment  of  Reissner's  membrane,  forms  a  kind  of  canopy  over 
both  pillars  and  hair-cells.  The  fact  that  the  hair-cells  of  Corti's 
organ  are  connected  with  the  fibres  of  the  cochlear  division  of  the 
auditory  nerve,  and  its  elaborate  structure,  suggest  that  it  must  play 
a  peculiar  part  in  auditory  sensation.  Comparative  anatomy  shows 
us  that  the  cochlea  is  the  most  highly-developed  portion  of  the 
internal  ear,  the  last  to  appear  in  its  evolution,  and  the  most 
specialized.  It  is  absent  in  fishes,  which  possess  only  a  vestibule 
and  one  to  three  semicircular  canals.  It  first  acquires  importance  in 
reptiles,  but  attains  its  highest  development  in  mammals ;  and  there 
is  every  reason  to  believe  that  it  is  the  terminal  apparatus  of  the 
sense  of  hearing. 


THE  SENSES  801 

Function  of  the  Auditory  Ossicles. — The  anatomical  arrange- 
ments of  the  middle  ear  suggest  that  the  tympanic  membrane 
and  the  chain  of  ossicles  have  the  function  of  transmitting 
the  sound-waves  to  the  liquids  of  the  labyrinth  ;  and  obser- 
vation and  experiment  fully  confirm  this  idea.  Tracings  of 
the  movements  of  the  ossicles  have  been  obtained  by  attach- 
ing very  small  levers  to  them,  and  their  movements  have 
been  directly  observed  with  the  microscope.  Even  in  man 
it  may  be  shown,  by  viewing  the  membrane  through  a  series 
of  slits  in  a  rapidly-revolving  disc  (stroboscope),  that  it 
vibrates  when  sound-waves  fall  on  it. 

When  the  handle  of  the  malleus  moves  inwards,  the  joint 
between  that  bone  and  the  incus  is  locked,  on  account  of 
the  shape  of  the  articular  surfaces,  and  the  stapes  is  pressed 
into  the  oval  foramen.  When  the  tympanic  membrane 
passes  outwards,  the  handle  of  the  malleus  and  foot  of  the 
stapes  do  the  same.  But  the  joint  now  unlocks,  and  exces- 
sive outward  movement  of  the  stapes,  which  might  result  in 
its  being  torn  from  its  orbicular  attachment,  is  prevented. 
The  ossicles  vibrate  en  masse.  It  is  only  to  a  trifling 
extent  that  sound  can  be  conducted  through  them  to  the 
labyrinth  as  a  molecular  vibration ;  for  when  they  are 
anchylosed,  and  the  foot  of  the  stapes  fixed  immovably  in 
the  foramen  ovale,  as  sometimes  occurs  in  disease,  hearing 
is  greatly  impaired. 

Of  course,  every  vibration  of  the  tympanic  membrane 
must  cause  a  corresponding  condensation  and  rarefaction  of 
the  air  in  the  middle  ear ;  and  this  may  act  on  the  mem- 
brane closing  the  fenestra  rotunda,  and  set  up  oscillations  in 
the  perilymph  of  the  scala  tympani.  That  this  is  a  possible 
method  of  conduction  of  sound  is  shown  by  the  fact  that, 
even  after  closure  of  the  oval  foramen,  a  slight  power  of 
hearing  may  remain.  But  under  ordinary  conditions  by  far 
the  most  important  part  of  the  conduction  takes  place  via 
the  ossicles.  And  when  it  is  remembered  that  the  tympanic 
membrane  is  about  thirty  times  larger  than  that  which  fills 
the  oval  foramen,  it  will  be  seen  that  the  force  acting  on  unit 
area  of  the  foot  of  the  stapes  may  be  much  greater  than  that 
acting  on  unit  area  of  the  membrana  tympani,  and  that  the 


802  A  MANUAL  OF  PHYSIOLOGY 

mode  of  transmission  by  the  ossicles  is  a  very  advantageous 
method  of  transforming  the  feeble  but  comparatively  large 
excursion  of  the  tympanic  membrane  into  the  smaller  but 
more  powerful  movements  of  the  stapes.  Even  the  so-called 
cranial  conduction  of  sound  when  a  tuning-fork  is  held  between 
the  teeth  or  put  in  contact  with  the  head,  which  was  at  one 
time  supposed  to  be  due  solely  to  direct  transmission  of  the 
vibrations  through  the  bones  of  the  skull  to  the  liquids  of 
the  labyrinth  or  the  end-organs  of  the  auditory  nerve,  has 
been  shown  to  take  place,  in  great  part,  through  the  mem- 
brana  tympani  and  ossicles  ;  the  vibrations  travel  through 
the  bones  to  the  tympanic  membrane,  and  set  it  oscillating. 
So  that  this  test,  when  applied  to  distinguish  deafness  caused 
by  disease  of  the  middle  ear  from  deafness  due  to  disease 
of  the  labyrinth  or  the  central  nervous  system  may  easily 
mislead,  although  it  enables  us  to  say  whether  the  auditory 
meatus  is  blocked  (by  wax,  e.g.)  beyond  the  tympanic 
membrane. 

When  a  tuning-fork  is  held  between  the  teeth,  a  part  of  the  sound 
passes  out  of  the  ear  from  the  vibrating  membrana  tympani ;  if  one 
ear  is  closed,  the  sound  is  heard  better  in  this  than  in  the  open  ear. 
If  the  tuning-fork  is  held  before  the  ear  till  it  just  ceases  to  be  heard, 
it  will  still  be  heard  on  placing  it  between  the  teeth  ;  if  it  be  kept 
there  till  it  again  becomes  inaudible,  it  will  be  heard  for  a  short  time 
if  one  or  both  ears  be  stopped  ;  and  when  in  this  position  the  sound 
again  becomes  inappreciable,  it  can  still  be  caught  if  the  handle  be 
introduced  into  the  auditory  meatus. 

A  membrane  like  a  drum-head  has  a  note  cf  its  own,  which  it 
gives  out  when  struck,  and  it  vibrates  more  readily  to  this  note  than 
to  any  other.  But  the  tympanic  membrane  receives  all  kinds  of 
vibrations,  and  responds  to  all ;  so  that  if  it  is  in  reality  attuned  to 
any  particular  note,  the  effect  is  weakened  in  some  way  or  other,  and 
does  not  obtrude  itself.  The  damping  of  the  movements  of  the 
membrane  by  the  ossicles  and  the  liquids  of  the  labyrinth  may  partly 
account  for  this;  and  it  is  to  be  remembered  also  that  it  is  not 
stretched,  but  lies  slackly  in  its  bony  frame,  so  that  when  the  handle 
of  the  malleus  is  detached  from  it,  it  retains  its  shape  and  position. 

The  tensor  tympani,  when  it  contracts,  pulls  inwards  the  handle 
of  the  malleus,  and  thus  increases  the  tension  of  the  tympanic  mem- 
brane. The  precise  object  of  this  is  obscure.  It  has  been  suggested 
that  damping  of  the  movements  of  the  auditory  ossicles  is  thus 
secured.  Another  theory  is  that  the  increased  tension  of  the  mem- 
brane renders  it  more  capable  of  responding  to  higher  tones,  and 
that  the  muscle  thus  acts  as  a  kind  of  accommodating  mechanism. 


THE  SENSES  803 

But  Henson  has  observed  that  the  tensor  only  contracts  at  the  begin- 
ning of  a  sound,  and  relaxes  again  when  the  sound  is  continued ; 
and  this  is  difficult  to  reconcile  with  either  of  these  hypotheses. 
The  muscle  is  normally  excited  reflexly  through  the  vibrations'of  the 
membrana  tympani,  but  some  individuals  have  the  power  of  throwing 
it  into  voluntary  contraction,  which  is  accompanied  by  a  feeling  of 
pressure  in  the  ear  and  a  harsh  sound.  The  function  of  the  stapedius 
is  unknown.  Its  contraction  would  tend  to  press  the  posterior  end  of 
the  foot-plate  of  the  stapes  deeper  into  the  foramen  ovale,  and  cause 
the  anterior  end  to  move  in  the  opposite  direction  ;  but  it  is  not  easy 
to  see  how  this  would  affect  the  action  of  the  auditory  mechanism. 
A  desire  to  explain  everything,  so  far  as  the  fitting  of  a  phrase  to 
every  fact  can  explain,  has  led  to  the  suggestion  that  the  role  of 
the  stapedius  is  to  damp  the  oscillations  of  the  stapes  and  orbicular 
ligament  when  very  loud  sounds  are  listened  to,  and  thus  prevent 
shocks  of  too  great  intensity  from  being  transmitted  to  the  labyrinth. 
The  tensor  tympani  is  supplied  by  the  fifth  nerve  through  a  branch 
from  the  otic  ganglion ;  the  stapedius  is  supplied  by  the  seventh. 
Paralysis  of  the  fifth  nerve  may  be  accompanied  with  difficulty  of 
hearing,  especially  for  faint  sounds.  When  the  seventh  nerve  is 
paralyzed,  increased  sensitiveness  to  loud  sounds  has  been  observed. 

The  Perception  of  Pitch — Analysis  of  Complex  Sounds. — 
As  the  eye,  or,  rather,  the  retina  plus  the  brain,  can  perceive 
colour,  so  the  labyrinth  plus  the  brain  can  perceive  pitch. 
The  colour-sensation  produced  by  ethereal  waves  of  definite 
frequency  depends  on  that  frequency;  and  upon  the  fre- 
quency of  the  aerial  vibrations  depends  also  the  pitch  of  a 
musical  note.  But  there  is  this  difference  between  the  eye 
and  the  ear  :  that  while  the  sensation  produced  by  a  mixture 
of  rays  of  light  of  different  wave-length  is  always  a  simple 
sensation — that  is,  a  sensation  which  we  do  not  perceive  to 
be  built  up  of  a  number  of  sensations,  which,  in  other  words, 
we  do  not  analyze — the  ear  can  perceive  at  the  same  time, 
.and  distinguish  from  each  other,  the  components  of  a  com- 
plex sound.  When  a  number  of  notes  of  different  pitch  are 
sounded  together  at  the  same  distance  from  the  ear,  the 
disturbance  which  reaches  the  membrana  tympani  is  the 
physical  resultant  of  all  the  disturbances  produced  by  the 
individual  notes,  and  it  strikes  upon  the  membrane  as  a 
single  wave.  The  ear  or  brain  must,  therefore,  possess  the 
power  of  resolving  the  complex  vibrations  into  their  con- 
stituents, else  we  should  have  a  mixed  or  blended  sensation, 
.and  not  a  sensation  in  which  it  is  possible  to  distinguish  the 

51—2 


804  A  MANUAL  OF  PHYSIOLOGY 

constituents  of  which  it  is  made  up.  Two  chief  hypotheses 
have  been  proposed  to  explain  this  physiological  analysis  of 
sound :  (i)  the  theory  that  the  analysis  takes  place  in  the 
labyrinth  ;  (2)  the  theory  that  it  takes  place  in  the  brain. 

(i)  Helmholtz  attempted  to  explain  the  perception  ol 
pitch  on  the  assumption  that  in  the  internal  ear  there  exists 
a  series  of  resonators,  each  of  which  is  fitted  to  respond  by 
sympathetic  vibration  to  a  particular  note,  while  the  others 
are  unaffected ;  just  as  when  a  note  is  sung  before  an  open 
piano  it  is  taken  up  by  the  string  which  is  attuned  to  the 
same  pitch  and  ignored  by  the  rest.  Let  us  suppose  that  a 
given  fibre  of  the  auditory  nerve  ends  in  an  organ  which  is 
only  set  vibrating  by  waves  impinging  on  it  at  the  rate  of 
100  a  second,  and  that  the  end-organ  of  another  fibre  is 
only  influenced  by  waves  with  a  frequency  of  200  a  second. 
Then,  on  the  doctrine  of  *  specific  energy '  (according  to 
which  the  sensation  caused  by  stimulation  of  a  nerve 
depends  not  on  the  particular  kind  of  stimulus  but  on 
the  anatomical  connection  of  the  nerve  with  certain  nerve 
centres),  in  whatever  way  the  first  fibre  is  excited,  a  sensa- 
tion corresponding  to  a  note  with  a  pitch  of  100  a  second 
will  be  perceived.  Whenever  the  second  fibre  is  excited, 
the  sensation  will  be  that  of  a  note  of  200  a  second,  or  the 
octave  of  the  first.  If  both  fibres  are  excited  at  the  same 
time  the  two  notes  will  be  heard  together.  Now,  Hensen 
actually  observed  that  in  the  auditory  organs  of  some 
crustaceans  the  hair-like  processes  of  certain  epithelial  cells 
can  be  set  swinging  by  waves  of  sound,  and,  further,  that 
they  do  not  all  vibrate  to  the  same  note  unless  the  sound 
is  very  loud.  In  the  lobster  there  are  between  four  and 
five  hundred  of  these  hairs,  varying  in  length  from  14  ^  tc 
740  fj,;  and  in  some  insects,  such  as  the  locust,  similai 
hairs,  also  graduated  in  length,  exist. 

To  gain  an  anatomical  basis  for  his  theory,  Helmholtz 
supposed  first  of  all  that  the  pillars  of  Corti  were  the 
vibrating  structures,  and  that,  directly  or  through  the  hair- 
cells,  their  mechanical  vibrations  were  translated  into 
impulses  in  the  auditory  nerve-fibres.  But  apart  from  the 
fact  that  their  number  is  too  small  (about  3,000)  to  allow 


THE  SENSES  805 

us  to  assign  one  rod  to  each  perceptible  difference  of  pitch, 
and  their  dimensions  too  similar  to  permit  of  the  requisite 
range  of  vibration  frequency,  it  was  pointed  out  that  birds 
do  not  possess  pillars  of  Corti — a  fact  which  was  decisive 
against  the  assumption  of  Helmholtz,  since  nobody  denies 
to  singing  birds  the  power  of  appreciating  pitch.  Helmholtz 
accordingly,  choosing  between  the  remaining  possibilities, 
gave  up  the  pillars  of  Corti,  and,  adopting  a  suggestion  of 
Hensen,  substituted  the  radial  fibres  of  the  basilar  mem- 
brane as  his  hypothetical  resonators.  But  while  it  is  true 
that  these  are  much  more  adequate  to  the  task  imposed  on 
them,  since  their  range  of  length  is  far  greater  (41  //,  at  the 
base  to  495  //,  at  the  apex  of  the  cochlea — Hensen) ;  and 
while  the  structure  of  Corti's  organ  certainly  suggests  that 
some  one  or  other  of  its  elements  may  be  endowed  with 
such  a  function,  the  theory  of  peripheral  analysis  of  pitch 
tends  upon  the  whole  rather  to  break  down  than  to  be 
strengthened  as  evidence  gathers. 

When  two  notes  of  different  frequency  are  sounded  together,  they 
1  interfere '  with  each  other.  If  two  tuning-forks  A  and  B,  making 
100  and  101  vibrations  a  second  respectively,  be  started  together, 
at  the  end  of  the  first  vibration  of  A,  B  will  be  yj^th  of  a  vibration 
ahead,  at  the  end  of  the  second  y^ths  of  a  vibration,  at  the  end  of 
the  fiftieth  half  a  vibration.  Here  the  crest  of  B's  wave  will  coincide 
with  the  trough  of  A's,  and  if  the  forks  are  vibrating  with  the  same 
amplitude  the  resultant  for  this  vibration  will  be  zero,  the  wave  will 
be  blotted  out.  If  the  amplitudes  are  not  the  same,  the  wave  will 
srill  be  weakened.  At  the  end  of  the  hundredth  vibration  of  A,  B 
will  nave  gained  a  whole  vibration,  the  tops  of  the  two  waves  will 
coincide,  and  the  sound  will  be  strengthened.  We  recognise  the 
alternate  changes  in  the  amplitude  of  the  interfering  sound-waves  by 
a  change  in  the  auditory  sensation,  which  is  called  a  beat;  and  in  the 
case  supposed  there  will  be  one  beat  a  second.  If  the  difference  in 
the  frequency  of  the  forks  is  five  there  will  be  five  beats  a  second.  If 
the  difference  is  twenty  there  will  be  twenty  beats  a  second.  As  the 
difference  is  increased  the  beats  will  ultimately  follow  each  other 
so  rapidly  that  they  will  themselves  be  fused  into  a  note — a  beat-tone 
as  it  is  called,  whose  pitch  will  correspond  to  the  frequency  of  the 
beats.  Now,  Hermann  has  found  that  the  ear  may  perceive  a  beat- 
tone  which  elicits  no  response  from  a  resonator  attuned  to  its  note  and 
readily  set  into  vibration  by  the  same  note  when  sounded  by  a  tuning- 
fork.  This  shows  that  the  process  by  which  pitch  is  appreciated, 
whatever  it  may  be,  is  not  entirely  explicable  on  the  theory  of 
resonance. 


8o6  A  MANUAL  OF  PHYSIOLOGY 

(2)  The  second  theory,  in  accordance  with  the  simile  used 
by  Rutherford,  to  whom  we  owe  it  in  its  present  form,  may 
be  conveniently  labelled  the  'telephone  theory.'  He  sup- 
poses that  the  organ  of  Corti  (or,  at  any  rate,  the  hair-cells) 
is  set  into  vibration  as  a  whole  by  all  audible  sounds,  and 
that  its  vibrations  are  translated  into  impulses  in  the  auditory 
nerve,  which  are  the  physiological  counterpart  of  the  aerial 
waves  and  the  waves  of  increased  and  diminished  pressure 
in  the  liquids  of  the  labyrinth  to  which  they  give  rise. 
Thus,  a  sound  of  100  vibrations  a  second  would  start  100 
impulses  a  second  in  the  auditory  nerve ;  a  loud  sound 
would  set  up  impulses  more  intense  than  a  feeble  sound ; 
and  a  complex  wave,  which  is  the  resultant  of  several  sounds 
of  different  vibration-frequency,  would  also  in  some  way 
or  other  stamp  the  impress  of  its  form  on  the  auditory 
excitation-wave ;  just  as  in  a  telephone  every  wave  in  the  air 
causes  a  swing  of  the  vibrating  plate,  and  thus  sets  up  a 
current  of  corresponding  intensity  and  duration  in  the  wires. 
This  theory  evidently  abandons  the  doctrine  of  specific  energy 
for  the  particular  case  of  the  analysis  of  pitch,  for  it  assumes 
that  differences  of  auditory  sensation  are  related  to  differ- 
ences in  the  nature  of  the  impulses  travelling  up  the  auditory 
nerve,  and  not  merely  to  differences  in  the  anatomical  connec- 
tions (peripheral  and  central)  of  the  auditory  nerve-fibres. 

The  statement  of  Ewald,  that  after  extirpation  of  the  membranous 
labyrinth  on  both  sides  pigeons  can  still  hear,  would  have  an  im- 
portant bearing  on  the  question  of  the  perception  of  pitch,  if  it  could 
be  definitely  accepted,  and  particularly  if  it  were  shown  that  differences 
of  pitch  could  still  be  appreciated.  But  it  has  not  been  proved 
beyond  a  doubt  that  the  apparent  reaction  to  sound  is  due  to  any- 
thing else  than  stimulation  of  tactile  end-organs. 

Smell  and  Taste. 

Smell  was  defined  by  Kant  as  '  taste  at  a  distance ';  and 
it  is  obvious  that  these  two  senses  not  only  form  a  natural 
group  when  the  quality  of  the  sensations  is  considered,  but 
are  closely  associated  in  their  physiological  action,  especi- 
ally in  connection  with  the  perception  of  the  flavour  of  the 
food.  The  olfactory  end-organs  are  situated  in  the  mucous 
membrane  of  the  upper  part  of  the  nostrils,  the  so-called 


THE  SENSES  807 

regio  olfactoria.  They  are  cells  prolonged  externally  into 
long  narrow  rods  which  terminate  at  the  free  surface  of  the 
mucous  membrane,  and  prolonged  towards  their  deep  ends 
into  processes  which  become  continuous  with  fine  branches 
of  the  first  nerve.  These  olfactory  cells  are  scattered  among 
the  ordinary  cylindrical  cells  which  line  the  mucous  mem- 
brane. In  cases  of  anosmia,  in  which  the  olfactory  nerve  is 
absent  or  paralyzed,  smell  is  abolished;  but  substances  such 
as  ammonia  and  acetic  acid,  which  stimulate  the  ordinary 
sensory  nerves  (nasal  branch  of  fifth)  of  the  olfactory  mucous 
membrane,  are  still  perceived,  though  not  distinguished  from 
each  other.  In  fact,  the  so-called  pungent  odour  of  these 
substances  is  no  more  a  true  smell  than  the  sense  of  smarting 
they  produce  when  their  vapour  comes  in  contact  with  a 
sensory  surface  like  the  conjunctiva  or  a  piece  of  skin  devoid 
of  epidermis. 

It  was  at  one  time  believed  that  odoriferous  particles 
could  not  be  appreciated  unless  they  were  borne  by  the  air 
into  the  nostrils  ;  but  this  appears  not  to  be  the  case,  for 
the  smell  of  substances  dissolved  in  normal  saline  solution  is 
distinctly  perceived  when  the  nostrils  are  filled  with  the 
liquid;  and  fish,  as  every  line-fisherman  knows,  have  no 
difficulty  in  finding  a  bait  in  the  dark. 

Beaunis  has  classified  the  substances  which  can  affect  the  olfactory 
mucous  membrane  as  follows  : 

1.  Those  which  act  only  on  the  olfactory  nerves  : 

(a]  Pure  scents  or  perfumes,  without  pungency. 

(b)  Odours  with  a  certain  pungency,  e.g.,  menthol. 

2.  Substances  which  act  at  the  same  time  on  olfactory  nerves 

and  on  nerves  of  common  sensation  (tactile  nerves), 
e.g.,  acetic  acid. 

3.  Substances  which  act   only  on   the   nerves   of  common 

sensation  (tactile  nerves),  e.g.,  carbon  dioxide. 
Electrical  excitation  of  the  olfactory  mucous  membrane  causes  a 
sensation  like  the  smell  of  phosphorus.    The  sensation  is  experienced 
at  the  kathode  on  closure  and  the  anode  on  opening. 

Taste. — The  sense  of  taste  is  not  so  strictly  localized  as  the 
sense  of  smell.  The  tip  and  sides  of  the  tongue,  its  root, 
the  neighbouring  portions  of  the  soft  palate,  and  a  strip  in 
the  centre  of  the  dorsum,  are  certainly  endowed  with  the 
sense  of  taste  ;  but  the  exact  limits  of  the  sensitive  areas 


8c8  A  MANUAL  OF  PHYSIOLOGY 

have  not  been  denned,  and,  indeed,  seem  to  vary  in  different 
individuals. 

The  nerves  of  taste  are  the  glossopharyngeal,  which  innervates 
the  posterior  part  of  the  tongue ;  and  the  lingual,  which  supplies  its 
tip.  The  end-organs  of  the  gustatory  nerves  are  the  taste-buds  or 
taste-bulbs,  which  stud  the  fungiform  and  circumvallate  papillae,  and 
are  most  characteristically  seen  in  the  moats  surrounding  the  latter. 
They  are  barrel-like  bodies,  the  staves  of  the  barrel  being  repre- 
sented by  supporting  cells  ;  each  bud  encloses  a  number  of  gustatory 
cells  with  fine  processes  at  their  free  ends  projecting  through  the 
superficial  end  of  the  barrel.  Their  deep  ends  also  terminate  in 
processes  which  become  continuous  with  the  fibres  of  the  gustatory 
nerves. 

As  to  the  properties  in  virtue  of  which  sapid  substances 
are  enabled  to  stimulate  the  gustatory  nerve  endings,  we 
know  that  they  must  be  soluble  in  the  liquids  of  the  mouth, 
and  there  our  knowledge  ends.  An  attempt  has  been  made 
by  various  authors  to  connect  the  taste  of  such  bodies 
with  their  chemical  composition,  but  researches  of  this  kind 
have  not  hitherto  yielded  much  fruit.  Sapid  substances  have 
been  divided  into  four  classes  :  I,  sweet ;  2,  acid  ;  3,  bitter ; 
4,  saline. 

Sweet  and  acid  tastes  are  best  appreciated  by  the  tip,  and 
bitter  tastes  by  the  base,  of  the  tongue. 

Normal  lymph,  which  bathes  the  gustatory  end-organs,  does  not 
excite  any  sensation  of  taste,  but  when  the  composition  of  the  blood 
is  altered  in  disease  or  by  the  introduction  of  foreign  substances, 
tastes  of  various  kinds  may  be  perceived.  Sometimes  this  may  be 
due  to  the  stimulation  of  substances  excreted  in  the  saliva ;  but  in 
other  cases  it  seems  that,  without  passing  beyond  the  blood  and 
lymph,  foreign  substances  may  excite  the  gustatory  nerves. 

When  a  constant  current  is  passed  through  the  tongue,  an  acid 
taste  is  experienced  at  the  positive,  and  an  alkaline  taste  at  the  nega- 
tive, pole ;  and  it  is  said  that  this  is  the  case  even  when  the  current 
is  conducted  to  and  from  the  tongue  by  unpolarizable  combinations, 
which  prevent  the  deposition  of  electrolytic  products  on  the  mucous 
membrane  (p.  526). 

Flavour  is  a  mixed  sensation,  in  which  smell  and  taste  are  both 
concerned,  as  is  shown  by  the  common  observation  that  a  person 
suffering  from  a  cold  in  the  head,  which  blunts  his  sense  of  smell, 
loses  the  proper  flavour  of  his  food,  and  that  some  nauseous  medi- 
cines do  not  taste  so  badly  when  the  nostrils  are  held. 

In  common  speech,  the  two  sensations  are  frequently  confounded. 
Thus  the  '  bouquet '  of  wines,  which  most  people  imagine  to  be  a 
sensation  of  taste,  is  in  reality  a  sensation  of  smell ;  the  astringent 


THE  SENSES  809 

1  taste '  of  tannic  acid  is  not  a  taste  at  all,  but  a  tactile  sensation ; 
the  '  hot '  taste  of  mustard  is  no  more  a  true  sensation  of  taste  than 
the  sensation  produced  by  the  same  substance  when  applied  in  the 
form  of  a  mustard  poultice  to  the  skin. 

Tactile  Sensations. 

Under  the  sense  of  touch  it  is  usual  to  include  a  group 
of  sensations  which  differ  in  quality — and  that  in  some 
instances  to  as  great  an  extent  as  any  of  the  sensations 
which  are  universally  considered  as  separate  and  distinct — 
but  agree  in  this,  that  the  end-organs  by  which  they  are 
perceived  are  all  situated  in  the  skin,  the  mucous  membrane, 
or  the  subcutaneous  tissue.  Such  are  the  common  tactile 
sensations — including  pressure — and  the  sensations  of  tem- 
perature, or,  more  correctly,  of  change  of  temperature.  The 
sensation  of  pain  cannot  be  justly  grouped  along  with  these. 
It  is  called  forth  by  excessive  stimulation  of  any  of  the  sense- 
organs,  or  by  the  stimulation  of  afferent  nerve-fibres  in  their 
course ;  and  it  may  originate,  under  certain  conditions,  in 
internal  organs  which  are  devoid  of  tactile  sensibility,  and 
the  functional  activity  of  which  in  their  normal  state  gives 
rise  to  no  special  sensation  at  all.  The  peculiar  sensation 
associated  with  voluntary  muscular  effort,  to  which  the 
name  of  the  muscular  sense  has  been  given,  also  deserves 
a  separate  place;  for  although  it  may  in  part  depend  on 
tactile  sensations  set  up  through  the  medium  of  end-organs 
situated  in  muscle,  tendon,  or  the  structures  which  enter 
into  the  formation  of  the  joints,  other  elements  are,  in  all 
probability,  involved. 

The  simplest  form  of  tactile  sensation  is  that  of  mere  contact,  as 
when  the  skin  is  lightly  touched  with  the  blunt  end  of  a  pencil. 
This  soon  deepens  into  the  sensation  of  pressure  if  the  contact  is 
made  closer;  and  eventually  the  sense  of  pressure  merges  into  a 
feeling  of  pain.  It  is  not  easy  to  say  whether  these  various  sensa- 
tions are  due  to  the  stimulation  of  different  nervous  elements,  or  to 
different  grades  of  stimulation  of  the  same  elements.  But  there  is 
some  pathological  evidence  in  favour  of  the  former  view,  e.g.,  it  is 
said  that  the  sensation  of  contact  is  abolished  in  cicatrices  where 
the  true  skin  has  been  destroyed,  although  sensibility  to  pressure 
persists.  The  existence  of  different  forms  of  sensory  end-organs  in 
the  skin  and  other  tissues  (touch-corpuscles,  corpuscles  of  Pacini, 
end-bulbs  of  Krause,  etc.)  is  also,  so  far  as  it  goes,  in  favour  of  the 


8io 


A  MANUAL  OF  PHYSIOLOGY 


same  view.  The  minimum  pressure  necessary  to  evoke  a  sensation 
of  contact  is  not  the  same  for  every  portion  of  the  skin.  The  fore- 
head and  palm  of  the  hand  are  most  sensitive. 

If  two  points  of  the  skin  are  touched  at  the  same  time  there  is 
a  double  sensation  when  the  distance  between  the  points  exceeds 
a  certain  minimum,  which  varies  for  different  parts  of  the  sensitive 
surface. 


Distance  at  which  two  points 
can  be  distinctly  felt,  in  mm. 

Point  of  tongue 

I'l 

Palmar  surface  of  third 

phalanx  of  finger 

2'2 

Dorsal  surface  of  third 

• 

phalanx  of  finger 

67 

Tip  of  nose  - 

67 

Back     - 

1  1  '2 

Eyelids 

11*2 

Skin  over  sacrum  - 

4°'5 

Upper  arm 

67-6 

Practice  increases  the  acuity  of  touch.  Even  in  a  few  hours  it 
may  be  temporarily  quadrupled  on  some  parts  of  the  skin.  Since 
at  the  same  time  it  is  increased  in  the  corresponding  part  of  the 
opposite  side  of  the  body,  it  is  argued  that  the  modification  takes 
place  in  the  central  nervous  system,  not  in  the  end-organs  them- 
selves. 

Few  of  the  internal  organs  seem  to  be  supplied  with 
tactile  nerves.  The  movements  of  a  tapeworm  in  the  intes- 
tines are  not  recognised  as  tactile  sensations,  nor  the  move- 
ments of  the  alimentary  canal  during  digestion,  nor  the 
rubbing  of  one  muscle  on  another  during  its  contraction. 

It  would  seem  that  pressure  is  only  perceived  when  it  affects  two 
neighbouring  areas  to  a  different  degree.  Thus,  the  atmospheric 
pressure,  bearing  uniformly  on  the  whole  surface  of  the  body,  causes 
no  sensation ;  we  are  so  entirely  unconscious  of  it  that  it  needed  the 
inspiration  of  genius  to  discover  it,  and  the  patience  of  genius  to 
force  the  discovery  on  the  world.  When  the  finger  is  dipped  in  a 
trough  of  mercury  at  its  own  temperature,  no  sensation  is  perceived 
except  a  feeling  of  constriction  at  the  surface  of  the  liquid. 

Sensations  of  Temperature. — When  a  body  colder  or  hotter 
than  the  skin  is  placed  on  it,  or  when  heat  is  in  any  other 
way  withdrawn  from  or  imparted  to  the  cutaneous  tissues 
with  sufficient  abruptness,  a  sensation  of  cold  or  heat  is 
experienced.  And  when  two  portions  of  the  skin  at  different 


THE  SENSES  811 

temperatures  are  put  in  contact,  we  feel  that,  relatively  to 
one  another,  one  is  warm  and  the  other  cold.  But  it  is 
worthy  of  remark  that  it  is  only  difference  of  temperature, 
and  not  absolute  height,  that  we  are  able  to  estimate  by 
our  sensations.  Thus,  a  hand  which  has  been  working  in 
ice-cold  water  will  feel  water  at  10°  as  warm ;  whereas  it 
would  appear  cold  to  a  warm  hand.  When  the  temperature 
of  the  skin  is  raised  above  or  diminished  below  a  certain 
limit,  the  sensation  of  change  of  temperature  gives  place  to 
one  of  pain ;  and  this  may  be  considered  as  due  either  to 
excessive  stimulation  of  the  end-organs  of  the  temperature 
sense,  or  as  due  to  stimulation  of  the  ordinary  sensory 
nerves,  which  are  normally  insensible  to  more  moderate 
variations  of  temperature. 

The  recent  researches  of  Blix,  Goldscheider,  and  others 
have  thrown  new  light  upon  the  anatomical  basis  of  the 
sensations  which  have  their  origin  in  the  skin.  They  have 
found  that  the  whole  skin  is  not  endowed  with  the  capacity 
of  distinguishing  temperature.  The  temperature  sense  is 
confined  to  minute  areas  scattered  over  the  cutaneous 
surface,  some  of  which  are  *  cold '  points,  i.e.,  respond  to 
variations  of  temperature  only  by  a  sensation  of  cold,  while 
others  are  *  warm  '  points  and  respond  only  by  a  sensation 
of  heat.  '  Cold '  points  are  present  in  greater  number  than 
'  warm/  It  has  even  been  stated  that  electrical  or  mechani- 
cal or  thermal  stimulation  of  a  nerve-trunk  like  the  radial 
in  its  course,  may  give  rise  to  sensations  of  temperature. 
But  there  is  strong  evidence  on  the  other  side,  and  even  if 
this  were  shown  to  be  the  case,  it  might  be  due  merely  to 
excitation  of  nerves  of  the  temperature  sense  supplying  the 
sheath  (nervi  nervorum).  When  a  nerve  is  compressed,  the 
sensibility  of  the  tract  supplied  by  it  disappears  for  cold 
sooner  than  for  heat. 

The  simplest  explanation  of  these  facts  seems  to  be  that  the  skin 
is  supplied  with  several  kinds  of  nerve-fibres,  anatomically  as  well  as 
functionally  distinct.  Some  fibres  minister  to  the  sensation  of  cold, 
others  to  that  of  heat,  others  to  that  of  pressure,  others,  perhaps,  to 
that  of  contact,  and,  possibly,  others  still  to  common  sensation. 
And  just  as  stimulation  of  the  optic  nerve  gives  rise  to  a  sensation  of 
light,  so  stimulation  of  any  one  of  the  cutaneous  nerves  gives  rise  to 


8i2  A  MANUAL  OF  PHYSIOLOGY  - 

the  specific  sensation  proper  to  the  group  to  which  it  belongs.  But 
with  the  eyes  closed  a  thermal  may  sometimes  be  mistaken  for  a 
tactile  stimulus. 

It  is  not  only  of  physiological  interest,  but  of  practical  importance, 
that  most  mucous  membranes  are  in  comparison  with  the  skin  but 
slightly  sensitive  to  changes  of  temperature ;  some,  as  the  mucous 
membrane  of  the  greater  portion  of  the  alimentary  canal,  seem  to  be 
entirely  devoid  of  nerves  of  temperature.  Only  towards  its  ends  in 
the  mouth,  pharynx  and  rectum,  and  to  some  extent  in  the  stomach, 
does  a  blunted  sensibility  appear.  The  uterus,  too,  is  quite  insensible 
to  heat;  and  hot  liquids  may  be  injected  into  its  cavity  at  a  temperature 
higher  than  that  which  can  be  borne  by  the  hand,  without  causing 
inconvenience — a  fact  which  finds  its  application  in  the  practice 
of  gynaecology  and  obstetrics.  It  is,  indeed,  obvious  that  in  the 
greater  number  of  the  internal  organs  the  conditions  necessary  for 
stimulation  of  temperature  nerves,  even  if  such  were  present,  could 
hardly  ever  exist. 

It  has  already  been  mentioned  that  changes  of  external  temperature 
exert  a  remarkable  influence  on  the  intensity  of  metabolism  (p.  495), 
and  it  has  been  supposed  that  this  is  brought  about  by  afferent 
impulses  travelling  up  the  cutaneous  nerves.  We  have  also  seen 
that  for  certain  kinds  of  stimuli  the  excitability  of  nerve-fibres  is 
increased  by  cooling  (p.  574).  It  is  possible  that  this  is  the  case  for 
the  fibres  in  the  skin  which  are  concerned  in  the  regulation  of  the 
production  of  heat,  and  it  has  been  suggested  that  this  fact  may  have 
a  bearing  on  the  reflex  regulation  of  temperature  (Lorrain  Smith). 

The  Muscular  Sense. 

Voluntary  muscular  movements  are  accompanied  with  a 
peculiar  sensation  of  effort,  graduated  according  to  the 
strength  of  the  contraction,  and  affording  data  from  which 
a  judgment  as  to  its  amount  and  direction  may  be  formed. 
To  these  sensations  the  name  of  the  muscular  sense  has  been 
given. 

Some  writers  have  supposed  that  the  muscular  sense 
does  not  depend  upon  afferent  impulses  at  all,  but  that 
the  nervous  centres  from  which  the  voluntary  impulses 
depart,  take  cognizance,  retain  a  record,  so  to  speak,  of  the 
quantity  of  outgoing  nervous  force ;  that  the  effort  which 
we  feel  in  lifting  a  heavy  weight  is  an  effort  of  the  cells  of 
the  motor  centres  from  which  the  innervation  of  the  groups 
of  muscles  takes  origin,  and  not  of  the  muscles  themselves. 

But  although  this  feeling  of  central  effort  or  outflow  (we 
can  hardly  say  of  central  fatigue)  may  play  a  part  in  the 


THE  SENSES  813 

muscular  sense,  it  cannot  be  doubted  that  the  brain  is  kept 
in  touch  with  the  contracting  muscle  by  impulses  of  various 
kinds  which  reach  it  by  different  afferent  channels. 

The  corpuscles  of  Pacini,  which  exist  in  considerable  numbers  in 
the  neighbourhood  of  joints  and  ligaments,  and  in  the  periosteum  of 
bones,  would  seem  well  fitted  to  play  the  part  of  end-organs  for 
the  tactile  sensations  caused  by  the  movements  of  flexion,  extension, 
or  rotation  of  one  bone  on  another,  which  form  so  large  a  portion  of 
all  voluntary  muscular  movements.  And  it  has  been  stated  that 
paralysis  of  these  bodies  in  the  limbs  of  a  cat  by  section  of  the 
nerves  going  to  them  causes  a  characteristic  uncertainty  of  move- 
ment which  suggests  that  something  necessary  to  normal  co-ordination 
has  been  taken  away.  We  have  already  seen  that  the  skeletal  muscles 
possess  numerous  afferent  fibres  (p.  696).  Some  of  these  may  be 
nerves  of  ordinary  sensation.  For  although,  when  a  muscle  is  laid 
bare  in  man  and  stimulated  electrically,  the  sensation  does  not  in 
general  amount  to  actual  pain,  it  is  capable,  under  the  influence  of 
strong  stimuli,  of  taking  on  a  painful  character.  And  nobody  who 
has  felt  the  severe  and  sometimes  almost  intolerable  pain  of  muscular 
cramp  would  be  likely  to  deny  the  existence  of  sensory  muscular 
nerves.  But  after  deducting  these,  we  must  assume  that  a  very  large 
proportion  of  the  afferent  nerves  of  muscle  have  other  functions,  and 
among  them  may  be  the  conveyance  of  impulses  connected  with  the 
muscular  sense. 

In  the  spinal  cord,  these  impulses  are  probably  conducted  up 
through  the  posterior  column  ;  and,  although  nothing  is  known  as  to 
the  paths  they  follow  in  the  higher  parts  of  the  central  nervous 
system,  it  is  certain  that  there  is  some  afferent  bond  of  connection 
between  the  cortical  motor  areas  and  the  muscles  which  they  control 
(p.  718). 

Tactile  sensations  set  up  in  the  skin  or  mucous  membrane  lying 
over  contracting  muscles  may  also  help  the  nervous  motor  mechanism 
in  appreciating  and  regulating  the  amount  of  contraction ;  but  the 
fact  that,  in  anaesthesia  of  the  mucous  membrane  covering  the  vocal 
cords  produced  by  cocaine,  the  voice  is  not  at  all  impaired,  shows 
that  muscular  contractions  of  extreme  nicety  can  be  carried  on  without 
any  such  aid. 

Pain. 

Pain  has  been  defined  as  *  the  prayer  of  a  nerve  for  pure  blood.' 
The  idea  is  not  only  true  as  poetry,  but,  with  certain  deductions  and 
limitations,  true  as  physiology.  That  is  to  say,  pain,  as  a  rule,  is  a 
sign  that  something  has  gone  wrong  with  the  bodily  machinery; 
freedom  from  pain  is  the  normal  state  of  the  healthy  body.  Physio- 
logically, pain  acts  as  a  danger-signal ;  it  points  out  the  seat  of  the 
mischief,  and  even,  in  certain  cases,  by  compelling  rest,  favours  the 
process  of  repair.  Thus,  the  surgeon  has  sometimes  looked  upon 
pain  as  '  Nature's  splint.'  But  as  a  matter  of  fact,  a  certain  amount 
of  pain  occurring  at  intervals  is  not  incompatible  with  high  health ; 


814  A  MANUAL  OF  PHYSIOLOGY 

and  probably  nobody,  even  when  accidents  and  indiscretions  of  all 
kinds  are  avoided,  is  entirely  free  from  pain  for  any  considerable 
time.  Sometimes,  indeed,  the  mere  fixing  of  the  attention  on  a 
particular  part  of  the  body  is  sufficient  to  bring  out  or  to  detect  a 
slight  sensation  of  pain  in  it ;  and  it  is  matter  of  common  experience 
that  a  dull  continuous  pain,  like  that  of  some  forms  of  toothache,  is 
aggravated  by  thinking  of  it,  and  relieved  when  the  attention  is 
diverted. 

In  general,  the  skin  is  far  more  sensitive  to  pain  than  the  deeper 
structures.  The  most  painful  part  of  an  operation  is  generally  the 
stitching  of  the  wound.  The  cutting  of  healthy  muscle  causes  no 
pain.  In  an  operation  in  which  an  artificial  connection  was  estab- 
lished between  the  stomach  and  the  small  intestine  (gastro-enteros- 
tomy),  and  in  which  no  anaesthetic  was  administered,  the  only  pain 
of  which  the  patient  complained  was  produced  by  the  incision  in  the 
skin  (Senn).  The  spasmodic  contraction  of  the  intestines  and 
stomach  causes  the  intense  pain  of  colic  and  gastralgia.  Labour  is 
an  example  of  a  strictly  physiological  function  which  is  the  occasion 
of  severe  pain.  Tissues  normally  insensible  to  pain  may  become 
acutely  painful  when  inflamed. 

It  is  not  quite  settled  as  yet  whether  the  afferent  fibres  which 
minister  to  painful  sensations  are  anatomically  distinct  from  the 
fibres  of  tactile  sensation,  and  of  the  other  sensations  included  under 
the  sense  of  touch ;  but,  upon  the  whole,  the  balance  of  evidence, 
physiological  and  pathological,  seems  to  incline  to  the  view  that  there 
is  such  a  distinction.  For  the  conducting  paths  in  the  spinal  cord 
appear  not  to  be  the  same  for  tactile  and  for  painful  impressions. 
And  in  certain  cases  of  disease  sensibility  to  pain  may  be  lost,  while 
tactile  sensations  are  still  perceived ;  or,  on  the  other  hand,  pain  may 
be  felt  in  cases  where  tactile  sensibility  is  abolished.  Loss  of  tem- 
perature sensation,  however,  is  almost  always  accompanied  by  loss  of 
sensibility  to  pain. 

Relation  of  Stimulus  to  Sensation. 

It  is  impossible  to  measure  sensation  in  terms  of  stimulus.  All 
that  we  can  do  is  to  compare  differences  in  the  intensity  of  stimuli 
and  differences  in  the  resultant  sensations,  or,  in  other  words,  to 
compare  stimuli  together  and  to  compare  sensations  together.  And 
when  we  determine  the  amount  by  which  a  given  stimulus  must  be 
increased  or  diminished  in  order  that  there  may  be  a  just  perceptible 
increase  or  diminution  in  the  sensation,  it  is  found  that  (with  certain 
limitations)  the  two  are  connected  by  a  simple  law :  Whatever  the 
absolute  strength  of  a  stimulus  of  given  kind  may  be,  it  must  be 
increased  by  the  same  fraction  of  its  amount  in  order  that  a  difference 
in  the  sensation  may  be  perceived  (sometimes  called  Weber 's  law]. 
Thus,  a  light  of  the  strength  of  one  standard  candle  must  be  increased 
by  -j^th  candle,  a  light  of  10  candles  by  T\)VnsJ  and  a  light  of  100 
candles  by  a  candle,  in  order  that  the  eye  may  perceive  that  an 
increase  has  taken  place>  just  as  the  weight  necessary  to  turn  a 


PRACTICAL  EXERCISES  815 

balance  increases  with  the  amount  already  in  the  pans.  The  frac- 
tion varies  for  the  different  senses.  It  is  about  yj-^  for  light,  J  for 
sound.  But  it  would  appear  that  Weber's  law  does  not  hold  for  the 
pressure  sense,  nor  for  the  other  senses  above  and  below  certain 
limits.  Fechner,  making  various  assumptions,  has  thrown  Weber's 

law  into  the  ioimy  =  k  — - — ,  where  y  is  the  intensity  of  sensation, 

xo 

x  the  intensity  of  stimulation,  and  XQ  the  smallest  intensity  of 
stimulus  which  can  be  perceived  (liminal  intensity).  This  so-called 
psycho-physical  law  of  Fechner  states  that  the  sensation  varies  as 
the  logarithm  of  the  stimulus.  But  Fechner's  law  has  been  subjected 
to  serious  criticism,  and  the  subject  cannot  be  further  pursued  here. 


PRACTICAL  EXERCISES  ON  CHAPTER  XIII. 

1.  Formation  of  Inverted  Image  on  the  Retina. — Fix  the  eye  of 
an  ox  or  of  a  dog  or  rabbit  (preferably  an  albino),  after  removal  of 
part  of  the  posterior  surface  of  the  sclerotic,   in  a  hole   cut  in  a 
blackened  box.     Place  a  candle  in  front  of  the  eye.     Look  from 
behind,  and  observe  the  inverted  image  of  the  candle  formed  on  the 
retina.     Move  the  candle  until  the  image  is  as  sharp  as  possible. 
Now  bring  between  the  candle  and  the  eye  a  concave  lens.     The 
image  becomes  blurred,  the  candle  must   be  put  farther  away  to 
render  it  distinct,  and  perhaps  no  position  of  the  candle  can  be  found 
which  will  give  a  sharp  image.     If  the  lens  is  convex,  the  candle 
must  be  brought  nearer,  and  a  sharp  image  can  always  be  formed  by 
bringing  it  near  enough.     If  both  a  convex  and  a  concave  glass  be 
placed  in  front  of  the  eye,  they  will  partially  or  wholly  neutralize 
each  other. 

2.  Helmholtz's  Phakoscope  (Fig.  294).— This  instrument  is  em- 
ployed in  studying  the  changes  that  take  place  in  the  curvature  of 

the  lens  during  accommo- 
dation. It  is  to  be  used 
in  a  dark  room.  A  candle 
is  placed  in  front  of  the 
two  prisms  P,  P'.  The 
observer  looks  through  the 
hole  B ;  the  observed  eye 
is  placed  opposite  the 
hole  A.  The  candle  or 
the  observed  eye  is  moved 
till  the  observer  sees  three 
FIG.  294.— PHAKOSCOPE.  pairs  of  images,  one  pair, 

the  brightest  of  all,  re- 
flected from  the  anterior  surface  of  the  cornea ;  another,  the  largest  of 
the  three,  but  dim,  reflected  from  the  anterior  surface  of  the  lens  ;  and 
a  third  pair,  the  smallest  of  all,  reflected  from  the  posterior  surface 


8i6 


A  MANUAL  OF  PHYSIOLOGY 


of  the  lens  (Fig.  263).  The  last  two  pairs  can,  of  course,  only  be 
seen  within  the  pupil.  The  observed  eye  is  now  focussed  first  for  a 
distant  object  (it  is  enough  that  the  person  should  simply  leave 
his  eye  at  rest,  or  imagine  he  is  looking  far  away),  and  then  for 
a  near  object  (an  ivory  pin  at  A).  During  accommodation  for  a 
near  object  no  change  takes  place  in  the  size,  brightness,  or  position 
of  the  first  or  third  pair  of  images ;  therefore  the  cornea  and  the 
posterior  surface  of  the  lens  are  not  altered.  The  middle  images 
become  smaller,  somewhat  brighter,  approach  each  other,  and  also 
come  nearer  to  the  corneal  images.  This  proves  (a]  that  the  an- 
terior surface  of  the  lens  undergoes  a  change ;  (b)  that  the  change  is 
increase  of  curvature  (diminution  of  the  radius  of  curvature),  for  the 
virtual  image  reflected  from  a  convex  mirror  is  smaller  the  smaller  is 
its  radius  of  curvature.  (The  third  pair  of  images  really  undergo  a 


FIG.  295. — SCHEINER'S  EXPERIMENT. 

In  the  upper  figure  the  eye  is  focussed  for  a  point  farther  away  than  the  needle  ;  in 
the  lower,  for  a  nearer  point.  The  continuous  lines  represent  rays  from  the  needle, 
the  interrupted  lines  rays  from  the  point  in  focus.  But  the  lines  inside  the  eye,  which 
by  an  error  in  engraving  are  drawn  as  continuous  lines,  ought  to  be  interrupted,  and 
vice  versd. 

slight  change,  such  as  would  be  caused  by  a  small  increase  in  the 
curvature  of  the  posterior  surface  of  the  lens ;  but  the  student  need 
not  attempt  to  make  this  out.) 

3.  Schemer's  Experiment. — Two  small  holes -are  pricked  with  a 
needle  in  a  card,  the  distance  between  them  being  less  than  the 
diameter  of  the  pupil.  The  card  is  nailed  on  a  wooden  holder,  and 
a  needle  stuck  into  a  piece  of  wood  is  looked  at  with  one  eye  through 
the  holes.  When  the  eye  is  accommodated  for  the  needle,  it  appears 
single ;  when  it  is  accommodated  for  a  more  distant  object,  or  not 
accommodated  at  all,  the  needle  appears  double.  The  two  images 
approach  each  other  when  the  needle  is  moved  away  from  the  eye, 
and  separate  out  from  each  other  when  it  is  moved  towards  the  eye. 
When  the  eye  is  accommodated  for  a  point  nearer  than  the  needle, 
the  image  is  also  double ;  the  images  approach  each  other  when  the 


PRACTICAL  EXERCISES  817 

needle  is  brought  closer  to  the  eye,  and  move  away  from  each  other 
when  it  is  moved  away  from  the  eye.  If  while  the  needle  is  in  focus 
one  of  the  holes  be  stopped  by  the  finger,  the  image  is  not  affected. 
When  the  eye  is  focussed  for  a  greater  distance  than  that  of  the 
needle,  stopping  one  of  the  holes  causes  the  image  on  the  other  side 
of  the  field  of  vision  to  disappear ;  if  the  eye  is  focussed  for  a  smaller 
distance,  the  image  on  the  same  side  as  the  blocked  hole  disappears 
(Fig.  295). 

4.  Kiihne's  Artificial  Eye. --This  is  an  elongated  box  provided 
with  a  glass  lens  to  represent  the  crystalline,  and  a  ground-glass  plate 
to  represent  the  retina.  The  box  is  filled  with  water  to  which  a  little 
eosin  has  been  added.  The  water  must  be  perfectly  clear.  A  beam 
of  sunlight  or  electric  light,  or,  in  case  these  are  not  available,  a 
beam  from  an  oil  stereopticon,  is  made  to  pass  through  the  box. 
Many  of  the  facts  of  vision  can  be  illustrated  by  means  of  this  piece 
of  apparatus. 


FIG.  296. — MAP  OF  BLIND  SPOT  (REDUCED  BY  ONE-HALF). 
Right  eye.     Distance  of  eye  from  paper,  12  inches. 

(a)  Let  the  rays  of  light  pass  through  an  arrow-shaped  slit  in  a 
piece  of  cardboard.     An  inverted  image  of  the  arrow  is  formed  on 
the  retina.     Move  the  retina  nearer  to  or  farther  from  the  lens  to 
make  the  image  sharp.     In  the  eye,  accommodation  is  not  brought 
about  by  a  change  in  the  distance  of  retina  and  lens,  but  by  a  change 
of  curvature  in  the  lens. 

(b)  Remove  the  lens.     The  focus  is  now  far  behind  the  retina. 
This  illustrates  the  state  of  matters  after  the  lens  has  been  removed 
for  cataract.     The  arrow  can  again  be  sharply  focussed  on  the  retina 
by  putting  a  convex  lens  in  front  of  the  artificial  eye.     But  this 
must  be  much  weaker  than  the  lens  which  has  been  removed,  for  if 
the  latter  be  placed  in  front  of  the  eye,  the  image  is  formed  a  little 
behind  the  cornea. 

(c)  Replace  the  lens.     Move  the  retina  so  far  back  that  the  image 
is  focussed  in  front  of  it.     This  is  the  condition  in  the  myopic  eye. 
Put  a  weak  concave  lens  in  front  of  the  eye ;  the  image  now  falls 

52 


8i8 


A  MANUAL  OF  PHYSIOLOGY 


more  nearly  on  the  retina.  Move  the  retina  forward,  so  that  the 
focus  is  behind  it.  This  corresponds  to  the  hypermetropic  eye.  Put 
a  weak  convex  lens  in  front  of  the  eye  to  correct  the  defect. 

(d)  Observe  that  a  plate  with  a  hole  in  it,  placed  in  front  of  the 
eye,  renders  an  indistinctly  focussed  image  somewhat  sharper  by 
cutting  off  the  more  divergent  peripheral  rays. 


FIG.  297. — COMPOSITE  PICTURE  OF  BLIND  SPOT  (NOT  REDUCED). 

The  blind  spot  of  the  right  eye  was  mapped  by  31  men,  the  eye  being  always  at  a 
distance  of  12  inches  from  the  paper.  The  maps  were  then  superposed.  The  amount 
of  white  at  any  point  of  the  figure  is  intended  to  correspond  to  the  number  of  maps 
which  overlapped  at  that  point.  Although  the  mechanical  process  of  reproduction 
gives  rather  an  imperfect  view  of  the  composite  map,  the  area  in  the  centre  of  the  figure 
where  the  white  is  most  continuous,  and  which  represents  the  shape  of  the  majority  of 
the  blind  spots,  evidently  bears  a  general  resemblance  to  the  outline  in  Fig.  296. 

(e)  Fill  with  water  the  chamber  in  front  of  the  curved  glass  that 
represents  the  cornea.  The  focus  is  now  behind  the  back  of  the  eye 
altogether.  Refraction  by  the  cornea  is  here  abolished,  as  is  the 
case  in  vision  under  water.  An  additional  lens  inside  the  eye,  or  a 


PRACTICAL  EXERCISES  819 

weaker  one  in  front  of  it,  corrects  the  defect.     Fishes  have  a  much 
more  nearly  spherical  lens  than  land  animals,  and  a  flat  cornea. 

(/)  Fill  the  hollow  cylindrical  lens  with  water,  and  place  it  in 
front  of  the  artificial  eye.  It  is  now  astigmatic.  A  point  of  light  is 
focussed  on  the  retina,  not  as  a  point,  but  as  a  line.  The  vertical 
and  horizontal  limbs  of  a  cross  cut  out  of  a  piece  of  cardboard  and 
placed  in  the  path  of  the  beam  of  light  cannot  be  both  focussed  at 
the  same  time. 

5.  Mapping  the  Blind-spot. — Make  a  black  cross  on  a  piece  of 
white  paper  attached  to  the  wall,  the  centre  of  the  cross  being  at  the 
height  of  the  eye  in  the  erect  position.     Stand  about  12  inches  from 
the  wall,  the  chin  supported  on  a  projecting  piece  of  wood.     Fix  the 
centre  of  the  cross  with  one  eye,  the  other  being  closed,  and  move 
over  the  paper  a  pencil  covered,  except  at  the  point,  with  white  paper, 
until  the  point  just  disappears.     Make  a  mark  on  the  paper  at  this 
point,  and  repeat  the  observation  for  all  diameters  of  the  field.     The 
blind-spot  is  thus  marked  out  (Fig.  296).     Its  shape  is  not  the  same 
in  all  eyes  (Fig.  297).     Its  size  and  distance  from  the  fovea  centralis 
can  be  calculated  from  the  formula  on  p,  746. 

6.  Ophthalmoscope — (i)    Human  Eye  (p.  761). — Let   A  be   the 
observer,  and  B  the  person  whose  eye  is  to  be  examined.     A  and  B 
are  seated  facing  each  other.     A  little  behind  and  to  the  left  of  B  is 
a  lamp  on  a  level  with  his  eyes  ;  the  room  is  otherwise  dark.     For  a 
clinical  examination,  the  pupil  should  be  dilated  by  putting  into  the 
eye  a  drop  of  a  -5  per  cent,  solution  of  atropia  sulphate,  but  this  is 
not  indispensable  for  the  experiment. 

(a)  Direct  Method. — A  takes  the  mirror  in  his  right  hand,  and, 
holding  it  close  to  his  own  eye,  looks  through  the  central  hole,  and 
throws  a  beam  of  light  into  B's  eye.      A  red  glare,  the  so-called 
'  reflex '  from  the  choroidal  vessels,  is  now  seen.     A  then  brings  the 
mirror  to  within   2  or  3  inches  of  B's  eye,  keeping  his  own  eye 
always  at  the  aperture.     A  and  B  both  relax  their  accommodation, 
as  if  they  were  looking  away  to  a  distance.     If  both  eyes  are  emme- 
tropic,  the  retinal  vessels  will  be  seen.     A  should  now  move  the 
mirror  or  B  his  eye  so  as  to  bring  into  view  the  white  optic  disc  with 
the  central  artery  and  vein  of  the  retina  crossing  it. 

(b)  Indirect  Method. — A  takes  the  mirror  in  his  right   hand  to 
examine  B's  right  eye,  places  his  own  eye  behind  the  aperture  as 
before  at  a  distance  of  about    18  inches  from  B,  and   throws  a 
beam  of  light  into  B's  eye.     Then  A  takes  a  small  biconvex  lens  in 
his   left   hand,  and   places  it  2  or  3  inches   in   front   of  B's  eye, 
keeping  it  steady  by  resting  his  little  finger  on  B's  temple.     A  now 
moves  the  mirror  until  he  sees  the  optic  disc. 

(2)  Examine  a  rabbit's  eye  by  the  direct  and  indirect  method. 
Dilate  the  pupil  by  a  drop  or  two  of  atropia  solution. 

For  practice,  before  doing  (i)  and  (2)  the  student  should  examine 
an  artificial  *  eye '  by  both  methods,  so  as  to  get  a  clear  view  of  what 
represents  the  retina.  A  substitute  for  the  artificial  eye  may  be 
made  by  unscrewing  the  lower  lens  of  the  eyepiece  of  a  microscope, 

52 — 2 


820 


A  MANUAL  OF  PHYSIOLOGY 


and  fastening  in  its  place  a  piece  of  paper  with  some  printed  matter 
on  it     The  letters  must  be  made  out  with  the  ophthalmoscope. 

7.  Pupillo-dilator  and  Constrictor  Fibres. — (a)  Set  up  an  induc- 
tion machine  arranged  for  tetanus,  and  connect  a  pair  of  electrodes 
through  a  short-circuiting  key  with  the  secondary.  Etherize  a 
cat  by  putting  it  into  a  large  vessel  with  a  lid,  slipping  into  the 
vessel  a  piece  of  cotton-wool  soaked  with  ether,  and  waiting  till  the 
movements  of  the  animal  inside  the  vessel  have  ceased,  Then 


FIG.  298.— APPARATUS  FOR  COLOUR-MIXING. 

quickly  put  the  cat  on  a  holder  and  maintain  anaesthesia  with  ether. 
Expose  the  sympathetic  in  the  neck ;  the  carotid  is  taken  as  the 
guide  to  it.  Ligature  the  nerve,  and  cut  below  the  ligature.  On 
stimulating  the  upper  (cephalic)  end,  the  pupil  of  the  corresponding 
eye  dilates. 

(fr)  Observe  in  the  eye  of  a  fellow-student,  or,  by  means  of  a 
looking-glass,  in  your  own  eye,  that  when  light  falls  on  one  eye  both 
pupils  contract. 

(c)  Observe  that  when  the  eye  is  accommodated  for  a  near  object 


PRACTICAL  EXERCISES  821 

the  pupil  contracts,  and  that  it  dilates  when  a  distant  object  is 
looked  at. 

8.  Colour-mixing. — (a)  Arrange  a  red  and  a  bluish-green  disc  on 
one  of  the  steel   discs   of  the  colour-mixing  apparatus  shown  in 
Fig.  298,  so  that  a  part  of  each  is  seen.     On  another  arrange  a  violet 
and  a  yellow  disc,  and  on  the  third  an  orange  and  a  blue  disc.     By 
adjustment  of  the  proportions  of  the  two  colours  a  uniform  grey  can 
be   obtained    from   each    of    these   combinations   (complementary 
colours)  when  the  discs  are  rapidly  rotated. 

(b)  Mix  two  colours  that  are  not  complementary,  e.g.,  blue  and 
red  ;  grey  or  white  cannot  be  obtained  by  any  adjustment  of  pro- 
portions ;   the  result  is   always   a   mixed   colour,  the   precise   hue 
depending  on  the  amount  of  each  ingredient. 

(c)  Take  papers  of  any  three  colours  from  widely-separated  parts  of 
the  spectrum,  e.g.,  blue,  green,  and  red,  and  arrange  them  on  one  of 
the  rotating  discs.    By  varying  the  proportions  white  can  be  produced, 
and  any  other  coloured  paper  fastened  on  another  of  the  rotating 
discs  can  be  matched  by  adding  white  to  the  three  colours. 

9.  Talbot's  Law. — Rotate  a  disc  one  sector  of  which  is  black  and 
the  rest  white,  or  a  disc  like  that  in  Fig.  283.     A  uniform  shade  is 
produced  as  soon  as  a  speed  of  about  25  revolutions  a  second  has 
been  attained,  and  this  is  not  altered  by  further  increase  in  the 
speed. 

10.  Purkinje's  Figures. — (a)  Concentrate  a  beam  of  sunlight  by  a 
lens  on  the  sclerotic  at  a  point  as  far  as  possible  from  the  corneal 
margin,  passing  the  ray  through  a  parallel-sided  glass  trough  filled 
with  a  solution  of  alum  to  sift  out  the  long  heat-rays.     The  eye  is 
turned  towards  a  dark  ground.    The  field  of  vision  takes  on  a  bronzed 
appearance,  and  the  retinal  bloodvessels  stand  out  on  it  as  a  dark 
network,  which  appears  to  move  in  the  same  direction  as  the  spot  of 
light  on  the  sclerotic.     A  portion  of  the  field  corresponding  to  the 
yellow  spot  is  devoid  of  shadows  (p.  771). 

(b)  Direct  the  eyes  to  a  dark  ground  while  a  flame  held  at  the  side 
of  the  eye,  and  at  a  distance  from  the  visual  line,  is  moved  slightly 
to  and  fro.     A  picture  of  branching  bloodvessels  appears.     This 
experiment  is  performed  in  a  dark  room  (p.  772). 

(c)  Immediately  on  awaking  look  at  a  white  ceiling  for  an  instant; 
a  pattern  of  branched  bloodvessels  is  seen.     If  the  eye  be  at  once 
closed,  and  then  opened  with  a  blinking  movement,  this  may  be 
observed  again  and  again.     Ultimately  the  appearance  fades  away. 

11.  Study  by  means  of  the  monochord,  a  stretched  string  with  a 
movable  stop,  the  relation  between  the  pitch  of  the  note  given  out 
by  a  vibrating  string,  and  its  length  and  tension. 

12.  Cause  two  tuning-forks  of  nearly  equal  pitch  to  vibrate  at 
the  same  time.     Make  out  the  beats,  and  count  their  number  per 
second. 

13.  Measure  on  different  parts  of  the  skin  and  accessible  mucous 
membranes  the  distances  at  which  the  points  of  a  pair  of  compasses 
must  be  held  apart  in  order  that  two  distinct  sensations  may  be 
experienced  (p.  810)  (aesthesiometer). 


CHAPTER   XIV. 
REPRODUCTION. 

Regeneration  of  Tissues. — Since  cells  are  constantly  dying  within 
the  body,  they  must  be  constantly  reproduced.  In  some  tissues  the 
process  by  which  this  is  accomplished  is  more  evident,  and  therefore 
better  known,  than  in  others.  The  most  highly-organized  tissues  are 
with  difficulty  repaired,  or  not  at  all.  The  epidermis  is  always 
wearing  away  at  its  surface,  and  is  being  constantly  replaced  by  the 
multiplication  of  the  cells  of  the  stratum  Malpighii.  In  the  corneous 
layer  we  have  only  dead  cells  ;  in  the  Malpighian  layer  we  have  every 
histological  gradation  from  squames  to  columns,  and  every  physio- 
logical gradation  from  cells  which  are  about  to  die  to  cells  that  have 
just  been  born.  The  corpuscles  of  the  blood  undoubtedly  arise  at 
first,  and  are  recruited  throughout  life,  by  the  proliferation  of  mother- 
cells.  The  gravid  uterus  grows  by  the  formation  of  new  fibres  from 
the  old,  and  by  the  enlargement  of  both  old  and  new.  A  severed 
muscle  is  generally  united  only  by  connective  or  scar  tissue,  but 
under  favourable  conditions  a  complete  muscular  '  splice '  may  be 
formed.  A  broken  bone  is  regenerated  by  the  proliferation  of  cells 
of  the  periosteum,  which  become  bone-corpuscles.  We  do  not  know 
whether  there  is  any  new  formation  of  nerve-cells  in  the  adult 
organism  (but  see  p.  713),  but  nerve-fibres  which  have  been  destroyed 
by  accident  or  operation  are  readily  regenerated  by  the  growth  of  new 
processes  from  the  cells  that  originally  produced  them  ;  and  some  of 
the  end-organs  of  efferent  nerves  may  share  in  this  regeneration. 

In  lower  forms  of  animals,  and  in  all  or  most  vegetables,  the  power 
of  regeneration  is  much  greater  than  in  man.  The  starfish  can  not 
only  repair  the  loss  of  an  arm,  but  from  a  severed  arm  a  complete 
animal  can  be  developed.  A  newt  can  reproduce  an  amputated  toe, 
and  every  tissue — skin,  muscle,  nerves,  bone — will  be  in  its  place. 
After  extraction  of  the  crystalline  lens  in  triton  larvae,  &  new  lens  is 
formed  from  the  iris  epithelium. 

Thus,  in  a  sense^  reproduction  is  constantly  going  on  within  the 
bodies  even  of  the  higher  animals.  But  since  the  whole  organism 
eventually  dies,  as  well  as  its  constituent  cells,  a  reproduction  of  the 
whole,  a  regeneration  en  masse,  is  required. 

A  cell  of  the  stratum  Malpighii  can  only,  so  far  as  we  know, 
reproduce  a  similar  cell,  and  this  is  characteristic  of  cells  that  have 


REPRODUCTION  823 

undergone  a  certain  amount  of  differentiation,  especially  in  the 
higher  animals.  The  fertilized  ovum,  on  the  other  hand,  has  the 
power  of  reproducing  not  only  ova  like  itself,  but  the  counterparts  of 
every  cell  in  the  body.  And  this  is  only  the  highest  development  of 
a  power  which  is  in  a  smaller  degree  inherent  in  other  cells  in  lower 
forms.  Plants  and  the  lowest  animals  are  far  less  dependent  upon 
reproduction  by  means  of  special  cells.  A  piece  of  a  Hydra  separated 
off  artificially  or  by  simple  fission  becomes  a  complete  Hydra,  as 
was  shown  by  Trembley  a  century  and  a  half  ago.  A  cutting  from  a 
branch,  a  root,  a  tuber,  or  even  a  leaf  of  a  plant,  may  reproduce  the 
whole  plant.  It  is  as  if  each  cell  in  these  lowly  forms  carried  within 
it  the  plan  of  the  complete  organism,  from  which  it  built  up  the 
perfect  plant  or  animal.  But  the  special  bias  or  trend  of  growth 
characteristic  of  each  form  is  not  a  rigid  rule.  It  can  be  modified ; 
it  is  modified  in  every  garden  and  pond  by  influences  coming  from 
without.  The  inborn  rule  of  life  for  many  plants  is  to  grow  straight 
up ;  but  this  rule  is  often  traversed  by  circumstances — by  differences 
in  the  amount  of  sunshine,  for  example,  caught  by  one  side  or  the 
other,  or  by  the  position  of  neighbouring  objects  which  hinder  or 
help  a  vertical  growth.  And  in  animals  Pfliiger  has  shown  that  the 
direction  of  the  lines  of  cleavage  of  the  ovum  of  a  frog  depends  on 
the  direction  in  which  gravity  acts,  although  Driesch  and  Hertwig 
find  that  the  nucleus  can  even  be  made  artificially  to  change  its  place 
with  reference  to  the  yolk,  without  hindering  the  development  of  a 
normal  animal.  Artificial  mouths,  surrounded  by  tentacles,  can  be 
formed  in  Cerianthus,  an  animal  belonging  to  the  same  group  as  the 
sea-anemones,  merely  by  making  a  cut  in  the  body-wall  and  prevent- 
ing it  from  closing.  In  an  Ascidian,  too  (the  Cynone  intestinalis), 
artificial  openings  in  the  branchial  sac,  surrounded  by  numerous  pig- 
mented  points  similar  to  the  eye-spots  around  the  natural  mouth  and 
anus,  have  been  produced  (Loeb).  Even  in  Amphioxus,  the  lowest 
of  the  vertebrates,  the  eggs  have  been  broken  up  by  shaking,  and  a 
complete  animal  evolved  from  as  little  as  one-eighth  of  an  ovum. 
If  the  separation  was  incomplete  a  kind  of  Siamese  twins,  or  even 
triplets,  could  be  obtained  (Wilson  and  Mathews). 

Reproduction  in  the  Higher  Animals. — In  all  the  higher  animals 
reproduction  is  sexual,  and  the  sexes  are  separate. 

In  regard  to  the  secretions  of  the  reproductive  glands,  all  that 
is  necessary  to  be  said  here  is  that,  unlike  other  secretions,  their 
essential  constituents  are  living  cells.  The  spermatozoa  in  the 
male  have,  indeed,  diverged  far  from  the  primitive  type.  Certain 
(spermatogenous)  cells  in  the  tubules  of  the  testicle  divide  so  as  to 
form  spermatoblasts.  Each  spermatoblast  becomes  a  spermatozoon, 
the  head  of  the  latter  representing  the  nucleus  of  the  former;  and  it 
is  this  nucleus  which  is  the  essential  contribution  of  the  male  to  the 
reproductive  process.  The  tail  of  the  spermatozoon  is  simply,  from 
the  physiological  point  of  view,  a  motile  arrangement,  whose  function 
it  is  to  carry  the  nucleus  of  the  spermatoblast,  freighted  with  all  that 
the  father  can  transmit  to  the  offspring,  into  the  neighbourhood  of 
the  female  reproductive  e'ement  or  ovum. 


824  ^  MANUAL  OF  PHYSIOLOGY 

The  ovum  also  begins  as  a  typical  cell  with  nucleus  (germinal 
vesicle)  and  nucleolus  (germinal  spot),  and  it  forms,  by  its  repeated 
subdivision,  all  the  cells  of  the  fcetal  body.  But,  except  in  some 
(parthenogenetic]  forms,  it  never  awakens  to  this  reproductive  activity 
till  fecundation  has  occurred  ;  and  fecundation  essentially  consists  in 
the  union  of  the  male  with  the  female  element,  or  rather  in  the  union 
of  the  male  and  female  nucleus. 

From  time  to  time  a  Graafian  follicle,  over-distended  by  its  liquor 
folliculi,  bursts  on  the  surface  of  the  ovary  and  discharges  an  ovum. 
The  frayed  end  of  the  Fallopian  tube,  rising  up  finger-like  from  the 
dilatation  of  its  bloodvessels,  grasps  the  ovum,  and  it  is  passed 
slowly  along  the  tube  by  the  downward-lashing  cilia  which  line  it. 
If  not  impregnated,  it  soon  perishes  amid  the  secretions  of  the 
uterus — how  soon  has  been  matter  of  discussion,  and  can  hardly  be 
considered  as  settled.  If,  however,  impregnation  occurs,  the  ovum 
becomes  fixed  in  one  of  the  crypts  or  pouches  of  the  uterine  mucous 
membrane  (decidua  serotina\  which  grows  round  it  as  the  decidua 
reflex  a. 

Menstruation. — In  the  mature  female,  from  puberty,  the  age  at 
which  the  reproductive  power  begins  (thirteenth  to  fifteenth  year), 
on  till  the  time  of  the  menopause  (fortieth  to  fiftieth  year),  at  which  it 
ceases,  an  ovum — or  it  may  be  in  some  cases  more  than  one — is  dis- 
charged at  regular  intervals  of  about  four  weeks.  This  discharge  is 
accompanied  by  certain  constitutional  symptoms  and  local  signs  that 
last  for  a  variable  number  of  days.  The  genital  organs  are  congested, 
and  a  quantity  of  blood,  which  varies  in  different  individuals,  but  is 
usually  from  100  to  200  grammes — that  is  to  say,  ^th  to  -^tli  of  the 
whole  of  the  blood  in  the  body — is  shed.  At  the  same  time,  the 
whole  or  a  portion  of  the  mucous  membrane  of  the  uterus  is  cast  off. 

As  to  the  physiological  meaning  of  this  menstruation,  as  it  is 
called,  opinion  is  divided.  Two  chief  theories  have  been  proposed  to 
account  for  it,  both  of  which  agree  in  considering  the  phenomenon  to 
be  connected  with  a  preparation  of  the  uterus  for  the  reception  of  the 
ovum.  But  according  to  the  theory  of  Pfliiger  the  mucous  membrane 
is  stripped  off  (by  a  process  analogous  to  the  'freshening  'or  paring 
of  the  indurated  edges  of  a  wound  by  the  surgeon,  in  order  that 
union  may  occur  when  they  are  brought  together)  on  the  chance,  so  to 
speak,  that  an  impregnated  ovum  may  arrive.  On  the  alternative 
theory,  this  change  takes  place  because  the  ovum  has  not  been 
impregnated,  and  the  bed  prepared  for  it  is  therefore  not  required 
(Reichert,  Williams,  etc.). 

Development  of  the  Ovum. — Before  fecundation,  and  apparently 
as  a  preparation  for  it,  the  ovum  is  the  seat  of  remarkable  changes, 
which  have  been  most  fully  studied  in  the  eggs  of  certain  invertebrate 
animals.  A  spindle-shaped  structure  appears  stretching  between  the 
nucleus  and  the  surface  of  the  ovum ;  at  its  outer  end  a  small  round 
body,  the  first  polar  body,  rises  up  from  the  surface  of  the  egg  as  if  it 
were  being  squeezed  out  of  it,  and  is  finally  extruded.  In  most  cases 
the  process  is  repeated;  a  new  spindle  forms  and  a  second  polar 
body  or  directive  corpuscle  is  cast  out.  As  to  the  significance  of 


REPRODUCTION  825 

these  changes  there  has  been  much  discussion.  It  seems  to  be  agreed 
that  the  spindle  is  formed  in  part,  at  any  rate,  from  the  nucleus  or 
germinal  vesicle,  and  that  the  result  of  the  process  is  the  expulsion 
of  a  portion  of  the  chromatin  skein  (p.  18),  which  is  restored  by  the 
male  pronucleus  when  it  arrives  and  penetrates  the  ovum. 

Not  till  all  these  events  have  taken  place — extrusion  of  the  two 
polar  bodies,  or  maturation,  penetration  of  the  spermatozoon  and 
blending  of  its  head  (the  male  pronucleus)  with  the  remnant  of  the 
nucleus  of  the  ovum  (female  pronucleus),  or  fecundation — not  till  then 
does  the  ovum  begin  to  divide.  The  germinal  spot,  or  nucleus,  splits 
into  two,  and  the  yolk  being  also  cleft  by  a  corresponding  furrow, 
two  complete  nucleated  cells  make  their  appearance.  These  divide 
in  turn,  till  at  length  (in  the  mammal)  the  embryo  is  represented  by  a 
hollow  sphere  or  vesicle,  with  a  cellular  crust.  During  division  the 
upper  or  outer  cells  have  always  been  larger  than  the  inner  and 
lower,  and  have  multiplied  more  rapidly ;  and  thus  it  comes  about 
that  the  hollow  sphere  of  large  cells  encloses  a  mass  of  smaller  cells, 
along  with  remnants  of  broken-down  yolk  and  of  fluid  derived  by 
absorption  from  the  contents  of  the  uterus.  The  smaller  cells  con- 
tinue to  multiply  and  arrange  themselves  as  a  lining  to  the  sphere 
already  formed,  so  that  in  a  short  time  it  becomes  double,  and  we 
have  already  differentiated  two  of  the  primary  embryonic  layers,  the 
epiblast,  or  superficial,  and  the  hypoblast,  or  deep  layer.  The  whole 
sphere  is  called  the  blastoderm^  or  the  blastodermic  vesicle. 

While  this  inner  shell  of  hypoblastic  cells  is  gradually  creeping  on 
to  completion,  there  appears  at  a  part  where  it  is  already  fully  formed 
a  small  opaque  whitish  disc,  the  germinal  area  or  embryonal  shield. 
This  represents  the  stocks  on  which  the  framework  of  the  embryo  is 
to  be  laid  down.  The  area  elongates  ;  at  its  posterior  end  appears  a 
thickened  line,  the  primitive  streak,  soon  furrowed  by  a  longitudinal 
groove,  the  primitive  groove,  that  marks  the  direction  in  which  the 
long  axis  of  the  future  embryo  will  lie,  but  is  not  itself  a  permanent 
line  in  the  building,  and  ultimately  vanishes.  The  appearance  of 
the  primitive  streak  is  the  signal  that  a  rapid  proliferation  of  the 
cells  of  the  germinal  area,  and  especially  of  the  epiblast,  has  begun  ; 
and  this  goes  on  until  a  third  layer  is  formed  intermediate  in  position 
to  the  original  two,  and  therefore  named  the  mesoblast.  While  this 
is  pushing  its  way  over  the  germinal  area  and  into  the  rest  of  the 
blastodermic  vesicle,  the  epiblast  in  front  of  the  primitive  streak  rises 
up  in  two  lateral  ridges,  enclosing  between  them  the  medullary 
groove.  The  medullary  groove  is  the  beginning  of  the  cerebro-spinal 
axis ;  its  walls  first  come  to  overhang  the  furrow,  and  then  to 
coalesce ;  and  the  medullary  groove  has  now  become  the  neural 
canal.  Immediately  under  it  the  mesoblast  forms  a  rod  of  cells,  the 
notochord^  which  is  the  forerunner  of  the  vertebral  column  ;  around 
this  the  bodies  of  the  vertebrae  are  afterwards  developed  from  cubical 
masses  of  mesoblastic  cells,  arranged  in  pairs  along  the  notochord, 
and  called  the  protovertebrcz.  The  rest  of  the  mesoblast,  running 
out  on  each  side  from  the  protovertebrse,  splits  into  two  layers,  an 
upper  or  somatic  layer,  which  unites  with  the  epiblast,  and  a  lower  or 


826  A  MANUAL  OF  PHYSIOLOGY 

splanchnic  layer  >  which  unites  with  the  hypoblast.  Between  the  two 
layers  is  a  space  called  the  ccelom,  or  pleuro-peritoneal  cavity 
(Fig.  299). 

Up  to  the  present,  apart  from  the  enclosure  of  the  neural  canal. 
all  this  formative  activity  is  buried  beneath  the  surface  of  the  blas- 
toderm, arid  has  not  showed  itself  by  any  external  token;  the 
embryo  still  appears  as  a  portion  of  the  germinal  area,  and  lies  in  its 
plane.  But  now  a  pocket,  or  crease,  or  moat,  beginning  at  the  head 
as  the  head-fold,  then  pushing  under  the  tail,  gradually  creeps  round 
and  undermines  the  whole  embryo,  which  is  raised  above  the  general 
level,  and,  as  it  were,  scooped  out  from  the  rest  of  the  blastoderm  , 
till  at  length  it  lies  on  the  latter,  something  like  an  upturned  canoe, 
enclosing  a  tube,  complete  in  front  and  behind,  but  still  open  in  the 
middle,  where  it  communicates  with  the  interior  of  the  yolk-vesicle. 
Since  this  tube  has  been  formed  by  the  tucking  in  of  the  three 
ancestral  layers  of  the  blastoderm,  it  follows  that  it  is  lined  by  hypo- 
blast,  supported  externally  by  the  splanchnic  sheet  of  mesoblast. 
So  that  now  the  body  consists  of  a  dorsal  tube  (the  neural  canal), 
essentially  of  epiblastic  origin,  a  ventral  tube  (the  alimentary  canal), 
essentially  of  hypoblastic  origin,  and  between  the  two  a  massive 
double  layer  of  mesoblastic  tissue,  which  contributes  supporting 
elements  to  both.  At  this  point  it  may  be  well  to  emphasize  the 
fact  that  this  embryological  distinction  of  the  three  primitive  layers 
has  a  deep  and  fundamental  meaning,  and  corresponds  to  a  phys;> 
logical  distinction  that  endures  throughout  life.  The  hypoblast,  the 
lowest  layer  in  position,  may  also  be  described  as  the  lowest  in  the 
physiological  hierarchy.  It  furnishes  the  epithelial  lining  of  the 
alimentary  canal  from  the  beginning  of  the  oesophagus  to  near  the 
end  of  the  rectum,  as  well  as  the  epithelium  of  the  organs  which 
arise  from  diverticula  of  the  primitive  intestine,  viz.,  the  digestive 
glands  with  the  exception  of  the  salivary  glands,  the  lungs,  and  the 
passages  leading  to  them,  the  thyroid,  and  the  greater  part  of  the 
thymus  gland  in  its  primitive  condition  before  the  lymphoid  tissue 
derived  from  the  mesoblast  has  as  yet  grown  into  it.  According 
to  some  authorities,  the  notochord  is  also  derived  from  the 
hypoblast. 

Upon  the  whole,  it  may  be  said  that  the  tissues  of  hypoblastic 
origin  are  essentially  concerned  in  chemical  labours,  in  the  absorption 
of  food  material  and  excretion  of  waste  products,  The  mesoblastic 
tissues  are  essentially  concerned  in  mechanical  labour ;  they  are  the 
tissues  of  movement  arid  of  passive  support.  The  epiblastic  tissues 
are  at  the  top  of  the  pyramid ;  they  govern  the  rest. 

From  the  mesoblast  arise  the  muscles,  the  entire  vascular  system 
with  its  blood  and  lymph  corpuscles,  the  bones  and  connective 
tissues ;  and  the  Wolffian  body  and  its  appendages,  which  are  the 
predecessors  of  the  genital  glands  and  ducts,  and  of  the  chief  portion 
of  the  renal  apparatus. 

The  epiblast  forms  the  epidermis  and  its  appendages,  the  epithelial 
end-organs  of  the  nerves  of  special  sense,  and  the  nervous  system, 
cerebro-spinal  and  sympathetic,  although  some  have  asserted  that 


REPRODUCTION  827 

the  latter  is  of  mesoblastic  origin.  The  salivary  glands  and  the 
mucous  lining  of  the  mouth  and  anus  are  developed  from  the  epi- 
blast,  which  is  indented  to  meet  the  intestinal  canal  and  give  it 
access  to  the  exterior  at  either  end. 

It  is  not  possible  here  to  trace  in  detail  the  development  of  all  the 
organs  of  the  embryo.  Its  nutrition  and  metabolism  not  only 
distinctly  belong  to  the  physiological  domain,  but,  carried  on  as  they 
are  under  conditions  that  seem  so  strange,  and  even  so  bizarre,  to 
one  acquainted  only  with  adult  physiology,  are  calculated  to  throw 
light  on  the  metabolic  processes  of  the  fully  developed  body.  And 
they  cannot  be  understood  without  reference  to  the  peculiarities 
of  the  vascular  system  in  fcetal  life.  These  we  shall  accordingly 
describe,  but  for  further  details  as  to  the  anatomy  of  the  embryo  the 
student  is  referred  to  some  standard  anatomical  text-book,  such  as 
Quain's  '  Anatomy.' 

Physiology  of  the  Embryo. — In  the  first  period  of  its  develop- 
ment the  ovum,  nestling  in  the  pouch  formed  by  the  decidua 
serotina  and  reflexa,  is  fed  simply  by  imbibition  through  the  hollow 
finger-like  processes  or  villi  with  which  its  external  layer,  the  zona 
pellucida,  becomes  studded.  Soon  the  heart  appears  as  a  tube  (at 
first  double),  formed  by  cells  belonging  to  the  splanchnic  layer  of 
the  mesoblast.  It  begins  to  pulsate  in  the  chick  as  early  as  the 
middle  of  the  second  day,  although  it  as  yet  contains  neither  nerve- 
cells  nor  fully-formed  muscular  fibres.  In  the  mammal  pulsation  is 
late  in  making  its  appearance,  in  man  about  the  beginning  of  the 
third  week.  A  bloodvessel  grows  out  from  the  anterior  end  of  the 
heart  and  divides  into  two  primitive  aortic  arches,  from  each  of  which 
a  vessel  (omphalo-mesenteric  or  vitelline  artery,  runs  out  in  the 
mesoblast  covering  the  umbilical  vesicle  or  yolk-sac.  The  blood  is 
returned  to  the  heart  by  the  vitelline  veins  coursing  in  on  the  walls  of 
the  vitelline  duct.  In  this  way  the  store  of  nutriment  in  the  umbilical 
vesicle  of  the  chick,  which  is  the  only  solid  or  liquid  food  it  receives 
or  needs  during  the  whole  period  of  development,  is  tapped,  and  a 
regular  channel  of  supply  established.  Oxygen  is  at  the  same  time 
absorbed  through  the  porous  shell ;  but  later  on  this  respiratory 
function  is  taken  over  by  the  second  or  allantoic  circulation.  In  the 
mammal  the  circulation  on  the  umbilical  vesicle  is  of  much  less 
consequence,  for  the  quantity  of  material  left  over  after  the  formation 
of  the  blastoderm  is  exceedingly  small ;  it  is  only  with  a  few  days' 
provision  in  its  haversack  that  the  embryo  starts  out  on  its  develop- 
mental march.  And  the  vitelline  vessels  deriving  their  further 
supply  of  food  and  oxygen  from  the  tissues  of  the  mother  in  contact 
with  the  ovum,  cease  to  be  of  use  as  soon  as  the  second  and  more 
perfect  placental  circulation  is  established,  and  soon  shrivel  up  and 
disappear,  as  the  umbilical  vesicle  shrinks. 

The  second  circulation  of  the  embryo  is  developed  in  connection 
with  a  remarkable  off-shoot  from  the  hind-gut  called  the  allantois, 
which,  before  the  fifth  day  in  the  chick  and  during  the  second  week 
in  man,  pushes  its  way  out  between  the  somatic  and  splanchnic 
layers  of  the  mesoblast,  -i.e.,  in  the  pleuro-peritoneal  cavity,  and 


828 


A  MANUAL  OF  PHYSIOLOGY 


grows  through  the  umbilicus,  carrying  bloodvessels  along  with  it  in 
its  mesoblastic  layer.  Still  earlier,  and,  indeed,  while  the  embryo  is 
being  separated  off  from  and  raised  above  the  level  of  the  rest  of  the 
blastoderm  by  the  deepening  of  the  ditch  around  it,  the  further  banks 
of  this  furrow,  formed  of  epiblast  and  somatic  mesoblast,  have  risen 
up  on  every  side  and,  growing  over  the  back  of  the  embryo,  have 
finally  coalesced  and  enclosed  it  in  a  double-walled  pouch  (Fig.  299). 
The  superficial  layer  of  the  pouch  is  called  thefa/se  amnion  ;  it  soon 
blends  with  the  tufted  chorion  or  common  outer  envelope  of  the 
ovum.  The  inner  layer  persists  as  the  true  amnion;  a  liquid,  the 

amniotic  fluid,  is 
secreted  in  the 
cavity  which  it 
encloses ;  and  the 
embryo,  loosely 
anchored  for  the 
rest  of  its  intra- 
uterine  life  by 
the  umbilical 
cord  alone,  floats 
freely  within  it. 
The  amniotic 
fluid  acts  as  a 
water  jacket  or 
cushion,  to  break 
the  force  of  the 
inevitable  shocks 
and  jars  trans- 
mitted from  the 
mother  to  the 

A,  cavity  of  true  amnion  ;  F,  F,  folds  about  to  coalesce  and  foetus    and    from 

complete  the  amniotic  cavity  ;  m,  mesoblastic  layer  of  amnion  ;  ^e  fo^us  to  the 
B,  allantois;  I,  intestinal  cavity  of  embryo  ;  Y,  yolk-sac;  A,  , 

hypoblastic  layer ;  e,  epiblastic  layer  of  embryo.     The  embryo  mottier. 
is  the  shaded  portion  in  the  middle  of  the  figure.     E  is  placed         The    allantois, 

over  the  head  region.    No  attempt  is  made  to  delineate  its  actual  o-rowincr     out     at 

form.     The  mesoblast  is  represented  by  the  interrupted  line.  °  »  ...  7 

the  umbilicus,  in 

the  manner  described,  insinuates  itself  between  the  true  and  false 
amnion  and  soon  blends  with  the  latter.  For  a  time  the  secretion  of 
the  primitive  kidneys  continues  to  be  poured  into  the  cavity  of  the 
allantois,  so  that  it  serves  in  part  as  an  excretory  organ,  while  in  the 
bird  it  also  performs  the  function  of  respiration ;  and  in  the  mammal 
both  food  and  oxygen  are  carried  by  its  vessels  to  the  foetus  during 
the  greater  part  of  mtra-uterine  life.  But  later  on  the  outgrowth 
atrophies  and  disappears,  all  except  its  origin  from  the  alimentary 
canal,  which  dilates  and  persists  as  the  urinary  bladder,  and  its 
bloodvessels,  which  grow  in  the  form  of  tufts  or  loops  into  the 
chorionic  villi.  The  vessels  are  fed  by  two  umbilical  arteries  which 
arise  from  the  hypogastric  arteries  and  run  out  at  the  umbilicus  on  the 
allantois.  The  blood  is  returned  by  an  umbilical  vein,  whose  further 
course  we  shall  have  soon  to  trace.  The  shrivelled  stalk  of  the 


FIG.  299. — DIAGRAM  TO  ILLUSTRATE  FORMATION  OF 

AMNION. 


REPRODUCTION  829 

allantois,  projecting  through  the  umbilicus,  becomes  with  its  blood- 
vessels the  umbilical  cord.  The  vascular  tufts  of  the  chorion,  which 
at  first  cover  the  whole  surface  of  the  ovum  and  suck  up  food  and 
oxygen  from  decidua  serotina  and  reflexa  alike,  disappear  in  the 
region  of  the  reflexa,  hypertrophy  all  over  the  serotina — that  is, 
where  the  ovum  is  in  actual  contact  with  the  uterine  wall — and 
this  part  of  the  chorion  is  now  distinguished  as  the  chorion  frondosum. 
The  giant  villi  of  the  chorion  frondosum  push  their  way  into  the 
thickened  decidua  serotina,  and  ultimately  penetrate  into  the  great 
capillaries  or  sinuses  of  the  uterine  mucous  membrane.  At  the  same 
time  the  tissue  of  the  villi  external  to  the  vessels  becomes  reduced 
to  a  mere  film,  so  that,  except  for  a  thin  covering  of  decidual  cells, 
the  foetal  vessels  are  bathed  in  maternal  blood.  By  this  inter- 
weaving of  decidua  and  chorion  frondosum  is  formed  the  placenta, 
which  for  the  rest  of  intra-uterine  life  acts  as  the  great  respiratory, 
alimentary  and  excretory  organ  of  the  foetus.  The  maternal  blood, 
as  it  streams  through  the  colossal  capillaries  of  the  decidua,  gives  up 
to  the  foetal  blood  oxygen  and  food  substances,  and  receives  from 
it  carbon  dioxide  and  in  all  probability  urea.  It  is  true  that  the 
blood  in  the  uterine  sinuses  is  not  itself  fully  oxygenated ;  it  is  not 
bright  red  arterial  blood.  But  it  yet  contains  more  oxygen  than  the 
purest  blood  of  the  foetus,  and  is,  therefore,  able  to  part  with  some  of 
the  surplus  to  the  dark  stream  of  oxygen-impoverished  blood  brought 
by  the  umbilical  arteries  to  the  placenta.  Thus,  it  has  been  found 
that  while  the  blood  of  the  umbilical  artery  of  the  foetus  of  a  sheep 
had  47  volumes  per  cent,  of  carbon  dioxide,  and  only  2*3  of  oxygen, 
that  of  the  umbilical  veins  had  6-3  volumes  of  oxygen,  and  only  40-5 
of  carbon  dioxide  (Kuntz  and  Cohnstein).  This,  although  far  from 
the  level  of  ordinary  arterial  blood,  is  yet  the  best  the  foetus  ever 
gets ;  and  by  a  series  of  contrivances  it  is  assured  that  this  best 
should  go  first  to  the  most  important  parts,  the  liver,  the  heart  and 
the  head,  while  the  legs  and  most  of  the  abdominal  organs  have  to 
put  up  with  an  inferior  supply.  This  is  brought  about  mainly  by  the 
existence  of  three  short-cuts  for  the  blood,  which  disappear  in  the 
adult  circulation,  the  ductus  venosus,  the  ductus  arteriosus  and  the 
foramen  ovale  (Fig.  300). 

The  blood  of  the  umbilical  vein,  rich  in  oxygen  for  foetal  blood, 
passes  partly  through  the  circulation  of  the  liver,  but  a  part  takes  the 
route  of  the  ductus  venosus,  and  empties  itself  directly  into  the  inferior 
vena  cava.  The  latter  gathers  up  the  more  or  less  vitiated  blood  from 
the  inferior  extremities  and  the  renal  and  hepatic  veins,  and  pours 
its  mixed  but  still  fairly  oxygenated  contents  into  the  right  auricle. 
By  means  of  the  Eustachian  valve,  the  jet  coming  from  the  mouth  of 
the  inferior  vena  cava  is  directed  into  the  left  auricle  through  the 
foramen  ovale  in  the  inter-auricular  septum.  There  it  is  joined 
by  the  trickle  of  blood  which  is  creeping  through  the  unexpanded 
lungs.  The  left  ventricle  propels  its  contents  through  the  aorta, 
and  thus  a  large  part  of  this  comparatively  pure  or  second-best 
blood  is  sent  to  the  head  and  upper  extremities.  It  returns  in 
a  vitiated  state  by  the  superior  vena  cava  into  the  right  auricle,  and 


830  A  MANUAL  OF  PHYSIOLOGY 

owing  to  the  position  of  the  Eustachian  valve  and  the  direction  of 
the  current,  it  flows  now  not  through  the  foramen  ovale,  but  into  the 
right  ventricle.  Thence  it  is  driven  through  the  pulmonary  artery, 
but  only  a  small  quantity  of  it  finds  its  way  through  the  lungs ;  the 
main  stream  is  short-circuited  through  the  ductus  arteriosus,  and 
mingles  with  the  contents  of  the  thoracic  aorta  below  the  origin  of 
the  cephalic  and  brachial  vessels. 

We  may  now  give  something  more  of  precision  to  the  statements 
that  different  parts  of  the  body  receive  blood  of  different  quality ; 

The  arrow  is  in 

the  Foramen  Ovale 


Right  Auricle 

Right  Ventricle   ^^^BffSG&HSH&iSSfflS^    Lun£s 

Pulmonary  Artery 

Inf.  Vena  Cam  I  •  2WI    Ducms  Arteriosus 


Inf.  Vena  Cava 

Ductus  Venosus 

Liver 

Portal  Vein  

«t-ra»  __M^_    Kidney 

Intestine 


Umbilical  Artery 

Umbilical  Vein 

FIG.  300.— DIAGRAM  OF  THE  SECOND  CIRCULATION  IN  THE  FCETUS. 
The  arrows  show  the  direction  of  the  blood-flow. 

and  it  is  possible  roughly  to  divide  the  organs  in  this  respect  into 
four  categories  :  (i)  The  liver,  which  partakes  both  of  the  best  and 
the  worst,  the  purified  blood  of  the  umbilical  veins  and  the  vitiated 
blood  of  the  intestines  and  spleen  ;  (2)  the  heart,  head,  and  upper 
limbs,  which  receive  the  blood  from  the  inferior  extremities  and 
kidneys,  mixed  with  the  pure  blood  of  the  venous  duct ;  (3)  the  legs, 
trunk,  intestines,  and  kidneys,  which  are  fed  chiefly  by  the  off- 
scourings of  the  cephalic  end,  mitigated,  however,  by  a  proportion 
of  mixed  blood  from  the  inferior  cava ;  (4)  the  lungs,  which  receive 
only  a  feeble  Stream  of  unmixed  venous  blood. 


REPRODUCTION  831 

These  peculiarities  of  the  embryonic  circulation  are  in  obvious 
correspondence  with  the  physiological  events  taking  place  in  the 
foetal  body.  The  liver  is  not  only  the  greatest  gland  in  the  embryo, 
as  it  continues  to  be  in  the  adult,  but  its  activity  seems  to  dwarf  that 
of  all  the  other  glands  put  together,  and  is  in  striking  contrast  with 
the  functional  torpor  of  the  lungs.  From  the  third  month  of  intra- 
uterine  life  the  secretion  of  bile  begins  and  the  intestines  gradually  fill 
with  meconium,  of  which  the  principal  constituent  is  bile.  Accord- 
ingly the  liver  is  most  lavishly  supplied  with  blood,  while  the  lungs 
are  stinted.  And  since  the  liver  has,  as  we  have  already  learnt, 
other  and,  in  the  adult  at  least,  even  more  important  labours  than 
excretion,  a  large  portion  of  the  blood  it  receives  is  of  the  best 
quality  :  it  enters  the  gland  comparatively  rich  in  oxygen,  and  passes 
out  comparatively  poor ;  while  the  lungs,  which  have  to  be  nourished 
only  for  their  own  sake,  and  are  of  no  use  whatever  till  the  child  is 
born  and  respiration  has  begun,  must  be  content  with  the  poorest 
fare — with  the  crumbs  that  fall  from  the  table  of  foetal  nutrition.  The 
full-fed  cephalic  end  of  the  embryo  grows  far  more  rapidly  than  the 
half-starved  inferior  extremities,  and  the  head  of  the  new-born  child  is 
large  in  proportion  to  the  rest  of  the  body. 

There  are  same  other  points  in  the  physiology  of  intra-uterine  life 
which  call  for  remark ;  and,  to  sum  up  in  a  few  words  the  grand 
distinction  between  foetal  and  adult  life,  we  may  say  that  growth  is 
the  keynote  of  the  former,  work  (functional  activity)  of  the  latter. 
Thus,  the  muscles  at  an  early  period  in  their  development  become 
the  seat  of  a  great  accumulation  of  glycogen,  an  accumulation  which 
would  entirely  unfit  them  for  the  labours  of  fully-formed  muscles, 
but  which  seems  to  be  intimately  connected  with  their  own  growth, 
and  perhaps  also  with  the  growth  of  other  tissues.  Later  on,  when 
the  muscles  have  been  formed,  their  powers  still  lie  dormant,  but  for 
the  infrequent  and  feeble  movements,  generally  regarded  as  reflex, 
but  possibly  to  some  extent  originated  in  the  cerebral  cortex,  which 
gives  the  mother  the  sensation  of  'quickening.'  But  the  store  of 
glycogen  now  becomes  reduced  to  its  permanent  amount,  and  the  liver 
takes  on  its  glycogenic  function.  It  can  hardly  be  doubted  that 
the  glycogen  found  in  the  placenta  (bitch)  is  also  deposited  there  in 
the  interest  of  the  rapidly  growing  foetal  tissues,  as  a  kind  of  current 
account  on  which  they  can  operate  at  any  moment  of  emergency, 
when  the  more  distant  maternal  reserves  cannot  be  drawn  upon 
in  time. 

The  excretory  glands  of  the  embryo,  except  the  liver,  scarcely 
awaken  to  activity  during  foetal  life.  Urine  may,  indeed,  be  some- 
times found  in  the  bladder  at  birth,  but  it  is  often  absent:  and 
although  a  portion  of  the  amniotic  fluid,  which  contains  traces  of 
urea  and  salts,  in  addition  to  small  quantities  of  albumin,  may  be 
secreted  by  the  renal  tubules,  and  find  its  way  through  the  still 
open  urachus  into  the  amniotic  sac,  this  contribution  cannot  imply 
more  than  a  very  slight  degree  of  glandular  action.  The  experi- 
ments of  Kuntz,  indeed,  go  far  to  show  that  this  liquid  comes 
essentially  from  the  mother  rather  than  from  the  child.  He  found 


832  A  MANUAL  OF  PHYSIOLOGY 

that  sulphindigotate  of  sodium  injected  into  the  bloodvessels  of  a 
pregnant  animal  (sheep)  coloured  the  amniotic  fluid  and  the 
placental  tissues,  but  not  the  fcetus ;  while  after  injection  into  the 
latter  the  foetal  kidneys  contained  particles  of  the  pigment,  while  the 
amniotic  fluid  remained  uncoloured.  The  sebaceous  glands  have 
certainly  begun  their  work  by  the  secretion  of  the  vernix  caseosa,  an 
oily  material  which  covers  the  skin  and  serves  to  protect  it  from  the 
continual  irritation  of  the  fluid  in  which  the  embryo  floats. 

The  nervous  system  is  even  less  active  than  the  glandular  tissues, 
and  not  more  active  than  the  muscles.  There  is  evidently  no  scope 
for  the  exercise  of  the  special  senses.  Psychical  activity  of  every 
kind  must  be  at  the  lowest  ebb.  Consciousness,  if  it  exists  at  all, 
must  be  dull  and  muffled.  And  if  motor  impulses  are  discharged 
from  the  cortex,  the  psychical  accompaniments  of  such  discharge  are 
doubtless  widely  different  from  those  which  we  associate  with  volun- 
tary effort. 

This  functional  calm,  broken  only  by  the  beat  of  the  heart,  is 
accompanied  by  a  very  feeble  metabolism.  The  amount  of  oxygen 
carried  to  the  tissues  of  aa  embryo  sheep  weighing  3*6  kilos,  by  the 
blood  of  the  umbilical  vein,  was  only  1*7  c.c.  per  minute;  2*8  c.c.  of 
carbon  dioxide  per  minute  was  given  up  to  the  blood  of  the  mother 
in  the  placenta  (Kuntz  and  Cohnstein).  The  gaseous  exchange  was, 
therefore,  not  one-tenth  as  much  as  in  the  adult  sheep.  In  fact,  the 
heat-production  of  the  foetus,  sheltered  as  it  is  from  loss  except  by 
the  placental  circulation,  is  only  sufficient  to  raise  its  temperature  by 
a  small  fraction  of  a  degree  above  that  of  the  mother.  And  it  is  not 
difficult  to  see  that  a  large  portion  of  this  production  must  be  due  to 
the  action  of  the  heart.  This  beats  at  the  rate  of  about  140  times  a 
minute  at  full  term.*  The  blood-pressure  in  the  umbilical  artery  of 
the  mature  embryo  (sheep)  varies  from  60  to  80  mm.  of  mercury; 
but  at  the  beginning  of  the  aorta  it  will  be  more.  The  pressure  in 
the  pulmonary  trunk  must  be  about  equal  to  that  in  the  aorta,  since 
the  comparatively  short  and  easy  circuit  through  the  lungs  does  not 
as  yet  exist ;  and  in  accordance  with  this  equality  of  pressure  (of  work 
to  be  done)  is  the  equality  of  thickness  (of  working  power)  in  the 
walls  of  the  two  sides  of  the  heart. 

Suppose,  now,  that  the  embryo  contains  60  grammes  of  blood  for 
every  kilo  of  body-weight,  and  that  the  whole  of  the  blood  passes 
through  the  circulation  in  twenty  seconds.  Then  in  twenty-four 
hours  259*2  kilos  of  blood  will  be  forced  through  the  heart  for  every 
kilo  of  body-weight  against  a  pressure  of,  say,  80  mm.  of  mercury, 

*  It  has  not  been  finally  determined  whether  the  rate  of  the  heart 
varies  with  the  size,  or  what  probably  comes  to  the  same  thing,  with  the 
sex  of  the  foetus.  As  we  have  seen,  the  variation  of  the  rate  in  the  adult 
with  the  size  of  the  body  is  associated  with  a  corresponding  variation  in 
the  metabolism  and  heat-loss,  which  are  proportionally  greater  in  a  small 
than  in  a  large  animal.  If  this  is  a  causal  connection  we  should  not 
expect  that  in  the  embryo  in  utero,  where  the  conditions  as  regards  heat- 
loss  are  entirely  different,  such  a  relation  should  exist,  at  any  rate  within 
the  same  species. 


REPRODUCTION  833 

or  i  metre  of  blood.  This  is  equivalent,  in  round  numbers,  to  260 
kilogramme-metres  of  work,  or  600  small  calories.  Now,  taking  the 
total  heat-production  of  the  heart  at  four  times  the  equivalent  of  its 
mechanical  work,  we  get  2,400  calories  per  kilo  of  body-weight  in 
twenty-four  hours  (see  p.  488),  or  about  TV  to  —^  of  the  heat-produc- 
tion of  a  resting  adult. 

So  low  is  the  intensity  of  metabolism  in  the  embryo,  so  slight  the 
demand  for  oxygen,  that  not  only  is  even  the  purest  blood,  as  has 
already  been  stated,  far  from  saturated  with  that  gas,  but  the  relative 
proportion  of  haemoglobin,  the  oxygen -carrier,  is  less  than  in  the 
adult ;  and  although  constantly  increasing  in  amount  from  the  moment 
of  its  first  appearance,  it  is  still  somewhat  deficient,  even  at  full  term, 
but  leaps  sharply  up  at  birth.  At  an  early  period  of  development 
the  embryo  also  contains  much  more  water  than  the  adult;  the 
specific  gravity  of  its  tissues  increases  as  development  goes  on. 

The  remarkable  vitality  of  the  foetus,  and  its  resistance  to  asphyxia, 
are  related  to  the  feebleness  of  its  metabolism  and  to  the  compara- 
tively slight  excitability  of  nervous  centres  like  the  respiratory,  vaso- 
motor,  and  cardio-inhibitory.  Even  when  totally  deprived  of  oxygen, 
as  by  pressure  on  the  umbilical  cord  during  delivery,  the  child  does 
not  perish  in  the  two  or  three  minutes  which  decide  the  fate  of  the 
asphyxiated  adult ;  nor  are  the  convulsions,  rise  of  blood-pressure, 
and  slowing  of  the  heart-beat,  associated  with  asphyxia  in  the  latter, 
so  readily  induced,  nor  premature  and  fatal  efforts  at  respiration 
easily  excited  in  utero.  But  although  in  such  a  case  the  embryo 
behaves  as  a  separate  organism,  governed  by  its  own  laws,  there  are 
circumstances  in  which  it  becomes  merely  a  part  of  the  mother  and 
participates  in  her  fate.  Thus,  the  stream  of  oxygen  which  normally 
passes  from  the  maternal  to  the  foetal  blood  is  turned  back  if 
asphyxia  threatens  the  mother ;  the  blood  of  the  umbilical  arteries, 
instead  of  being  purified  in  the  placenta,  loses  the  little  oxygen  it 
holds  to  the  blood  of  the  uterine  sinuses,  and  the  sluggish  tissues  of 
the  embryo  are  impoverished  to  feed  the  more  active  metabolism  of 
the  maternal  organs.  In  the  same  way,  the  phenomena  of  starvation 
have  taught  us  that  the  nutrition  of  the  organism  is  net  subject  to 
the  rules  of  red  tape.  In  normal  circumstances  the  flow  of  nutriment 
follows  definite  lines :  the  blood  feeds  the  tissues  through  its  inter- 
mediary, the  lymph,  and  recoups  itself  from  the  contents  of  the 
alimentary  canal.  But  when  the  normal  sources  of  nutrient  material 
fail,  the  body  falls  back  upon  its  stores.  The  organs  immediately 
necessary  to  life  are  kept,  as  far  as  possible,  on  full  diet ;  organs  of 
secondary  importance  have  to  be  content  with  half-rations ;  organs 
less  important  still  are  drawn  upon  for  supplies. 

At  birth,  great  changes  take  place  in  me  circulation,  and  these 
are  intimately  connected  with  the  commencement  of  the  respiratory 
activity  of  the  lungs.  The  causes  of  the  first  respiration  are  :  ( i)  The 
increasing  venosity  of  the  blood  circulating  in  the  bulb,  which 
stimulates  the  respiratory  centre  when  the  umbilical  cord  has  been 
cut  or  tied  and  the  placental  circulation  thus  interfered  with  ;  (2)  the 
stimulation  of  the  skin  by  the  air,  which,  as  we  have  seen,  acts 

53 


834  A  MANUAL  OF  PHYSIOLOGY 

reflexly  upon  the  respiratory  centre.  That  both  of  these  factors  may 
be  involved  is  shown  by  the  fact  that  either  compression  of  the 
umbilical  cord  alone,  or  exposure  of  the  fcetus  by  opening  the  uterus 
of  an  animal  without  interference  with  the  circulation,  has  been 
observed  to  be  followed  by  attempts  at  breathing.  Once  distended, 
the  lungs  never  again  completely  collapse — not  even  after  death,  nor 
when  the  chest  is  opened.  The  aspiration  caused  by  the  elevation 
of  the  chest-walls  in  inspiration  (for  the  respiration  of  the  new-born 
child  is  mainly  costal)  sucks  blood  into  the  thorax,  and  expands  the 
vessels  of  the  lungs  for  its  reception ;  and  in  the  measure  in  which 
the  blood  passing  through  the  pulmonary  trunk  finds  an  easy  way 
through  the  lungs,  the  quantity  which  takes  the  route  of  the  ductus 
arteriosus  diminishes.  The  pulmonary  veins,  and  consequently  the 
left  auricle,  are  better  filled;  and  the  increasing  pressure  on  this 
side  of  the  septum  tends  to  oppose  the  passage  of  blood  through  the 
foramen  ovale,  to  approximate  its  valve,  and  to  close  its  orifice. 

By  the  second  or  third  day  the  ductus  arteriosus  has  usually 
become  obliterated.  The  umbilical  arteries  and  vein  and  the  ductus 
venosus  become  impervious  soon  after  the  interruption  of  the  placental 
circulation.  The  vein  and  venous  duct  remain  in  the  adult  as  the 
round  ligament  of  the  liver,  the  arteries  as  the  lateral  ligaments  of 
the  bladder. 

Although  from  birth  onwards  the  young  mammal  obtains  its 
oxygen  and  gets  rid  of  its  carbon  dioxide  through  its  own  pulmonary 
surface  instead  of  through  the  placenta,  it  still  lives,  as  regards  its 
food  proper,  on  the  tissues  of  the  mother,  and  that  in  as  literal  a 
sense  as  when  it  drew  its  supplies  directly  from  the  maternal  blood. 
Milk,  indeed,  represents  in  large  part  the  fragments  of  cells  lining 
the  alveoli  of  the  mammary  glands,  which  have  undergone  a  fatty 
change  and  been  bodily  broken  down.  This  is  particularly  the  case 
with  the  first  milk  of  each  lactation,  the  colostrum  as  it  is  called, 
which  consists  of  little  else  than  the  debris  of  fattily  degenerated 
cells.  In  addition  to  the  fat,  which  when  milk  is  allowed  to  stand 
rises  to  the  top  as  cream,  milk  contains  a  considerable  quantity  of 
a  nucleo-proteid,  casein,  to  whose  coagulation,  under  the  influence  of 
the  lactic  acid  produced  from  the  lactose,  or  milk-sugar,  by  certain 
bacteria,  spontaneous  curdling  is  due.  Another  proteid,  lact-albumin 
(Halliburton),  a  large  amount  of  water,  and  some  inorganic  salts,  are 
the  most  important  of  its  remaining  constituents. 

Pregnancy  is  accompanied  with  vascular  dilatation  and  hyper- 
trophy of  the  mammary  glands,  but  the  mechanism  by  which  these 
changes  are  produced  is  unknown.  Precisely  similar  phenomena 
are  occasionally  seen  in  animals  which  have  not  been  impregnated 
and  even  in  men.  Humboldt  relates  the  case  of  an  Indian  father, 
who  so  well  understood  the  responsibilities  of  paternity,  and  was  so 
capable  of  fulfilling  them,  that  he  suckled  his  child  for  five  months 
on  the  death  of  the  mother. 


APPENDIX. 


COMPARISON  OF  METRICAL  WITH  ENGLISH   MEASURES. 


Measures  of  Length. 

i  millimetre  =  0-03937  inch, 
i  centimetre  =  0*3937 1     „ 
i  decimetre  =  3'937o8  inches, 
i  metre         =39*37°79    » 

i  inch  ==25'3995  millimetres. 


Measures  of  Weight. 

i  gramme       =  15-432349  grains, 
i  kilogramme  ==  2-2046213  pounds. 

i  ounce  =28-3495  grammes. 

T  pound          =453-5926  grammes. 


Measures  of  Volume. 

i  cubic  centimetre  =  o '06102 7  cubic  inch. 

i  litre  (1,000  cubic  centimetres)  =  61-02705 2  cubic  inches. 

=  1760773  pints 
=  0-22009668  gallon. 

i  cubic  inch  =  16*3861759  cubic  centimetres. 

i  cubic  foot  =  28*3153119  cubic  decimetres  (or  litres). 

i  pint  =0-567932  litres. 

i  gallon         =4-5434579  litres. 


Measures  of  Work. 

i  kilogram m etre  =  about  7-24  foot-pounds, 
i  foot-pound       =0-1381  kilogrammetre. 


53—2 


INDEX. 


%*  References  to  the  Practical  Exercises  are  in  black  figures. 


ABDOMINAL  breathing,  202 
Abducens,  or  sixth  nerve,  689 
Aberration,  chromatic,  755 

spherical.  755 
Absorption  of  light,  739 
of  the  food,  363 

physical  introduction  to,  360 
theories  of,  366-368 
of  cane-sugar,  365,  382 
of  carbo-hydrates,  371 
of  fat,  370,  381 
of  proteids,  372 

from  the  stomach,  352,  365 
Accelerator  nerves  of  heart,  139 
Accommodation,  747,  815 

mechanism  of,  749,  750 
Acid  albumin,  21,  302,  377 
Acidity  of  gastric  juice,  301.  351 
Action  currents,  606,  612-614,  628 
diphasic,  607 

electromotive  force  of,  609 
of  eye,  624 
of  glands,  623 
of  heart,  608.  621,  628 
of  human  muscles,  611 
of  phrenic  nerves,  609 
in  polarized  nerves,  620 
of  spinal  cord,  622,  636 
theories  of,  611 
'  Adequate '  stimuli,  733 
Aerotonometer,  240 
Afferent  impulses,  decussation  of,  671 

paths  of,  669 
After-images,  786 
Agraphia,  715 
Albumin,  reactions  of,  21 

in  urine,  392,  402,  424 
Albuminates  or  derived  albumins,  21 
Albuminous  glands,  295 
Albumoses,  action  of,  on  blood-pressure, 
188 

on  coagulation,  43,  45,  188 
tests  for,  22,  377 
in  urine,  425 
Alcohol,  action  of,  on  respiratory  centre, 

165,  220 
in  diet,  470 
Alimentary  canal,  anatomy  of,  281 

length  of,  280 
glycosuria,  513 
Alkali-albumin,  22,  306,  379 
Allantois,  formation  of,  828 
Amnion,  828 


Amoeboid  movement,  28,  529 

Ampere,  519 

Amyl  nitrite,  action  on  the  pulse,  93,  183 

Amylolytic  stage  of  gastric  digestion,  350 

Amylopsin,  306,  379 

Anabolic  changes  in  living  matter,  19 

Anacrotic  pulse,  94 

Anaesthesia  by  chloral,  189 

by  morphia,  58,  176 
^Anelectrotonus,  574,  576 
Animal  heat,  477 
Anions,  362 
Ankle-clonus,  676 
Annulus  of  Vieussens,  139,  179 
Anterior  horn,  cells  of,  647 
Antero-lateral  ascending  tract,  649,  654 

descending  tract,  659 

ground  bundle,  650 
Anti-peptone,  308 
Antipyretics,  501 

Antiseptics  for  operations,  190,  515 
Antrum  pylori,  288 
Aorta,  effect  of  compression  of,  179 
Apex-beat,  79,  182 
Aphasia,  motor,  714 

sensory,  716 

temporary,  716 
Apncea,  218 

Apomorphine  as  an  emetic,  378 
Argyll-Robertson  pupil,  751 
Artery,  to  insert  cannula  into,  58 
Articulation,  positions  of,  267 
Ascending  degeneration,  649 
Asphyxia,  217 

effect  of,  on  circulation,  162, 179,  187 

in  the  foetus,  833 
Association  fibres,  662 
Astatic  system  of  magnets,  521 
Astigmatism,  irregular,  759 

regular,  760,  819 
Atelectasis,  210 

^Atropia,  action  of,  on  heart,  141,  174 
on  digestive  secretions,  347 
on  pupil,  754 
on  salivary  secretion,  376 
Auditory  centre,  713 

nerve,  689 

vestibular  branch  of,  659 

ossicles,  799-801 
Auerbach's  plexus,  281 
Augmentation  of  heart's  beat,  133,  175 

primary,  136  138 

secondary,  136 


INDEX 


837 


Auriculo-ventricular  junction,  stimulation 

of,  135,  174 

Auto-digestion  of  stomach,  330,  383 
Automatic  actions  of  spinal  cord,  681,  684 

Bacteria  in  intestine,  316,  357 

Bactericidal  action  of  gastric  juice,  355 

Basal  ganglia,  692 

Batteries,  173,  517 

Beat-tones,  805,  821 

Beaumont  on  digestion,  300 

Benzoic  acid,  388 

Bichromate  cell,  173,  517 

Bidder's  ganglia,  129 

Bile,  309-315,  380  v 

acids,  311,  312,  380 

formation  of,  327 
composition  of,  310 
curve  of  secretion  of,  346 
in  emulsification  of  fats,  313 
influence  of  nerves  on  secretion  of, 

345 

mucin,  310,  380 

pigments,  310,  327,  380 

reactions  of,  380 

salts,  preparation  of,  381 

secretory  pressure  of,  345 

spectrum  of,  311 
Biuret  reaction,  20,  377 
Blastoderm,  825 
Blind  spot,  778,  817 
Blood,  coagulation  of,  36,  58 

composition  of,  45 

conductivity  of,  34 

distribution  of,  52 

functions  of,  54 

gases  of,  235 

in  embryo,  829 

guaiacum  test  for,  64 

laking  of,  35,  61 

opacity  of,  35.  61 

quantity  of,  51,  52 
in  lungs,  197 

reaction  of,  33,  34,  57 

specific  gravity  of,  34,  57 

stains,  examination  of,  66 

sugar  in,  442 

velocity  of,  105-115 
in  arteries,  114 
in  capillaries,  109,  118 
in  veins,  109,  122 

volume  of  corpuscles  and  plasma,  35 

why  it  does  not  clot  in  the  vessels,  44 
Blood-corpuscles,  26 

composition  of,  46 

crenation  of,  27 

enumeration  of,  30,  61 

life-history  of,  31 
Blood-plates,  29 
Blood-pressure,  mean  arterial,  102-105 

curves,  with  elastic  manometers,  100 
with  mercurial  manometer,  102, 
185 

measurement  of,  99,  185 

effect  of  haemorrhage  on,  165,188 

in  capillaries,  119 

in  right  and  left  ventricles,  82,  105 

respiratory  vari.  lions  in,  249-256 
Bloodvessels,  structuie  of,  60 


Blood-pump,  233 

Bones,  composition  of,  464 

Bone-faeces,  383 

Bone-marrow  and  blood-formation,  32 

Brain,  circulation  in,  727 

functions  of,  692-726 

development  of,  638 

in  sleep,  724 

respiratory  changes  in  volume  of,  255 

size  of,  and  intelligence,  726 
Break-contraction,  Tigerstedt's  theory  of, 

616 

Bronchi,  195 
Bronchial  breathing,  203 
'  Buffy '  coat,  41 
Brunner's  glands,  315,  324 
Burdach's  column.     See  Postero-median 

column 

Burdon-Sanderson  on  negative  variation, 
612-614 

Calcium,  influence  of,  on  coagulation,  42, 

59 

Caisson  disease,  257 
Calorie,  definition  of,  479 
Calorimeter,  respiration,  484,  513 
Calorimetry,  479 
Cannula,  to  put  into  artery,  58 
vein,  177 
trachea,  177 
gastric,  378 
Cane-sugar,  absorption  of,  365,  382 

inversion  of,  23,  382 
Capillaries,  structure  of,  70 
Capillary  electrometer,  523,  524,  628 
tubes,  flow  of  liquid  through,  73 
Carbo-hydrates,  composition  of,  17 
metabolism  of,  439-446 
reactions  of,  23 
Carbon  dioxide,  action  of  on  respiratory 

centre,  217 

estimation  of,  224,  234,  275,  276 
formation  of,  from  proteids,  438 
production  of,  in  muscular  work, 

227 

in  different  animals,  229 
in  blood,  235,  237 
in  foetal  blood,  829 
in  rigor  mortis,  247 
in  serum,  238 
Carbon  equilibrium,  461 
Carbonic  oxide  haemoglobin,  49,  63 
Cardiac  cycle,  75,  76,  87 

changes  in  endo-cardiac  pressure 

during,  87 
impulse,  79,  182 

sound  (Chauveau  and  Marey's),  85 
Cardiograph,  80,  182 
Catheterism,  429 
Cells,  structure  of,  18 
Central  nervous  system,  development  of, 

637 

Central  nervous  system,  general  arrange- 
ment of,  644 
functions  of,  663 
histology  of,  638,  639 
localization  of  function  in,  719 
grey  axis,  644 
Centres  of  cord  and  bulb,  684 


INDEX 


Centres,  cardio-inhibitory  and  augmentor, 

144 

neat-,  500 

motor,  of  cortex,  707-711 
sensory,  of  cortex,  711-714 
vaso-motor,  158,  159 
Centre  of  gravity  of  body,  702 
Centrifuge,  59 

Cerebellum,  connections  of,  659 
functions  of,  694-699 
structure  of  694 

Cerebrum,  excision  of,  703,  729,  730 
Chalk-stones,  437 
Cheyne-Stokes'  respiration,  221 
Chiasma,  687 

Chloral,  anaesthesia  by,  189 
Chlorides,  estimation  of,  416 
Chloroform,  action  of,  on  respiratory 

centre,  219 
on  vaso-motor  centre,  162,  164, 

187 

Cholagogues,  348 
Cholesterin,  312,  380 
Chorda  tympani,  332,  375 

hypothetical  fibres  in,  339 
antagonism  of  sympathetic  with, 

337,  376 

Chordae  tenuineae,  75 
Choroidal  epithelium,  743,  773,  776 
Chromatin,  18 
Chromatic  aberration,  755 
Chyle,  composition  of,  53 
Chyme,  to  obtain,  377 
Cilia,  530,  593 
Ciliary  muscle,  749,  780 

nerves,  750,  751 
Circulation,  artificial,  246 

changes  in,  at  birth,  833,  834 
comparative,  67 
cross,  through  brain,  218 
general  view  of,  68 
in  brain,  727 
in  the  capillaries,  117 
in  the  embryo,  827,  830 
in  the  frog's  web,  26, 168 
in  lungs,  196 
in  the  veins,  120 
of  lymph,  166 
time,  122,  192 
Clarke's  column,  647 
Coagulation  of  blood,  36,  58 
prevention  of,  37 
theories  of,  43 

temperature,  to  determine,  21 
Coagulated  proteids,  reactions  of,  22 
Cocaine  fever,  491 
Cochlea,  800 
Collaterals,  639,  653,  679 
Colloids  of  Grimaux,  effect  of,  on  coagu- 
lation, 43 

Colour,  body-  and  surface-,  740 
blindness,  790 
mixing,  785,  820 
triangle,  783 
vision,  781 

Hering's  theory  of,  788 
Young-Helmholtz  theory  of,  784 
Colours,  complementary,  782,  820 
primary,  784 


Colostrum,  834 
Coloured  shadows,  787 
Comma  tract,  650 
Commutator,  Pohl's,  527 
Compensator,  523 
Compensatory  pause  of  heart,  132 
Complemental  air,  207,  274 
Complementary  colours.  782,  820 
Condensed  air,  effects  of  breathing,  255, 

257 
Conductivity,  molecular,  363 

specific,  363 

of  nerve,  effect  of  temperature  on,  574 

effect  of  voltaic  current  on,  579 
Conduction,  double,  580 

isolated,  581 
Consonants,  266,  267 
Contraction,  law  of,  576,  632,  578 

without  metals,  605,  627 

secondary,  621,  627 
Contrast,  787 

Co-ordination  of  movements,  700 
Cornea,  radius  of  curvature  of,  744 
Corona  radiata,  645,  652 
Corpora  quadrigernina,  687,  692,  693 

striata,  500,  645,  694 
Corpus  callosum,  646,  66 1 
Cortex  of  brain,  functions  of,  704 
motor  areas  of,  707 
sensory  areas  of,  711 
Corti's  organ,  800 
Costal  breathing,  202 
Coughing,  222 
Cranial  conduction  of  sound,  802 

nerves,  685-691 
Crossed  pyramidal  tract,  650 
Cross-circulation  through  brain,  218 
Crura  cerebri,  652 
Crusta,  652 
Cuneate  funiculus,  651 

nucleus,  651,  655 
Curara,  action  of,  on  skeletal  muscle,  534, 

593 

on  heart,  141 
on  heat-production,  495 
Curdling  of  milk  by  rennin,  304,  377 
Currents  of  action.     See  Action  currents 
Cutaneous  burns,  death  from,  259 

excretion,  412 

respiration,  258 

Cybulski's  method  of  measuring  velocity 
of  blood,  113 

Daniell  cell,  173,  517 
1  Dead  space,'  respiratory,  209* 
Deaf-mutes,  equilibration  in,  699 
Decussation  of  afferent  impulses,  671 

of  efferent  impulses,  670 

of  optic  nerve,  687 

of  pyramids,  651,  658 
Defaecation,  291 
Deficiency  phenomena,  664 
Degeneration  of  muscles,  586,  683 

of  nerves,  584 

reaction  of,  586 
Deglutition,  285 

centre,  287 

nerves  of,  287 

sounds,  349 


INDEX 


839 


Demarcation  current,  606,  628 

theories  of,  611 
Dendrons,  640 

Dentate  nucleus  of  cerebellum ,  659 
Depressor  nerve,  145   160,  190 
Descending  degeneration,  650,  656 
Development  of  embryo,  825 
Dextrin,  tests  for,  23 

formed  in  salivary  digestion,  298,  375 
Dextrose,  Trommer's  test  for,  23 

estimation  of,  in  urine,  426 
Diabetes,  392,  442 

levulose  used  up  in,  445 

pancreatic,  445,  472 

phloridzin,  445,  512 

'  puncture,'  513 

sugar-destroying  power  of  blood  in, 

446 

Diapedesis,  56 

Diaphragm  in  respiration,  199 
Diastase,  299 
Dicrotic  wave,  92 
Dietaries,  standard,  464-467 
Dietetics,  464-471 
Differential  rheotome,  610 
Diffusion,  360 

of  gases,  230 
Digestion,  bacteria  and,  357 

chemical  phenomena  of,  294-315 

of  fats,  356 

in  intestine,  353 

in  stomach,  350 

mechanical  phenomena  of,  283-289 

time  required  for,  381,  382 
Digestive  glands,  structure  of,  318 

juices,  action  of  drugs  on,  347 
secretion  of,  317 

organs,  in  different  animals,  280 
Diopter,  749 
Diplopia,  765 
Direct  cerebellar  tract,  650,  654 

pyramidal  tract,  650 
Discharge  of  ventricle,  period  of,  87 
Dispersion  in  eye,  756 

by  a  prism,  737 
Diuretics,  410 

Double  conduction  in  nerve,  580 
Double  images,  neglect  of,  767 
Dromograph,  in 
Ductus  arteriosus  and   ductus   venosus, 

830 
Dyspnoea,  217,  272 

heat-,  218,  272 

Ear,  anatomy  of,  798 

ossicles  of,  798,  801 

resonance  tone  ot,  557 
Eck's  fistula,  328,  435 
Ectoderm,  19 
Efferent  impulses,  decussation  of,  658,  670 

paths  of,  670 
Egg-albumin,  excretion  of,  399 

reactions  of,  21 
Elasticity  of  muscle,  531 
Electric  fishes,  624 
Electrodes,  unpolarizable,  526,  628 
Electrolytes,  362 

Electrometer,  capillary,  523,  524,  628 
Electromotive  force,  518 


Electrotonic  alterations  of  excitability  and 
conductivity,  630 

currents,  616,  629 

negative  variation  of,  618,  629 
Electrotonus,  574 
Embryo,  asphyxia  in,  833 

circulation  in,  827,  830 

development  of,  826' 

gases  of  blood  in,  829 

heat-production  in,  833 

liver  in,  831 

metabolism  of,  832 

physiology  of,  827 
Emetics,  293,  378 
Emmetropic  eye,  758 
Emulsification  of  fats,  24,  313 
Endocardiac  pressure,  81-88 
curves  of,  81,  84,  85 
amount  of,  82 
measurement  of,  82,  &s 
Endoderm,  19 
Endolymph,  798 
Enemata,  373 
Epiblast,  825,  826 
Epiglottis,  285 
Epilepsy,  cortical,  717,  731 

produced  by  absinthe,  718 
Equilibration,  cerebellum  and,  695 

semicircular  canals  and,  697  ~ 

in  pigeon,  698 

Equimolecular  solutions,  572 
Ergograph,  597 
Erythroblasts,  32 
Erythrodextrin,  298,  375 
Eserine,  action  of,  on  pupil,  754 
Eustachian  valve,  829 
Excitability,  direct,  of  muscle,  534,  693 

of  nerve,  effect  of  temperature  on,  574 
effect  of  voltaic  current  on,  574, 
Expectoration,  384  [630 

Expiration,  201 

forced,  203 

Expired  air,  composition  of,  224,  275 
Extensibility  of  muscle,  531 
Extra  contraction  of  heart,  132 
Eye,  compound,  of  insects,  741 

currents  of,  624 

defects  of,  755 

movements  of,  793 

muscles  of,  795 

nerves  of,  751 

optical  constants  of,  744 

Kiihne's,  817 

reduced,  745 

structure  of,  742 
Eyes,  primary  position  of,  794 

wheel-movements  of,  794 

Facial  nerve,  689 

Faeces,  composition  of,  358,  381 

odour  of,  359 

bone-,  383 
Fainting,  166 
Falsetto  voice,  265 
Far  point  of  vision,  758 
Fat,  absorption  of,  370,  381 

composition  of,  17,  22,  451 

digestion  of,  313,  356 

emulsification  of,  24 


840 


INDEX 


Fat,  excretion  of,  into  intestine,  324,  374 
formation   of,    from   carbo-hydrates, 

449 

from  fatty  acids,  373 
from  proteids,  448 

metabolism  of,  446-450 

proteid-sparing  action  of,  455 

sources  of,  in  body,  446,  447 

in  faeces  in  jaundice,  314 
Fat-splitting  action  of  pancreatic  juice, 

380 

Fatigue,  muscular,  549,  596,  597 
Fatty  acids,  absorption  of,  373 
Fehling's  solution,  427 
Ferments,  294 

mother  substances  of,  325 

quantitative  estimation  of,  326 
Fever,  501-505 

produced  by  cocaine,  491 

retention  theory  of,  503 

significance  of,  504 
Fibrillar  contraction  of  heart,  179 
Fibrin-ferment,  39,  60 

nature  of,  40 

source  of,  41 
Fibrin,  formation  of,  36 
Fibrinogen,  38 
Fibrinoglobulin,  38 
Fick  and  Wislicenus'  experiment,  459 
Fillet,  655 
Flavour,  808 
Flow  of  liquids,  71 
Focal  illumination  of  eye,  770 
Fcetus.     See  Embryo 
Food,  relation  of,  to  surface,  468 
Foods,  composition  of,  466 

isodynamic,  565 
Forced  movements,  699 
Fore-brain,  638 
Formatio  reticularis,  655 
Fourth  or  trochlear  nerve,  688 
Funiculis  gracilis  and  cuneatus,  651 
Freezing-point  and  osmotic  pressure,  361 
Ftindus  of  stomach,  in  digestion,  288 

Gall-bladder,  nerves  of,  345 
Galvani's  experiment,  605,  627 
Galvanometer,  520,  521 
Galvanotonus,  537 
Galvanotropism,  634 
Ganglion-cells,  changes  in,  with  age,  642 
Gaseous  exchange,  242,  276 
Gases,  of  blood,  235 
diffusion  of,  230 
partial  pressure  of,  231-233 
solution  of,  230 
Gas-pump,  233 

Gasserian  ganglion,  developing,  640 
Gastric  digestion,  amylolytic  stage  of,  350 
glands,  changes  in  during  secretion, 

320 

influence  of  nerves  on,  342 
structure  of,  321 
juice,  300-305,  376-378 

acidity  of,  301,  351,  378 
artificial,  376 
bactericidal  action  of,  355 
Beaumont's  researches  on,  300 
lactic  acid  in,  350 


Gastric  juice,  to  obtain,  378 
Gelatin,  proteid-sparing  acdon  of,  456 
Geminal  fibres  of  cord,  658 
Geniculate  bodies,  687,  692 
Gianuzzi,  crescents  of,  318 
Globulicidal  action  of  serum,  62 
Globulins,  reactions  of,  21 

in  urine,  424 
Glomeruli,  395,  403 
Glossopharyngeal  nerve,  690 
Glottis,  265,  266 
Glycin,  312,  388 
Glycocholic  acid,  311 
Glycogen,  439,  511 

disappearance  in  fasting,  441 

formation  of,  442,  450 

in  embryo,  831 

in  liver-cells,  440 

in  muscles,  441 

in  placenta,  441 

preparation  of,  511 

used  up  in  muscular  contraction,  564 

in  strychnia-poisoning,  442 
Glycosuria,  399 

alimentary,  442,  513 

in  diabetes,  445,  446 

after  injection  of  sugar  into  blood, 

512 

Gmelin's  test  for  bile-pigments,  380 
Golgi's  method,  643 
Goll's    column.      See    Postcro  -  median 

column 

Gower's  tract.    See  Antero-lateral  ascend- 
ing tract 

Graafian  follicle,  824 
Gracile  and  cuneate  nuclei,  651,  655 
Gramme-molecular  weight,  360 
'  Granule-cell,'  640 
Gravity,  centre  of,  in  standing,  702 

influence  of,  on  circulation,  164,  187 
Ground-bundle,  antero-lateral,  650 
Guaiacum  test  for  blood,  64 
Guanin,436 

Gunsburg's  reagent,  378 
Gymnotus,  625 

Haematin,  50,  64 
Haematoblasts,  32 
Haematocrite,  35,  362 
Haematoidin,  328 
Hasmatoporphyrin,  50,  64 

in  urine,  389 

Haemautographic  tracing,  101 
Haemin,  50 

test  for  blood,  66 
Hasmochromogen,  50,  64 
Haemoglobin,  composition  of,  46 

crystals  of,  47,  62 

derivatives  of,  49.  50,  62-64 

dissociation  of,  236 

iron  and  sulphur  in,  47 

quantitative  estimation  of,  65 

spectrum  of,  49,  62 
Haemometer,  Fleischl's,  65 
Haemophilia,  42 
Haemorrhage,  effect  of,  on  blood-pressure, 

165, 188 

Harmonics,  or  overtones,  264 
Hayem's  solution,  29 


INDEX 


841 


HeaH  on  referred  pain,  666 

Hearing,  797 

Heart,  action-current  of,  621,  6£9 

action  of  drugs  on,  141,  174 

anatomy  of  frog's,  168.  1C9 

beat,  74,  168,  176 
cause  of,  129 
voluntary  accelerat  on  of,  147 

embryonic,  827 

fibrillar  contraction  of  179 

ganglion-cells  of,  120 

heat  produced  by,  4^8 

impulse  of,  79,  182 

mammalian,  action  of,  176 

muscle,  70,  131 

nature  of  contraction  of,  132 

influence    of   temperature   on,    169, 
172 

nerves  of,  augmentor,  136,  140 
extrinsic,  133-147 
inhibitory,  134,  139 
intrinsic,  128 

output  of,  127 

pressure  in,  81-88 

refractory  period  of,  133 

sounds  of,  77,  78 

tracings,  169,  170,  171 

work  of,  126 
Heat-centres,  500 
Heat,  distribution  of,  505 

equivalent  of  food-substances,  485 
of  work  of  heart,  488 

given  off  in  respiration,  483,  513 

loss  from  body,  483-486 
by  evaporation,  483 
after  varnishing  skin,  498 
involuntary  regulation  of,  491 
voluntary  regulation  of,  493 
Heat-production,    effect    of    curara    on, 
489 

in  brain,  490 

in  embryo,  833 

in  fever,  491 

in  glands,  489 

in  muscles,  487 

in  heart,  488 

in  sleep,  486 

and  size  of  body,  497 

involuntary  regulation  of,  495 

voluntary  regulation  of,  494 

relation  to  muscular  work,  490,  560 

seats  of,  487-491 

sources  of,  484 
Heat  rigor,  568 

units,  479 

Heidenhain's  experiments  on  renal  secre- 
tion, 401 

Heller's  test  for  albumin,  424 
Helmholtz's  wire,  526 
Hemianopia,  687,  712 
Hemisection  of  cord,  728 
Hemi-peptone,  308 
Hering's  theory  of  colour  vision,  788 
Hiccup,  222 

Hippuric  acid,  388,  438,  424 
Holder  for  animal,  176 
Homoiothermal  animals,  477 
Horopter,  766 
Hydrobilirubin,  311 


Hydrocele  fluid,  clotting  of,  39 
Hydrochloric  acid  in  gastric  juice,    301, 

formation  of,  326 

Hydrolytic  action  of  ferments,  294 
Hydrostatic  and  hydrodynamic  elements 

in  blood-pressure.  164 
Hypermetropia,  759 
Hyperpncea,  217 
Hypnosis,  725 
Hypoblast,  825,  826 
Hypobromite  method  of  estimating  urea, 

419 

Hypoglossal  nerve,  691 
Hypoisotonic  solutions,  362 
Hypoxanthin,  436 

Identical  points,  theory  of,  765 

Ileo-cascal  valve,  289 

Image  on  retina,  size  of,  746 

Income  and  expenditure  of  body,  450 

Incongruence  of  retinae,  766 

Incus,  798,  801 

Indigo-carmine,  excretion  of,  by  kidney, 

401 
Indol,  308 

formation  of,  in  intestine,  357 

in  urine,  385,  390,  393,  418 
Induced  currents,  524 
Induction  machine,  525 

arranged  for  single  shocks,  590 

tetanus,  175 
Inferior    peduncle    of    cerebellum.      See 

Restiform  body 
Infundibulum,  694 
Inhibition  of  heart,  133 

reflex,  145 

by  ammonia,  146,  184 
.  nature  of,  143 
Inspiration,  199 

forced,  202 

Insufficiency  of  cardiac  valves,  181 
Intercostal  muscles,  200 
Internal  capsule,  659-662 
Internal  secretion.     See  Secretion 
Intestinal  juice,  315,  347 
Intestines,  bacteria  in,  354,  357 

digestion  in,  353 

movements  of,  289 

nerves  of,  290 

reaction  of  contents  of,  354 
Intra-thoracic  pressure,  198,  209 

in  foetus,  210 
Intra-vascular  clotting,  40 
Invertin,  316 
Ions,  35,  362 
Iris,  centre  for  movements  of,  750 

functions  of,  754 

effect  of  stimulation  of  sympathetic 
on,  752,  820 

local  mechanism  of,  753 

nerves  of,  751,  752 
Iron,  absorption  of,  359 

in  bile,  312 

in  liver,  32,  328,  381 
Irradiation,  793 

Isodynamic  relation  of  foods,  565 
Isotonic  solutions,  362 

and  isometric  contraction,  545 


INDEX 


Jaundice,  fat  in  faeces  in,  314 

Judgment,  false,  as  explaining  contrast,  788 

Karyokinesis,  18 

Katabolic  changes  in  living  matter,  19 

Kations,  362 

Key,  short-circuiting,  527 

Kidney,  bloodvessels  of,  395 

internal  secretion  of,  472 

nerves  of,  152,  405,  406 

secretory  pressure  in,  404 

tubules  of,  395 

Kjeldahl's  method  for  total  nitrogen,  421 
Knee-jerk,  676,  677 
Kreatin,  388,  436 
Kreatinin,  388,  424,  438 
Kiihne's  eye,  817 
Kymograph,  99 

Labyrinth  of  ear,  798 

extirpation  of,  722,  806 
Lactic  acid,  action  of,  on  bloodvessels,  154 
in  gastric  juice,  301,  350 
in  intestine,  358 
in  muscle,  563,  603 
Ueffelmann's  test  for,  378 
1  Laky  '  blood,  35,  61 
Laryngoscope,  264 
Larynx,  anatomy  of,  260 

abductors  and  adductors  of,  260,  261, 

270 

nerves  of,  269,  270 
paralysis  of,  270 
Lateral  nucleus  of  bulb,  655 
Lavoisier  and  carbon  dioxide,  223 
Law  of  contraction,  576 
Lecithin  in  bile,  312 
Leclanche  cell,  173,  517 
Lens,  radii  of  curvature  of,  744 
Lenses,  refraction  by,  738,  739 
Leucin  and   tyrosin,   formed   in    tryptic 

digestion,  306,  379 
in  urinary  sediments,  394 
Leucocytes,  28 

classification  of,  29 
composition  of,  51 
formation  of,  33 
and  absorption  of  fat,  370 

of  peptone,  372 
Leukaemia,  blood-corpuscles  in,  30 

uric  acid  in,  393 

Levatores  costarum,  action  of,  in  respira- 
tion, 200 

Lieberkiihn's  crypts,  315,  317,  373 
Lilienfeld's  theory  of  coagulation,  43 
Listing's  law,  794 

Liver,  and  coagulation  of  blood,  45 
bile-pigments  and  acids  in,  327 
formation  of  sugar  in,  439 

urea  in,  434 

glycogen  in,  439,  440,  511 
internal  secretion  of,  471 
iron  in,  32,  328,  381 
Minkowski's  experiments  on,  434,  435 
Living  matter,  composition,  17 
functions,  19 
structure,  18 

Localization  of  function  in  brain,  719 
Locomotor  ataxia,  knee-jerk  in,  676 


Locomotion,  703 

Lungs,  influence  of,  on  coagulation,  44 

quantity  of  blood  in,  196,  197 

secretory  action  of,  242 

vaso-motor  nerves  of,  154 
Luxus-consumption,  457 
Lymph,  circulation  of,  166 

composition  of,  53 

formation  of,  368 

functions  of,  54 

hearts,  167 
Lymphagogues,  368 
Lymphocytes,  29,  370 

Malapterurus,  625,  642 

Malleus,  798,  801 

Manometer,  Pick's  C-spring,  82 

Pick's  elastic,  83 

Hurthle's  elastic,  83 

maximum  and  minimum,  82 
Marckwald  on  respiratory  paths,  213 
Mariotte's  experiment,  779 
Mastication,  283,  284 
Massage  of  muscles,  effect  of,  on  blood- 
pressure,  162 
Maturation  of  ovum,  825 
Maxwell's  spot,  789 
Meconium,  359,  831 
Medulla  oblongata,  anatomy  of,  651 

centres  of,  684 
Meissner's  plexus,  281 
Menstruation,  824 
Mesoblast,  825.  826 
Metabolism  of  carbo-hydrates,  439-446 

of  embryo,  832 

of  fat,  446-450 

of  proteids,  430 

in  fever,  504 

in  starvation,  453,  454 

nitrogenous,  laws  of,  457-460 

in  muscular  work,  458 
Methaemoglobin,  49,  64 

in  urine,  389 
Methylene  blue,  reduction  of,  in  tissues, 

193 

Metronome,  170 
Micturition,  410-412 

centre,  411 
Milk,  834 

curdling  ferment,  303,  306,  377,  378 
Millon's  reagent,  20 
Mirrors,  reflection  from,  735,  736 
Moist  chamber,  628 
Molecular  concentration,  360 
Morphia,  action  of,  on  motor  centres,  719 

quantity  of,  for  dog,  58,  176 
Mother-substances  of  ferments,  323,  324 
Motor  areas,  706-709,  730 
removal  of,  731 
sensory  functions  of,  718 

path,  658 

Mountain  sickness,  258 
Movements,  co-ordination  of,  700 

forced,  699 
Mucous  glands,  changes  in  activity,  322, 

376 

Miiller's  experiment,  256 
Murexide  test  for  uric  acid,  422 
Muscae  volitantes,  757 


INDEX 


843 


Muscarine,  action  of,  on  heart,  141,  174 
Muscle,  afferent  impressions  from,  696 
composition  of,  562,  601-603 
degeneration  of,  683 
diffraction  spectrum  of,  541 
direct  excitability  of,  534,  593 
elasticity  and  extensibility  of,  531 
glycogen  in,  441,  564 
reaction  of,  563,  603 
respiration  of,  245-248 
rigor  of,  565,  566 
stimulation  of,  533 

by  voltaic  current,  536,  592 
structure  of,  538 

in  polarized  light,  540 
sound,  557 

Muscle-nerve  preparation,  to  make,  590 
Muscular   contraction,    chemical   pheno- 
mena of,  562 
duration  of,  541 
formula  of,  576,  578,  632 
heat  produced  in,  560 
influence  of  fatigue  on,  549,  596 
of  load  on,  544,  596 
of  suprarenal  extract  on,  475, 

603 

of  temperature  on,  547,  594 
of  veratria  on,  551,  598 
isometric  and  isotomc,  545 
lactic  acid  formed  in,  563,  603 
latent  period  of,  542,  598 
mechanical  phenomena  of,  541- 

optical  phenomena  of,  538 
recording  of,  594 
reversal  of  stripes  in,  539 
source  of  energy  of,  564,  565 
superposition  of,  552,  599 
velocity  of  wave  of,  555 
voluntary,  557 
work  done  in,  546,  597 
Muscular  fatigue,  549 

seat  of  exhaustion  in,  596,  597 
exercise,  effect  on  the  pulse,  94,  183 
sense,  812 
tetanus,  553,  599 
tone,  682 

work,  nitrogenous  metabolism  in,  458 
relation  of,  to  energy  expended, 

56i 

Mydriatics,  754 
Myograph,  pendulum,  543 
spring,  542 
simple,  595 
Myopia,  758 
Myosin,  567,  603 
Myotatic  irritability,  677 
Myotics,  754 
Myxcedema  and  thyroidectomy,  474 

Near  point  of  vision,  758 

Negative  variation.     See  Action  current 

Nerve,  chemical  changes  in,  571 

composition  of,  583 

conductivity  of,  579 

degeneration  of,  584 

double  conduction  in,  580 

effect  of  temperature  on  excitability 
and  conductivity  of,  573 


Nerve,  effect  of  voltaic  current  on,  574,  630 

isolated  conduction  in,  581 

minimum  stimulus  of,  573 

polarization  of,  615,  633 

regeneration  of,  584 

stimulation  of,  572 

structure  of,  570 
Nerves,  classification  of,  589 

trophic,  587 
Nerve-cells,  639,  641 

changes  in,  with  age,  642 

growth  of,  641 

Nerve-impulse,  velocity  of,  582,  600 
Nerve-muscle  preparation,  to  make,  590 
Neural  axis,  primitive,  644 

canal,  development  of,  637 
Neuroglia,  643 
Neuron,  639 
Nicotine,  action  of,  on  sympathetic  cells, 

JS7 

on  ganglion -cells  of  heart,  141 

of  salivary  glands,  335 
Nissl's  bodies  in  nerve-cells,  639 
Nitrogen  of  body,  451 
in  proteids,  451 
estimation  of  total,  421 
Nitrogenous  equilibrium,  452-456 
metabolism,  430-438,  452-461 

influence  of  fat  and  carbo-hydrates 

on.  456 

of  muscular  work  on,  458 
laws  of,  457-460 
in  starvation,  453 
Nucleins,  18 
Nucleo-proteids,  17,  40 

influence  of,  on  coagulation,  40 
Nucleus,  structure  of,  18 
Nussbaum's  experiments  on  renal  excre- 
tion, 402 

Octopus  macropus,  saliva  of,  332,  354 

Oculo-motor,  or  third  nerve,  687 

(Esophagus,  contraction  of,  286 

Ohm,  519 

Ohm's  law,  518 

Olfactory  nerve,  686 

Olive,  651 

Oncometer,  405 

Opacities  in  the  eye,  770 

Ophthalmoscope,  748 

Ophthalmoscope  (direct  method),  761,  819 

(indirect  method),  764,  819 

testing  errors  of  refraction  by,  764 
Optical  constants  of  the  eye,  744. 

of  reduced  eye,  745 
Optic  axis,  757 

disc,  743 

nerve,  687 

thalami,  661,  693 
Optimum  temperature,  294 
Optogram,  775 

Osmotic  pressure,  35,  360,  361 
Output  of  heart,  127 
Overtones,  264 
Ovum,  development  of,  824 
Oxalates  and  coagulation,  42,  58 

in  urinary  sediments,  387 
Oxidation,  seats  of,  243 
Oxygen,  amount  consumed,  226 


844 


INDEX 


Oxygen,  amount  consumed  in  muscular 
work,  227 

in  blood,  235 

deficit,  463 

toxic  effects  of,  257 
Oxyntic  cells,  325 

Pacinian  corpuscles,  809,  813 
Pain,  813 

referred,  666 

Painful  impressions,  paths  of,  673 
Pancreas,  changes  in,  during  secretion, 

319 

internal  secretion  of,  472 
nerves  of,  344 

Pancreatic  juice,  artificial,  378 
composition  of,  305 
ferments  of,  306,  378-380 
rate  of  secretion  of,  344 
secretory  pressure  of.  345 
to  obtain  normal,  379 
Papain,  308 
Papillary  muscles,  76 
Paradoxical  contraction,  620,  630 
Paralytic  secretion,  340,  344,  347 
Parotid,  changes  in,  during  secretion,  320 
Partial  pressure,  231 

measurement  of,  240 
of  air  of  alveoli,  241 
of  blood-gases,  240 
Pause  of  heart,  76 
Peduncle,  inferior  cerebeilar.     See  Resti- 

form  body 

middle  cerebeilar,  659 
superior  cerebeilar,  655,  659 
Pekelharing's  theory  of  coagulation,  43 
Pendulum  myograph,  543 
Pepsin,  301 

rate  of  secretion  of,  349 
Peptones,  absorption  of,  372 
reactions  of,  22,  377,  425 
effect  of,  on  coagulation,  43,  45 
Perimeter,  790 
Perimetric  chart,  791 
Peripheral  nervous  centres,  664 
Peristalsis,  289,  291 
Personal  equation,  723 
Pettenkofer's  test  for  bile-acids,  380 
Phagocytosis,  54-56 
Phakoscope,  748,  815 
Phenol,  formation  of,  in  intestine,  357 

in  urine,  385,  390,  393 
Phenyl-hydrazine  test  for  sugar,  426 
Phloridzin  diabetes,  445,  512 
Phosphates  in  urinary  sediments,  387 
Phosphoric  acid,  estimation  of,  417 
Phosphorescence,  oxidation  in   244 
Phrenic  nerves,  212 

action  current  of,  609 
nuclei,  connections  of,  212  [777 

Pigmented  epithelium  of  retina,  743,  773, 
Pilocarpine,  action  of,  on  digestive  secre- 
tions, 347 
on  pupil,  754 
on  salivary  secretion,  376 
Pilo-motor  nerves,  157 
Pineal  body,  694 
Pitch,  263 

appreciation  of,  804,  806 


Pithing  a  frog.  168 
Pilot's  tubes,  in 
Pituitary  body,  694 

internal  secretion  of,  475 
Placenta,  formation  of,  829 

glycogen  in,  441 

Plants  and  animals  compared,  19 
Plasma,  blood-,  45 
Plasmine  of  Denis,  38 
Plethysmograph,  116,  183 
Pneumonia  after  section  of  vagi,  220,  278 
Poikilothermal  animals,  477 
Poiseuille's  space,  107 
Polar  bodies,  824 
Polari  meter,  427 
Polarization  of  light,  540 

of  muscle  and  nerve,  615-620 

positive,  616,  633 
Poliomyelitis,  anterior,    degeneration  in, 

657 

knee-jerk  in,  676 
Pons,  652 
Posture,  influence  of,  on  blood-pressure, 

164,  187 

on  pulse  rate,  147,  184 
Posterior  horn,  cells  of,  648 
longitudinal  bundle,  655 
roots,  degeneration  after  section  of, 

585,  653 
loss  of  movement  after  section  of, 

718 
Postero  -  external    and    postero  -  median 

columns,  649,  652 
Potential,  518 
Predicrotic  wave,  93 
Presbyopia,  760 

Pressor  and  depressor  nerves,  163 
Pressure,  arterial,  98-105 

endocardiac,  81-88 

intra-thoracic,  198,  209 

negative,  in  heart,  82,  88 

respiratory,  210 

secretory,  of  saliva,  334 

sensations,  809,  810 
Primary  colours,  784 

position  of  eyes,  794 
Projection  of  image  into  space,  765 
Pronucleus,  825 
Proteids,  absorption  of,  372 

composition  of,  17,  451 

living  and  dead,  431 

reactions  of,  20,  22 

in  urine,  425 

Proteid-sparing  action  of  other  food  sub- 
stances, 455,  456 
Proteoses,  tests  for,  377 
Protoplasm,  17,  18 
Pseudopodia,  29 
Pseudo-reflexes,  676,  677 
Ptyalin,  297 

Pulmonary  catheter,  ^41 
Pulse,  the,  88-98 

anacrotic,  94 

characters  of,  96 

dicrotic  wave  of,  92 

frequency  of,  95 

influence  of  posture  on,  90,  147 

venous,  119 
Pulse-tracings,  91,  182 


INDEX 


845 


Pulse-tracings  from  different  arteries,  94, 

183 
effect  of  ainyl  nitrite  on,  93,  183 

muscular  exercise  on,  94,  183 
Pulse- wave,  velocity  of,  97 
Pulvinar,  687 
Pupil,  Argyll-Robertson,  751 

changes  in,  during  accommodation, 

75° 

constrictor  nerves  of,  751 

dilator  nerves  of,  752,  753,  820 

eccentricity  of,  756 

influence  of  drugs  on,  754 

light  on,  751 
Purkinje's  cells  in  cerebellum,  694,  695 

figure,  771,  821 

Purkinje-Sanson  images,  747,  748,  815 
Pus  cells,  origin  of,  57 
Pyloric  sphincter,  288 
Pyramids,  651 

decussation  of,  651 
Pyramidal  tracts,  650 

connections  of,  656 

Reaction  of  degeneration,  586 

of  intestine,  354 

time,  723 
Recurrent  fibres,  586 

sensibility,  669 
Red  nucleus,  659 
Reduced  eye,  745 
Referred  pain,  666 
Reflection  of  light.  735 
Reflex  action,  674.  729 

anatomical  basis  of,  678 

centres  in  cord,  677 

time,  680,  729 
Reflexes,  676 

inhibition  of,  674,  730 

from  sympathetic  ganglia,  63o 
Refraction  of  light,  736,  737 

in  eye,  743 
Refractive  index,  736 

of  media  of  eye,  744 
Refractory  period  of  heart,  132 
Regeneration  of  nerve,  584 

of  nerve-cells,  713 

of  tissues,  822 
Renal  secretion,  theories  of,  397 

tubules,  395 
Rennin,  303,  377,  378 
Reproduction,  sexual,  823 
Reserve  air,  207 
Residual  air,  208 
Resistance,  electrical,  518 

measurement  of,  519 

thermometer,  479,  559 
Resonance  tone  of  ear,  557 
Respiration,  accessory  phenomena  of,  203 

afferent  nerves  of,  214,  272 

apparatus,  224 

chemistry  of,  223-248,  275-278 

Cheyne-Stokes',  221 

comparative  physiology  of,  192 

cutaneous,  258 

efferent  nerves  of,  211 

external  and  internal,  193 

frequency  of,  206 

heat  lost  in,  483,  513 


Respiration,  internal,  243 

influence  of  vagi  on,  213,  272,  278 
of  '  higher  paths  '  on,  213 
of  muscular  exercise  on,  216 
influence  of,  on  blood- pressure, 

249-256 
on  capacity  of  pulmonary  vessels, 

252 

in  condensed  and  rarefied  air,  255-258 
gaseous  changes  in,  224-229 
mechanical  phenomena  of,  197 
of  muscle,  245-248 
the  first,  833 
types  of,  202 

Respiratory  automatism,  684 
capacity,  208,  274 
centre,  211 

action  of  alcohol  on,  165,  220 
chloroform  on,  219 
venous  blood  on,  217 
centres,  spinal,  220 
'dead  space,1  209 
impurity,  permissible,  227 
organs,  anatomy  of,  193 
pressure,  210 
quotient,  225,  278 

in  excised  muscles,  248 
in  muscular  work,  227 
sounds,  203 
tracings,  204,  205,  272 
Restiform  body,  651,  659 
Retina,  curves  of  excitation  of,  785 
development  of,  638 
fatigue  of,  786 

minimal  stimulus  of,  573,  779 
sensibility  of,  for  colours,  789 
structure  of,  743 

Retinal  bloodvessels,  shadows  of,  771,  821 
image,  formation  of,  815 

size  of,  746 
Rheocord,  523 

simple,  592 
Rigor  mortis,  565 

analogies   to  muscular  contrac- 
tion, 567  [247 
production  of  carbon  dioxide  in, 
removability  of,  569 
time  of  onset  of,  568 
heat-,  603 

Ritter's  tetanus,  616,  633 
Rods  and  cones  in  vision,  773 
Rolando,  fissure  of,  711 

substance  of,  643 

Rontgen  rays,  for  study  of  gastric  move- 
ments, 289  [729 
Roots  of  spinal  nerves,  functions  of,  666, 

section  and  stimulation  of,  729 
Root-fibres,  posterior,  course  of,  in  cord, 
653.  679 

Saliva,  amylolytic  action  of,  375 

chemistry  of,  295,  374 

functions  of,  297 

paralytic  secretion  of,  340 

reflex  secretion  of,  340 

in  vomiting,  292 
Salivary  centre,  341 

corpuscles,  296 

glands,  296 


846 


INDEX 


Salivary  glands,  action-currents  of,  623 

cranial  nerves  of,  334 

sympathetic  nerves  of,  336 

removal  of,  476 
Salts  in  diet,  469 

in  metabolism,  463,464 
Salt-hunger,  464 
Saponin,  action  of,  on  blood-corpuscles, 

35-  62 
Sarcolactic  acid  in  muscle,  563 

in  rigor  mortis,  567,  603 
Scalene  muscles,  in  inspiration.  200 
Scheiner's  experiment,  760,  816 
Sciatic  nerve,  to  expose,  186 
Secondary  contraction,  621,  627 

with  heart,  621,  179 
Secretion,  internal,  471-476 

of  kidney  and  pancreas ,  472 

of  liver,  471 

of  pituitary  body,  475 

of  suprarenals,  474,  603 

of  testes,  473 

of  thyroid,  473,  515 

of  thymus,  476 
paralytic,  340 

Secretory  pressure  of  saliva,  334 
Self-digestion  of  stomach,  383 
Semicircular  canals,  697 
Sensation,  relation  of,  to  stimulus,  814 
Senses,  the,  732 
Sensory  areas,  711-714 

paths  to  brain,  658,  659 
Sensori-motor  functions  of  motor  cortex, 

718 

Serous  glands,  295 
Serum,  36,  45 

albumin,  45,  60 
globulin,  38,  45,  60 
proteids  in  starvation,  431 

source  of,  431 
Shock,  663 
Sighing,  222 

Single  vision,  theories  of,  765 
Sixth  nerve,  or  abducens,  689 
Skate,  electrical  organ  of,  626 
Skatol,  308,  357 
Skin  currents,  623 

impulses  from,  in  equilibration,  697 
varnishing  of,  259 
Sleep,  724 

depth  of,  725 
Smell,  806 

centre  for,  713 

Snake  venom,  effect  of,  on  coagulation,  43 
Sneezing,  222 

Soret's  haemoglobin  band,  49 
Sound,  cranial  conduction  of,  802 
Specific  energy,  721,  804 
Spectroscope,  46,  62 
Speech,  266 

Spermatozoa,  development  of,  823 
Spherical  aberration,  755 
Sphygmograph,  90,  182 
Sphygmomanometer,  104 
Spinal  accessory  nerve,  690,  691 
Spinal  cord,  action  currents  of,  622 

anatomy  of,  646 

ascending  tracts  of,  649 

automatic  functions  of,  681-684 


Spinal  cord,  centres  of,  684 

conduction  or  impulses  by,  665 
descending  tracts  of,  650 
excitability  of  fibres  of,  665 
functions  of,  665 
hemisection  of,  671,  728 
complete  section  of,  663 
removal  of,  664 
action  of  strychnine  on,  729 
white  matter  of,  648 
Spinal  reflexes,  677 
Spirometer,  207 
Splanchnic  nerves,  152 
Spleen  and  blood-formation,  32 
and  blood-destruction,  33 
removal  of,  476 
Spring  myograph,  542 
'  Staircase'  or  '  treppe,'  133,  548 
Stammering,  230 
Standing,  702 

Stannius'  experiment,  142, 175 
Stapedius,  803 
Stapes,  798,  801 

Starch,  action  of  acids  on,  23,  300 
digestion  by  saliva,  297,  374 
tests  for,  23 
Starvation,  metabolism  in,  453,  454 

serum  proteids  in,  431 
Stasis,  57 
Stationary  air,  208 
Steapsin,  306,  380 
Stercobilin,  311,  358 
Stereoscope,  768 
Stereoscopic  vision,  767 
Stilling's  sacral  and  cervical  nuclei,  648 
Stimulants,  470 

Stimuli,  summation  of,  552,  599 
Stomach,  absorption  from,  352 
auto-digestion  of,  383 
excision  of,  355 
movements  of,  288 
nerves  of,  290 
Stromuhr,  no 

Strychnia,  action  of,  on  cord,  558,  729 
Sublingual  ganglion,  333 
Succus  entericus,  315 

action  of,  in  digestion,  357 
influence  of  nerves  on,  347 
Sugar,  absorption  of,  393 

destruction  of,  in  blood,  445 
estimation  of,  by  Fehling's  solution, 

427 

by  polarimeter,  428 
in  blood,  399,  439 
excretion  of,  by  kidneys,  402 
fate  of,  in  organism,  442 
formation  of,  in  liver,  439 
and  muscular  contraction,  565 
in  urine,  394 

phenyl-hydrazine  test  for,  426 
Trommer's  test  for,  23 
yeast  test  for,  427 
Sulphocyanide  in  saliva,  296,  374 

in  urine,  391 

Sulphates  in  urine,  estimation  of,  418 
Summation  of  stimuli,  552,  599 
Superior  laryngeal  nerve  and  respiration, 

215,  272 
Superposition  of  contractions,  552,  595 


INDEX 


847 


Supplemental  air,  207,  274 

Suprarenal  capsules,  secretion  of,  474,  603 

extract,  action  of,  147,  475,  604 
Surface  of  body,  relation  to  mass,  468,  497 
Suspensory  ligament,  743 
Sutures,  190 
Swallowing,  effect  of,  on  pulse-rate,  146, 

184 
Sweat,  412 

centres,  414 

nerves,  413-415 

quantity  of,  414 
Swim-bladder,  gases  of,  243 
Sympathetic,  cardiac  fibres  of,  in  frog, 

134.  175 
in  mammals,  139 

cervical,  vaso-motor  fibres  in,  150, 189 

dissection  of,  in  frog,  172 
in  dog,  179 

fibres  for  salivary  glands,  333,  336 

pupillo-dilator  fibres  of,  752,  820 

ganglia,  supposed  reflexes  from,  680 
Syncope,  166 
Systole  of  heart,  75 

Tachograph,  gas,  112 

Tachycardia  in  disease,  691 

Tactile  impressions,  path  of,  in  cord,  673 

sensations,  809 

centre  for,  714 
Talbot's  law,  780,  821 
Tartar,  296 
Taste,  807 

nerves  of,  808 
Taurocholic  acid,  311 
Tears,  384 
Teeth,  283 
Tegmentum,  652 
Tegmental  afferent  path,  658 
Temperature  of  blood,  507 

of  brain,  508 

in  cavities  of  the  heart,  506 

of  skin,  508 

measurement  of,  477,  478 

nerves  of,  812 

paths  for  impressions  of,  in  cord,  673 

post-mortem  rise  of,  510 

regulation  of,  491 

sensations,  811 
'  Tendon-reflex,'  676,  677 
Tension  of  blood-gases,  240 

of  oxygen  in  human  blood,  242 
Tensor  tympani,  802 
Tetanus,  553-555 

composition  of,  553,  599 

frequency  of  stimulation   necessary 
for,  554 

Ritter's,  616,  633 

secondary,  558,  627 
Thermo-electric  junctions,  479 
Thermometers,  478 

resistance,  479-559 
Thermopile,  559 
Thermotaxis,  491-501 
Third  nerve,  687 
Thiry's  fistula,  315 
Thoracic  duct,  166,  370 
Thrombosin,  38 
Thymus,  removal  of,  476 


Thyroid,  effects  of  excision  of,  473 
Thyroidectomy,  operation  of,  515 

with  thyroid  feedine,  516 
Thyroids,  accessory,  516 
Thyro-iodine,  474 
Tidal  air,  207,  274 
Timbre,  263 
Time  markers,  170.  527 
Tissue-fibrinogen,  40 
Tone,  muscular,  682 

trophic,  683 
Tonus,  acerebral,  699 
Torpedo,  625 
Torricelli's  theorem,  71 
Touch,  acuity  of,  810,  821 
Trachea,  to  put  a  cannula  in,  177 
Tracts  in  cord,  649 
Transfusion,  166,  188 
Traube-Hering  curves,  250,  254 
Trigeminus  nerve,  688 
Triple  phosphate,  387 
Tristearin,  17 

Trochlear,  or  fourth  nerve,  688 
Trommer's  test  for  reducing  sugar,  23 
Trophic  nerves,  587 

tone,  683 
Trypsin,  306 

Tryptic  digestion,  306-308,  379 
Tympanic  membrane,  798 
Tympanum,  798 
Tyrosin,  in  pancreatic  digestion,  307,  379 

in  urinary  sediments,  394 

Ueffelmann's  test  for  lactic  acid,  378 
Unpolarizable  electrodes,  526,  628 
Urates  in  urinary  sediments,  387 
Urea,  387,  393 

estimation  of,  419,  420 
formation  of,  432-435 

in  liver,  434 
variation  with  proteids  in  food,  457, 

515 

daily  curve  of,  509 
in  fever,  504 
Uric  acid,  388,  393,  436 

estimation  of,  422,  423 
formation  of,  in  birds,  434 
in  mammals,  437 
from  nucleo-proteids,  388 
in  gout,  393,  437 
in  leukaemia,  393 
Urine,  acidity  of,  386 

acid  fermentation  of,  386 
alkaline  fermentation  of,  387 
aromatic  bodies  in,  390,  393,  418 
blood  in,  394 
chlorides  in,  390,  416 
composition  of,  385,  386 
examination  of,  428 
ferments  in,  389 
haematoporphyrin  in,  389 
hippuric  acid  in,  388 
incontinence  of,  412 
indoxyl  in,  390,  393,  418 
in  disease,  391-394 
in  starvation,  400 
kreatinin  in,  388,  424 
leucin  and  tyrosin  in,  394,  435 
methaemoglobin  in,  389 


848 


INDEX 


Urine,  phenol  in,  390 

phosphoric  acid  in,  390,  417 
pigments  of,  389 
proteids  in,  393,  394,  424-426 
quantity  of,  385,  392 
secretory  pressure  of,  404 
sediments  of,  387,  393 
specific  gravity  of,  385,  416 
sugar  in,  393,  426-428 
sulphuric  acid  in,  390,  418 
total  nitrogen  in,  421 
urates  in,  387 
urea  in,  387,  393,  419 
xanthin  bases  in,  388,  393 
secretion  of,  395 

action  of  glomeruli  in,  402 
action  of  '  rodded'  epithelium  in, 

401 

Adami's  experiments  on,  403 
Heidenhain's  experiments  on,  401 
Nussbaum's  experiments  on,  402 
influence  of  circulation  on,  405 
of  drugs  on,  410 
of  nerves  on,  405-409 
theories  of,  397 
Urobilin,  311,  358,  389 
Urochrome,  389 
Uroerythrin,  389 

Vagi,  section  of  both,  220,  278 

Vagus  nerve,  690 

Vagus,  cardiac  fibres  of,  in  frog,  134, 171, 

174 
centre,  effect  of  suprarenal  extract  on, 

604 

in  mammals,  139,  178,  185 
tracings,  135,  136,  173 
relation  of,  to  respiration,  213,  272 
Valsalva's  experiment,  256 
Valves  of  heart,  action  of,  75,  181 

moment  of  opening  and  closure 

of,  87 

of  veins,  69 

Valvulse  conniventes,  365 
Varnishing  skin,  498 
Va so-con strictors  and  dilators,  differences 

between,  150 
Vaso-dilator  fibres  of  chorda  tympani,  154 

nervi  erigentes,  155 
Vaso-motor  centres,  158,  159 

peripheral,  159 
Vaso-motor  nerves,  148-166 

methods    of    investigating,  148, 

149 

ot  brain,  151,  154 
cervical  sympathetic,  150,  189 
course  of,  156 
of  heart,  153 
of  kidney,  152 
of  limbs,  152 
of  lungs,  154 
of  muscles,  153 
of  veins,  155 
in  splanchnics,  152 
in  trigeminus,  151 
Vaso-motor  reflexes,  160,  185 
Vein,  to  put  a  cannula  in,  177 
Veins,  circulation  in,  120 


Veins,  pulse  in,  119 

vaso-motor  nerves  of,  155 
velocity  of  blood  in,  122 
Vella's  fistula,  315 
Velocity  of  blood,  105-115 

in  arteries,  114,  115 
in  capillaries,  109,  118 
in  veins,  109,  122 
measurement  of,  110-112 
Velocity-pulse,  curves  of,  113,  114 
Velocity  of  the  nerve-impulse,  582,  600 
Ventilation,  226 
Vesicular  murmur,  203 
Vestibule,  800 
|    Villi,  368 
Vision,  colour,  781 
far  point  of,  758 
near  point  of,  758 
physical  introduction  to,  734 
stereoscopic,  767 
Visual  angle,  746 
axis,  757 
centres,  711 
judgments,  769 
purple,  775 

regeneration  of,  777 
Vital  capacity.  208,  274 
Vitreous  humour,  742 

opacities  in,  742,  771 
Vocal  cords,  260,  262 

paralysis  of,  271 
Voice,  production  of,  259,  261 

pressure  in  trachea  in,  262 
in  children,  263 
Volt,  519 
Volume    of   corpuscles    and  plasma    in 

blood,  35 
Voluntary  contraction,   fatigue  in,    550, 

597 

Vomiting,  292 
centre,  293 

caused  by  apomorphine,  378 
Vowels,  Helmholtz's  theory  of,  267 

Hermann's  theory  of,  268 
Vowel  cavities,  268 

Water,  production  of,  in  body,  463 
Weber's  law,  814 
Weyl's  test  for  kreatinin,  424 
Wharton's  duct,  333 
Wheatstone's  bridge,  519 
Wheel-movements  of  eyes,  794 
Whispering  voice,  267 
White  blood-corpuscles,  28,  51,  54 
Work,  muscular,  546 
of  heart,  126 

Xanthin,  436 

Xanthin-bases  in  urine,  388,  393 
Xanthoproteic  reaction,  20 
Xerostomia,  342 

Yawning,  222 
Yellow  spot,  743,  789 
Yolk-sac,  828 

Zonule  of  Zinn,  743 
Zymogens,  323,  324 


Bailliere,  Tindall  and  Cox,  King  William  Street,  Strand. 


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